On the effect of flat energy directors thickness on heat generation during ultrasonic welding of thermoplastic composites

Abstract

This paper presents a detailed experimental assessment of the effect of the thickness of flat energy directors (ED) on heat generation at the interface during ultrasonic welding. Power and displacement data showed clear differences caused by the change of thickness, related to heat concentration at the weld line during the process. The extent of the heat-affected zone was assessed by welding specimens without consolidation at different stages of the process. It was confirmed through optical microscopy that heat is generated at the interface and transferred to the bulk adherends earlier in the process for thinner ED. The analysis of their fracture surface under optimum welding conditions revealed signs of matrix degradation, leading to less consistent quality, likely due to faster heat generation rate in both the ED and the substrates, and incidentally, higher temperatures surrounding the energy director.

Ultrasonic welding of CF/PPS composites with integrated triangular energy directors: melting, flow and weld strength development

“…It should also be noted that this maximum strength is almost reached at the beginning of stage 3, where already the whole overlap is affected by the welding process, which coincides with our observations on optimum processing parameters for thin flat energy directors (about the same thickness as the resin-rich interface at the beginning of stage 1 in this research). [19] Finally, it must be noted that despite the statistically low number of samples mechanically tested in this study, the LSS scatter values depicted in Figure 13 and Table 1 are in any case well below 10% of the corresponding average LSS. This result corroborates the high consistency of the ultrasonic welding process, already indicated in our previous work.…”

Thermal Welding by the Third Phase Between Polymers: A Review for Ultrasonic Weld Technology Developments

“…There are considerable research literatures on the USW process for thermoplastic materials at the coupon level [125][126][127][128][129][130][131][132][133][134][135]. The welded condition parameters including welding time, welding pressure, and vibration amplitude, were investigated and the relationship between the welded ability and the parameters were reported.…”

Towards robust sequential ultrasonic spot welding of thermoplastic composites: Welding process control strategy for consistent weld quality

“…The reader should note that displacement-controlled welding of the SSW joints required the welding force to be continuously increased during the vibration phase of the welding process. Using a constant welding force, which is the common procedure used for displacement-controlled welding of full overlaps [2,3,4,14], was however found to result in a displacement plateau as shown in Fig. 12a, referred to as "displacement ceiling" hereafter.…”

“…Ultrasonic welding is an attractive joining technique for thermoplastic composites (TPCs), owing to the short welding times, absence of foreign materials at the weldline, possibility for in-situ monitoring and ease of automation [1][2][3]. However, upscaling of the ultrasonic welding process for assemblies with large overlaps is still a challenge [4]. Ultrasonic welding is by nature a spot welding technique, hence the most straightforward upscaling route is sequential welding of consecutive spots resulting in a multi-spot welded (MSW) joint.…”