Influence of contacting, material and shape on the resistance heating of continuous fiber reinforced thermoplastics

Especially in the automotive industry, continuous fiber reinforced thermoplastics are currently experiencing a steadily increasing demand. Thermoplastic matrix systems promise shorter cycle times and improved joining and recycling characteristics when compared to fiber reinforced thermosets. In order to process continuous fiber reinforced thermoplastics, semi-finished parts are usually produced first. These are afterwards heated and post-processed in a back injection molding process. This means that design elements such as load transfer elements and ribs are injected onto the usually flat semi-finished part. The effect of Joule heating can be exploited to heat the part. The electrically conductive carbon fibers are heated by an applied voltage. The temperature is then distributed through heat conduction into the part's thermoplastic matrix. By using Joule heating, high heating rates with low energy consumption are possible. For the industrial use of Joule heating of continuous fiber reinforced thermoplastics, further correlations between influencing parameters must be investigated and specified. The part's shape in particular has a decisive influence on the quality of heating. Within the scope of this study, heating experiments are compared using a thermographic image system. In principle, rounded corners and small changes in shape result in homogeneous temperature distributions. Complex shapes should be avoided and design elements such as gaps, thickness steps and corners designed small compared to the overall area of the part.