Homogenization of temperature distribution at metal-polymer interface during Laser Direct Joining

The strength of joints produced by Laser Direct Joining depends on several factors and it is greatly influenced by the temperature at the metal-polymer interface. The temperature should be kept within a certain processing window to increase the overall strength of the joint to enable enough polymer melting and avoid detrimental phenomena such as polymer degradation. The influence of laser beam defocusing, and laser beam position has been investigated. To this end, a FE model of the process was developed to predict the thermal field during the joining process. Measurements of experimental tests were used to calibrate and validate the numerical model. Particularly, the peak temperature measurements were used for determination of absorption coefficient by means of inverse analysis technique. On the other hand, the model validation was performed by comparing the thermal field predicted by the model with the morphology of the joints. Once validated, the numerical model was used to understand how laser beam defocusing and laser beam position affect the temperature gradients at the metal-polymer interface. In addition, energy efficiency issue was also investigated. The results indicated that laser beam defocusing can be mainly exploited to reduce the temperature peaks within a narrow region (beam spot). On the other hand, the laser beam position enabled to modify the thermal field over a wider region, but it involved lower energy efficiency.