Advanced Techniques for Assessment Surface Topography: Development of a Basis for 3D Surface Texture Standards

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Advanced Techniques for

Surface Topography

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Advanced Techniques for

Assessment Surface Topography Development of a Basis for 3D Surface Texture Standards "SURFSTAND"

edited by

Liam Blunt & Xiangqian Jiang

First published in Great Britain and the United States in 2003 by Kogan Page Science, an imprint of Kogan Page Limited Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms and licences issued by the CLA. Enquiries concerning reproduction outside these terms should be sent to the publishers at the undermentioned addresses: 120 Pentonville Road London N1 9JTM UK www.koganpagescience.com

22883 Quicksilver Drive Sterl ing VA 20166-2012 USA

© Kogan Page Limited and contributors, 2003 The right of Liam Blunt and Xiangqian Jiang to be identified as the editors of this work has been asserted by them in accordance with the Copyright, Designs and Patents Act 1988. ISBN 1 90399611 2

British Library Cataloguing-in-Publication Data A CIP record for this book is available from the British Library.

Library of Congress Cataloging-in-Publication Data Advanced techniques for assessment surface topography : development of a basis for 3D surface texture standards "surfstand" / edited by Liam Blunt and Xiangqian Jiang. p. cm. Includes bibliographical references and index. ISBN 1-903996-11-2 1. Surfaces (Technology)—Measurement. 2. Three-dimensional display systems. I. Blunt, L. (Liam) II. Jiang, Xiangqian. TA418.7.A4542003 620'.44--dc21

2003009012 Typeset by Kogan Page Printed and bound in Great Britain by Selwood Printing, West Sussex

Contents

1. Introduction: The History and Current State of 3D Surface Characterisation Liam Blunt

1

Part 1: Characterisation

15

2. Numerical Parameters for Characterisation of Topography Liam Blunt andXiangqian Jiang

17

3. Novel Areal Characterisation Techniques Paul J. Scott

43

4. Advanced Gaussian Filters Stefan Brinkman and Horst Bodschwinna

63

5. Multi-scalar Filtration Methodologies Xiangqian Jiang

91

Part 2: Instrumentation

117

6. Calibration Procedures for Stylus and Optical Instrumentation Jean Franqois Ville

119

7. Calibration Procedures for Atomic Force Microscopes Anders Ktihle

175

Part 3: Case Studies

195

8. The Interrelationship of 3D Surface Characterisation Techniques with Standardised 2D Techniques Robert Ohlsson, Bengt Goran Rosen and John Westberg

197

9. Applications of Numerical Parameters and Filtration Liam Blunt andXiangqian Jiang

221

vi

Advanced Techniques for Assessment Surface Topography

10. Functionality and Characterisation of Textured Sheet Steel Products Micheal Vermeulen and Henrik Hobleke

249

11. Characterisation of Automotive Engine Bore Performance using 3D Surface Metrology Stefan Brinkman and Horst Bodsckwinna

307

Part 4: Future Developments

323

12. Surface Texture Knowledge Support - ISM Robert Ohlsson and Bengt Goran Rosen

325

13. Future Developments in Surface Metrology Liam Blunt, Xiangqian Jiang and Paul J. Scott

339

Index

349

Acknowledgements

The editors would like to thank the following list of people: Peter Breger for keeping us on the straight and narrow, Professor Tom Thomas for his constant encouragement and friendship, Professor David Whitehouse's encouragement and friendship, Evaristus Mainsah and Weiping Dong for the groundwork, Professor Harry Trumphold's encouragement and friendly criticism, Dr Brian Griffiths for his encouragement and honest friendship, and a special mention to our colleagues at DFM for pulling out for us when we needed it most. The mysterious Mr Strobel "you know who you are", the directors and colleagues at Taylor Hobson for their support over recent years. The University of Huddersfield for provision of our wonderful facilities, a special mention must be made to our wonderful group: Dr Shaoujun Xiao, Dr Feng Xie, Miss Leigh Brown, and Miss Adelle Waterworth. Last and by no means least, a special mention to Professor Ken Stout who made all of our research possible, and in particular for his initiation, organisation strategic view and constant friendship over the years. Liam and Jane


1 Introduction: The History and Current State of 3D Surface Characterisation Liam Blunt Taylor Hobson Professor of Surface Metrology, School of Engineering, University of Huddersfield, UK

1.1 Defining the nature of a surface An appropriate question at the beginning of a text like this might be "what is a surface? ". The answer to this question is not simple, though considering a surface as a boundary is a good start. Bearing this in mind, the surface of an engineering component can therefore be thought of as the physical boundary between the work piece and the surrounding environment. The real surface of a workpiece has been defined in international standards (ISO) as: A set of features which physically exist and separate the entire workpiece from the surrounding medium (ISO 14460-1) [1], It would be false to assume that the surface of a workpiece is invariably mechanical in nature. In fact the electromagnetic surface of a workpiece is an equally valid concept. The definitions ISO 16610-1, of both are rather cumbersome but are given below. Real surface of a workpiece (mechanical) Boundary of the erosion, by a spherical ball of radius r, of the locus of the centre of an ideal tactile sphere, also with radius r, rolled over the real surface of a workpiece. Real surface of a workpiece (electro-magnetic) Locus of the effective ideal reflection point of the real surface of a workpiece, by electromagnetic radiation with a specified wavelength. For most purposes, however, especially where the workpiece interacts with its working environment through some form of mechanical contact it is the mechanical surface that is of interest. This is the surface that is measured using standard surface metrology

2


techniques and it is this surface that is referred to on engineering drawings of components to be manufactured. A further rhetorical question might be, why are we interested in surfaces? The clear reason is that it has been shown that 90% of all engineering component failures in practice are surface initiated, through mechanisms such as fatigue cracking, stress corrosion cracking, fretting wear, excessive abrasive or adhesive wear, corrosion, erosion etc. Clearly then, it is important to understand the properties of the surface and near surface zones of a component. These properties can be grouped together under the term surface integrity [2]. A glance at the nominal technical drawing of an engineering component clearly shows that the drawing assumes that each surface of the component is perfectly smooth, straight, clean and free from defects. There is an assumption that the manufacturing engineer can achieve this using the techniques at his disposal. This surface, the one assumed by the drawing is called the nominal surface. The manufacturing engineer now studies the drawing and attempts to manufacture the component to the specified dimensions within the tolerance limits. When manufacturing the component the engineer knows that it is impossible to manufacture a perfectly smooth surface, as the particular manufacturing method chosen will leave a micro-scale "fingerprint" on the surface which is unique to that manufacturing process. The nature of that "fingerprint" is referred to as the surface texture or surface topography of the component. Normally, this consists of a series of peaks and valleys that have characteristic shape size and spacing. As well as affecting the shape of the surface texture the manufacturing method chosen also affects the layers directly below the surface of the component. For example, if we take the machined surface of a metal such as steel and take a cross section through the surface we can see the surface is made up of a number of layers (Figure 1.1).

Figure 1.1 Schematic cross sectional view of a surface showing the surface and sub surface layers

Introduction

3

These layers consist of: • •

• • •

An oxide layer, which all metals possess, this layer being several nanometers thick. The topographic layer, the hills and valleys that make up the shape of the surface. These result from the material removal (or addition) process and are produced by the unit manufacturing process (tool passage, electrical discharge, plating process etc.). A plastically deformed layer produced by the machining operation. A metallurgically deformed layer resulting primarily from heating during machining. The bulk material.

Figure 1.2 Ground surface cross section a) abusively ground b) gently ground Figure 1.2 shows an example of a cross section through (a) an abusively ground steel surface, and (b) a gently ground steel surface. What is clear from the image is the distinct layering of the surface zone and also how the severity of the grinding operation has affected the surface layers and the surface roughness. Whilst the sub surface layers are critically important, they are very difficult to measure without destroying the component. Therefore engineers have concentrated on measuring the surface roughness as both a means of quality assurance and as a means of inferring functional performance. The geometrical form of any surface is usually referred to as the surface texture. Conventionally the texture is made up of features defined as roughness, waviness and form (Figure 1.3). Traditionally, when the surface texture is quantitatively measured it is only the roughness that is analysed and the waviness and form elements are mechanically, electrically or digitally filtered out from the recorded data.

4


Figure 1.3 Roughness, waviness and form of an engineering surface [3]

The difference between the roughness, waviness and form characteristics of the surface texture is based on the surface wavelength or peak to peak spacing. The great problem with these conventional definitions is that the point at which roughness becomes waviness (cut off) is arbitrary and is usually related to the manufacturing process from which the surface derived or from the intended function of the workpiece. For example, what would be considered as roughness on an automobile axle would be considered waviness of form error on a watch spindle [3]. As a rule roughness can be considered as being produced by the method of manufacture rather than the machine, and constitutes tool or grit marks and is usually of a periodic nature. On a finer scale there is tearing of material, as a result of built up edge formation and tool tip irregularities. Waviness is usually attributed to an individual machine, for example an unbalanced grinding wheel, tool feed irregularities and general chatter vibrations. Form errors are usually caused by a lack of rigidity of the workpiece during the machining operation allowing it to flex or bend. Slide way undulation can also cause form error. Strains in the material, surface induced trough heating or excessive surface residual stress can cause flexure and form error. Usually, form errors produce only one or two undulations over the dimensions of the assessed surface.

1.2 Surface creation Surfaces are created by a large variety of manufacturing processes and each manufacturing technique leaves its own fingerprint on the surface produced. Sometimes, the fingerprint from a surface can produce a beneficial effect on the character of the surface but on other occasions the resulting surface can deleteriously affect the ability of the surface to perform its intended function. It is therefore important that the "fingerprint" which is produced as a result of any surface manufacturing method be understood in terms of its effect on the function for which the surface is intended. If the general nature of the surface is deemed unacceptable then a surface modification technique should be

Introduction

5

undertaken to modify its suitability for the intended function. In many cases it is not the inherent nature of the machining process that is at fault but the machining conditions under which the surface has been finished. As a consequence, modifying the parameters of the final process may yield a satisfactory result. This implies that the engineer must improve his understanding of surface production methods and the effects that these production methods may have on the functional properties of the surface. Many surfaces are designed to interact with other solids and as a consequence are sometimes subjected to surface treatments that alter the properties of the surface layers. The processes most often used are plating, blasting, peening, carburising, nitriding, ion implantation etc. these treatments produce the so-called "functional surfaces". The relationship between surface topography and the functional surface has only been partially investigated and the most work that has been conducted in this area was undertaken using 2D surface analysis, using profile analysis or through the application and interpretation of auto-correlation functions.

1.3 Evolution of assessment The earliest assessments of surface finish were made simply by running a fingernail across the surface. This technique survives to this day as tactile comparison, where the finish of the workpiece is compared manually with a set of calibrated surfaces of different known roughnesses produced by the same finishing process [4]. The first quantitative measuring instrument was the light-section microscope, developed by Gustav Schmaltz in Germany early in the 20th Century [5]. An image of an illuminated slit was projected on the workpiece at an angle to the vertical, and the distortions in its reflection magnified the surface irregularities. Peak and valley heights could then be read off the calibrated eyepiece. The subject of surface finish assessment began properly when Professor Schmaltz developed a simple profilometer to enable the deviations on a selected line of a surface to be measured and recorded. This process was simply achieved by drawing a stylus across a surface and recording the vertical deviations of the surface that had been suitably differentially magnified by an optical lever (the vertical magnification being greater than the horizon). The magnified image was recorded on photosensitive paper and was presented in a partial circular arc since the screen was rotated as the stylus progressed across the surface. This simple mechanical process enabled the roughness to be measured in terms of peak to valley deviation of the surface profile and the less extreme average of the five highest peaks to the average of the five lowest valleys on the profile to be determined. It was not long before a British company, Taylor & Hobson (now known as Taylor Hobson) produced a simple instrument that enabled an electrical signal that represented the deviation of a surface to be simply processed to produce a small range of surface parameters. The first electronic surface profile employed analogue electronics to capture data from the surface, and as well as peak to valley deviation, an extreme surface amplitude parameter, and averaging of the surface roughness became possible. As a

6


consequence a more useful parameter, the centre line average roughness (CLA) was calculated using an analogue computer. It was this instrument, and its German counterpart, that became an important measurement tool in metrology laboratories throughout the industrialised world. In principle, the instrument did not change except that the analogue electronics improved as the subject developed. As a result of its use and the growing need to communicate surface finish values between manufacturing organisations and within manufacturing organisations, it became necessary to develop standards that were acceptable in industries in many countries. These standards all contained the definition of average surface roughness, CLA, now termed average roughness Ra. It is because of the early analogue instrumental convenience of computing the average roughness parameter (Ra) that it became the most widely used and accepted descriptor of a surface, and as a consequence it was widely used in many industries; and to some extent although Ra is extremely limited in value, it is still widely used today even though it is determined in a different way (through digital processing) by modern instruments. By the late 1960s surface characterisation was gaining interest in the academic community and the limitations of the simple parameters described above were becoming obvious, and researchers were devising a wide range of descriptors for a surface, few of which really overcame the limitations imposed by the original descriptors. So a plethora of parameters were developed, many of which were just variants on each other but gave the researcher the opportunity to investigate whether they would improve the understanding of the character of the surface under assessment. At this time some researchers were involved with digitising the data from the electrical output of the stylus and convert this data into a form that could be processed on the mainframe computers that were available at this time. Different countries developed different routes to the establishment of the surface parameters that they preferred. In the United Kingdom the height parameters which gained most favour was the average roughness of the surface Ra and root mean square of surface roughness Rq whilst in Germany and Russia peak height and valley depth parameters were preferred (Rt, later Rtm and Rz). The original major industrial nation in Asia, Japan, chose a variation of the extreme peak height parameter, R3z which closely approximated Rz. The significance of these developments was that the UK and USA concentrated on statistically reliable and measurable parameters whilst in Germany and Russia parameters which were related to the functional significance of surfaces, but were more difficult to measure. All of the parameters were limited in their potential application and on their own did little to describe the real parameter relationship to function. Nevertheless, workers in each country felt that the parameters which were selected offered the best early compromise and offered some information which could be used in a process monitoring sense. Since the late 1970s analogue instruments have been replaced by mechanical devices supported by digital electronic computers digital computers having become available. The subject thus had the scope to develop dramatically, and much of the early development took place in academia and research establishments mostly on the continent

Introduction

7

of Europe. Digitisation of data directly from the stylus enabled data files to be established and manipulated directly on a computer dedicated to the stylus instrument. Instruments such as the Taylor Hobson Form series Talysurf and the Somicronic Surfascan 3D have led the way. The introduction and continual improvement of computers allowed engineers to develop in an unstructured way numerous numerical parameters until eventually; by the 1980s, over one hundred primary descriptors had been developed and were described in numerous national standards. Many of these parameters were poorly defined and have very limited use. This explosion in parameters was aptly defined as "parameter rash" by Whitehouse [6].

1.4 Development of the 3D approach In the early 1980s many researchers in the academic community were experimenting with the characterisation of surfaces in 3 dimensions. Work at Teesside under Dr. Thomas and at Coventry Polytechnic under Dr. Stout, was early pioneering work on the subject, though probably the first true 3D system was developed by Williamson [7], Other groups in both industry and academia, mainly in Europe, were developing their own approaches to the subject. Although there was considerable academic interest, three dimensional topography had a difficult start in terms of acceptance, since the leading manufacturers of stylus instruments at that period shunned the development, insisting at the time that three dimensional topography was an academic curiosity and did not have a place in the industrial scene. The group at Coventry developed a system of hardware with supporting software which eventually became the first prototype for the first commercial software package and provided the first comprehensive range of surface visualisation techniques. In the early 1990s Rank Taylor Hobson brought out a 3D stylus instrument using the software OEM package developed by the group originally at Coventry. There is some debate over which company was the first to launch a 3D stylus-based surface profiler, and as a consequence the answer is somewhat complicated. Somicronic, a small company near Lyon in France, delivered a prototype 3D system to the Ecole Centrale de Lyon on 1990. The system that they delivered was a pre-production prototype of their final production system. In 1991 Rank Taylor Hobson produced and marketed the first commercial "add on" system to their 2D Form Talysurf measuring system. This system had OEM software that had been specifically tailored to the RTH requirements. This early pioneering commercial system allowed only surface visualisation techniques The first stylus system manufacturer to introduce a comprehensive range of parameters to their software was Somicronic who had a range of parameters available on their system in 1994. The next major step forward in the development of characterisation of engineering surfaces came in 1990 with the European Community supported BCR research contract [1] awarded to the University of Birmingham which was coordinated by Professor Stout, formerly of Coventry Polytechnic. The research group had transferred from Coventry and

8


became involved in a major European initiative which was to develop a document which could be used as a temporary standard which was available in advance of there being an international standard prepared for the subject. This document was subjected to an overview by 38 industrialists representing the major interested groups in the subject in Europe and thus this ensured a wide acceptance of the technology [8]. The outcome from this research was a report some three hundred pages long which proposed 14 3D surface parameters that described amplitude properties, spatial properties, hybrid properties and functional properties of a surface. In addition to the parameters the work investigated communication protocols which included data file formats as well as providing useful information on the way surfaces should be measured and filtered. In 1996 the "Birmingham 14" parameters were implemented on the Somicronic 3D surface profiler as well as the standard data file format which enables the data produced on their system to be transferred to other computer systems for extensive analysis. Whilst the original BCR project was deemed a success it was regarded as a rather theoretical exercise. It was considered that before a draft standard could be proposed more practical application of the work was needed as well as formalising the numerical approaches the characterisation [8]. As a result of this opinion the SURFSTAND project was born. Certainly the subject is rapidly gaining greater industrial recognition and the relevant ISO committee has commissioned John Westburg from Volvo to specify the basis of an International Standard on the subject, and we confidently expect that the "Birmingham 14" parameters will be included in the standard as well as protocols for, filtering, data file format and data communication. A number of manufacturers have now entered the market in all the fields of instrumentation. To our knowledge Taylor Hobson, Somicronic and Hommelwerke and TSK (Japan) offer 3D stylus systems. During the period of development of the more traditional stylus type instrumentation huge progress was made in the USA with regard to the development of optical interferomeric systems. These systems were capable at a very early stage (in advance of commercial 3D stylus systems) of rapid 3D surface measurement on a range of relatively smooth surfaces and the manufacturers aimed their instrumentation at the burgeoning silicon wafer market and to a lesser extent the optics industries. These instruments were the first group of real stand-alone 3D surface measurement instruments and have made a great impact in the field of surface characterisation. The main instrument manufacturers WYKO and ZYGO have made great improvements in their instrumentation, utilising techniques such as vertical scanning interferometery, extended range interferometery and now have instruments capable of measurement from sub nanometer resolution to millimetre range. Latterly, other companies have offered optical instruments such as Phase Shift Technology and Micromap. Optical focus detection systems, offered by UBM and Rodenstock, are no longer marketed. But a further group of instruments using triangulation and confocal techniques, such as those offered by the Scantron company, are now becoming available and increasingly used in applications where mechanical contact during measurement is undesirable.

Introduction

9

Last and by no means least, at the present time by far and away the greatest numbers of 3D surface measurement systems currently being sold are atomic force microscopes (AFM's) from companies such as Digital Instruments, DME, Nanoscope and others. These instruments have exploded on the scene of ultra high scale 3D surface characterisation and now represent the largest number of users. However, the users are not usually metrologists in the traditional sense and the concept of full traceable measurement is not foremost in the minds of the common user. A few metrological AFM's do exist but mostly in national laboratories. It is clear however that eventually the instruments will become a production process control tool and it is absolutely essential that standards drafted with more traditional metrology tools in mind are widely applicable to this new generation of instruments.

1.5 "SURFSTAND" The results from the SURFSTAND project form the basis of this book. The project was a multinational and multi-partner project. The primary aims of the project were firstly to evaluate the functional usefulness of the "Birmingham 14" parameters through a series of practical case studies. Secondly, the 3D surface parameter definitions were revisited in order to "tighten up" the parameter definitions, suggesting appropriate changes and even new parameters. Thirdly, a significant portion of the project dealt with the development of new surface data filtering techniques based around robust Gaussian methodologies and the use of wavelet technology as a filtering tool. Finally, issues dealing with 3D instrument calibration were investigated. The project partners and their industrial/research backgrounds are shown in Figure 1.4a and the workpackages within the project are outlined in Figure 1.4b. a)

Bioengineering

Academic University of Huddersfield (UK) Chalmers University (Swe) University of Hannover (D)

Somicronic(Fr)| Taylor Hobson (UK) DFM (DK)

Volvo (Swe)

OCAS (Bel)

DePuy J &J (UK)

10


b)

Figure 1.4 a) Partner profile of SURFTAND project b) Schematic program of work packages in SURFSTAND project The following chapters bring together leading research in the field of 3D surface characterisation and are the theoretical backbone of the proposed new ISO standard in 3D surface texture. The vast majority of the reported work is novel and will provide the basis for real ground breaking progress in the field. In more detail, Chapter 2 deals with the improved definitions of the parameters which will form the basis of the new ISO standard proposal. Chapter 3 concerns the new field of areal characterisation introducing the concept of feature parameters within the context of pattern recognition methodologies. Chapter 4 introduces multi-scalar wavelet filters as a tool for surface characterisation. In particular, both first and second generation wavelet techniques are introduced. Chapter 5 is concerned with the development of robust regression Gaussian filters initially starting with 2D techniques before moving to 3D equivalents. Chapter 6 presents a practical methodology for the calibration of 3D scanning contact stylus instruments. Chapter 7 continues the instrumentation theme and discusses the issues associated with calibration and traceable measurement using scanning probe microscopes. Chapter 8 presents a study concerning the relationship between the use of traditional 2D surface parameters and 3D surface parameters in describing the functionality of automotive cylinder bores and steel sheet. Chapters 9, 10 and 11 outline a series of case studies on a range of functional surfaces which seek to provide information on the usefulness of the 3D parameter set and the surface data filtering techniques developed within the project. The specific functional surfaces studied include automotive cylinder liners, steel sheet, bearing surfaces and medical implant surfaces. Chapter 12 discusses the issues surrounding the development of expert systems and advanced databases for hosting surface measurement, function and manufacturing information. Finally, the book is concluded with Chapter 13 which deals

Introduction

11

with the perceived future development of 3D surface metrology and the forthcoming issues of standardisation of the results of the SURFSTAND and other projects. Particular attention is given to the future of characterisation in terms of feature characterisation and its implication for the characterisation of structured micro and nano-scale structured surfaces. At this point it should be made clear that the SURFSTAND project was not the only surface metrology based project sponsored by the EC in the recent period. A further three projects have been undertaken and completed CALISURF [9], AUTOSURF [10] and a project dealing with calibration of scanning probe microscopes [11]. During the lifetime of the SURFSTAND project much liaison and cross fertilisation of ideas occurred between the projects and this proved extremely useful for all concerned providing a critical mass for real progress in the whole broad spectrum of the subject.

1.6 Potential applications of project results The project promises great potential benefit in industry through improved surface characterisation that should lead to improved manufacturing surface quality and vastly improved understanding of surface functionality. Specific perceived industrial benefits are discussed below. 1.6.1 Automotive industry The automotive industry has traditionally been most receptive to the type of research carried out in the SURFSTAND project and it is anticipated that they will lead the way in the application of the research results. Fundamental to recent developments in engine technology has been the driving force of emissions regulation and the most critical part of the engine in terms of emissions is the cylinder bore/piston ring pack interaction. The research involved in the project has given rise to a greater understanding of this system and better modeling of the functional surfaces has resulted. Clearly, the potential of better understanding is the ability to further reduce system wear and in turn emissions. Reduced emission engine technology has a definite commercial advantage for automotive manufacturers. One of the biggest users of textured steel sheet is the automotive industry with around 55% utilised in automotive applications (cars and trucks), all demanding high quality steel with appropriate surface roughness. Other important steel sheet customers where surface roughness is important are: domestic appliances and building industries. By way of example the total EU production in cold rolled steel is about 34 Mtons per annum. A conservative estimate of the amount rejected on the basis of surface roughness is 30% and assuming an average cost of 400ECU/ton the roughness related problems in sheet steel production represents an annual budget of 4 billion euro. The results of the present project have significantly increased the knowledge of sheet formability as a function of surface topography. This increased knowledge will benefit end users in terms of savings on scarp and increased market share. The automotive industry is by far and away the biggest user of bearings and again service life and wear limitation are critical to market share. The 3D surface parameters and the

12


knowledge-based expert system will allow much better modelling of bearing performance and specification. 1.6.2 Biomedical industry This industry has long-standing expertise in the development and manufacture of artificial human joint implant systems. With these products, predictable and long service life are fundamental their function. The metrology techniques for specifying and characterising these systems has lagged behind for some time; however, the present project has utilised 3D surface characterisation to significantly improve the specification of the bearing surfaces in such products. The understanding of the surface interaction has greatly increased and with this it will be possible to make better quality products in the future. The project partner in this industry have now invested heavily in 3D surface metrology and have seen clear benefits from its use in terms of product quality and new product development. 1.6.3 Metrology instrumentation industry The developments in the surface roughness parameters, data filtering techniques calibration procedures and artefacts will directly benefit surface metrology instrument manufacturers. The companies will be able to quickly implement the results of the project into their proprietary equipment. These manufacturers will then be the first to implement the new standard and will lead the world in the levels of sophistication and power of their instrumentation and software thus giving them a clear advantage to service the increasing demand for surface measurement in 3 dimensions. 1.6.4 Electronics and MEMS industry Advanced economies such as those in Europe are increasingly reliant of high added value manufacturing industries and manufacture such as electronics, wafer production and MEMS. The developments in technologies such as MEMS require sophisticated high precision traceable metrology and data analysis techniques to be carried out in three dimensions and this will become increasingly important as industry approaches engineering on a nanotechnology scale. The ideas set out in this project in terms of surface characterisation and, importantly, the generic aspects of instrument calibration when applied to atomic force microscopes will give a sound basis for the development of traceable measurement which the developing electronics MEMS and wafer industry require. 1.6.5 Structured surfaces Increasingly, surfaces are engineered to give very specific functions such as reflectance properties or geometrically fixed abrasives or surface geometries ideal for bone ingrowth. These surface are highly structured in their geometry and it is doubtful if traditional statistical approaches to characterisation will suffice. However, the approach given in this text concerning feature characterisation should provide a basis for developing the extraction and characterisation of the functionally important geometrical features of the surface.

Introduction

13

1.7 References 1. ISO 14460-1, "Geometrical Product Specification (GPS) - Geometric Features Part 1: General terms and definitions". 2. B Griffiths, "Manufacturing Surface Technology", Penton Press, 2001. 3. H.. Dagnall, "Exploring Surface Texture", Rank Taylor Hobson, Leicester, 1980. 4. J. Haesing, "Determining Surface Finish of Workpieces by means of Surface Standards", Microtechnic, VI5,1961, pp 24-28. 5. G. Schmaltz, "Technische Oberflachenkunde", Springer-Verlag, Berlin, 1936. 6. D.J. Whitehouse, "The Parameter Rash", Proceedings of the 2nd International Conference on the Metrology and Properties of Engineering Surface, Leicester, April 1981. 7. J. P. B. Williamson, "Microtopography of Surfaces", Proc, Inst. Mech. Eng., Vol. 182, Pt.3K, 1967-68, pp 21-30. 8. E. Mainsah and K. J. Stout, "Second International Workshop on the Development of Methods for the Characterisation of Roughness in Three-dimensions", Brussels, April 1993, Precision Engineering, Vol. 15, No. 4,1993, pp 287-288. 9. Final Report "Calisurf Project (SMT4-CT97-2176), European Commission, 2000. 10. Final Report AUTOSURF Project (BE-97-4140), European Commission, 2000. 11. Final Report "Transfer Standards for Calibration of Scanning Probe Microscopes", Project (SMT4 CT98-2209), European Commission, 2000. 12. C.J. Evans and J.B. Bryan, "Structured, Textured or Engineered Surfaces", Keynote Paper, Ann. CIRP 48 (2), 1999.


Parti Characterisation


Numerical Parameters for Characterisation of Topography Liam Blunt and Xiangqian Jiang School of Engineering, University of Huddersfield, UK

2.1 Introduction Numerical parameters for surface texture as used in engineering drawings are the means of communication between design, manufacture and functional performance, and the means of communication between a supplier and a customer. These parameters are not only used as a benchmark for manufacture and surface tolerance specification, but also especially in the case of 3D parameters to predict functional properties. The initial numerical parameter set for areal surface texture was developed in the early 1990s; the so-called Birmingham 14 parameters as shown in Figure 2.1 [1]. The amplitude parameters S , Sz, Sxk, and Sku as well as the spatial parameter S^ are extensions of those previously employed in the 2D characterisation methods. The other spatial parameters Str, Sal, are extracted from the areal autocorrelation function, and Std is determined through the areal power spectral density. The functional parameters are associated with the bearing area ratio curve, normalised by S^. The parameter set, though widely accepted as a success, was considered to be of somewhat theoretical nature and lacked sufficient practical evidence of applicability [2, 3].

Figure 2.1 The Birmingham 14 parameters

18


There are, however, still some problems with the definitions of these parameters, the mathematical descriptions in certain instances being ambiguous. Firstly, for example, when the connectedness of summits or valleys/pits on a random surface are considered, how does one calculate the number of summits or valleys and their mean size as a function of height from the mean/reference surface? How do summits join together to form ridges, or how do valleys link up? Secondly, does one improve the accuracy of the definitions and define more useful algorithms for hybrid parameters? Furthermore, suitable parameters relevant to the material ratio curve need to be more indicative, in order to characterise common functional properties, for instance, area and volume geometrical properties, or to describe wear and tribological properties. Under the SURFSTAND project, the improvement and verification work was carried out with the emphasis on much stronger practical evidence and more feasible applications. As a result, an improved and updated set of numerical parameters was built up during the project. This was reported to CEN/TC 290 on June 2001 and forwarded to ISO/TC 213 on February 2002 [4, 5]. The work has now been taken up by both the European and International Standard Organisations and forms a core part of the new basis for 3D surface texture standards [6-9]. The new numerical parameter set for 3D surface texture is intended to address geometrical properties, namely field and feature characteristics. The field parameter set, as outlined in this chapter, is used to classify indications of averages, deviations, extremes, spacing information and generic functional properties. The feature extraction methodologies will be introduced in the next chapter and allow dominant topographical features to be identified and catalogued. The feature extraction techniques are also a strong base defining summit/valley parameters and their mean size. One thing to note is that it is not always necessary to characterise surfaces using all the parameters. Statistical techniques such as significance testing and correlation analysis are useful in defining subsets of applicable parameters. Examples of this approach are given in later chapters dealing with specific case studies; in addition, a comparison study for 2D and 3D roughness parameters discussed in Chapter 8.

2.2 General terms Big fleas have little fleas which sit on 'em and bite 'em but little fleas have smaller fleas and so on, ad infinitum The useful value of the information conveyed by surface parameters is contained in the appropriate surface components according to the functional requirements, such as rough, wavy and primary surfaces. This mainly depends on the bandwidth for the surface analysis (obtained by using digital filtration techniques [10-13]) and the associated sampling conditions. 2.2.1 Bandwidth of surface wavelength Real surfaces contain surface features of many scales and sizes. Not all of these surface features will contain useful information for monitoring the surface creation process or contribute significantly to the function of the surface. The range of the

Numerical Parameters for Characterisation of Topography

19

sizes of the surface features with useful information needs to be identified before the surface is analysed. For example, in unpainted car body panels surface wavelengths of 1mm to 8mm are of interest since it is these surface wavelengths that correlate with the paint appearance and especially the "orange peel effect" in the final car body panel. Suitable surface analysis over these surface wavelengths will help control the manufacturing process and help eliminate the "orange peel effect". One way to specify a range of sizes of feature surface is via the bandwidth of the surface wavelengths. That is, to specify the range of wavelengths on the surface in two directions that are of interest. Once this range has been specified the filter can be tuned to accept only this range of wavelengths on the surface via its cut-off wavelengths (nesting index). 2.2.2 Sampling conditions Digital computers can only handle digital data with a finite number of points whereas real surfaces are a continuum. This means that before surface data can be used by a digital computer, the surface must be sampled. To make sure that the sampled surface is representative of the real surface and to avoid problems such as ailasing, the real surface must be smoothed to remove all small-scale features. Once the real surface has been smoothed it can be sampled. Sampling conditions give the conditions for acceptable sampling, against an agreed loss in surface information, for a particular level and type of smoothing. For example, the Nyquist sampling condition states that if there is a high frequency limit to a set of infinitely long profile data (defines level and type of smoothing} then there is no loss in information (agreed loss of information) if one samples at a higher rate than twice the high frequency limit (conditions for acceptable sampling}.

2.3 Field parameters The field parameters consist of the S-parameter set and the V-parameter set. The Sparameters depend on the height amplitude and spacing frequency, for description of both amplitude and spatial information. The V-parameters give fundamental information based on a material ratio curve (or so-called Abbott-Firestone curve or bearing ratio curve).

20


Figure 2.2 The S-parameter set

2.4 S-parameter set The S-parameter set contains 15 parameters and has been classified into five types, amplitude, spacing, hybrid, fractal dimension and other parameters, as shown in Figure 2.2. 2.4.1 Amplitude parameters The amplitude parameters depend on the height deviation, for description of amplitude-related properties of a surface. Six parameters are designed to characterise the amplitude property of surfaces. They are classified into two categories, average of ordinates and extreme peak and valley parameters. 2.4.1.1 Average of ordinates These parameters [1, 14] are used to describe (i) dispersion; (ii) asymmetry of the height distribution; (iii) sharpness of the height distribution as shown in Figure 2.3, the set includes: Root-mean-square deviation of the surface, Sq, is a dispersion parameter defined as the root mean square value of the surface departures within the sampling area.

where M is the number of points of per profile, and N is the number of profiles. rj(x,y) is the data set of the rough surface or the wavy surface or the primary surface texture, depending on a requirement of the surface analysis. In general, ;/(*,)>) is obtained by using filtration techniques [10-13]. Sq is a very general and widely used parameter. In statistics, it is the sample standard deviation (Figure 2.3a). Skewness of topography height distribution, Ssk, is the measurement of asymmetry of surface deviations about the mean /reference plane.


21

This parameter can effectively be used to describe the shape of the topography height distribution (Figure 2.36). For a Gaussian surface, which has a symmetrical shape for the surface height distribution, the skewness is zero. For an asymmetric distribution of surface heights, the skewness may be negative if the distribution has a longer tail at the lower side of the mean/reference plane (e.g. a honed surface) or positive if the distribution has a longer tail at the upper side of the mean/reference plane (a shaped surface). In a physical sense this parameter can give some indication of the existence of "spiky" features. Kurtosis of topography height distribution, Sku, is a measure of the peakedness or sharpness of the surface height distribution.

This parameter characterises the spread of the height distribution (Figure 2.3c). A Gaussian surface has a kurtosis value of 3. A centrally distributed surface has a kurtosis value larger than 3 whereas the kurtosis of a well spread distribution is smaller than 3. By a combination of the skewness and the kurtosis, it may be possible to identify surfaces that have a relatively flat top and deep valleys such as honing. In a physical sense the kurtosis indicates the peakedness of a surface.

Figure 2.3 Height distribution

22


2.4.1.2 Peak and valley These parameters are used to describe extremes of the height distribution as shown in Figure 2.4. The maximum surface peak height, Sp, defined as the largest peak height value from the mean/reference surface within the sampling area.

where 77 is the highest surface summit on the surface. The lowest valley of the surface, SV, defined as the largest valley depth value from the mean/reference surface within the sampling area. S

(2-5)

where rjv is the lowest surface valley on the surface. Maximum height of the topographic surface, Sz, defines the sum of the largest peak height value and largest valley depth value within the sampling area.

Figure 2.4 The extremes of height distribution

Typical values of amplitude parameters of a honed rough surface and a ground surface illustrated in Figure 2.5.


23

Figure 2.5 The amplitude parameters from different rough surfaces

2.4.2 Spacing parameters The spacing parameters refer to the spatial properties of surfaces and are primarily dependent on the information in the scanning and tracing directions. These parameters are designed to assess the peak density, and texture strength. These parameters are particularly useful in distinguishing between highly textured and random surface structures. Three parameters are used to characterise spatial properties, density of summits, fastest decay autocorrelation length and texture aspect ratio [1, 15]. Density of summits of the surface, Sds, is the number of summits of a unit sampling area. Sds should be assessed after Wolf pruning at 5% of Sz (default) [16, 17].

The density of summits of a grinding wheel surface before and after Wolf pruning at 5% of Sz is shown in Figure 2.6, after Wolf pruning Sds = 60 (I/mm2).

Figure 2.6 Density summits on a grinding wheel surfaces

24


The fastest decay auto-correlation length, Sal, is a parameter with the dimension of length and is used to describe the autocorrelation character of surface AACF's. It is defined as the horizontal distance of the AACF that has the fastest decay to 0.2. In other words the Sal is the shortest autocorrelation length that the AACF decays to 0.2 in any possible direction.

where

ACF(i:x,iv) is the areal auto-correlation function (ACF) of a surface as shown in Figure 2.6. For an anisotropic surface Sal is in a direction perpendicular to the surface lay. A large value of Sal denotes that the surface is dominated by low frequency (or long wavelength) components, while a small value of the Sal denotes the opposite case. Texture aspect ratio of the surface, Str, is a parameter used to identify texture strength i.e. uniformity of the texture aspect. Str can be defined as the ratio of the fastest to slowest decay to correlation length, 0.2, of the surface areal ACF function.

In principle, the texture aspect ratio has a value between 0 and 1. Larger values, say Str>0.5, of the ratio indicates uniform texture in all directions i.e. for no defined lay, for example, the EDM surface is as shown in Figure 2.7. Smaller values, say Str>-axis and carefully centred on the x-axis of the image. A series of measurements are performed at different positions on the standard. Other operating parameters should also be changed between measurements (see section 7.7.4). Each image is line-wise levelled to order 1 and the average profile is calculated. The image bow (see Figure 7.14) is quantified as the second order term CX2 of a polynomial least mean square fit to the average profile of an observed image of a flat surface or the equivalent peak to peak height Azflt of the second order term within the image area. In fact,, two fits to the measurement are made, one which follows the surface of the step and one which follows the surface on both sides of the step (see Figure 7.14). The vertical distance between the two best fits gives the observed step height, H. The average and the standard deviation is calculated for the measurements. The variation in sensitivity as a function of z offset is determined by measuring a step height for different average z-positions. An uncertainty budget is calculated on the basis of the standard deviation of the measurements, the measured variation in sensitivity (as function of offset) and the uncertainty stated on the calibration certificate of the standards.

192


7.8.4 Example of calibration Table 7.4 shows [6] the measured step height as function of the reference step for three standards: 13 nm, 80 nm and 800 nm (nominally). It can be seen that the uncertainties of the reference heights of 13 nm and 80 nm are much larger than the experimental standard deviation for the AFM measurements. Subdivision of the zscale thus requires further justification. Figure 7.14 shows the measured step height as function of the average z-position during recording for a 180 nm step height standard. For an average offset within ± Ij^m the correction factor is within ± 0.8%. From images of a flat surface (not shown) it was found that image bow in the x-direction of the tested microscope were 5±1 nm for offset within ± 1 um. After subtraction of the fitted plane, the roughness, Sq , for the remaining surface was approximately 1 nm. Table 7.4 The observed step height and the certified reference step height Standard deviation. For> 10 measurements

Relative stand, dev.

s(Azo) [nm]

s(Az0)/Az0 [%]

759.7

1.1

0.14

759.7

4.1

81.66

0.35

0.44

81.4

2.3

12.8

0.14

1.2

13.2

1.6

Observed step height Azo [nm]

Certified value A^nm]

Uncertainty on certified value u(Azref) [nm]

Figure 7.15 The measured correction factor C2for a 180 nm step as function of the average z position Za during recording of the image

7.8.5 Stated uncertainty for calibration In the present study the z-axis (height) of a metrological AFM equipped with distance sensors was successfully calibrated by the use of certified reference standards. Based on the investigation of flat surfaces and tilted step heights the non-linearity and measurement uncertainty of the system was assessed. If z is the observed height and Azmax is the maximal height in the image an expanded uncertainty of Uz = 2 nm + Q.02-Azmax (confidence of 95%) can be achieved with the calibrated microscope.

Calibration Procedures for Atomic Force Microscopes

193

7.9 References [1] J. E. Griffith, D. A. Grigg, J. Dimensional metrology with scanning probe microscopes, Appl. Phys. 74, R83-R109 (1993). [2] R. leach, J. Haycocks, K. Jackson, A. Lewis, S. Oldfield and A. Yacoot Advances in traceable nanometrology at the National Physical Laboratory, Nanotechnology 12, Rl (2001). [3] J. Garnaes, N. Kofod, J. F. J0rgensen, A. Kiihle, P. Besmens, O. Ohlsson, J. B. Rasmussen, P. E. Lindelof, G. Wilkening, L. Koenders, W. Mirande, K. Hasche, J. Haycocks, J. Nunn, M. Stedman, Nanometre scale transfer standards, Proceedings for euspen 1 st international conference and general meeting of the european society for precision engineering and nanotechnology, Edited by: P. McKeown, J. Corbett et al., on May31st-June 4th 1999, Congress Centre Bremen, Germany, Vol 2, 134-137 (1999). [4] K. Dirscherl, J. Garnaes, L. Nielsen, J. F. J0rgensen, M. P. S0rensen, J, Modelling the hysteresis of a scanning probe microscope, Vac. Sci. Technol. B 18(2), 621625 (2000). [5] A. Kiihle, A. H. S0rensen, J. B. Zandbergen, and Jakob Bohr, Contrast artifacts in tapping tip atomic force microscopy, Appl. Phys. A 66, S329-S332 (1998). [6] J. Garnaes, N. Kofod, A. Kiihle, C. Nielsen, K. Dirscherl, L. Blunt Treaceable step height and roughness measurements with atomic force microscopes, extended abstract for the 2nd International Conference of the european society for precision engineering and nanotechnology, Turin May 29th-31st 2001. A paper will be submitted to the proceedings of the above conference. The proceedings will appear in the international scientific journal of Precision Engineering. [7] Dimension 3100 with metrology head from Digital Instruments (now Veeco), Santa Barbara, CA, USA, www.di.com. [8] National Physical Laboratory (NPL), United Kingdom by the use of Littrow diffraction (green He-Ne laser) using a manual angle table with two readings on an optical screen. [9] N. Kofod, J. Garnaes, J. F. J0rgensen Methods for lateral calibration of Scanning Probe Microscopes based on two dimensional transfer standards, Proceedings of the 4th seminar on Quantitative Microscopy QM 2000 Dimensional measurements in the micro- and nanometre range, Edited by Klaus Hasche, Werner Mirande, Giinter Wilkening, Semmering, Austria, January 12-14 2000, PTB-Bericht, page 36-43 (2000). [10]N. Kofod, J. Garnaes, J. F. J0rgensen Calibrated line measurements with an atomic force microscope, European society for precision engineering and nanotechnology: Proceedings for the 1st Topical Conference on Fabrication and Metrology in Nanotechnology, Edited by L. De Chiffre, K. Carneiro, Copenhagen May 28-30, Vol. 2, page 373-381 (2000). [ll]Nils Koppels Alle Scanning Probe Image Processor, Image Metrology Aps., 402, DK-2800 Lyngby, Denmark, www.imagemet.com.

194


[12JISO/BIPM, "ISO Guide to Expression of Uncertainty in Measurement", Corrected and reprinted, 1995, 1993(E).

Part 3 Case Studies


8

The Interrelationship of 3D Surface Characterisation Techniques with Standardised 2D Techniques Robert Ohlsson, Bengt Goran Rosen and John Westberg Volvo Truck Corporation, Goteborg, Sweden; and School of Business and Engineering, Halmstad University, Sweden; and Volvo Car Corporation, Goteborg, Sweden

8.1 Introduction The objectives and main aim of the work discussed in this chapter is to compare 2D with 3D surface roughness parameters measured on functional surfaces. The functional surfaces provided were automotive cylinder liners, steel sheet product and ball bearings. Tests designed to throw light on the dispersion and variability, when measuring and calculating 2D and 3D parameters, were also carried out. These results indicated the number of measurement needed for a surface to receive a stable mean value for the topography. Additionally, work is discussed which shows the functional relationship between traditional 2D surface parameters and a range of the newly developed 3D parameters. This study allowed a deeper understanding of the functionality of automotive cylinder bores, and empirical wear relationships are proposed. Finally, studies were carried out on sheet steel for the purpose of comparing optical and tactile measurement techniques

8.2 Surface roughness parameters in relation to functional demands It is important to find relationships between functional performances for different surfaces and specific surface roughness parameters. By accomplishing this goal it should be easier to control the optimal manufacturing of these surfaces and it will also help to justify specification of functionally critical surface roughness parameters. This is especially important for the development of 3D parameters since one goal is to keep their number to a minimum. Three different types of surfaces have been evaluated: cylinder liners, ball bearings and a set of steel sheets with different textures. For the cylinder liner and its counterpart, the piston ring, the most important functional demands are oil consumption, blow-by, and wear specially at the TDC (top-dead centre). One important performance characteristic

198


for the steel sheets is lubricated friction and this has been investigated through a set of BUT (bending-under-tension) tests.

8.3 Cylinder liner topography and functionality For this work a factorial designed experiment (FDE) was performed where surface roughness was correlated to functional performance indicators such as oil consumption, wear, and blow-by in a 10 litre truck engine. The choice was to vary the roughness of the piston ring over three levels (Ra) and the cylinder liners with two variables both varied over three levels. For the liners the variables were the so-called "plateaux ness" (Rvk/Rk), which described the surface structure and an amplitude parameter (Rz), described the size of the topography. The values can be seen in Table 8.1. Table 8.1 The test plan used in the FDE Piston Ring

Test no

Rz

Ra 1

a

3 4 5 6 7

Cylinder Liner -v?%:j,i •-.,» • .; RvW^fcXE 3 3

16

0,5-0,6 Sibetex C > Sibetex A

10.5 Galling experiments according to DBS multi-strip approach Before starting the actual galling experiments, a full characterisation of the surface topography of all materials that were be used in the galling experiment was carried out. A full description of the roughness instruments and the measuring methods is given in section 10.5.1, as well as a survey of the measurement results for the full set of materials. The galling tendency of the set of materials has been assessed by application of the DBS multi-strip test. Results of the galling experiments have been analysed and discussed. After testing, samples were analysed and evaluated by visual inspection of the surface within the zone touched by the tools. In order to quantify the galling severity for all materials and to rank them unambiguously, a new approach has been elaborated based on 2D profile measurements and leading to the definition of a new index, which proved to be a good measure for the galling severity. The correlation between galling behaviour and surface topography of the steel sheet has been addressed based on the outcome of this galling experiment. 10.5.1 Roughness measurements Roughness instruments Introduction Two roughness instruments have been used for the roughness characterisation of the full set of materials used for the galling experiments according to the DBS multi-strip test: • Rank Taylor Hobson (Form Talysurf Series S6 PGI) based on the mechanical stylus measuring principle allowing both 2D and 3D surface characterisation. • WYKO RST+ based on vertical scanning interferometry (VSI) principle only allowing 3D-characterisation of the surface.

276

Advanced Techniques for Assessment Surface

Topography

3D-characterisation Table 10.12 3D roughness characterisation Characteristics Manufacturer Type Measuring Principle Vertical Range Vertical Resolution # Data Points (X/Y) X / Y resolution

Stylus Taylor Hobson FormTalysurfS6PGI Mech. Stylus (radius 2um) 10mm 13nm 4096 / 256 0.25um/ lum

Optical Wyko RST+ VSI and PS1 SOOum(VSI), 160nm(PSI) 50nm (VSI), [3 nm (VSI), 3 A (PSI) ] 736 / 471 or 368 / 236 or 256 / 256 3.38 / 3.80um, 0.9 / 1 ,lum,...= f (objectives)

Software Data format Inputs Data Format Outputs Conversion to ASCII?

Mountains 1.0 MAP, SUR SUR SDF Technician, high level

Vision 1.8 OPD OPD, SDF, TIFF SDF (only for < 368/236) Technician, high level

Operator Skill ID-characterisation

Table 10.13 2D roughness characterisation Stylus Characteristics Taylor Hobson Manufacturer FormTalysurfS6PGI Type Traverse Unit (+ max. travel) 120mm Phase Grating Interferometry Pick Up 2^m, 1.5mm Stylus (tip) radius No skid Skid lOrnm Vertical Range 13nm Vertical Resolution 0.25nmor lym Horizontal Resolution 0.5jim over 1 20mm, 0. 1 jim over 20mm Straightness Software Data Format Inputs Data Format Outputs Conversion to ASCII Operator Skill

FTS V6. 1 3, Talyprofile V 1 .3 PRF, PRO, PRA PRF, PRA PRA (ASCII, imitj»m • ' ' : - : ' ' - • ::- •• v twfcWWCSSppisp^.^^/^'^^:^,/^^^-

. -, -• :•.

Manufacturer Type Lt (travel length) Lo (assessment length) # data points Skid Travel speed Filter DIN filter Cut-off Xc X*/Xs = 300 Measuring direction Parameters (only those mostly used!)

Sg&f

;.:.,,-

Taylor Hobson FormTalysurfS6PGI 15mm 12.5mm 60000

No

lmm/s Gauss M1/DIN4777 2.5mm

yes 45° Ra, Rz, Sm, PC and Abbott

10.5.2 Surface topography characterisation of EBT, EDT and ECD materials As already stated a full 2D (RTH, stylus) and 3D (WYKO) roughness characterisation was carried out on all materials (EBT, EDT, ECD) before starting the galling experiment. Materials with EBT texture were delivered by the Sidmar plant and other materials were collected from competitors. Table 10.16 shows the main mechanical properties of these materials. Note the similarity in material thickness.

SI S3 S5 S6 S9 S10 g4CRS sSCRS s7CRS

Bl B3 B6 B8 H2 Hll P2

EBT EBT EBT EBT EBT EBT EBT EBT EBT EDT EOT EDT EDT EDT EDT ECD

D B C C C A A C B

w> a

ie U

ELO ELO

GI GI GA ELO CRS CRS CRS ELO ELO

GI GA GI GA GI

database). Here, experts using the system have verified the data stored in the database.

328


Figure 12.2 Information flow when all information is structured and stored in a central database available for all users within the company

123 What is a knowledge based expert system? The definition of a "knowledge based expert system", in this context is founded on the idea of several users working in different networks, spread globally, sharing the same data and generating new data for the shared database. The new data is generated with help from different support-applications that are available in the system.

Figure 12.3 Information is retrieved from the database and used to generate new data The users of the system act in different roles depending on the purpose of their transactions with the database. The users belong to one or both of the following main categories: 1. Product developers. 2. Measuring engineers, test engineers.

Surface Texture Knowledge Support

329

The product developers use the database to extract information from the data that is produced by the tests that the measuring/test engineers carry out. The extracted information is used as a decision support tool for the design parameter determination. The measuring/test engineers use raw data from the measuring machines to produce representative data for the tests, e.g. different surface parameters, Sa, Ssc etc, or different functionality parameters e.g. skew, lift off, speed.

12.4 Knowledge database The "database" will consist of different "islands" of information. Each "island" is built by relationships between object-classes' and modelled according to a classic relational database model. The different "islands " are: • • • • •

test database (raw test data); expert knowledge (rules); specifications; standards (ISO, company, etc.); external (other published material).

12.5 The (expert) knowledge structure The "expert knowledge" subject for storage is categorised in three main competence categories each described as a set of rules. The set of rules are design rules, manufacturing rules and measuring/quality rules. Each set of rules can be accessed at different levels (see Figure 12.4) for different purposes of use.

Figure 12.4 The structure of the "expert-knowledge " area in the database. Design rules are decomposed in three different levels. Here, from pure test data to an abstract level of theoretical formulas

Object class: database term that roughly means a clearly distinct subject that contains concrete data, such as parameters, administrative data. Relational classes connect object classes.

330


12.6 Test data database

Figure 12.5 The relational database model for the test-data. The model illustrates the functional relationship between different sets of data

Figure 12.5 above shows a general model that can be used for most kinds of products and different kinds of tests, e.g. heat tests, surface roughness tests etc. The difficulties arise in the representative data entry. To extract data and to compare two different measurements, there must be some kind of standard format for the representative data entry. However, this model takes care of different standards by splitting the contents of the representative data into a number of value pairs, there is then the possibility of dynamically defining which parameters are to be included in the representative data entry. The cost of the dynamic structure is paid for in the implementation model. In this case it will be harder to develop templates for the representation of the data; instead, there must be an interface that can adjust to any number of parameters and their corresponding values.

12.7 The distribution of database information in a network This section deals with some alternatives, regarding network topology and software, for distributing data between users located in the same, or a different local networks.


331

12.7.1 Internet/World Wide Web The internet is a global network where companies, universities, individual users etc are connected via modems or leased lines. The internet has been fully operational for the last twelve years and it is not "owned" by any specific organisation However the World Wide Web is a recent phenomenon that started seeing widespread use from the mid 1990s. Soon after the invention of advanced graphical web browsers like Mosaic and Netscape, companies and their customers gave the web their attention. The new tools made it easy to graphically transfer rich information with just a click with the mouse, instead of having to know a numerous cryptic commands that have to be typed in by hand. 12.7.2 The intranet Instead of using the classical client-server model, there is an option to use internet techniques for sharing and distributing data among users in a local intranet, and external users via the internet. This model makes the system transparent, with respect to the OS. The idea is to have web-servers that contain both the databases and the applications. The client application interfaces are available via html-files that are downloaded via the http-protocol. When it comes to the execution of programs, which are started by the users through the html-interfaces in a web-browser, there are three options: 1. Program processing is executed on the server. Eventual confirmation is sent to the user in html-form (see Figure 12.6). 2. Program processing is executed on the client side. When the user downloads the html-application-interface, the user also downloads the application Java. The application, however, connects to the server to perform eventual database transactions (see Figure 12.7). 3. Program processing is executed on the user side. When the user downloads the html-application-interface the user also downloads the application (ActiveX). The application opens a connection to a server-database on the same local net. The first alternative makes use of CGI techniques (common gateway interface.) to connect to the server. It provides the server with the actions taken by the user on the html-page (e.g. values entered by the user in the html-form). When the server receives the request to process a program-execution the program reads the parameters entered by the users. The program is then executed. During the program-execution the program stores information in an html-file that is returned to the user (see Figure 12.6).

332


Figure 12.6 Persistent data and information-flow, process initiation from the server, on request from the client The second alternative uses Java to execute the application on the client computer, after downloading both an html-file and a Java-applet from the web-server. The client computer then compiles the downloaded Java-applet. The application executes at the client computer and connects to the remote database via JDBC, which is an interface between the application and the database, Figure 12.7.

Figure 12.7 Persistent-data/ information flow and process execution/compilation, the client requests a html-page via a web browser and receives the html-page and the Java-code, which is compiled at the client by the clients' web browser. The Java-application is then executed at the client. The Java application finally connects to a database server and commits transactions via TCP/IP The distribution of Java-applets through html-pages makes the system platform independent. This is because the received Java-applet is a 6yte2-code that has been 2

The byte-compiled code is evaluated by the byte-code interpreter, instead of being executed directly by the machine's hardware (which true compiled code is), byte-code is completely transportable from machine to machine without recompilation.


333

virtually compiled (see glossary, under Java) by the provider. The client has to compile the code for the client hardware, using a compiler that is provided by the web-browser program.

12.8 Java-JDBC The system consists of the following components: • • • •

Database. JDBC, or ODBC-JDBC bridge. Java applet, or Java-application. Html-page embedding the Java-applet.

Compared to the CGI-ODBC connection, the Java-JDBC connection performs the database transfers and communication on the client machine. Because of this, there might be problems connecting to the database if there is a firewall between the client network and the server network. The client must also be able to authenticate the right to connect to the database. Currently, there is much development going on with the JDBC and all major database and software vendors join and support the JDBC. There also exists a bridge for databases that does not support the JDBC: the ODBC-JDBC bridge. This bridge allows a connection with the help of ODBC. The strongest argument for using Java is platform independence. Theoretically, all clients who can access the web-server containing an html-page are able to download the Java applet/application. One advantage is that the security in Java protects the client machine and "put sticks in the wheel" because the applet is not allowed to do file operations such as make files, delete files and read files. The Java applets and Java applications were developed with Microsoft Visual J++ 1.01. There were no testing of JDBC, but Microsoft provides a special database interface (limited functionality) object in Visual J++ that was used to connect to local desktop databases. The development environment is very sophisticated (the standard Microsoft developer studio environment that are used for most Microsoft software products e.g. C++), but the features in Visual J++ for visual programming is yet not that good. The functionality to develop good user interfaces exists in a very limited way, however Java is in an early development phase.

12.9 Bearing surface application In order to test the feasibility of the test database discussed above, a prototype system based on the Oracle relational database, Java application, Java applet, JDBC and html was implemented. The specifications applied to the system were to enable central archiving of measured surfaces and functional tests. The system should also permit different clients to browse the database, extend the database with new tests and finally to generate answers on user queries combining the stored functional and surface data into new knowledge, hence utilising a demonstrator of an interactive decision support for surface texture specification.

334


The application consists of two parts. Part one is an administrative application with a users interface to store new or modify old test data in the central database. Here, tests consist of measured functional and surface data, as well as representative data compiled by domain experts to support user queries. The second part is an application permitting browsing through the test database and queries to extract information. The browsing part is accessible for the clients via the Internet on an html page has been queried for surfaces being subjected to input parameter Velocity less than SOrpm and output data from the test Traction (friction) between 0.05 and 0.1. The search resulted in a surface WB0983b with the surface parameters and visual appearance as shown below. In this way, all tests in the database can be combined to extract surfaces fitting users' specific requirements thus generating new knowledge combining surface texture and functional behaviour. All queries are based on the data stored as the representative data in the database.

Figure 12.8 A query to the database regarding velocity and traction (friction) resulted here in a link to a surface in a specific named test. Here, both the 3D texture parameters and one of the surfaces' images is visible Part one, the administrative application, is via a separate Java based applications file accessible for the administrative user via a batch file starting the Java applet shown. Here, the administrator can store tests along with data and descriptions according to the structure given in Figure 12.18 above. Representative data, descriptive documents and source data can here be added or modified to new or existing tests in the database.

12.10 Conclusion Agile manufacturing concepts stress the need for computer aided tools to increase lead times and promote co-operation within and between organisations. Within distributed organisations, the need for fast access to data and the broad variation of information types, (documents, pictures, tables, raw test data, extracted


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high level knowledge etc calls for distributed web-base solutions and standardised information formats. To improve the usability of computer-based decision support, the use of the concept of user views to the knowledge database system, e.g. designer, manufacturing and quality control views is beneficial. The user views are pre-defined sets of data suitable for the individual users needs. Representative data extracted from tests enable the comparison of different tests and the possibility to continuously add new data to a database. This is a key feature of a successful knowledge database. The distribution of knowledge support will be eased by the use of platformindependent solutions e.g. based on Java applets and applications. A pilot system has been developed to illustrate the usage of knowledge support in surface texture applications - the bearing surface application. Here, an initial workbench to further investigate the possibilities with distributed knowledge support was created and showed good promise. In the future, use of computer aided knowledge support will be forced upon organisations by the agile production and systems based upon those described in this section will be necessary tools to ensure competitive business.

12.11 Glossary ActiveX: Components developed in PC-operative-system programming languages e.g. Visual Basic, C++ or Delphi. The components are compiled by the host programming language as ActiveX-components, which means that dll-files are created (with an .ocx extension instead of.dll). The components could be embedded in an html.page an downloaded to users via Internet. The technique is platform dependent (Windows 95, 98, NT, 2000). The component is permitted to use the clients operative-system e.g. to make file-manipulation etc (compared to Java which is not allowed to use file-handling functions). Microsoft developed the ActiveX-technology to compete with Java. CGI: (Common Gateway Interface}. A standard communications interface that allows web servers to communicate with back-end processes e.g. database applications, or other server based applications. Client-server: Distributed data processing between a client and a server connected via a network. The server is a computer (or many) that owns programs or data that it can provide to clients asking for it. The client is the computer (or process) that requests a service from the server computer (or process). The client handles the user interface and sends input data to the server, which processes the input-data and responds to the client. Extranet: For corporate businesses who want to co-operate on certain projects. Useful to join parts of their intranets with each other over the Internet. The connection must be transparent so that the users on each intranet could co-operate as if they were

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on the same intranet. The technique to go through firewalls via Internet is called tunnelling (see glossary: tunnelling). For example: imaging Microsoft and IBM in a project, they would like to reveal some parts of their intranets to each other (the concerned departments), but they would not like to have their merged intranets exposed on the Internet. Not only intranet users, but also standalone users sometimes wish to set up this kind of communication to other stand-alone users/intranets. Groupware: Software that allows multiple users to work as a group on the same set of data or documents. Groupware often consists of several types of office-software e.g. e-mail and other group-oriented communication features. Lotus Notes is an example of a groupware. Most groupware use client-server architecture. Intranet: A network that uses http and other internet-techniques to view and deploy information, within the network only, not to the public. A TCP/IP protocol is necessary to set the communication up. The network does not have to be connected to internet. Java: A programming language created specifically for the web environment. In contrast to traditional programming languages like C/C++, which must be compiled into versions that only run on specific platforms, Java is delivered in an uncompiled form and is interpreted at the web client end. Javascript: An interpreting language that is used to enhance html pages. The language differs quite a lot from Java, it is written in the html page that should use it and the language is not truly object oriented. Javascript is a tool for non-programmers and provides a fast way to enhance html pages (e.g. add functions that can be invoked by pressing input buttons on the html page). JDBC: Java Database Connectivity Standard is part of the Java Enterprise API3. JDBC is an SQL based database access interface. It provides Java programmers with a uniform interface to a wide range of relational databases, and also provides a common base on which higher-level tools and interfaces can be built (similar to ODBC, but platform independent). ODBC: Open Database Connectivity. A methodology for communication with databases through a driver interface that works on the same principle as a printer driver. In this way an application can control a certain database by choosing the ODBC for that database, (see JDBC for a similar approach for a platform independent method.) TCP/IP: Transport Control Protocol / Internet Protocol includes standards for how computers communicate and conventions for connecting networks and routing traffic.

3

API: Application Programming Interface, A set of routines or function calls that allow an application to control, or be controlled by, other applications.


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Tunnelling: Relative to the Internet, tunnelling is using the Internet as part of a private secure network. The "tunnel" is the particular path that a given company message or file might travel through the Internet. A protocol or set of communication rules called Point-to-Point Tunnelling Protocol (PPTP) has been proposed that would make it possible to create a private network through "tunnels" over the Internet. Effectively, a corporation would use a WAN as a single large local area network. This would mean that companies would no longer need their own leased lines for widearea communication, hence securely using the public networks. VBscript: An interpreting script language that Microsoft invented together with the ActiveX technology. VBscript is similar to Javascript. The intention of VBscript is to make html pages use ActiveX components and provide non-programmers with some functionality to enhance their html pages.

12.12 References 1. K.J. Stout, P.H. Osanna, B.-G. Rosen, The Structure for functional control of manufacturing processes, submitted end of December to IQMM'2001 International NAISO Symposium on Information Science Innovations in Intelligent Quality Management and Metrology, Dubai, February 2001. 2. Hongjun Wang, B.G. Rosen, J. Rosen, Inspection Information Modelling based on STEP in Agile manufacturing, abstract submitted to the CIRP conference in Design in the New Economy, Stockholm, in the summer 2001. 3. Rosen B-G., Mathematical Machining, a way to control the surface engineering cycle, presented at the Workshop on Engineered Surfaces, June 3-4, Hotel de la Poste Corps la Salette, Grenoble, France, (1998). 4. Rosen B.-G., Ohlsson R., Westberg J., Interactive surface modelling, an implementation of an expert system for specification of surface roughness and topography, In; K.J. Stout (ed.) Proceedings of the 6th Int. Conf.: Metrology and Properties of Engineering Surfaces, Birmingham, UK, April 6-8, (1994). & Int. J. of Machine Tools & Manufacture, Vol.35, No.2, pp. 317-324, (1995). 5. Rosen B.-G., Crafoord R., Interactive surface modelling: model of a functionoriented expert system for specification of surface properties, Industrial metrology, Vol.2, Nr.2, pp. 107-119, (1992).


13

Future Developments in Surface Metrology Liam Blunt, Xiangqian Jiang and Paul J. Scott School of Engineering, University of Rudders field, UK; and Taylor Hobson Ltd, Leicester, UK

13.0 Introduction Although the SURFSTAND project laid the foundations for areal surface texture standardisation, there is still a lot of work to be carried out before international standardisation is finalised with full integration into the Geometrical Product Specifications and Verification (GPS) system. GPS defines, in technical documentation such as engineering drawings, the geometry, dimensions and surface characteristics of a workpiece which ensure optimum functioning of the workpiece, together with the dispersion around the optimum where the function is still satisfactory. Further, the system specifies how these workpieces will be measured in order to compare them with the specification. The GPS system includes: size, location, orientation, form, surface texture etc. and is the common language between designers, production engineers and metrologists to control the geometrical requirements of engineered components. Figure 13.1 shows the relationship between designer, production engineer and metrologist in the GPS system.

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Figure 13.1 Relationship between designer, production engineer and metrologist in the GPS system Standards in the field of GPS are being prepared within the International Organisation for Standardisation (ISO) by Technical Committee 213 "Dimensional and geometrical product specifications and verification'' (ISO TC213). ISO TC213 was formed in June 1996 and has a remit that deals with basic definitions, symbolic representation, specification and verification principles, measuring equipment and calibration requirements including the uncertainty etc. in the GPS system [1]. Since surface metrology is part of the GPS system, as the GPS system develops so may surface metrology and visa versa.

13.1 The next generation GPS system The current GPS system developed from three distinct sources: 1. Geometrical tolerancing. 2. Co-ordinate metrology. 3. Surface texture and form measurement. Initially, experts from ISO TC213 developed a masterplan [2] to bring the three areas together, to systematically identify the contradictions and gaps in the standards that cover GPS. As experience was gained and general GPS principles developed, experts in ISO TC213 soon recognised that a truly integrated GPS system was possible, based on fundamental GPS principles rather than sticky plastering the three GPS sources together. The new integrated GPS system was termed 'the next generation GPS" [3]. Most of the current workload of ISO TC 213 is aimed at developing the fundamental GPS principles for the next generation GPS using well-founded mathematics. One particular challenge with the current GPS system that affects surface texture is the fact that there are two workpiece co-ordinate systems. The workpiece co-ordinate

Future Developments in Surface Metrology

341

system for surface texture is based on the direction of the surface lay. A surface texture profile is measured perpendicular to the surface lay. The rest of the current GPS system uses a workpiece co-ordinate system that is based on the geometry of the workpiece. For example, a straightness profile is measured parallel to an edge of a face or parallel to an axis. The fundamental GPS principle, which can address this particular challenge, is the recognition that it is surfaces that interact with each other functionally, not profiles. Hence, the principal GPS definitions should be based on surfaces, with profile definitions as secondary simplified operators. Thus, the next generation GPS will be one system based on surfaces. Currently, the principal surface texture definitions are based on profiles [4-6]. Adoption of the next generation GPS will mean a paradigm shift for surface texture with areal surface metrology becoming the principal definition and profile surface texture a secondary simplified operator. It is envisioned that areal surface texture will be mainly used for research, diagnostics and function and that profile surface texture will still be the dominant approach for control of the production process.

13.2 The surface texture toolbox The full specification of surface texture has many stages: from the size, shape and location of the measuring window (partition), the sampling procedure (extraction), the scale of the features of interest (filtration) to the definition of the surface texture characteristic (measurand), see Figure 13.2. At each stage there are many choices to be made, depending on the design requirements of the surface to be specified. The challenge for the future is to standardise a set of tools for each stage that will enable optimisation of the design requirements and especially the functional requirements of a surface. The increasing demand for the manufacture of more precise parts at less cost and the improvement in technology has required more flexibility in surface texture standards. The toolbox approach to specifying surface texture provides this flexibility and will include already established tools as well as the development of new tools. For example, consider the filtration stage. Currently (2002), only the Gaussian filter is standardised in the GPS system [7]. ISO TC 213 set up Advisory Group Nine (AG9) to include investigation into possible filtration techniques that could be used as new filter tools for GPS. AG9 have recommended a toolbox of new and novel filter tools that include mean line filters, envelope filters, robust filters and techniques that decompose surface texture into different scale components. The recommended toolbox was developed to meet current and future GPS requirements in filtration. Further, all of the recommended filter tools in the filtration toolbox are applicable to surface texture. It is intended to publish the filtration toolbox as an ISO technical specification so GPS users can assess their utility first, before publication as a full standard.

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Figure 13.2 The duality principle which defines the relationship between specification and verification

133 Default rules In the past designers have not adequately specified their surface texture requirements but left many of the specification stages for others to specify. Ambiguities in specification, if left unresolved, can lead to very real economic problems. This is especially true in today's global economy where outsourcing of manufacturing can mean that the designers, production engineers and metrologists are not necessarily on the same site to clarify the ambiguities. Further one fundamental GPS principal, the duality principle, states that specification determines the verification (Figure 13.2). In other words, the tools and their values chosen in the specification should determine the tools and their values in the verification. This puts greater emphasis on the designers to adequately specify their design requirements and not to let the metrologists surmise which tools and values to use during verification. Thus each callout on technical documentation shall include all the relevant information for an unambiguous specification. To stop technical documentation becoming cluttered with long callouts, with all the relevant information for an unambiguous specification, the GPS system provides a mechanism to simplify callouts through default rules. A default rule is a standardised way to predetermine a specification tool with fixed values if not otherwise indicated in a callout. For example if only Rz=0.2^m was indicated in a surface texture callout then the default rules predetermined in ISO 4288 [5] would be used. Here there is a table and an iterative algorithm to determine the default filter cut-off values and evaluation length to use, dependent on the measured value of Rz.


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For surface texture, only default rules for surface roughness profile parameters currently exist [5]. The default rules for areal surface texture are still being debated and are part of a general discussion within ISO TC 213 on a generic approach to default rules. The default rules for surface texture (areal and profile) shall have to be consistent with the agreed generic default rules for the GPS system, though it is envisioned that any changes to the profile default rules will be minor, consisting of tightening up the mathematical definitions.

13.4 Comparison rules Comparison rules are used to compare a measured parameter value(s) with the specified value to check if it is within tolerance. The uncertainty of the measurement procedure is an important element of comparison rules. The tolerance zone, in which the measured value(s) must lie, may have to be modified to take into account the uncertainty. For profile surface texture parameters there are two standardised comparison rules [5]. The default comparison rule is called the 16% rule. Here 16% of the measured values taken in an (unspecified) neighbourhood around the place of "maximum roughness" on the surface are allowed to be larger than the specified tolerance value. The 16% rule modifies the tolerance zone to take into account the fact that for surface texture the largest uncertainty contributor for a measured parameter value is usually the variation of the parameter's value over the surface. The other comparison rule is called the max rule. Here all measured values taken on the surface under inspection shall be smaller than the specified tolerance value. The comparison rules for areal surface texture are still being debated, though it is envisioned that they will be the same, or very similar to, the profile comparison rules with any changes being very minor and consisting of tightening up the mathematical definitions.

13.5 Pattern analysis and structured surfaces The surface creation process (such as grinding, milling, turning, etching, rolling etc.) all leave their unique signatures in the surface texture of the surface. These signatures consist of various types of patterns on the surface with different creation processes forming different patterns. For surface texture the analysis and characterisation of these patterns can help with diagnostics of the surface creation process as well as with functional prediction and diagnostics. Many of the traditional surface creation processes (such as grinding, milling, turning etc.) leave stochastic patterns on the surface. Surface texture parameters that characterise the cloud of surface points, using statistical techniques, are called field parameters. Field parameters are quite good at characterising stochastic patterns. This is one reason why traditional profile parameters have been so successful in process monitoring traditional surface creation processes.

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Advanced Techniques for Assessment Surface

Topography

Figure 13.3 A typical structured surface 1 x 1mm Improvement in technology, however, has resulted in optimised-engineered surfaces being increasingly used by industry to both increase functional performance and to lower costs. Many of these optimised-engineered surfaces leave highly distinctive structured patterns on the surface such as for example nominal square based abrasive pyramids (Trizact™) [8], see Figure 13.3. The definition of the structured surfaces was given by Evans and Bryan[8] as structured surfaces are those where the surface structure is a design feature intended to give a specific functional performance(e.g. retro-reflective pyramids in a road sign) These so-called structured textured patterns are becoming economically more and more important. For example 3M reported that in 2000 its microreplication process, used to produce structured surfaces, had grown into a $1 billion business [9]. Unfortunately, field parameters are not very good for characterising structured surfaces. Rather than characterising the required differences between features, characterisation using field parameter is dominated by the regular structure of the features. Its is becoming increasing clear that much development in the field of structured surfaces at both the micro and nano-scale will result in high aspect ratio, highly structured surfaces. Micro replication surfaces such as the 3M surfaces and very high aspect ratio surface features resulting from etching of silicon will represent a new challenge to surface metrologists. What is likely to result are hybrid techniques utilising feature extraction technology as well as techniques borrowed from the coordinate measuring machine world. It is envisaged that the analytical approach will be initially used to isolated the dominant features, recognise their standard geometry, and then finally perform a statistical analysis on the deviation from the idealised form of the structural elements within the surface. The information in all surface geometrical patterns is contained in the attributes of the individual pattern features and the structural relationships between these features.


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Thus, to extract this information the individual pattern features need first to be identified before characterisation. Care is need in extracting these features since the measurement process can produce many insignificant artificial features that swamp the subsequent pattern analysis. The stable extraction of significant surface features is discussed in detail in Chapter 3. Surface texture parameters that characterise feature attributes or the structural relationships between these features are called feature parameters. Feature parameters are much more diagnostic than field parameters. A medical analogy is useful to illustrate this point. Many field parameters such as Sq are analogous to taking a patient's temperature - a high temperature indicates that something is wrong but it could be anything from a cold to cancer. In contrast, characterising symptoms from the patient (sore throat, running nose, chest pains, shadow on a chest X-ray etc.) are diagnostic. Techniques to characterise structured surfaces are still being researched with some very promising novel ideas being developed [10]. It is envisioned that pattern analysis, through feature parameters, will become a very important tool for the future in the surface texture toolbox and this will be an essential requirement of precision and nanoscale metrology of high aspect ratio features such as those resulting from MEMs processes

13.6 Instrumentation There are many different types of instrumentation that measure surface texture, each using a different physical principle to interact with the "surface" (e.g. mechanical stylus, white light interferometry, scanning probe, capacitative, pneumatic etc.). The type of surface that results from a measurement depends on the nature of the species of the object that interacts with the "surface". Currently, the two most common are based on a mechanical stylus and light photons resulting in the "mechanical surface" and an "optical surface" respectively. By convention, in the next generation GPS system the default surface is the mechanical surface based on a rolling sphere [11], and hence mechanical stylus instrumentation (CMMs, contact stylus texture instruments, AFMs etc.) will remain the reference surface measurement method. This does not preclude other approaches from being used in practice. In fact, it is envisaged that though contact stylus instrumentation will remain the principal method for surface texture profile measurement, other true areal measuring systems, such as white light interferometry, will prevail in practice for areal surface texture measurement due to their speed of measurement, amongst other factors. Whichever exotic approach is used to measure a surface there is an important requirement to make that measurement traceable to international standards. Further, since the mechanical surface is the default surface if no other surface is specified there will be a need to relate the actual measurement surface back to the mechanical surface. Tracability of both hardware and software is very important, especially for outsourcing in a global economy. For only through tracability and the associated uncertainty calculations can different surface texture measurement instruments throughout the world hope to achieve compatible results. Traceability of hardware is

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currently achieved via certified calibration standards [12]. Calibration standards will need to be evolved to include areal calibration of surface texture instrumentation (see Chapter 6. Traceability of software will be achieved via certified softgauges and reference software [13], though here there is still much work to be done. A lot of future work, especially at national laboratories, will go into achieving global traceability. It is envisioned that there will be many international collaborative projects developing standardised procedures for traceability, especially for certified softgauges and reference software for areal surface texture.

13.7 Timetable of events As mentioned in the introduction, although the foundations for areal surface texture standardisation have been laid, there is still a lot of work to be carried out before international standardisation is finalised. The following presents a timetable of events leading to international standardisation of areal surface texture. Some events are historical, others are in the future: April 1990

Start of project " Development of Methods for the Characterisation of Roughness in Three Dimensions" under the leadership of Birmingham University.

April 1993

End of project "Development of Methods for the Characterisation of Roughness in Three Dimensions" under the leadership of Birmingham University.

Sept 1993

"Blue book" published [14] containing the Birmingham 14 Parameters.

May 1998

Start of SURFSTAND project under the leadership of Huddersfield University.

May 2001

End of SURFSTAND project under the leadership of Huddersfield University.

Jan 2002

SURFSTAND & AUTOSURF projects presentations to ISO/TC213 in Madrid, Spain.

June 2002

Surface texture taskforce set up by ISO/TC213 to determine requirements for standardisation of areal surface texture.

Jan 2003

ISO TC213 set up new Working Group WG16 to develop new surface texture system as part of GPS 2002.

2006

Publication of areal surface texture technical specification documents by ISO.

2007

Publication of areal surface texture standards documents by ISO.

2400

Dr Spock uses Taly-triquarter 2400 on the Enterprise to measure surface geometry characteristics of dilithium crystals.


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13.8 References [I] [2] [3] [4] [5] [6] [7] [8] [9]

[II] [12] 13] [14]

GPS Business plan http://l 29.142.8.149/isotc213/213business%20plan.pdf. ISO/TR 1463 8 Geometrical product specification - Masterplan (1995). ISO/TC 213 N 355 Annex 1 Next generation of the Geometrical Product Specifications (GPS) language, the vision for an improved engineering tool (2001). ISO 4287 Geometrical Product Specifications (GPS) - Surface texture: Profile method- Terms, definitions and surface texture parameters (1997). ISO 4288 Geometrical Product Specifications (GPS) - Surface texture: Profile method-Rules and procedures for the assessment of surface texture (1996). ISO 3274 Geometrical Product Specifications (GPS) - Surface texture: Profile method - Nominal characteristics of contact (stylus) instruments (1996). ISO 11562 Geometrical Product Specifications (GPS) - Surface texture: Profile method - Metrological characteristics of phase correct filters (1996). Evans, C.J. & Bryan, J.B. Structured, textured or engineered surfaces, Keynote Paper, Ann. CIRP 48 (2) (1999). 3M The one-billion-dollar lens, [10] Porrino A, Sacerdotti F, Visintin M, Benati F, "Applications of Gram-Schmidt Filtering technique to ElectronBeam-Textured Surfaces", Proceedings of the 17 Instrumentation and Measurement technology Conference, Baltimore (USA), May 2000, p 442446. ISO 14 406 (to appear) Geometrical Product Specifications (GPS) Extraction. ISO 5436-1 Geometrical Product Specifications (GPS) - Surface texture: Profile method; Measurement standards - Part 1: Material measures (2001). ISO 5436-2 Geometrical Product Specifications (GPS) - Surface texture: Profile method; Measurement standards - Part 2: Software measurement standards (2001). Stout, K.J. et. al. "The development of methods for the characterisation of roughness in three dimensions", Report EUR 15178 EN, EC Brussels, ISBN 0 704413132(1993).


Index

16% rule 343 2B finish, stainless steel flat products on 239 characterisation of 239 2D profile filtering 65 regression filter 65, 67 2D and 3D dispersion in 216 parameters, comparison 206 roughness characterisation, full 249 surface roughness measurements 210 3D approach 7 characterisation, uncertainties in 216 functional surfaces, extraction 109 Gaussian regression form filter >nd order of 77 parameter study and, application of 85 morphological feature surfaces 110 parameters, 2D and comparison 206 plasticity index 250 dominant summits of 298 regression filter 72 n-th order 74 relevant surfaces 106 roughness characterisation, full 2D and 249 surface characterisation 1 et seq techniques, standardised 2D technique 197etseq filtering 72 metrology

automotive engine bore performance using 307 et seq topography, functional performance and 316 3D Gaussian regression form filter, 2nd order 77 3D techniques, standardised relationship with 2D surface characterisation techniques 197 et seq Abbott-Firestone curve 19 amplitude parameters 20 analysing filters 95 anodised extruded aluminium 58 areal characterisation technique, novel 43 et seq combination 48 material ratio curve parameters, linear 30 segment combination 48 arithmetic mean summit curvature 25 atomic force microscopes (AFM's) calibration lateral 184 procedures 175 et seq vertical 190 equipment, error sources measured using 175 auto-correlation length, fastest decay 24 automotive engine bore performance 3D surface metrology using 307 et seq industry 11 AUTOSURF 11 average roughness center line 6 surface 6

350


ball bearing topography 215 beamlet concept 304 bearing ratio curve 19 surface application 333 bending-under-tension (BUT) test forming process 207 friction, correlation to 208 biomedical industry 12 bi-orthogonal wavelet 95, 100 first 95 second generation 100 Birmingham 14 parameters 17 blow-by 201 brick wall, linear phase 99 calibration horizontal drives 129 lateral, atomic force microscope 184 mode, mathematical study of 152 principle 144 procedures atomic force microscopes 175 et seq stylus, optical instrumentation and 119etseq specimen, ES1 tests of 136 three dimensions of the, synthesis of 135 type 2 instruments, type 1 and 127 vertical amplitudes 127 atomic force microscope of 190 CALISURF 11 cantilever relaxation time 180 centre line average roughness 6 change tree 48, 55, 304 pruning 55 system 304 circular groove 132,164,166 specimen with (ER3) 132 class space 44 closed path based definitions, local 50 separation 51 cold welding, galling behaviour and 259

component, functional performance, control of 43 contact measurement techniques, optical and 203 continuous data, critical points 50 contour lines 54 core material volume 33 roughness depth 32 void volume 33 cubic-spline wavelet 102 curve 19,30,35 Abbott-Firestone 19 bearing ratio 19 parameters, linear areal material ratio 30 related parameters 35 cylinder liner topography 198, 213 functionality and 198 database information, distribution of in network 330 DBS (draw bead simulator) multifrottement 269 test 265 multi-strip approach 249, 302 test 272, 273, 280 galling 280 procedure 272 default rules 342 developed interfacial area ratio 27 dominant summits 250 duality principle 342 dynamometers, engine tests 307 electronic surface profile 5 electronics, MEMS industry and 12 engine bore performance, automotive 3D surface metrology 307 et seq bores, functional testing 314 tests, dynamometers 307 engineering surfaces, description of 81 ER type standards 164 (ER3), specimen with circular groove 132 error sources, measured using AFM equipment 175 ES standards 166 ESI calibration specimen, tests of 136

Index

master 141 estimators, robust 84 Euler criterion 51 extraction sampling procedure 341 fastest decay auto-correlation length 24 feedback loop scan speed 179 field parameters 19,43 filter Gaussian advanced 63 et seq ISO 11562 63 regression form of 2nd order, 3D 77 parameter study, application of 85 zero order of 76 regression, 2D and 3D 65, 67, 72 filtering 3D regression 72 profile 2D 65 robust 70 techniques, robust 81 filters 63 et seq, 95 analysing 95 Gaussian, advanced 63 et seq filtration 221,341 numerical parameters and 221 flat-cylindrical tool set-up 251 die multifrottement 267 -flat tool 251 force detection system 178 form roughness, waviness and 3 surfaces, rough, wavy and 106 Fourier transform 92 fractal 29 dimension 29 parameter 29 fretting 226 friction, surface roughness parameters and 207 functional diagnostics 43 performance 3D surface topography and 316 component, of the 43 prediction 43 surfaces, extraction of 3D 109

351

testing, engine bores 314 Gabor transform 92 galling behaviour, cold welding and 259 severity 249 index (GSI) 289, 303 test DBS multi-strip 280 device 263 Gaussian filter filters, advanced 63 et seq ISO 11562 63 regression 81 3D, parameter study and application of 85 form, 2nd order of, 3D 77 zero order of 76 robust 82 geometrical product specifications and verification (GPS) system 339, 340 next generation 340 grinding wheel 57 ground surface, evaluation of 87 hard on hard bearings, wear ranking of 230 prosthetic hip joints 230 height maximum, topographic surface of the 22 reduced peak 32 valley 32 ten point, surface of the 29 horizontal drives, calibration of 129 hybrid parameters 25 image bow 177 insignificant events 49 instrument verification 119 Internet/World Wide Web 331 intersection plane/sphere, specimen 133,134 intranet 331 ISM surface texture knowledge support 325 et seq system 327 ISO 11562 Gaussian filter 63

352


ISO 14460-1 1 Java-JDBC 333 journal bearings, machining assessment of 234 wavelet analysis 234 knowledge-based expert system 328 database 329 structure (expert) 329 kurtosis of topography height distribution 21 L12-design 253 lateral calibration, atomic force microscope 184 lattice data, critical points 51 least-squares ellipse 154,158 robust 158 light-section microscope 5 linear areal material ratio curve parameters 30 phase, brick wall 99 line-wise levelling 189 local closed path based definitions 50 located property 99 lowest valley of the surface 22 machining assessment, journal bearings of 234 wavelet analysis 234 manufacturing process, control of 43 et seq master certification 144 ESI 141 material/void volume parameters 32 matt finish femoral stems 221 max rule 343 measurand 341 measurement errors 120 techniques optical, contact and 203 MEMS industry, electronics and 12 metrology instrumentation industry 12 milled surface, evaluation of 86 mode switching 181 morphological

assessment, multi-scalar wavelets using 245 feature surfaces, 3D 110 multifrottement flat die 267 test 251,264 DBS 265 multi-scalar filtration methodologies 91 et seq wavelets morphological assessment using 245 orthopaedic implants using in vivo wear 243 named lifting factors 104 nominal surface 2 novel areal characterisation techniques 43 et seq n-th order, 3D regression filter 74 numerical parameters characterisation of topography 17 filtration and 221 etseq observable measurements 44 Ockham's Razor 47 oil consumption 201 optical instrumentation, stylus and calibration procedures 119 et seq instruments translation mechanisms driven by 120 interference 178 measurement techniques, contact and 203 optimol SRV 266, 271 orthogonality 177 orthopaedic implants, multi-scalar wavelets using 243 in vivo wear 243 parallel groove standard double net of 164, 166 two 164, 165 parameter fractal 29 S-, set 19,20 study, 3D Gaussian regression filter

Index

application of 85 V-, set 19,30 parameters 2D, 3D and comparison 206 amplitude 20 Birmingham 14, 17 curve related 35 field 19,43 hybrid 25 linear areal material ratio curve 30 material/void volume 32 numerical characterisation of topography 17 filtration and 221 et seq spacing 23 surface roughness friction and 207 relation to functional demands 197 valley depth 6 pattern analysis 44 neural 45 statistical 45 structured surfaces and 343 syntactic 45 generation 44 recognition 45 space 44 peak height 6 reduced 32 material component 32 volume 32 phase correct filter 64 pit 50 plane/sphere standard 166,167 plateau honed surface, evaluation of 87 profile filtering 70 2D 65 robust 70 profiles, individual processing of 146 profilometer 5 prosthetic hip joints 230 hard on hard bearings, wear ranking of 230

353

quality coefficient 156 real surface, workpiece of a 1 regression filter 3D 72 nth order 74 constants 90 form of 2nd order, 3D Gaussian 77 Gaussian 81 3D parameter study and, application of 85 robust 82 zero order of 76 remove point connected 51 ringing 180 root-mean-square deviation of the surface 20 slope, assessed topographic surface ofthe 27 surface roughness 6 rough, wavy, form surfaces and 106 roughness average centre line 6 surface 6 characterisation full 2D, 3D and 249 depth, core 32 measurements, 2D and 3D surface 210 parameters, surface friction and 207 relation to functional demands 197 surface, root-mean-square of 6 waviness, form and 3 running-in lengths 65 running-out lengths 65 saddle point 47, 50 scan speed 179 significant events 49 skewness of topography height distribution, Ssk 20 sliding velocity 258 slope-based definitions 50 spaced twin groove spaced specimen (ER1) 130 spacing parameters 23 S-parameter 19,20

354

Advanced Techniques for Assessment Surface Topography set 20

sphere/plane 148,166 intersection centre 148 standard 166 Sq, root-mean-square deviation of the surface 20 Ssk, skewness of topography height distribution 20 static noise 168 steel products, textured sheet functionality, characterisation of 249 et seq sheets, uncoated frictional study 207 sheet topography 211 measurement, functionality and 203 stainless, flat products 2B finish on, characterisation of 239 structured surfaces 12, 343 pattern analysis 343 stylus, optical instrumentation and 119 et seq calibration procedures 119 et seq sudden jumps 178 summits of the surface, density of 23 3D, characterisation 1 et seq techniques, standardised 2D techniques with 197 et seq application, bearing 333 creation 4 density of summits 23 filtering 3D 72 robust 79 ground, evaluation of 87 integrity 2 lowest valley of the 22 maximum height of the topographic 22 metrology 3D, automotive engine bore performance using 307 et seq future developments in 339 et seq milled, evaluation of 86 nature of 1

nominal 2 peak height, maximum 22 plateau honed, evaluation of 87 profile, electronic 5 real, workpiece of 1 root-mean-square deviation 20 slope of topographic 27 roughness average 6 measurements 2D,3Dand 210 parameters friction and 207 relation to functional demands 197 root-mean-square of 6 ten point height of the 29 texture 2 aspect ratio, surface of 24 knowledge support - ISM 325 et seq syntactical relational description 46 toolbox 341 topography 2, 221 3D, functional performance and 316 turned, evaluation of 86 wavelength, bandwidth of 18 SURFSTAND project 9 tactile instruments 119 test processing 168 texture aspect ratio, surface of the 24 direction 30 primitives, segmentation and 46 textured sheet steel products 249 et seq functionality, characterisation and 250 et seq thermal drift 177 three dimensional measurement processing of 145 test 140 three dimensions, calibration of synthesis of 135 TiN coated plates, wear of UHMWPE 227 tip 180

Index

/sample compression 180 shape 180 topographic surface assessed, root-mean-square slope 27 maximum height 22 topography ball bearing 215 characterisation of, numerical parameters 17 cylinder liner 213 functionality and 198 height distribution kurtosis of 21 skewness of 20 steel sheet 211 measurement, functionality and 203 surface 221 3D, functional performance and 316 translation mechanisms, optical instruments driven by 120 triangulation 53 tribological test rigs 263 turned surface, evaluation of 86 twin net, specimen with 131 type 2 instruments, type 1 and 127 calibration 127 UHMWPE, wear of 227 TiN coated plates 227

valley depth parameters 6 height, reduced 32 lowest, surface of the 22 void volume 34 verification tests 167 acceptance, periodical and 167 vertical amplitudes calibration of 127 calibration, atomic force microscope of 190 virtual 47 peak 47 pit 47

355

vivo wear, orthopaedic inplants, multiscalar wavelets using 243 void volume parameters, material 32 valley 34 volume core material 33 void 33 parameters, material/void 32 peak material 32 valley void 34 V-parameter set 19, 30 watershed merging 56 wavelet analysis 238 machining assessment, journal bearings of 234 bi-orthogonal first 95 second generation 100 cubic-spline 102 prototype 93 theory 92 wavelets, multi-scalar 243, 245 morphological assessment using 245 orthopaedic implants using in vivo wear 243 waviness, roughness, form and 3 wavy, rough, form surfaces and 106 wear 202, 227, 230, 243 in vivo orthopaedic implants, multi-scalar wavelets using 243 ranking, hard on hard bearings of prosthetic hip joints 230 UHMWPE, of TiN coated plates 227 Wigner distribution 92 Wigner-Ville distribution 92 Wolf pruning 55 workpiece, real surface of 1 World Wide Web/Internet 331

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