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.

激光直接连接产生的接缝强度取决于几个因素，并且受金属-聚合物界面温度的很大影响。温度应保持在一定的加工范围内，以增加接头的整体强度，以使聚合物充分熔融并避免有害现象，例如聚合物降解。研究了激光散焦和激光束位置的影响。为此，开发了该过程的有限元模型，以预测连接过程中的热场。实验测试的测量结果用于校准和验证数值模型。特别地，通过逆分析技术将峰值温度测量值用于确定吸收系数。另一方面，通过将模型预测的热场与接头的形态进行比较，进行模型验证。一旦通过验证，该数值模型将用于了解激光束散焦和激光束位置如何影响金属-聚合物界面处的温度梯度。此外，还研究了能效问题。结果表明，可以主要利用激光束散焦来减小狭窄区域（束斑）内的温度峰值。另一方面，激光束的位置能够在较宽的区域上修改热场，但它的能量效率较低。该数值模型用于了解激光束散焦和激光束位置如何影响金属-聚合物界面处的温度梯度。此外，还研究了能效问题。结果表明，可以主要利用激光束散焦来减小狭窄区域（束斑）内的温度峰值。另一方面，激光束的位置能够在较宽的区域上修改热场，但它的能量效率较低。该数值模型用于了解激光束散焦和激光束位置如何影响金属-聚合物界面处的温度梯度。此外，还研究了能效问题。结果表明，可以主要利用激光束散焦来减小狭窄区域（束斑）内的温度峰值。另一方面，激光束的位置能够在较宽的区域上修改热场，但它的能量效率较低。