A novel method for reducing the welding pressure requirement in resistance welding of thermoplastic composites

Resistance welding of thermoplastic composites often suffers from quality issues due to high-pressure requirements and nonuniform heating, leading to nonbonding at the overlap edge. This study proposes an ultrasonic-assisted resistance welding method aimed at enhancing joint quality while operating at lower welding pressures. Results indicate that in traditional welding, reducing pressure tends to create voids near the weld line, whereas increasing pressure results in nonbonding at the overlap edge due to reduced temperatures. Introducing ultrasonic during the final phase of the welding process efficiently raises the temperature at the overlap edge and enhances the uniformity across the joint. Moreover, applying ultrasonic facilitates the squeeze flow of the polymer melt, extending the melt front and enlarging the effective bonding area. An improved squeeze flow reduces void formation caused by trapped air, diminishing the need for high pressure. The ultrasonic effects are more pronounced with increasing welding pressure. Consequently, glass fiber reinforced polyphenylene sulfide joints exhibit a 12 % increase in the maximum lap shear strength (LSS) compared to those welded without ultrasonic. Additionally, the use of ultrasonic achieves a 27 % reduction in pressure while maintaining an LSS comparable to the maximum values of the joints welded without ultrasonic.