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The Science of Thermoforming
EGR News - Fall, 2004 |
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EGR
News recently caught up with Robert Browning
to discuss with him some of the key issues that are happening right now in the
world of thermoforming.
Robert said that he had attended the Society of Plastic Engineers European
Thermoforming Conference that was held in Viareggio - Italy earlier this year,
and one of the topics of interest is how Thermoforming is really coming into
its own as a forming technology compared to other methods such as injection
molding, blow molding or rotational molding.
"What symbolizes the rise of thermoforming in production circles is the
situation where you have a very well respected company like Toshiba now
thermoforming the whole back of their large screen televisions", said Robert. |
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Thermoforming has matured to the point where,
for some applications, it is challenging other forming methods such as
injection molding. Robert Browning, a Thermoforming Consultant to Fortune 500
companies, believes that Thermoforming is a very attractive production method
suitable for a wide range of product types. |
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In discussing what factors have contributed to the increased popularity of
thermoforming, Robert said that "given the fragile nature of the economy, both
in the United States and Europe, designers and engineers are beginning to
re-evaluate projects and question the reasoning behind automatically choosing
to injection mould a part. This is because this process will involve a longer
product development lead-time and increase the customer's commitment to
expensive up-front tooling".
"Lead-time and the sheer cost of tooling, together with the rise of new
generation high performance polymers, are causing companies to rethink their
approach to creating new plastic products using forming technologies that can
be expensive to tool up for" said Robert.
Robert went on to explain that one of the trends that he is seeing is a
tendency by new age designers and engineers leaning towards the use of
thermoforming technology in an increasing number of applications, compared to
straight away assuming the product must be injection or blow molded.
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 The advantages of producing products with thermoforming are
many and include getting faster turnaround, having access to a better range of
raw materials, gaining more control and achieving tighter tolerances.
Moreover, with improved machinery, manufacturers are able to cost effectively
perform the post manufacturing procedures and achieve high quality results.
He said that methods such as pressure forming and twin sheet forming are
gaining in popularity and he has been asked to help injection molders to add
thermoforming to their arsenal of production techniques.
"One of the really hot areas in thermoforming right now is the rise of greatly
improved, new generation blends of polymers. The blends of materials such as
PPX (polypropylene blends, poly carbonate/ABS blends of material) take
thermoforming into the realms of science and get it away from being a black
art" said Robert.
Expanding further, Robert added that "When you see a motor car company coming
out and forming gas tanks that consist of 9 different layers of material, then
it is a signal to the industry that thermoforming has arrived as a main stream
production method.
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Because you can specify a fairly tight set of
performance criteria for the supply of extruded raw materials, thermoforming
has moved away from being an art form into a repeatable science. Issues like
the materials melt index, impact resistance, orientation and tensile strength
can be specified so that the raw material conforms to a well documented
specification".
Armed with these high quality materials, Robert feels that the thermoformer can
achieve repeatable production of their products today, tomorrow and in six
months time.
Another factor that is making thermoforming an attractive production technology
is the fact that over the last five years, manufacturers of the forming
machines have improved their technology and can provide the thermoformer with
the means to carefully control the distribution and timing of heat.
"This type of control allows greater repeatability on the machine and provides
far better feedback so that an operator can control key aspects such as vacuum
pressure, blow back to form the undercuts together with heater control during
the forming cycle.
This control now extends to different zones that can be especially isolated to
control the saturation of heat. You can put thermoco  uples into the tool to allow measurements that give control
of the heating in multiple zones throughout the tooling.
When you combine this with the sheet being extruded to a set specification and
heated to a set specification, you can see how thermoforming is really an exact
form of science" said Robert.
Robert continued that ..."Improvements in the technology of the heaters
themselves is one of the great areas of gain. Today, you have ceramic, quartz
and halogen heater systems. On top of this, infra red scanning technology
allows you to get an instant thermal image of the material. This, in turn,
allows you to profile the heating distribution of a machine so that this
variable can be compensated for. This means that the process becomes a more
repeatable day by day system."
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| The thermoforming process allows parts to be
produced to very high tolerances to the point where the formed part is able to
conform to what is know as a "Class A" surface finish. This mirror finish is
really the ultimate goal of thermoforming". |
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Another part of the improvement Robert is
seeing is in the area of education and there are a number of excellent colleges
providing tuition together with organizations like the McConnell Company that
undertake specialised training.
McConnell Co., Inc. have been leading consultants to the Thermoforming Industry
for decades now and Bill, Art, Donald and Robert regularly conduct seminars in
North America on subjects such as part design, tooling design, thermoforming
techniques, material and equipment selection.
While education of staff is very important, Robert feels that you cannot
underestimate the impact that improvements in tooling have had on the
Thermoforming industry. |
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"The rise of computer control and 3D solid modelling, together with the
practice of overcasting the tooling, allows the toolmaker to come back and
machine it to a very high quality.
This machining process is also allowing the top toolmakers to produce castings
with very little porosity so that when you do the machine cut, the tool looks
like a billeted piece of aluminium.
So with a tool using raw materials that are manufactured to a tight
specification, and having the capability of distributing its heat in a very
controlled manner, tight control is achievable. As well, the tool then can
remove heat from itself in a very consistent manner to allow the material to
cool below its set point.
This process in turn allows the product to cool in a controlled way and so
minimizes any stresses to the material to virtually eliminate warpage and
bowing of the final product.
"In all this, the thermoforming process allows parts to be produced to very
high tolerances to the point where the formed part is able to conform to what
is know as a "Class A" surface finish. This mirror finish is really the
ultimate goal of thermoforming " said Robert.
Regular readers will remember Robert from his time in Australia as part of the
EGR sponsored "Innovations in Thermoforming Seminar" at Melbourne's Crown
Casino.
During the same tour, Robert was guest speaker at the Engineering Queensland
2002 Presentation luncheon and spoke on "Using Advanced Technologies to Sustain
Competitive Advantage in a Global Environment". |
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| Robert Browning |
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| About
the Author: |
| Robert is an Associate of McConnell Co. Inc, which is a consulting company that is based in Fort Worth, Texas. |
| Robert is widely considered to be an expert in the field of twin sheet thermoforming and pressure forming products, tooling and processes. He has six US patents and an additional two patents pending in the design of thermoforming and the tooling for thermoforming. |
| About
McConnell Co., Inc.: |
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The company was founded by Wm. K. "Bill" McConnell, Jr., and now consists of
three associates, Arthur Buckle, Robert Browning and Donald Hylton, who has
just joined and is a very well known chemist and polymer scientist.
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