Technology development for the pultrusion of hybrid laminates with reactive monomers

Hybrid laminates or fiber-metal laminates (FML) are a family of hybrid composite structures consisting of alternating layers of metal alloy and fiber-reinforced plastic (FRP). These mostly flat composite materials combine the positive properties of metal alloys and FRP and demonstrate an outstanding profile, especially in crash applications.

Challenges in manufacturing

The production of thermoset-based hybrid laminates has so far been predominantly sequential and discontinuous. This results in long cycle times, high costs, and time expenditures. Hybrid laminates with a thermoset matrix are usually manufactured in an autoclave under high pressure, vacuum, and elevated temperature. This requires complex pre- and post-treatment steps. A major challenge is the reliable adhesive bond between the different material classes.

Project RALPH – A new approach

In the IGF project RALPH “Reactively coated aluminum sheets in thermoplastically pultruded hybrid laminates for crash structures,” we are working together with the MERGE research cluster at Chemnitz University of Technology and the Leibniz Institute for Polymer Research IPF to develop an innovative, highly efficient pultrusion manufacturing route for the production of near-net-shape hybrid components on a scale suitable for large-series production. The hybrid laminate is made of glass fiber, polyamide 6, and aluminum.

Partners' main areas of research

Responsibilities within the project are divided according to each partner's core expertise:

• MERGE: Pre-treatment of aluminum sheets
• IPF: Development of a powder coating to create a covalent bond between plastic and aluminum
• Fraunhofer IWU: Process development for pultrusion and implementation of direct polymerization of caprolactam to polyamide 6 in the hot pultrusion tool. The use of a thermoplastic material enables complete recycling at a later stage.