Research addresses road bumps in RTM process

The manufacturing of composite parts using the resin transfer molding (RTM) process hasn’t always been a smooth ride.

RTM can help manufacturers reduce costs and cycle times when compared to costly and time-consuming autoclave and hand lay-up processing. However, for automotive parts manufacturers, the challenge has been to use RTM to produce parts with a class “A” surface finish.

“You don’t want to see the fiber’s print through the surface,” noted McGill University professor Pascal Hubert. “You want to have essentially almost a mirror-like finish so that the part can be painted or used right after molding.”

RTM is a low-pressure process that involves the injection of a resin into a closed two-sided mold with a preform. Pressure is applied to push the resin into the mold and through the fiber preform, and heat is applied to trigger the reaction. The material is then cured before demolding.

Canadian composite manufacturers are no strangers to the RTM process. For instance, Kelowna, B. C.-based FormaShape announced last year that it had used the closed-molded RTM process to produce the world’s largest waterslide part.

“RTM offers unparalleled control of shapes, forms and dimensions allowing for precise dimensional tolerance to be calculated, essential for safety,” explained Henry Czenczek, FormaShape’s manager of design engineering. “It has enabled us to make the waterslide parts stronger, lighter and to much closer tolerances.”

However, McGill’s Hubert notes that there are still some challenges in producing automotive parts that meet OEM surface specs.

“The challenge is to get a very good finish after RTM, and also you want that finish to survive the paint job,” said Hubert. “These paint jobs are done at high temperatures because they were all designed for steel painting, and they want to send the part to the same paint cycle.”

Manufacturers have remedied this issue by putting larger fibers in the middle and a surface veil up top, and modifying the resin with low-profile additives to compensate for shrinkage during processing.

Despite these advancements, “there are still some issues they still don’t fully understand, such as what are the critical factors affecting the surface finish,” said Hubert.

Hubert and his team of researchers, funded by the Auto21 Network of Centres of Excellence and the Ford Motor Company, are working to examine the fundamental properties of the material, in order to identify the “driving mechanisms” that control the surface finish.

“We conducted some parametric trials to identify the most important parameter to control,” he explained. “Our research’s goal is to really build a framework, a systematic approach of looking at what the issues are that will control surface finish.”

Once the relationship between the finish and the polymer microstructure is understood, Hubert’s group hopes to be able to define the optimum processing conditions for a quality part surface. The technology can then be harnessed

by Canadian molders who are looking to make the jump into the high-end automotive market.

“There are some small companies that just make composite parts that can use our findings to get into making class ‘A’ parts,” noted Hubert. “RTM is a relatively new process, so many companies are interested in seeing if it will have the potential for automotive manufacturing.”

Dr. Pascal Hubert (Montreal, Que.); 514-398-6303 AUTO21 Network of Centres of Excellence (Windsor, Ont.); www.auto21.ca; 519-253-3000 ext. 4130