The Secrets of Building a Plastic Vacuum Forming Machine

Forming Machine IVincent Gingery

THE SECRETS OF BUILDING A PLASTIC VACUUM FORMING MACHINE

Written & Illustrated by Vincent R. Gingery

Published by David J. Gingery Publishing LLC P.O. Box 318 Rogersville, MO 65742

Printed in the USA

CONTENTS

First Edition

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4. How vacuum forming is done . . . . . . . . . . . . . . . . . . . . . . . . .7 . Vacuum form safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10 . A few things to consider . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

First Printing 1999

Copyright

1999 Vincent R . Gingery All rights reserved @

What kind of plastic can we use and where can we buy it? . . . . . 16 . What is vacuum? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17 . Choosing a vacuum source . . . . . . . . . . . . . . . . . . . . . . . . . 18 . Vacuum storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22 The heating element and control switch . . . . . . . . . . . . . . . . .22

Library Of Congress Catalog Card Number 99-94589

ISBN # 1-878087-22-3

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NOTICE OF DISCLAIMER: There are serious hazards in the processes and procedures in this book . No attempt has been made to point out all of the danger or even a majority of them . The methods. materials and procedures that are suggested in this manual were developed by a nonprofessional. The author is not an engineer or scientist and no claim is made to the propriety of the methods suggested in these pages . The reader is fully responsible for developing save procedures for every operation. Both the author and David J . Gingery Publishing hereby disclaim any liability for injury to persons or property that may result while using this book . Neither intends by this publication to explain all dangers known or unknown that may exist in the building and operation of the project.

The adjustable platen . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24 . Other materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25 . Tools & construction methods . . . . . . . . . . . . . . . . . . . . . . .26 . Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26 . Material list for roll around cart . . . . . . . . . . . . . . . . . . . . . . 26 . Building the roll around cart . . . . . . . . . . . . . . . . . . . . . . . . 28 . Mounting the platen jack and control valves . . . . . . . . . . . . . . . 36 Parts list for the adjustable platen assembly . . . . . . . . . . . . . . . .41 Building the adjustable platen . . . . . . . . . . . . . . . . . . . . . . . .42 Parts list for clamp frame . . . . . . . . . . . . . . . . . . . . . . . . . . .57 . Building the clamp frame . . . . . . . . . . . . . . . . . . . . . . . . . . .58 Material list for heater . . . . . . . . . . . . . . . . . . . . . . . . . . . .66. . Building the heater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .67 Wiring material list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .81 Wiring the machine &building the control panel . . . . . . . . . . . .82

. Plumbing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .89 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Vacuum molds 92 . Final thoughts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .103 sources

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Introduction The term Vac~turnForming describes a process of forming sheet plastic into simple shapes. This is done by heating a sheet of thermoplastic until it is soft and pliable and then placing it over a mold forminga tight seal between the mold and the plastic. Thena vacuum is applied through small holes in the mold andlor work surface that draw the softened plastic into or over the mold. As the plastic cools, it rehardens. permanently taking on the shape of the mold. Plastic vacuum forming machines that perform this process can range in size from small table top models to huge industrial machines costing many thousands of dollars. When I first became interested in vacuum forming plastic :.......+.lii~i;:;; s ; ~ s ; ; z . . .. ...v.. . - .. . I did some research to find if I ' ' . .. . . 1. , there were plans available for constructing a vacuum forming machine. I came across a few. many of which used a vacuum cleaner as the vacuum source and the kitchen oven as a heat : source to soften the plastic. One i good idea for a small machine used an electric skillet as the heat source with a clamp frame hinged to a vacuum box. Both were set side by side. When the plastic was softened, the frame holding the plastic was flipped iI over the mold which rested on the vacuum box. Vacuum was applied and the pan was i formed. All excellent ideas for forming small items in thin sheets of plastic using positive molds, but I wanted a larger more versatile machine. Something that was selfcontained and

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capable of forming thicker sheets of plastic using either positive or negative molds. Anyway, to make a long story short, I set about seeing what I could put together. As I began the project I quickly realized there were a couple of hurdles to overcome. The first was to find a suitable heating element. I knew for sure I wanted the element to operate on 120 volts. After some checking, I discovered a wide array of 220 volt replacement heating elements available, but very few 120 volt elements. That's because most kitchen ovens use 220 volt elements. It was economics 101. Companies only stock what they can sell. I was finally able to locate a suitable 120 volt element through Chromalox which made this project possible. More about that later. The other hurdle was to find an inexpensive. but adequate vacuum source. There are electric vacuum pumps available that are specifically designed for the process, but they are expensive. I had seen an air venturi vacuum pump advertised by Harbor Freight to pull 4.2 cfm using an air compressor priced at $12.99. I already had the air compressor so this was encouraging. I purchased the venturi pump and it worked as advenised. Adding tanks to the machine for storing the vacuum ahead of time enabled the concept to work out very well. The air pump will pull a satisfactory vacuum of about 20 hg on both my 11 gallon storage tanks in about 3-112 to 4 minutes. Not fast enough for high production, but good enough for me considering the cost. If you are going to use the machine for large production runs where speed is important. then an electric vacuum pump with a high cubic feet per minute rating would be the way to go. We will discuss vacuum pumps a bit more later in the book. The final result of my endeavors and the subject of this book is the machine shown in figure 1. It uses a 120 volt heating element and is capable of forming 12" x IS" sheets of plastic up to 114" thick and uses both positive and negative molds. The machine shown in figure 1 is using an air venturi pump for the vacuum source, but the it is set up to easily operate with an electric vacuum pump if you so choose. The machine is built on wheels so it can be easily moved from place to place and another nice feature is the adjustable platen table making it possible to form molds of different sizes.

In the next section we will describe the machine in greater detail, and get you acquainted with the process of actually vacuum forming a sheet of plastic. Then it's on to building the machine and forming plastic.

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STATIONARY LEGS

INDICAIOR LIGHT

IF ONE IS USED.

HCATCR CONTROL INDlCAlOR LIGHT VACUUM GAUGE

POWCR OUTLET CONTROLLED

Figure 2

How vacuum forming is done Before learning how vacuum forming is done, we need to learn a little bit about the machine. The detailed drawing in figure 2 shows the main features of the machine. The 4 photos in figures 3-6 show the front, rear and side views of the machine. The machine is built around a sturdy roll around cart made of 118" x 1-112" angle iron. The bottom shelf of the machine is large enough to hold two 11 gallon vacuum storage tanks and a vacuum pump. The storage tanks are portable air tanks that have been converted to our purpose. The machine operates on a 20 amp, 120 volt AC circuit. The machine as shown is using a venturi vacuum pump, but an electric pump could be used as well. The control panel contains a vacuum gauge, an infinite range switch to control the heater temperature and an indicator light that shines when the heater is on. The switch on the right side of the panel activates an outlet receptacle mounted on the right front leg of the machine. If you were to use an electric vacuum pump it would plug into this outlet. The indicator light above the switch leu you know when the switch is on. The valve mounted on the left front leg of the can is used to control the incoming air supply to the venturi pump if one is used. The two valves on the top shelf of the can operate as follows: The valve on the left connects the vacuum pump directly to the storage tanks. With the valve open you can pull a vacuum on the tanks. After a vacuum has been pulled you close the valve to store the vacuum. The valve on the right opens and closes the vacuum line from the storage tanks to the platen.To form a sheet of plastic, you would open this valve. The platen is the solid surface on which the molds rest on during the vacuum forming process. Vacuum reaches the platen surface through a hole located in the center of the platen. On most vacuum forming machines I have seen. the platen is stationary, but on this machine it is adjustable. The assembly consists of the platen surface which is a solid board covered with formica or other smooth, heat resistant material. The platen surface rests on a frame built of 118" x 1-114" angle iron. Legs made of 1" square wall tubing are welded to each comer of the frame. In operation, the 1" legs on the platen

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Figure 3 Front view of machine. The small box on the ley? side of the bottom shelf is the venturi pump. Vacuum storage tanks are in the background. Notice the trailer tonguejack mourned on the top shelf. It is used to raise and lower theplaten. 7liecontrolpanel contains the vacuum gauge on the I@, the heater control dial and indicator light in the center and on the right side of the panel is the electric vacuum pump switch and indicator light.

Figure 4 Right side view of machine. Here youget a gwd view of the plumbing, storage tanks and crank handle.

Figure 5 Rear view ofmachine. Here you can see how the cord comingfrom the heating element plugs into the cord comingfrom tlze control panel. It's a hondy feature that lets you completely remove the heater box by simply unplugging it an lifting it off rhe hinge.

Figure 6 Lep side view. Here you can clearly see rhe air supply valve mounted on the front leg. Opening the valve supplies air to the venturi pump.

table, move up and down on stationary posts made of 314" square wall tubing attached to each top comer on the roll around can. It's a nice set up because the 1" square tubing fits nicely over the 314" square tubing. The result, a table that operates smoothly and is easy to raise and lower by way of the trailer tongue jack mounted in the center of the roll around can. It's important to note that the type of jack we are using is referred to as a rack and pinion type. With this type of jack, there is a clear path through the center of the jack shaft for running a vacuum hose up to the platen. The clamp fixture mounted at the top of the unit is used to hold the plastic firmly in position during the vacuum process. It's a simple fixture made of 112" x 1" aluminum or cold roll steel bar stock. The hood at the very top of the machine contains the heating element. If you look at the side views of the machine you can just barely see the element. We are using a 15 amp, 120 volt element. The hood is fitted with a swivel hinge so it can be moved over to one side for easy access to the clamp frame. Now that we understand the machine a bit better we can actually form a sheet of plastic. The series of photos shown in figures 7 - 18 take you through the process.

Vacuum form safety

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The vacuum forming process is fairly safe, but in all things, there are dangers both hidden and realized. Proceed carefully and think through each move until vou become familiar with the Vacuum forming creates some minor fumes which can be irritating, provide good ventila- Figxrc 7 7rri.c 1.r n slror qfrlrc iim(.Iriirclookirr,? doll~rtar rlrr l~lmmt.n t r rorozcl ltolo irr /Ire tion. cenrer of /lie plareir is the vacrtrrnt porr. nre mold will be centered over rhis hole.

Never leave your machine unattended during use. Pay close anention at all times because there is the danger of the plastic overheating. Overheating plastic creates a heavy smoke that can be hazardous and of course there is the added danger of the overheated plastic catching fire. Use extreme caution around the heater box! Its outside surface reaches high temperatures capable of causing bums. Treat it like you would any oven. Use the handle when moving the heater from side to side, and as an added protection, wear gloves.

Figure 8 7liis is a shor q f rlrc rrrr(l~~r~ri~~rrlr .si(li,(ofrltcmold we will be using for our demonstration. nre horrom qf rlre r~roldis recessed ro provide air space for the vacuum. Norice the large and small holes drilled into rhe mold. 7liese are vacuum draw holes [hat have been drilled through to the mold cavity. They are srrategically placed and generally locared ar those places that require the deepesr draw. There is a rubber seal glued around rhe outside botrom edge of rhe mold to prevent vacuum leaks between the mold ond platen.

Figure 9 This is a I ' I F I I . (!f rlrr i11010 (15 ir .s/r~rt/dresf centered over the vacuum port on the ploren. This panicrtlar ntokl is classified as a negarive mold which means the parrem shape is recessed in the mold.

Figure 10 Mold is it1 posiriorr on rite plaren srrrfoce and I an1 in rhe process of raising rheplaren fable.

Figure I2 The hearer is moved irl position over the ploren surfoce.

Figure I 1 A piece of SVrene p l m i c is held .sec!rre/\~in the ~IampjixIureand t l ~ platen e iable has been raised to prrsh the mold against rite surfnce ofrl~eplastic.

Figure 13 The venruri air pump is connected to an air supply. The valve i.7 placed in the open position.

Figure 14 7lle valve that opens and closes the line between the venmri pump and the storage tanks is opened and we begin pulling a vacuum on the tanks.

*Large commercial machines are automatically controlled using precise temperature indicators which indicate when to form a sheet of plastic. We don't have that convenience built into our machine. But then it's really not necessary because with a little experience we can make accurate determinations visually. In the example, I am forming a sheet of Styrene plastic that is .030thick. I will describe the visual changes that occur to the plastic during the heating process. The changes occur rapidly so you must keep your eye on things to prevent the plastic 1 from overheating klwe&we

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As the plastic begins to heat

Figure 15 The infinite range switch that controls the hearer is turned on andpositioned on high. T h e p M c begins to heat to forming temperature. (Approximately 300 degrees)

Figure 17 Theformed plastic sheer as it looks shonly arer the vacuum has been pulled. Figure 16 When a vacuum has been pulled on the storage tanks, and theplastic sheet has *sofreneds@cienrly, the valve that connects the vacuum storage ranks to the platen is opened and the plastic is slicked into the mold. The heater is moved over to one side. The vacuum is held on the moldfor a coriple of additional seconds unril the plastic has cooled then the vacuum valve i~sturned oft:

Fi,qrrre I 8 Tlrr cu~~rplf'll~fl iirpln re11ro1~edJro111 the mold.

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to warp in different directions. As the temperature rises further the surface quickly becomes taught, like a surface of a dmm. At this point you are very near forming temperature. Some plastics have a tendency to sag quite a bit in the frame at forming temperature, which can be a good indicator of when to form the sheet. But Styrene sags only slightly. It is a; the of slight sag that you want to form the pan. It will take careful observation to notice the sag. When you see it, form the part. It's as easy as that. There are other types of plastic that you may use such as ABS, CAB, PET-G only to name a few. Each have slightly different which you will soon become familiar with.

A few things to consider

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We've had a pretty good look at the machine and now have a basic understanding of how it works. But, before designing, buying or building a vacuum forming machine, there are still a few things to consider such as: 1. What kind of plastic can we use and where can we buy it? 2. What is vacuum? 3. Choosing a vacuum source. 4. Vacuum storage. 5. The heating element and control switch. 6. The adjustable platen.

What kind of plastic can we use and where can we buy it? You will be forming your items from flat sheets of thermoplastic material. Thermoplastic simply refers to a type of plastic that can he softened by heat and reshaped by some type of pressure. There are many types and grades of thermoplastic sheet available, each having different properties. Usually, depending on the type of plastic you are using, you will be able to choose between a variety of colors and thicknesses. Depending on where you live, finding a source for plastic can be as easy as looking in the phone book under the heading, "Plastics Supply Centers". I found 4 companies in my phone book, two of which were only a few miles away. I checked with the two that were closest to my house. In both instances, these were companies that were accustomed to dealing with commercial customers. A little guy like me kind of took them by surprise. Even so, when I explained what I was doing and that I really didn't need 500 sheets of plastic they were still more than helpful. The first company was a local manufacture of plastic items and was more than happy to sell me a few smaller pieces of ABS and Stryrene that were left over from

previous jobs. Plastic generally comes in 4' x 8' sheets so I welcomed the opportunity to buy the smaller quantity. The other company I contacted was a branch office for a national company called, "Regal Plastics Supply". Since this was a national company, I listed the address of their corporate office at the back of the book. You can contact them to see if they have a store near you. They are also willing to sell by mail order. Anyway, they were equally kind and more than helpful. I purchased a single 4 x 8 sheet of ,060 black ABS and a 4' x 8' sheet of ,060 clear PET-G from them. I learned that plastic supply companies are only likely to stock types of plastic based on what the need in their immediate area is. What is easily available here may not be available or require a special order somewhere else. Expect to pay in excess of $1 .OO a square foot for most of the plastic sheets you buy. Thinner sheets of some types of plastic might cost a bit less and thicker sheets a bit more. As in anything, I am sure that prices can vary widely, so if possible comparison shop. Also, before you purchase your plastic, ask questions about its forming characteristics and if possible explain to the sales rep what you plan to use it for. They have a wealth of information available to them and often are more than willing to offer advice.

What is vacuum? One dictionary defines a vacuum as a space devoid of matter or from which air or other gas has been removed to a very high degree. Another simply says, pressure lower than atmospheric pressure. To understand vacuum a little better we must first know that air has weight. 14.7 pounds per square inch (psi) at sea level. A reading of "0" psi on a normal pressure gauge is equal to atmospheric pressure or 14.7 psi. An absolute pressure gauge registers "0" at a pressure which cannot be further reduced. In other words a perfect vacuum is "0" pounds per square inch absolute. When pulling a vacuum on a sheet of plastic one is inclined to think that suction is doing the work, when actually it is the weight of the atmosphere (14.7 psi) pushing against it that does the forming. To demonstrate it a little better, think of the space within a vacuum as a thin piece of fresh white bread weighing much less than 14.7

pounds. Place a 14.7 pound brick on the piece of bread and see if it doesn't flatten it. It's the same principle, a heavier weight object vushing- against the lighter weight bbject and forming it. In a perfect vacuum, 14.7 psi is the maximum amount of forming pressure you can achieve. There are a couple of ways of measuring vacuum. The method we will be using is inches of mercury (in. hg). This refers to the amount of vacuum that it takes to lift a column of , mercury 1 ".A mercury gauge with a ROIIRP. nti.vg(ttt,y~ r-cod.\ from vacuum at the closed top of the tube 0 psi to 30 /r..,

Make the lower clamp side rails as a matched pair from 112" x 1" aluminum or c.r.s bar stock. Drill the holes in the rails as shown in figure 82. Make the uwer clam^ side rails as a matched pair from 112" x 1 " aluminum or c.r.s. ~ r i l and i tap holes as shown in figure 83.

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I DRILL 2 HOLES 5 / 8 DIAM. DRILL 2 HOLES 1/4

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You will also need to make a couple of frame spreaders from 112" x 1" aluminum or c.r.s bar stock. The length of the spreaders is determined by your mold size up to the 12" width capacity of the machine. We can start by making a 12" long set as shown in figure

84. After a while you will end up with a few sets of spreaders of

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Figure 84 CIomp spreaders. Length is detemnnrned by widfh @mold. Make 2from 1/2"x I" aluminum or c.r.s. bar stock.

from 112" x 1 " aluminum or c.r.s. bar stock.

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DRILL & TAP 2 HOLES 1/4-20

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varying lengths to accommodate DIAM. different mold sizes. Make the 2 hinges for the upper clamp side rails from 112" x 1" aluminum or c.r.s. See figure 85. Attach a hinge to the back inside of each upper clamp side rail. See figre 86. If You have 85 Hinges for the wper built your frame out of c.r.s simply $ide rail. ~d~ 2 frorn weld a hinge to the back end of 1/2-x ~ " d ~ n u m o r c . r . bar s. each rail. If you have made yours srock. out of aluminum you can bolt the hinee to the rail.

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Figure 83 Upper clamp side mils. Make 2 as a marched pair from 1/2" x I " aluminum or c.r.s. round

Figure 86 Anaching the hinges to the end of the Cside rails.

WELD OR BOLT HINGES TO THE SIDE RAILS.

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LOWER CLAMP SIDE RAIL /SHOWN IN FIG. 8 2

,2 HOLES DRILLED I / 4

SIDE FRAME SHOWN

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