3D printing has offered cost-effective, lightweight, and complex parts. To extend their applications, 3D printed parts need to be welded in order to form the larger functional assemblies. For this purpose, Laser Transmission Welding (LTW) is a promising joining technology. This paper aims to investigate the light scattering effect on the intensity profile of the laser heat source during the transmission through the 3D printed laser-transparent part. Indeed, the inherent design of the 3D printing technology results in a complex heterogeneous microstructure with a significant amount of porosity inside the printed parts. Such structure induces the optical diffusion (i.e. light scattering) of the laser beam within the 3D printed parts. This phenomenon leads to the reduction of the transmitted energy arriving at the weld interface, which directly influences the quality of the joint and its mechanical performance. The approach adopted in this paper is to propose a ray-tracing model to simulate the optical paths of the laser beam through the 3D printed laser-transparent part, which is able to evaluate changes in the laser heat source at the weld interface directly linked with the light scattering effect within the microstructure of the parts. Experimental measurements are performed to assess the transmitted intensity flux distribution using an image processing technique, instrumented with a digital camera and macro lens. The numerical results show good accordance with the experimental one, which proves the confidence of the proposed ray-tracing model. Finally, 3D transient thermal model of the LTW process is performed using the FEM software COMSOL Multiphysic® to confirm the influence of the scattering effect on the temperature field and thus on the quality of the weld.

3D 打印提供了经济高效、轻质且复杂的零件。为了扩展其应用，3D 打印零件需要进行焊接，以形成更大的功能组件。为此，激光透射焊接（LTW）是一种很有前途的连接技术。本文旨在研究激光热源在通过 3D 打印激光透明部件传输过程中的光散射对强度分布的影响。事实上，3D 打印技术的固有设计导致打印部件内部具有大量孔隙的复杂异质微观结构。这种结构会引起激光束在 3D 打印部件内的光学扩散（即光散射）。这种现象导致到达焊接界面的传输能量减少，直接影响接头的质量及其力学性能。本文采用的方法是提出一种光线追踪模型来模拟激光束穿过3D打印激光透明部件的光路，该模型能够评估与3D打印直接相关的焊接界面处激光热源的变化。零件微观结构内的光散射效应。使用配备数码相机和微距镜头的图像处理技术进行实验测量，以评估透射强度通量分布。数值结果与实验结果吻合良好，证明了所提出的光线追踪模型的可信度。最后，