Effect of processing parameters on meltdown in quasi-simultaneous laser transmission welding

Meltdown is the term used to describe the collapse of two thermoplastic parts during welding. It is a critical process parameter in the laser-transmission welding of thermoplastics. This study examines the effect of quasi-simultaneous (QS) laser transmission welding (LTW) processing parameters including input power (P), number of passes (N), scan speed (V), total scan length (LS) and weld pressure on the meltdown behavior of polycarbonate (PC) and polypropylene (PP), using a T-shaped test assembly. The total meltdown is shown to depend linearly on the total line energy (LET) defined as the product of P and N divided by V. Increasing LS increases the critical LET for meltdown to begin. A simple model is presented that captures the main elements of meltdown in this thermoplastic welding process.