Testing and identification method for the interfacial heat transfer coefficient between CFRTP and tools under fast hot-stamping conditions

Abstract

Carbon fiber reinforced thermoplastic composites (CFRTP) are increasingly applied in automobile structures. Hot-stamping is a fast forming process for complex components of CFRTP. During hot-stamping process, the variations of temperature field occur in entire forming process, which ultimately have an impact on the forming quality and dimensional precision of the part. The interfacial heat transfer behaviour between CFRTP and tools directly determines the temperature distribution in the part. However, the existing heat transfer testing and identification methods are designed for sheet metal, which may not be applicable for CFRTP due to the differences in material properties and forming processes. Therefore, in this work, a new test device was developed to reproduce the interfacial heat transfer behaviour of CFRTP under various hot-stamping conditions, and an inverse identification method of the interfacial heat transfer coefficient (IHTC) between CFRTP and tools was proposed. The influences of contact conditions on the IHTC were investigated, including the interfacial contact pressure, interfacial clearance, heating temperature of tools and sheets. The results showed that the IHTC demonstrated a positive correlation with the contact pressure. However, the IHTC would significantly decrease with the existence of a clearance at the interface. Within the entire heat transfer process, it was also found that an increase in tool temperature resulted in a decrease in the IHTC, while initial sheet temperature didn't exert a significant influence. Furthermore, the reliability of proposed testing and identification methods had been verified by the hot-stamping for U-shaped CFRTP parts. The temperature error between the simulation and experiment was less than 5 %.