Thermal degradation of PA66 during laser transmission welding

The thermal degradation of materials strongly influences the weld strength in laser transmission welding (LTW). Weld strength decreases at high temperatures because of material thermal degradation. Hence, it is necessary to investigate this phenomenon. Thermal degradation of polyamide 66 (PA66) was predicted by combining a pyrolysis kinetic model with a 3-D transient thermal model. Thermogravimetric analysis (TGA) was used to study the pyrolysis characteristic of PA66. The TGA data were used to obtain kinetic parameters of PA66 using an nth order model in MATLAB. In addition, material conversion as a function of temperature (time) was analyzed using this kinetic reaction model containing the relevant kinetic parameters. A 3-D transient thermal model based on a volumetric heat source was developed. The temperature-time data of the point located at the maximum temperature was predicted through this thermal analysis model under different weld parameters. This study demonstrates that the predicted power at which the material starts to degrade is generally consistent with the power at which shear strength begins to decrease. The present studies lay a theoretical foundation for the investigation of thermal degradation during LTW.