The research in this paper is an essential part of a bigger effort on developing robust sequential ultrasonic welding of multi-spot welded joints in thermoplastic composites. It mainly focused on assessing the impact of the changes in boundary conditions on the welding process and whether it could be circumvented by using an appropriate process control strategy. A two-step approach was followed by investigating: (1) the effect of boundary conditions on displacement- and energy-controlled single-spot welded joints and (2) displacement- and energy-controlled sequential ultrasonic welding of double-spot welded joints. The results showed that previous spots indeed affect the energy required to obtain an optimum new welded spot, which challenges the use of energy-controlled welding for this application. Contrarily, displacement-controlled welding was shown to provide consistent-quality welds with a constant set of welding parameters and it was hence identified as the most promising welding strategy for sequential ultrasonic welding of thermoplastic composites.

本文的研究是为开发热塑性复合材料中多点焊接接头的稳健顺序超声焊接而付出更大努力的重要组成部分。它主要侧重于评估边界条件的变化对焊接过程的影响，以及是否可以使用适当的过程控制策略来规避它。研究分为两个步骤：（1）边界条件对位移和能量控制的单点焊接接头的影响；（2）位移和能量控制的双点焊接接头的顺序超声焊接。结果表明，以前的焊点确实会影响获得最佳新焊点所需的能量，这对为此应用使用能量控制焊接提出了挑战。相反，