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1. The future of thermoplastics in the automotive industry and
process technologies towards mass production
Introduction
The use of thermoplastics in automotive manufacturing is not a new concept;
manufacturers have made use of composites in several applications for many years. They
have been used for non-load bearing parts and interiors such as battery frames and
bumpers in mass produced cars, and for more complex applications such as the
monocoque for high-end sports cars. However, until recently it has not been viable for
thermoplastics to be used in mass production for cars and commercial vehicles for various
reasons.
The time cycle, and therefore cost, of production of parts has been a particular stumbling
block for manufacturers. There is a requirement to ensure that any composites used are of
the necessary safety standards for today’s vehicles, along with the consideration of the
environmental impact and recyclability of components due to End-of Life Vehicle (ELV)
directives.
With car manufacturer’s constantly innovating design and looking for ways to make
vehicles lighter and more efficient, the use of steel for the body and chassis of cars has
been facing competition from other materials such as aluminium and fibre reinforced plastic
(FRP) for some time. The development of carbon fibre reinforced plastic (CFRP)
manufactured from thermoplastics, and the advancement of the process technologies to
make parts, has given manufacturers the opportunity to use CFRP’s in many new
applications and has made the possibility of mass production a very real prospect.
High performance composites
Thermoplastics were originally derived from structural polymer composites. (1) Epoxy and
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2. polyester thermosetting resins were reinforced with continuous filaments or fibres, and
although structural polymer composites demonstrated several key benefits such as low
density and good insulation, they were chemically unstable. Thermoplastics such as CFRP’s
do not contend with the same issue as they utilise a thermoplastic matrix. They can be
heated, re-molded and cooled several times without degradation, and are prone to less
damage from production machinery due to their superior strength. Crucially for the
automotive industry, they are recyclable; unlike thermoset composites.
CFRP materials possess an array of properties that make them attractive for
manufacturing. (2) They are typified by high strength and rigidity; they have a low density,
a greater dampening effect, and are highly resistant to impacting. They have excellent
electrical and thermal conductivity and modifiable thermal expansion properties.
CFRP’s have been used extensively in aerospace engineering, the Boeing 787 being one
such example (3), which uses composite materials in its airframe and primary structures.
Almost half of the airframe is made up of CFRP and other composites, which provides a
weight saving of around 20%. Formula One is another industry which has used CFRP for
many years (4); in fact McLaren International first used a CFRP monocoque for their
MP4/1C model in 1981 (pictured below).
The automotive industry as a whole aims to follow this
lead of using CFRP more widely with the intention of
weight saving and fuel economy at the forefront of
design. Manufacturing processes are continually being
developed, and will continue to be streamlined to
make it possible to produce parts in a mass production
scenario, both quickly and economically.
Source: f1-dictionary.110mb.com
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3. The challenges of large scale production
One of the great challenges of using CFRP in mass production is reducing the
manufacturing time for individual parts. Using the example again of a Formula One car, the
design and manufacture cycle of each part is estimated at eight weeks. Clearly a high-end
design like this has no place in the world of large scale production where the manufacturing
cycle needs to be considerably shorter.
Research carried out by the Fraunhofer Institute for Chemical Technology ICT (5) has shown
that the cycle time to produce parts from thermoset composites is often twenty minutes or
more, which in the real world of car production is simply too long. Engineers at the institute
have developed a process of Thermoplastic Resin Transfer Molding (T-RTM) which reduces
the manufacturing cycle to around five minutes, and makes it possible to manufacture up
to 100,000 parts per year. The process will be discussed in the next section, along with
some of the other new technologies in manufacturing.
New process technology
Developing the processes to enable grand scale production has been part of the ongoing
challenge for car manufacturers for several years. There are several methods of
manufacturing composites, and variants on the process within each method. Below we look
at some of the more prominent processes that may be used in the automotive industry.
Research and development is ongoing in each of these areas, both in terms of improving
the manufacturing process to achieve the quality of product which meets crash safety
standards, and to facilitate mass production.
Resin Transfer Molding (RTM)
Resin transfer molding has previously been considered a process which is for medium
volume production quantities, as it bridges the gap between slower contact molding
processes and faster compression molding methods(6). Continuous strand mats and woven
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4. reinforcement is placed dry in the bottom half of the mold, which is then clamped down. A
low viscosity catalysed resin is pumped into the mold, displacing the air which is forced out
through vents. Metering equipment is used to control the ratio of catalyst and resin. The
benefits of this type of molding are that it produces exact parts of uniform thickness with a
finish to both sides, and the manufacturing process has low emissions.
Thermoplastic Resin Transfer Molding (T-RTM)
The researchers at ICT have developed this method to create their own thermoplastic resin
transfer molding process, which enables them to form the composite in a single step. A
pre-heated textile structure is inserted into a molding tool which is thermostatically
controlled; it is inserted in such a way that the fibre structures are aligned with the
anticipated stress. The activated monomer melt is then injected into the molding chamber
to complete the process. By controlling the temperature during the processing stage, the
engineers are able to select the minimum required processing time.
ICT showcased this method of manufacturing by producing a trunk liner for the Porsche
Carrera 4 which weighed around 50% less than the conventional aluminium part, and
actually improved the cars overall structure in terms of crash behaviour by calculating the
optimum placement of fibres. The method has another benefit as it has been demonstrated
to half the cost of processing when compared with thermoset structures.
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References
(1) http://www.azom.com/article.aspx?ArticleID=85
(2) http://www.engineersparadise.com/en/ipar/18832
(3) http://www.boeing.com/commercial/aeromagazine/articles/qtr_4_06/article_04_2.html
(4) http://www.formtech-composites.co.uk/compositesUKcompositesubstitution.html
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5. (5) http://www.fraunhofer.de/en/press/research-news/2010-2011/08/making-vehicles-safer.jsp
(6) http://www.engineershandbook.com/MfgMethods/resintransfermolding.htm
(7) http://www.teufelberger.com/en/products/composite-braiding/braided-composite-parts.html
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IQPC GmbH | Friedrichstr. 94 | D-10117 Berlin, Germany
t: +49 (0) 30 2091 3330 | f: +49 (0) 30 2091 3263 | e: eq@iqpc.de | w: www.iqpc.de
Visit IQPC for a portfolio of topic-related events, congresses, seminars and conferences: www.iqpc.de