“Technologies like injection molding are not able to withstand these temperatures, while prepreg is not capable of achieving required high volumes,” says Mainka. “At the end of the day, everything comes down to reaching the volume that’s needed and implementing it in the plant without having any changes to the assembly line.”
As Shane Skop, SURF’s composites engineering manager, elaborates, “Typically with compression molding you’re working more with thermoset systems, so you’re getting higher temperature-rated materials, which can withstand automotive e-coat temperatures of nearly 400 degrees Fahrenheit. That’s a big advantage for compression molding over injection molding or thermoplastics. They have a lot of trouble getting through e-coat, which is a major hindrance to widespread adoption in the automotive industry.”
With support from SURF and its material supplier, IDI Composites, VWGoA developed a new Class A SMC and an advanced primer system. Mainka estimates that approximately half the component’s three-year development was spent creating the right material formula to achieve Class A requirements.
“The liftgates were shipped to our factory in Chattanooga, Tenn., and have been successfully painted using the paint line,” he adds. “That was a huge development from this project. We are able to run this component through the paint line like we can do with a steel part.”
Inside the Press
Mainka notes that SURF provides a unique opportunity for the industry to test new production methods in a setting that is very close to production ready. “Using this resource makes it possible to evaluate new production processes without interfering with current production in our plants,” he says. However, the team at SURF is constantly examining its processes to move composite manufacturing in new directions. This includes work to better understand the science behind material technologies.
“There isn’t a whole lot of dedicated science behind actually making a full-scale part,” says Skop, who previously worked for a Tier 1 supplier. “It’s a lot of getting the right ‘feel’ from the engineers in the plant. What we’re trying to do here is to bring it to more of a science than an art form.”
Today, Skop says, IACMI researchers are using SURF to remove some of the unknowns at play within the compression molding process. This work is meant to help engineers troubleshoot production in the event of material issues. “Every once in a while, you get things that just don’t make sense, where the material is not reacting how you think it should and there’s not a lot of data to explain it,” Skop says.
To this end, IACMI is working with researchers at Purdue University on a project to validate closed mold simulations to better understand what happens in the press and within tools as composite materials cure. The team runs an experiment on SURF’s small 75-ton compression molding equipment and then compares the data gleaned from that test to the simulations Purdue is running on the same tool geometry. In validating this part on a small scale, researchers can tailor the charge pattern on a full-size part to reduce weak areas when utilizing discontinuous fiber materials or create the best possible fit within the parameters of a manufacturable part.
“A lot of people see compression molding as you put some material in and it goes into a tool that’s like this ‘black box’ and then, poof, a part comes out,” Skop says. Understanding what happens to the material while in the tool has the potential to provide a lot of insight. If a material flows 10 inches versus 5 inches, how does that affect its strength? How does that affect its ability to be knit into another material?
“Once we have a better picture of what it looks like in the tool, we can start dialing in and optimizing parameters,” Skop says.
The SURF technical team is in the early stages of working with colleagues at Purdue, along with Volkswagen and material suppliers, to develop insight into pressing parameters for a range of materials within a co-molding method. The goal is to determine how to maintain good interface strength and co-mingling properties of continuous materials with discontinuous materials.
As Skop explains, continuous fiber materials can provide significantly greater properties than discontinuous materials, but come with drawbacks in part design and consolidation. “We’re looking at how we can bring those two types of materials together – continuous and discontinuous – to achieve the design and molding flexibility of an SMC (discontinuous format), but utilize the strength of prepreg materials (continuous format) as well,” Skop says.
Future Innovation
With the Ford and VWGoA projects completed, SURF is ready to move forward. In July, the DOE Vehicle Technologies Office granted two $7.5 million awards, one to Ford and one to General Motors, both of which SURF will support. The Ford team, in collaboration with Oak Ridge National Laboratory, will develop multifunctional composite structures with electronics integration for cross car beam applications.
As Boeman points out, SURF’s work thus far has been driven by weight-saving benefits, but there’s tremendous opportunity for improving component multifunctionality. For instance, components such as liftgates and cross car beams can be embedded with sensors or wiring harnesses, which in turn support simplified assembly. “By the nature of molding with conformable materials, you have the ability to look at creative engineering solutions,” Boeman says.
The General Motors team will develop FRP composites for high-volume manufacturing of structural battery enclosures using compression molding technologies. Boeman points out that hybrid molding technologies – which might be hybridization with metal inserts within composites or of low-cost discontinuous products merged with continuous fiber inserts – also hold great promise.
SURF is also supporting companies like BASF in moving novel applications forward. “We have a lot of startups come to us that are interested in learning about composites or don’t have the equipment for development,” Skop says. It’s up to Skop and his team to help those companies identify – or create – the solutions that can achieve the desired performance requirements.
