Factors influencing the fiber orientation in welding of fiber-reinforced thermoplastics

In welding of fiber-reinforced thermoplastics, the welding pressure initiates squeeze flow of melt into the weld bead. This leads to reorientation of fibers into the flow direction. Therefore, the fibers in the weld are mainly oriented perpendicular to the joining direction. Since this is mostly identical to the load direction, the reinforcing effect of fibers is not effective in the weld because fibers only have a reinforcing effect on the polymer when they are aligned along the load direction. Current investigations at the Kunststofftechnik Paderborn (KTP) aim at reaching an effective reinforcing effect of fibers in the weld of fiber-reinforced thermoplastics. The experiments are carried out on polypropylene and polyamide. Three different grades of PP are used: unreinforced, short glass fiber-reinforced, and long glass fiber-reinforced PP with 30% fiber content each. The used grades of PA differ in viscosity and shear thinning behavior. Experiments are being conducted on influences on the weld strength and the fiber orientation in the weld for hot plate welding. Common welding parameters are varied. One aim of the investigations is to find a correlation between the flow velocity during squeeze flow and weld strength or fiber orientation.