Ultrasonic Welding And Repair Of Short Carbon Fiber Reinforced Nylon 66 Composites

As one of the investigation contents of ZZU-GM united fund project, this study used UW technology to investigated the effect of welding parameters and gap of welded sheets on the quality of UW joints of the carbon fiber reinforced nylon 66 composite. A secondary UW technology was used to repair the defective UW joints. An innovative pre-press ring fixture and Bonding-UW combined joining technology were used to enhance the joint strength and improve the weld quality of UW joints. The experimental results show that:The UW joints strengths of 4mm carbon fiber reinforced nylon 66 composite with 25mm overlap were firstly increased and then decreased. The optimal process parameter was 2.1s weld time and 0.15MPa weld pressure and the optimal joint strength was above 5.5kN. The joint strength is always in proportion to the weld area. The gap between the welded sheets decreased the joint strength. Especial, the gap of above 0.5mm caused an obvious decrease in joint strength. It showed that the contact condition between the welded sheets had distinctly influence on the weld quality of UW joints.The secondary UW welding can evidently improve the weld quality and increase the joint strength of defective UW joints. The optimal repairing energy was 5kJ and the joint strength of repaired UW joints had a joint strength of above 5.0kN. The repairing mechanism of secondary UW is the boundary of existed weld area was remelted and increased the weld area of defective UW joint, which increased the load area and thus enhanced the joint strength of defective UW joints.The joint strength of UW joints fabricated with pre-press ring fixture had similar trend as that fabricated with normal fixture with welding time. The joint strength of UW joints fabricated pre-press ring was large than that fabricated with normal fixture for the same welding parameters. It can be attributed to the pre-press ring fixture improved the absorption of welded workpieces to the ultrasonic wave energy during UW process. Therefore, the weld of UW joints fabricated with pre-press ring was always first started from the center of weld area to form a central weld and then spread out gradually. It not only increased the weld size, but also increased the thickness of stable melt film, which decreased the stress concentration and the breaking probability of sheets in UW joints.The joint strength of Bonding-UW joints fabricated with pre-press ring is increased by 40% and its absorption energy increased 1.4 time than that of fabricated with normal fixture. It is possible that the adhesive in Bonding-UW joints improved the transformation of ultrasonic wave energy and promoted the melt of welded sheets.