Checking automotive surface quality

SMCs are a cost-effective and lighter alternative to metals and more resistant to corrosion. They not only help make nicer cars, but most importantly, lighter ones – reducing fuel consumption, carbon dioxide and other greenhouse gas emissions. Together with improved engine systems, these materials can contribute to meeting EU regulations concerning emissions, and to reducing the impact of modern transport on the environment.

“These composites are starting to be used more widely as a replacement for steel in automotive body panel applications,” says Véronique Michaud from main project participant the Polymer and Composite Technology Laboratory in Lausanne. “They suffer, however, from major drawbacks in terms of reliability, of surface appearance and performance. Simply stated, it is extremely difficult to obtain, in a reliable manner, a surface quality that matches that of steel, especially after the painting operation.”

The goal of the SURFAS project was to investigate problems of surface quality in SMC composites. Partners identified the presence of surface craters or pits on composite parts. “At that point, nobody knew why these craters appeared,” explains Michaud, “so a main goal was to understand what was happening, at all stages of the process, from fibre production and the deposition of the sizing layer to compounding of the composite pre-product, up to the final processing of the part. From there we hoped to make proposals on how to modify either the base material or the process to better control surface quality.” The project delivered an array of important scientific results. Partners gained a better understanding of the role of fibre sizing and over-sizing on the fibre assembly surface and how parameters such as energy, permeability and rigidity, affect final product quality. They also investigated the exact mechanisms of the so-called ‘low profile effect’, where a blend of thermoplastic and thermoset resin is used to improve the final surface quality.

Dr. Michel Arpin works for SURFAS industrial partner Vetrotex International and says the project was an excellent opportunity to investigate a technical issue from a more scientific perspective. “The direct outcome for our company is two-fold,” he says. ”First, we are now better armed to develop new products in this or similar domains of application, thanks to all the technical knowledge that we gained. This project has helped us to point out clearly how complex the materials-process-performance interaction is with this type of composite material.”

“EUREKA gave us the opportunity to cooperate on a European level,” adds Michaud, “without the heavy administrative constraints of a typical European project. All partners could deal with their local funding agencies, with whom they were already familiar and who reacted quickly and remained closely involved in project progress.”