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Innovative painting process for CFRP auto body panels

This innovation sheds light on the challenges of achieving a Class A surface finish using on-line/in-line painting processes. It proposes a new method for producing a CFRP trunk lid based on PCM and SMC processes.

CFRP parts for the automotive industry should be produced with well-defined engineering procedures, using a qualified manufacturing process in fit-for-purpose facilities. The autoclave process is the most commonly used for producing high-quality structures in the composites industry; however, it has its drawbacks. Due to its shortcomings, it was necessary to specifically address the need for a low-cost, high-quality manufacturing process. The new multi-material trunk lid developed by Hyundai Motor Group uses two novel curing techniques (PCM and carbon fibre SMC) for mass production. It was adopted for the Genesis G70 sports car, the new luxury sedan from Hyundai Motor Group that won Motor Trend’s 2019 Car of the Year Award.

Comparison of surface quality finish according to paint process

Comparison of surface quality finish according to paint process

This trunk lid results in a substantial weight reduction (up to 60%, 6.4 kg weight saving compared to conventional steel structures) and great component performance. The outer body panel uses 5 to 6 plies of unidirectional prepreg and the inner panel features 1.6-3.5mm-thick carbon fibre SMC in several locations for local reinforcement to reduce stress concentrations. The design concept was evaluated based on finite element numerical analyses and a series of structural tests involving repetitive open/close durability, oil canning and long-term environmental durability were conducted.

Key Benefits:
> CFRP on-line/in-line painting for mass production, solving “colour matching” issues
> Class A surface with a conventional automotive painting process
> Energy saving in the painting process due to a low-temperature-curing 2K clear coat
> Lightweight CFRP trunk lid with a 60% weight reduction through design optimization
> High cycle production of 5-minute cure PCM prepreg

This innovation can be implemented by introducing a new non-conductive primer (acryl-olefin) and a topcoat layer for painting auto body CFRP panels. Follow-up trials showed that CFRP panels that received a single primer coating after automated grit-blasting sanding can eliminate the fibre texture. A thick, non-conductive primer enables on-line painting and enough adhesion to the intermediate coating by increasing surface tension on the CFRP substrate. The surface quality is equivalent to conventional steel parts according to combined factors such as gloss, dullness and orange peel.


New method for producing a CFRP trunk-lid

The Hyundai Motor Group associated partners are: Hyundai Steel Company (South Korea), Hyundai Motor Group – Polymer research lab (South Korea), Mitsubishi Chemical Corporation (Japan), SK Chemicals (South Korea).

Companies: Hyundai

Countries: Japan, South Korea

Industries: Automotive and Road Transportation

Technologies: Other Processing Method

Terms: Innovations

This article has been edited by Basalt.Today
This article has been written on JEC Composites Magazine
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