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New solutions for automotive composites

News International-French

25 Jul 2017

Sponsored News - An ambitious program to fulfill new requirements of the automotive industry

The Chomarat Group is developing an ambitious strategic vision with regard to the automotive industry, in anticipation of future developments and changing environmental regulations. This vision covers technological aspects, products and industrial organization. 

To fulfill regulatory objectives to reduce CO2, the automotive industry needs to rethink its strategy and must innovate. By enabling the weight of structures to be reduced, continuous glass and carbon fiber composites offer a significant advantage in attaining these goals. 

In order to make their mark, composite products must be of economic benefit in a context where each process and each material must compete to find its place in an appropriate and optimized industrial procedure.
Over the last ten years, Chomarat has developed various solutions for thermoset and thermoplastic applications in the form of glass and carbon non crimp fibers (NCF), as well as woven fabrics. 

Development of carbon NCF based on heavy tow fibers  

Figure 1 C-PLY™ carbon NCF
Lowering weight at lower cost in the automotive industry depends on a long-term strategy to develop processes based on heavy-tow carbon fibers, which are made up of at least and sometimes more than 50,000 filaments (50K). These are the right materials in terms of technical performance/cost ratio. They offer a long-term economic vision and are not subject to market fluctuations.
These heavy-tow technologies make it possible to match the carbon fiber performance to the specific requirements of the automotive industry through changes to the precursor or to the oxidation processes, or by increasing the number of tow filaments.

The fibers require the use of equipment with the capability to efficiently produce different NCF configurations (thin ply, thick ply and shallow angles). Chomarat has invested heavily in these new technologies in recent years to promote innovation and competitiveness.

Guaranteeing optimized quality for all the different applications (structural or surface appearance) requires a perfect working knowledge of the fibers, with a heavy focus on in-line monitoring. Given this demanding context, Chomarat developed its C-PLY line, which integrates the technical, economic and qualitative constraints all together in order to keep up with the changing automotive industry and make the use of high-performance composites more accessible.

The initial research was carried out in collaboration with Dr. Stephen Tsai on the optimization of fiber orientation using a C-PLY for shallow angles, leading to the development of unique solutions to make carbon wheel rims. There is still a huge range of potential applications, which Chomarat continues to explore on parts with preferred direction, like pillars and cross beams.

Optimized carbon unidirectionals
Drawing on this work to move the composite industry towards more automation and minimize preform production time, Chomarat demonstrated the interest of working on multiaxials in addition to unidirectionals for the automated tape laying (ATL) processes used widely in the aerospace industry.

This optimization goal led to a number of research projects to establish a range of functionalized unidirectionals that address these technological changes and remove the bottlenecks to more widespread use of carbon in the automotive industry.

Created to combine economic performance and processability, the C-PLY™ UD range is a natural complement to the C-PLY™ Shallow Angles range for parts with preferred direction.

Adapting reinforcements for the processes
A number of processes provide solutions according to the now well-known approach that consists of “the right material in the right place at the right cost”. Chomarat works with technology specialists to meet the requirements of key processes like RTM, Prepreg Compression Molding, Wet Compression Molding, SMC, pultrusion, and  organo-sheet* overmolding.

For each process, the choice of the most appropriate fibers, always specific, and the functionalization of the reinforcements to assist process steps like fixation, preforming or permeability are always a challenge. 

Solutions for the “carbon look”

New solutions for automotive composites - Roding roadster
For luxury cars and in sports equipment, where carbon exemplifies strength, lightness, quality and performance, Chomarat proposes a range of premium 3K carbon-fiber fabrics for exposed-weave applications. 

Body panels (e.g. hoods, roofs, quarter panels) are also studied for potential weight reduction to lower the vehicle’s center of gravity. These bodywork parts are typically painted, so replacing 3K carbon-fiber fabrics with heavy tow non-crimp fabrics could result in savings.

Both the NCF technology used and Chomarat’s expertise in heavy tow NCF fabrication places C-PLY™ as the solution for original equipment manufacturers for their Class A applications. By minimizing the excesses of resin revealing local mold release problems, the use of C-PLY™ greatly reduces fiber print through.

Other technological improvements to the RTM process have made it possible achieve direct from the mold quality. This is the case with Surface RTM** technology.
C-PLY™ is recognized as the NCF reference for these applications for Class A painted parts.

Achieving Class A surface appearance on automotive parts 
Carbon fiber fabric offers a rigidity-to-weight ratio greater than that of steel or aluminum, but it can result in a visible pattern that is unacceptable on a finished part with a Class A rating. 
The Chomarat research center conducted a study to assess the impact of carbon multiaxial reinforcement on the surface appearance of bodywork parts manufactured using resin transfer molding (RTM). Initial trials confirmed that carbon NCF multiaxials perform better in terms of appearance than carbon fabrics.

Resin shrinkage is the main cause of fiber print through on a laminate surface, especially when the part is exposed to high temperature, such as under intense sunlight. However, the result also depends on the reinforcement used. Other parameters that need to be adjusted to achieve the best result in terms of surface appearance are the fiber sizing, construction and stitching pattern, and the use of binder or veil.

Glass reinforcement applications
Drawing on its know-how in optimizing fiber orientations, and with many applications in sports equipment, Chomarat has developed glass solutions for thermoset resins (epoxy or polyurethane) that are now becoming more and more popular in leaf-spring applications.

These parts require unidirectionals that are not only cost-effective, but also compatible with processes that are becoming increasingly faster, with stiff preformability and permeability requirements. Chomarat proposes its high-modulus woven G-Tape range or stitched UD G-PLY™ to meet these specific requirements.

The capability to functionalize the stitching and to add elements that can be heat-activated also makes the use of these reinforcements suitable for tape-laying processes.

Thermoset processes have traditionally been used for composites, although the automotive industry has developed expertise in thermoplastic injection processes with peerless cycle times.
The use of chopped fibers for these thermoplastic processes has undergone a number of developments over the past decade which, along with the use of simulation tools, has made it easier to design a part as a function of the expected performance.

The chemists who work in the automotive sector continue to explore the potential to use continuous fibers in these thermoplastic processes, with a number of demonstrators that use organo sheets. Chomarat has kept up with these developments, thanks to its G-Weave range of woven roving with thermoplastic sizing, which is now used to reinforce polypropylene (PP) and polyamide (PA) resins. These systems are found on many parts for impact resistance, where the glass/thermoplastic combination can play an important role. Chomarat provides the possibility to add angles to these fabrics in order to optimize the part geometry. 

Conclusion
Both our ability to adapt and develop technologies and our long-term strategic vision upheld by strong partnerships have enabled us to become a major player in composites for the automotive industry.

Author: Francisco De Oliveira, Automotive Market Manager, Chomarat, France

*consolidated thermoplastic composite sheet
**More information on Surface RTM : http://www.kraussmaffeigroup.com/rtm-en/

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