Reinforced Pultrusion Process – Carbon Fiber Automotive Parts Production Process

 

Thermosetting Arc Pultrusion

 

 

Thermoplastic Pultrusion

 

 

 

Using thermoplastic pultrusion with in-situ polymerization of caprolactam as a long-span structural part, and then hot forming the tail end to obtain the structural connection part, this skeleton design to obtain a more competitive composite automotive structure is a bold attempt! The project focuses on the production of a special demonstrator, namely the windshield frame located between the two A-pillars above the windshield.

 

The technology involves hot forming and overmolding of pultruded unidirectional (UD) carbon fiber thermoplastics in a two-step process with a cycle time of 75s to produce a structural roof beam that exceeds the requirements of all previous versions. It also integrates attachment clips and changes the collision behavior from brittle to ductile failure mode to improve the residual strength of the body in white.

 

“With our thermoplastic tapes, which are also based on pultrusion, we have extensive knowledge of semi-finished products, so we were able to quickly adapt the pultrusion technology we currently use to create our own profiles.

 

This process includes quality checks for fiber content, porosity and dimensional accuracy. Due to automation and robotics, dimensional accuracy is very important,” says Dr. Christoph Ebel, head of the Lightweighting and Application Center at SGL Carbon. “For example, there must be no bending due to residual stresses in the pultruded profiles.”

 

In addition to pultruded reinforcements, thermoplastic resins were also investigated in the MAI Skelett project.

 

Various types of polyamide 6 (PA6) were tested to determine the required viscosity and rheology for optimal pultrusion quality and pultrusion speed.

 

Through its thermoplastic toolbox, which includes UD tapes, organosheets, chopped fibers for short- and long-fiber reinforced compounds, and now pultruded profiles reinforced with unidirectional fibers, SGL offers a range of materials for this project, all based on SIGRAFIL 50K carbon fibers suitable for matrix impregnation with polypropylene and polyamides, including PA6 or in-situ PA6.

 

“To achieve the best performance in composite structures, the fibers, sizing and matrix materials must be coordinated with one another,” says Bühler.

 

She also explains in-situ PA6: “This is the long polymer chains that are formed during the molding process of the composite part when reacting caprolactam monomers or reacting monomers with catalysts and activators.” In other words, caprolactam is polymerized in-situ to form polyamides.

 

As a polymer group, polyamides include PA66 and PA12, as well as certain types of PPA as additional matrix material options, says Bühler.

 

Another important aspect in manufacturing the windshield frame is the ability to thermoform the thermoplastic semi-finished product during and after molding to further functionalize the shape and ensure melt bonding during overmolding, two important factors in the design of the MAI Skelett demonstration part.