Investigation of the weldability of PA6 and CF/PA6 based on a servo-driven ultrasonic welder without using energy director

Abstract

For ultrasonic welding (USW) of fiber reinforced thermoplastic composites without energy director (ED), the special contact surface and interphase structures due to the addition of fibers have strong relation to the weld quality. In this study, through the servo-driven USW experiments and the corresponding mini-anisotropy modeling for PA6 and CF/PA6 composites welding without ED, the fusion phenomena and weldability of the materials are addressed. The results show that as compared to pure PA6, CF/PA6 has the higher loss modulus and lower specific capacity, leading to more viscoelastic heat generation during USW. As the CF/PA6 surface has the higher roughness, the more significant local stress and energy concentrations occur around the initial contact area, leading to the increased welding area; while more pores are observed within the joints of composites due to the poor liquidity and air trap from larger contact gap. Due to the interphase structure between CF and PA6, the high strain and high temperature occur around the fibers, where pores form due to thermal decomposition.

Keywords

• Ultrasonic welding
• Carbon fiber reinforced thermoplastic composites
• Viscoelastic heat generation
• Fusion phenomena
• Joint attributes