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EDITORIAL REVIEW COMMITTEE P.W. Taubenblat, FAPMI, Chairman I.E. Anderson, FAPMI T. Ando S.G. Caldwell S.C. Deevi D. Dombrowski J.J. Dunkley Z. Fang B.L. Ferguson W. Frazier K. Kulkarni, FAPMI K.S. Kumar T.F. Murphy, FAPMI J.W. Newkirk P.D. Nurthen J.H. Perepezko P.K. Samal D.W. Smith, FAPMI R. Tandon T.A. Tomlin D.T. Whychell, Sr., FAPMI M. Wright, PMT A. Zavaliangos INTERNATIONAL LIAISON COMMITTEE D. Whittaker (UK) Chairman V. Arnhold (Germany) E.C. Barba (Mexico) P. Beiss, FAPMI (Germany) C. Blais (Canada) P. Blanchard (France) G.F. Bocchini (Italy) F. Chagnon (Canada) C-L Chu (Taiwan) O. Coube (Europe) H. Danninger (Austria) U. Engström (Sweden) O. Grinder (Sweden) S. Guo (China) F-L Han (China) K.S. Hwang (Taiwan) Y.D. Kim (Korea) G. L’Espérance, FAPMI (Canada) H. Miura (Japan) C.B. Molins (Spain) R.L. Orban (Romania) T.L. Pecanha (Brazil) F. Petzoldt (Germany) G.B. Schaffer (Australia) L. Sigl (Austria) Y. Takeda (Japan) G.S. Upadhyaya (India) Publisher C. James Trombino, CAE
[email protected] Editor-in-Chief Alan Lawley, FAPMI
[email protected] Managing Editor James P. Adams
[email protected] Contributing Editor Peter K. Johnson
[email protected] Advertising Manager Jessica S. Tamasi
[email protected] Copy Editor Donni Magid
[email protected] Production Assistant Dora Schember
[email protected] President of APMI International Nicholas T. Mares
[email protected] Executive Director/CEO, APMI International C. James Trombino, CAE
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powder metallurgy Contents 2 4 7 11 13
45/2 March/April 2009
Editor's Note PM Industry News in Review Company Profile Magnesium Elektron Powders PMT Spotlight On …Stan Cuthbert Consultants’ Corner Joseph Tunick Strauss
FOCUS: PM Metallography 17 Cutting-Edge PM Metallography T.F. Murphy, FAPMI
19 Three-Dimensional Characterization and Modeling of Porosity in PM Steels N. Chawla, J.J. Williams, X. Deng, C. McClimon, L. Hunter and S.H. Lau
29 Characterization of Powders and PM Components Utilizing Transmission Electron Microscopy C. Blais, G. L’Espérance, FAPMI, and P. Plamondon
39 Porosity Statistics and Fatigue Strength of Sintered Iron P. Beiss, FAPMI, and S. Lindlohr
49 Evaluation of PM Fracture Surfaces Using Quantitative Fractography T.F. Murphy, FAPMI
DEPARTMENTS 62 Meetings and Conferences 63 PM Bookshelf 64 Advertisers’ Index Cover: Epoxy skeleton showing morphology of pore network inside a compact. Photo courtesy Thomas Murphy, Hoeganaes Corporation.
The International Journal of Powder Metallurgy (ISSN No. 0888-7462) is a professional publication serving the scientific and technological needs and interests of the powder metallurgist and the metal powder producing and consuming industries. Advertising carried in the Journal is selected so as to meet these needs and interests. Unrelated advertising cannot be accepted. Published bimonthly by APMI International, 105 College Road East, Princeton, N.J. 08540-6692 USA. Telephone (609) 4527700. Periodical postage paid at Princeton, New Jersey, and at additional mailing offices. Copyright © 2009 by APMI International. Subscription rates to non-members; USA, Canada and Mexico: $100.00 individuals, $230.00 institutions; overseas: additional $40.00 postage; single issues $55.00. Printed in USA by Cadmus Communications Corporation, P.O. Box 27367, Richmond, Virginia 23261-7367. Postmaster send address changes to the International Journal of Powder Metallurgy, 105 College Road East, Princeton, New Jersey 08540 USA USPS#267-120 ADVERTISING INFORMATION Jessica Tamasi, APMI International INTERNATIONAL 105 College Road East, Princeton, New Jersey 08540-6692 USA Tel: (609) 452-7700 • Fax: (609) 987-8523 • E-mail:
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EDITOR’S NOTE
T
he ability to study surfaces and to delve into the interior of solids at a resolution approaching the atomic level serves as the basis for our understanding of material properties, in particular the behavior of solids under stress. To this end, metallography is the predominant and most powerful technique available to the materials scientist. This Focus Issue, coordinated by Tom Murphy, surveys cutting-edge metallographic techniques that characterize the complexities of the internal and external microstructures of powder metallurgy (PM) materials in which porosity is an intrinsic component. In addition to its analytical capability, metallography frequently exposes the aesthetic qualities of a microstructure. This duality is clearly illustrated by the PM micrograph on the front cover—an epoxy skeleton showing the morphology of the pore network that remains after extraction of the iron from a sintered compact using dilute acids. Joe Strauss again brings his unique flair and expertise to the “Consultants’ Corner.” The issues he addresses are quality assurance in PM part fabrication, the role of PM in rapid prototyping and the choice of powder grades, and a comparison of cold-spray and thermal-spray processing. Amid the current and widespread economic doom and gloom, Peter Johnson’s “Company Profile” on Magnesium Elektron Powders should evoke a welcome sense of confidence for the future. The company has carved out an important niche in the specialty metal powders market by focusing on advances in technology, quality, product customization, and new product development, as well as a rapid response to customer needs.
Alan Lawley Editor-in-Chief
Now in its second year, the e-version of the Journal, a facsimile of the familiar hard copy, offers APMI members user-friendly navigational features and powerful search capabilities. Of particular convenience is the ability of the software to locate technical information (articles, references, etc.) from previous issues of the Journal. To log in, all that is needed is a personal user ID and password. For no particulate reason, I recently found myself cleaning our old files. On reaching the letter “E”, I rediscovered a dog-eared file titled “English Food and Recipes.” The contents of this large file brought back instant memories of a misspent youth in post–World War II England. Taking license from the fact the PM plays an important role in the processing of food and beverages, I thought it might be of interest to share with you the essence of the file in the form of a quiz! Can you identify the primary constituent(s) of the following delicacies from the United Kingdom? Better still, have you ever had the privilege of following traditional recipes to prepare these dishes? Bangers and Mash; Black Pudding; Bubble & Squeak; Cornish Pasties; Haggis; Pikelets; Pork Pie; Spotted Dick; Toad-in-theHole; Yorkshire Pudding. Bon appetit!
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Volume 45, Issue 2, 2009 International Journal of Powder Metallurgy
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PM INDUSTRY NEWS IN REVIEW
PM INDUSTRY NEWS IN REVIEW
The following items have appeared in PM Newsbytes since the previous issue of the Journal. To read a fuller treatment of any of these items, go to www.apmiinternational.org, login to the “Members Only” section, and click on “Expanded Stories from PM Newsbytes.”
New ISO Certification The production and distribution operations of Advanced Metalworking Practices, LLC (AMP), Carmel, Ind., have been certified to ISO 9001:2000 (Without Design) International Quality System standard. AMP makes feedstocks for the metal injection molding (MIM) industry. New Tungsten Plan The Defense National Stockpile Center, Fort Belvoir, Va., has changed its awards announcement policy. It will report tungsten awards twice in a fiscal year, in April to announce first half sales and in October to announce second half sales. GKN Updates Performance GKN plc expects group revenues for 2008 will rise by about 12 percent and profit before taxes will approach £150–£170 million (about $215–$243 million). However, the company reports that conditions in global automotive markets have continued to decline since its last update. PowderMet2009 HOTEL OFFERS UNPRECEDENTED RATES In light of current economic and market conditions, MPIF has finalized a new agreement with The Mirage Hotel in Las Vegas, headquarters for PowderMet2009 this June, that will help maximize attendance. Reduced MPIF confer-
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ence rates are now only $95.00 per night, including weekends. Visit www.mpif.org for details. Industry Loses Noted Powder Metallurgist Howard I. Sanderow, 64, died on February 2. He was president of Management & Engineering Technologies (MET Group Inc.), a PM consulting company he founded with his wife Barbara in 1988. Powder Maker Reports Weak Fourth Quarter Höganäs AB, Sweden, production declined 28 percent in the fourth quarter of 2008 because of sharply reduced demand in all market regions, including Asia and South America. Net sales for the full year increased 4.5 percent to MSEK 6,103 (about $740 million), mainly attributed to price increases and higher scrap metal surcharges. President Obama Learns About PM President Barack Obama showed a serious interest in powder metallurgy during his visit to CMW Inc., Indianapolis, Ind., in 2008, reports Mark B. Gramelspacher, president & CEO. Obama spent several hours at CMW, a manufacturer of PM electrical contacts, PM tungsten alloys, and resistance welding consumables, in April 2008 while on a campaign swing through the Midwest.
PRIMA Collaborates in Roller-Contact Fatigue Testing Prima Business Specialists LLC, State College, Pa., and Product & Assurance & Services, Ridgway, Pa., will collaborate to provide Hoffman Roller Contact Fatigue (RCF) tests and analysis to prospective users. The RCF test provides early detection and remedial action for potentially damaging cracks during the manufacturing process. PowderMet2009 Las Vegas Program Now Online The complete program as well as registration and hotel information for PowderMet2009 in Las Vegas are now online at www.mpif.org/ meetings/2009/09_gateway.htm. Sponsored by the Metal Powder Industries Federation and APMI International, the PM industry’s largest annual conference will take place in Las Vegas, Nevada, June 28–July 1. Former Metaldyne Employees Sentenced Three former employees of Metaldyne Corp. were sentenced to prison terms in federal court in Detroit on February 13. They pleaded guilty to charges in connection with a conspiracy to steal confidential information about the company’s powderforged connecting rod manufacturing costs and processes. ijpm
Volume 45, Issue 2, 2009 International Journal of Powder Metallurgy
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PM INDUSTRY NEWS IN REVIEW
PM Parts Maker Adjusts Capacity Miba AG, Laakirchen, Austria, is addressing the crisis of declining demand from the international automotive market by adjusting capacity. The company’s measures include reducing employee overtime and excess hours, using up residual holidays, and cutting temporary workers and educational leave. Automotive Suppliers Face Challenging Business Conditions International automotive suppliers Tomkins plc and GKN plc report declining profits in 2008. Business conditions for both deteriorated especially during the final quarter.
Tungsten Sales Rise North American Tungsten Corp. Ltd. (NTC), Vancouver, B.C., Canada, reports a 49.7 percent sales increase to Can$17.6 million for the first fiscal quarter of 2009, ending December 31, 2008. NTC’s Cantung mine produced 79,978 metric ton units of tungsten concentrate, a 22 percent increase over the comparable quarter the previous fiscal year. Tungsten Powder Expansion Shelved H.C. Starck Canada Inc. has suspended further investment in expanding capacity at its Sarnia, Ontario, tungsten powder plant. The company attributed the decision to the cooling economic
climate and the resulting decline in demand in the North American tungsten market. New Developments to Be Aired at Refractory Metals and Hard Materials Meeting The Plansee Group announced the program of the 17th Plansee Seminar at its headquarters in Reutte, Austria, May 25–29. More than 200 presentations will focus on PM processing of refractory metals, hard materials and composite materials, including applications in energy, information technology, communications, and lighting. ijpm
PURCHASER & PROCESSOR
Powder Metal Scrap (800) 313-9672 Since 1946
Ferrous & Non-Ferrous Metals Green, Sintered, Floor Sweeps, Furnace & Maintenance Scrap
1403 Fourth St. • Kalamazoo, MI 49048 • Tel: 269-342-0183 • Fax: 269-342-0185 Robert Lando E-mail:
[email protected] Volume 45, Issue 2, 2009 International Journal of Powder Metallurgy
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2009 International Conference on Powder Metallurgy & Particulate Materials June 28–July 1, The Mirage Hotel, Las Vegas
• International Technical Program • Worldwide Trade Exhibition • Special Events
For complete program and registration information contact: INTERNATIONAL
METAL POWDER INDUSTRIES FEDERATION APMI INTERNATIONAL 105 College Road East Princeton, New Jersey 08540 USA Tel: 609-452-7700 Fax: 609-987-8523 www.mpif.org
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COMPANY PROFILE
Magnesium Elektron Powders By Peter K. Johnson* Magnesium Elektron Powders (MEP) services customers all over the world from plants in New Jersey, Pennsylvania, and Ontario, Canada. “We make powders, chips and granules for many markets, as well as market wrought and cast alloys,” says James G. Gardella, president. “Our Reade Manufacturing Co. in Manchester, New Jersey. has been a magnesium powder supplier since 1941.” The company is part of Magnesium Elektron, a division of the Luxfer Group. Luxfer employs 2,000 workers in 21 plants worldwide. In addition to magnesium powders and granules, Luxfer supplies high-pressure specialty gas cylinders, zirconium chemicals, aluminum and composite parts, wrought and cast magnesium alloys, and magnesium sheets & plates. Broadly speaking, magnesium’s most important uses are as an alloying agent in aluminum production, as die casting alloys, and as magnesium powders. MEP consists of three companies with a total of 100 employees: Reade Manufacturing Co., Hart Metals Inc., and Niagara Metallurgical Products, Ltd. Reade was acquired by Magnesium Elektron in 1990. Located on a 250,000 sq. m (62-acre) site (Figure 1), Reade makes magnesium and specialty alloy powders by mechanical comminution, better known as grinding. Magnesium ingot is converted into chips, granules, and coarse or fine powder using the following steps: chipping, grinding (coarse, fine, and ultrafine), screening, and blending. Specialty alloys are processed by crushing, grinding, and screening. A new automated production line for specialty alloys was recently added at the facility, Figure 2. Acquired in 1998, Niagara Metallurgical Products, Ltd. operates from a 1,340 sq. m (14,400 sq. ft.) plant in Stoney Creek, Ontario, Canada, Figure 3. In addition to producing magnesium *Contributing editor and consultant
Volume 45, Issue 2, 2009 International Journal of Powder Metallurgy
Figure 1. Reade Manufacturing Co., Manchester, New Jersey
Figure 2. New specialty alloy production line at Reade
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COMPANY PROFILE: MAGNESIUM ELEKTRON POWDERS
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chips and powders using mechanical grinding, the plant also has a blending capability. Hart Metals Inc. atomizes pure magnesium spherical powder via a proprietary technology. The company was acquired by MEP in 1998. Located on a 28,200 sq. m (7-acre) site in Tamaqua, Pennsylvania, the plant is undergoing a major expansion that will more than double its magnesium atomization capacity, Figure 4. “All three of our plants use chipping systems and mechanical grinding for magnesium chips, granules, and powders as well as screening and blending,” reports John E. McConaghie, vice president–operations. MEP atomized magnesium powders are available in a particle-size range from 5 µm to 5 mm for various applications and blending with aluminum PM grade powders. Specialty metal and alloy powders (Fe-V, Fe-Al, Fe-B, Fe-Nb, and Fe-Si) are made for welding applications like stick electrodes and cored-wire. The company expects to add additional specialty alloy powders to their product portfolio. Quality and safety are critical in MEP’s production processes, notes Deepak Madan, vice president, technology & new product development. “We
adhere to stringent military specifications as well as ISO 9001:2000 and ISO 14001:2004 registrations,” he says. “And all of our materials undergo 100 percent testing and sampling.” The in-house laboratory at the Manchester facility is typical of MEP’s other plants, Figure 5. Powder characterization includes Rotap sieve analysis, Microtrac laser diffraction, and a sedigraph analyzer. Careful documentation of customer orders provides details on materials purchased decades ago. MEP follows strict safety precautions in the handling of its materials and adheres to National Fire Protection Association guidelines. Production units are separated and powder handling is minimized. Magnesium chips, granules and powders run a wide gamut of applications, from defense and aerospace to pharmaceutical, industrial, and consumer products. The defense market accounts for the most interesting usage of magnesium powder. Typical applications are aircraft infrared counter -measure flares, illuminating and marker flares, and tracer bullets, Figure 6. Improvised explosive device (IED) simulators used in military training are a new
Figure 3. Niagara Metallurgical Products, Ltd.
Figure 4. Hart Metals Inc. atomizing plant
Figure 5. In-house laboratory monitors quality control
Figure 6. Military aircraft counter-measure flares use magnesium
Volume 45, Issue 2, 2009 International Journal of Powder Metallurgy
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COMPANY PROFILE: MAGNESIUM ELEKTRON POWDERS
application using magnesium. MEP’s high-purity magnesium chips and granules are used in the chemical and pharmaceutical industries. Magnesium granules and powders are also used for the manufacture of pesticides, herbicides, fungicides, chemical synthesis, and for the desulphurization of steel. Special-effect pyrotechnics use magnesium metal and alloy powders. Magnesium powders are mixed with aluminum powder to create PM pre-blends. Specialty alloy powders are used as sintering aids and alloying additives in PM. There is also a new interest in developing lightweight parts for military and automotive applications. Flameless ration heater (FRH) pads represent a growing market for Magnesium Elektron Powders. FRH pads consist of a proprietary blend of a magnesium-alloy with other ingredients. When acti-
Volume 45, Issue 2, 2009 International Journal of Powder Metallurgy
vated with water, these pads generate heat without the need for any exter nal power source. Applications include self-heating ready-to-eat meals (MRE) for the military and consumers. Reusable packs that provide hot water on demand are a new application that will be available to consumers in the near future. For example, 1.5 L of water can be heated in 20 to 30 min for coffee, tea, or hot chocolate. Though relatively unknown in the conventional PM parts business, Magnesium Elektron Powders has carved out an important niche in the specialty metal powders market. “Our strengths are keeping technology current, high-quality materials, product customization, new product development, and serving customer needs quickly,” stresses James Gardella. “We are confident about our future growth.” ijpm
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SPOTLIGHT ON ...
STAN CUTHBERT, PMT Education: BS, Metallurgical Engineering, Michigan Technological University, 1969 Why did you study powder metallurgy/particulate materials? My interest in powder metallurgy (PM) goes back a generation to my father (also Stan Cuthbert). He worked at RB&W, a PM facility in Coldwater, Michigan. Occasionally he would take me to work with him on Saturdays. He must have been ahead of his time because it was long before “take a child to work” was ever conceived. I was fascinated by the pounding of the presses and especially the sintering furnaces. I knew then I wanted to understand how a part that can crumble in your hand could pass through a sintering furnace and come out strong. When did your interest in engineering/ science begin? It is amazing how certain individuals can shape your life. I can trace my interest in science back to my sixth grade teacher, Mr. Sistanich. It was the year of the first Sputnik launch and he was most encouraging and supportive of my interest, helping me obtain information on the U.S. and Russian space programs. What was your first job in PM? What did you do? My first job happened by accident. I was interviewed by Glidden Metals (SCM Metals). Glidden was expecting a minerals beneficiation (extractive) metallurgist to work on alternative methods of producing copper powder, but my degree was in physical metallurgy. As an afterthought I was introduced to Arthur Backensto (APMI International Fellow, 2003) and was hired for his research group. There I began my career developing brazing and infiltrating materials. At that time interest was developing in a brazing material for the PM rotor in the Wankel engine. At Glidden, as sole inventor, I was awarded patents for an infiltrating paste and for brazing and soldering compositions. Volume 45, Issue 2, 2009 International Journal of Powder Metallurgy
Describe your career path and companies worked for, and responsibilities. I moved within the company to the SCM Metals group in Johnstown, Pennsylvania. There I was responsible for bringing their dispersion-strengthened copper materials from the research group into production. Today the “Glidcop” materials are probably best known for their use in the welding electrode industry. However, in one of the early commercial uses, this high-strength, high-conductivity material was extruded into bars and used as heat sinks for the welding of the Alaskan pipeline. My next job was at Vickers Hydraulics where I thought I may be moving away from PM but, instead, I began working with PM parts to supply hardware for the hydraulics industry. This included hardware from large Ferro-Tic rotors to small copper-infiltrated piston shoes and low-carbon iron solenoids. The current stop in my career is at TRW, an independent supplier to the global automotive industry, and a leader in active and passive safety technology. The applications that we find for PM continue to grow. The variety of materials used keeps the work interesting, embracing everything from standard iron–carbon to MIM stainless steel. Our suppliers employ conventional sintering, sinter hardening, and vacuum sintering. What gives you the most satisfaction in your career? Without a doubt it is the variety of challenges and the fact that I have never strayed far from basic metallurgical laboratory work. To me, there is nothing more exciting than working on a failure analysis problem involving a combination of scientific knowledge, detective work, Metallurgist TRW Inc. 4505 West 26 Mile Road Washington, Michigan 48094 Phone: 586-786-7640 E-mail:
[email protected] 11
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SPOTLIGHT ON ...STAN CUTHBERT, PMT
common sense—and almost always under pressure to complete the project immediately! List your MPIF/APMI activities. I am a Past Chairman of the Michigan chapter of APMI International. I was also a speaker at APMI meetings, giving a presentation on “Powder Metal’s Role as a Substitute for Strategic Materials.” What major changes/trend(s) in the PM industry have you seen? The PM industry has previously described itself, in its own literature, as a “black art.” This concept has given way to automated handling systems, dedicated cells, and fully computer-monitored sintering and heat-treating furnaces. Now and in the future the emphasis will remain on global sourcing from a parts-purchasing point of view. I now have to be familiar with MPIF Standard 35, and also global material specification systems. In the automotive world the demand for quality and lower pricing will continue to increase. That is where PM will continue to shine with improvements in techniques for producing near -net shapes at higher output rates and with enhanced tool life. Why did you choose to pursue PMT certification? I had been out of the mainstream PM industry for awhile so it was natural for me to want to know if I had kept up with the technologies. Pursuit of certification was a natural way to find out. In addition, I was continuing to be increasingly involved in PM part selection within TRW.
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How have you benefited from PMT certification in your career? I was surprised at how well APMI distributes its technical information, and by how many people use it. There have been instances where our hardware engineers have been in casual discussions with PM parts suppliers and the suppliers have asked to have me join the discussion because they knew I was here. Maybe they did some homework by checking the Who’s Who in PM and observed that I had PMT Level I certification! This has happened more than once. What are your current interests, hobbies, and activities outside of work? Again, let me go back to my father, who is an avid golfer. He told me if I wanted to live a long, stressfree life, “do not take up golf.” So unlike many of your readers, I do not play golf. Playing golf in college presented a challenge in the snowbound upper peninsula of Michigan—but at least I met my wife Cookie there. Several years ago I realized that in my entire career I have only written technical reports, so I started taking classes in creative writing. In my spare time I now write poetry. I am currently compiling my first book, tentatively titled, “A Stain on Stainless Steel.” Look for it in the future! ijpm
Would you like to be featured here? Have you been PMT Certified for more than 2 years? Contact Dora Schember (
[email protected]) for more information.
Volume 45, Issue 2, 2009 International Journal of Powder Metallurgy
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CONSULTANTS’ CORNER
JOSEPH TUNICK STRAUSS* Q
Our PM process periodically produces parts out of specification (low density or out of geometric tolerance). We have tightened up on our process and our Cpk is capable of 1.33, which we have promised to our customer or we lose the order. We have calibrated all pertinent transducers (temperature, pressure, flow rates) and checked the validity of the incoming material certifications. Regardless, we still have the same periodic problem. What should we do? Let me preface a response by recounting a story that Matt Bulger (NetShape Technologies—MIM) passed on to me. A Fortune 500 company rolls into a small PM house and demands of the QA manager, "I need all critical dimensions on the parts you make for us to have a 2.00 Cpk or better! Can you make this happen?" The QA manager says, "Sure, if you'll grant me one small request." Fortune 500 company: "I guess so, what is it?" QA manager: "Change all nominal dimensions and tolerances to those that the tooling creates and which my process produces." If it were only so easy! But do not dismiss this because it is fantasy. In many instances this discussion needs to take place, if for no other reason than to point out that there are two sides to any specification issue—the producer (striving to meet the specification), and the consumer (setting what the specification should be). In this case you state that the system is “capable” of producing a Cpk of 1.33 and it is this level of control that is required by the customer. Are you implying that you do not achieve this level of control all of the time, but you bid on the job as if you could? There are two issues: 1. What can be done to improve the process control of your manufacturing process? 2. What can be done to achieve a specification that is compatible to you and the customer?
A
Issue 1: It is not unusual to see companies that either inherited a process or developed a process and then fired all the cognizant engineers. The facility is now run by equipment “operators," expediters on the floor, and some managers up front. There is not an engineer in sight. Or, if there is an engineer, he/she is too busy adhering to ISO, putting out fires, or solving banal scheduling problems to examine the problem. This is what keeps me employed as a consultant! To companies that fire their engineers, or do not allow their engineers to do engineering, thank you. It is encouraging to note that your process is within specification, your equipment works, and your incoming material meets specification. This tells me that the entire process was set up on the edge of workability. Has there been any sensitivity analysis done on any of the inputs? A process should be designed with as high a margin of safety around each input as possible; this is what makes a robust process. It is easy to design a process that falls off precipitously under the right (or wrong) combination of conditions. This is one of the dangers of blindly following the statistics as an “end-all” for characterizing a process, especially when the distribution of the process outputs may not be centered on the mean. Returning to your specific problem, notwithstanding all the statistical and quality controls you have put in place, these are just measurements and these tools cannot replace a fundamental understanding of the process. There is a metallurgical and/or mechanical reason that your parts are out of specification, regardless of what statistical tests of the process tell you. And, a Cpk of 1.33
*Engineer & President, HJE Company, Inc., 820 Quaker Road, Queensbury, New York 12804; Phone: 518-792-8733, Fax: 518792-8735; E-mail:
[email protected] Volume 45, Issue 2, 2009 International Journal of Powder Metallurgy
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CONSULTANTS’ CORNER
today will be a Cpk of 1.42 tomorrow, 1.21 the next day, and 1.19 the day after that, etc. If you are close to a cliff, you will fall off eventually, and the cause may be a small number of trivial changes that combine to make the “perfect storm.” Get the help you can from suppliers, consultants, or from your workforce. Work the problem to the best of your ability until you get that margin of error. Issue 2: Here is a paraphrased quote from Arlan Clayton, the first recipient of the Kempton H. Roll Powder Metallurgy (PM) Lifetime Achievement Award and an individual who has been around the PM block a time or two: "90% of all quality issues are really business issues." So, with this in mind ask yourself: “Why did I win this contract? Did I win it on price? Why was my price lower than the competition? Is it because I had a fundamental economic advantage or because everyone else quoted the part with a secondary operation that they estimated was needed to bring the part into specification, and I missed it?” Many quality issues would pose no problem at all if you can get the price you need; the price that makes you profitable. Then, when there are rejectable parts, it does not throw the project immediately into the red. You should be making a profit even with some finite reject rate. If a secondary operation is needed to achieve the quality level, this is satisfactory as long as it is accounted for in the quote, and not added on after the customer has accepted your bid. When the basic process capability intersects with a low-margin part, the trouble begins. No manufacturing process is perfect, so do not bid on this assumption, especially when you do not have one. If you have a good process, then bid with your good process. In any case, bid with the process you have, not the one you want, or the customer demands. You may have a perfectly good process at a Cpk of 1.2 but it becomes a failure when filling an order that requires a higher Cpk. Improving your process under the gun is always more expensive than normal evolutionary improvement. What to do? The first step is to be honest with the customer. The cold hard fact is that if you cannot solve this issue, sooner or later you will do one of three things: (i) drop the part, leaving the customer in the lurch with no supply on a custom PM part; (ii) raise the price, but that may make the customer's end product uncompetitive and kill the
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program; or (iii) start cutting inspection corners, leading to line problems with the customer, retur ned shipments, and messy arguments. Sooner or later you will do either (i) or (ii) anyway. Customers do not like to hear about problems from suppliers, but they know problems develop. The issue is how to deal with them. If a supply chain is threatened, or a dramatic price increase looms, you will be amazed at how quickly a tolerance may be loosened, or how a measurement technique may be changed to bring a part into specification. But this should be done up front, not after the fact. The discussion has to be initiated by the supplier. Unless you tell the customer there is a problem, how will he/she know? There are always people in your company unwilling to admit a mistake, or unwilling to take any "blame" in a project. In the end, the facts will be the facts, and oftentimes customers will prefer an honest supplier to one that never comes clean until the dam breaks. Give yourself and your customer a chance to find a solution. Getting into this kind of predicament with a PM parts customer is bad for your company. However, you must also realize that getting into a predicament with a first-time application of PM is bad for the entire PM industry. What is the role of metal powder in rapid prototyping (RP)? Is there a grade of powder that RP requires? RP and rapid manufacturing (RM) continue to undergo considerable development and their applications and markets are expanding rapidly. Many of the RP and RM technologies involve the use of metal powder, and although the volume used may never compete with those for press-andsinter or metal injection molding (MIM), RP and RM should be embraced by the powder metallurgy (PM) industry. RP and RM are manufacturing technologies that build the part by additive methods and also without specific or dedicated tooling. That is, rather than starting with a bulk material and cutting away excess material until you have a part, RP and RM build the part using essentially only the material used in the final part. In addition, RP is a totally flexible process in which all parts can be made using the same basic tools or method; no fixed tooling is necessary. The manufacturing strategy in RP is usually to divide the part into
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Volume 45, Issue 2, 2009 International Journal of Powder Metallurgy
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CONSULTANTS’ CORNER
planes of finite thickness and to build up the part layer by layer. The use of CAD/CAM is an integral and essential part of rapid prototyping. It should be noted that there is a difference in RP and RM. RP is the manufacture of a prototype part, which implies that the part is a compromise in the actual part desired. For instance, a metal part may be prototyped in a plastic but obviously the part, e.g., a turbocharged rotor, cannot be tested in service. The RP’d part provides the shape but not necessarily all of the attributes of the desired part. RM is the production of a part to be used in service. Thus, the material used in RM must be equivalent to the material used in other manufacturing methods. In many cases plastics are adequate. However, the holy grail of RP and RM is to be able to directly make metal parts. In order to build a part layer by layer, the material must be applied layer by layer. For RP/RM methods that use powder as the material it is necessary to introduce a layer of powder of a precise thickness. Once the powder is distributed in a uniform layer the portions of the layer that are to be incorporated into the part are “fixed” in place. In general, two methods are used: (1) application of a binder, and (2) laser “sintering.” In the first case a binder (generally organic) is applied using technology similar to the printhead in your inkjet printer, which allows precise placement of the binder. The final three-dimensional (3D) part is similar to a MIM part in that it must be debound and sintered to obtain the attributes of a fully metallic part. In the case of laser sintering, the laser bonds the particles by melting the powder. This can entail full or partial melting or liquid-phase sintering and high densities are achievable. Machines using an electron beam for melting/sintering are also available. Regardless of the RP/RM method used, one of the most important properties of the powder is its ability to be able to be doctored into a uniformly dense layer of a precise thickness. Certainly the flow properties of the powder are important, which implies that coarse spherical powder is desired. However, coarse material will be difficult to sinter to high densities, especially for processes using the binder print method. Powder with a maximum packing factor is also desired to minimize shrinkage, which allows for tighter control of dimensional tolerance. For laser or electron-beam sintering, a high packing factor is also desirable to provide adequate ther mal mass to prevent “punch through” or excessive melting. However, high packVolume 45, Issue 2, 2009 International Journal of Powder Metallurgy
ing factors and flowability do not necessarily go hand in hand. Thus, the powder’s flow requirements and attributes that enable sintering are in conflict. The powder that is ultimately used is a compromise between flow and sintering. There is no single grade (particle-size distribution) of powder used in RP/RM. Rather, those practicing the technologies make do with what is available. From our experience a good compromise entails a -270 or -325 mesh upper sieve cut. However, what appears to be more important is the amount of material that is
