Laser transmission welding of polymers is a relatively new joining technique. It is based on the fact that the majority of thermoplastics are transparent to infrared radiation. A laser beam passes through the transparent part, and is then absorbed by a part rendered absorbent by additives such as carbon black. Absorbed laser energy is transformed into heat that melts the polymer at the interface between two parts, thus forming a weld.

Many industrial applications have quite a complex geometry. This may often make it impossible to irradiate small elements of the joint interface directly. One of the possible solutions for this problem is to employ an oblique mirror to redirect a laser beam to the desired direction. In present work, transparent nylon tubes were welded to absorbing nylon plaques using a conical mirror inserted in the tube. The effects of the laser power, the angular motion speed, and the number of cycles on the joint shear strength were examined. Additionally, a two–dimensional axi-symmetric transient finite element heat transfer model was developed and evaluated. It simulated the temperature developed in the specimen during the welding cycle;​ the model was validated with the welding and mechanical testing results.

The experimental results demonstrated good joint strength, confirming the feasibility of this technique. It was also found that welding at a lower laser beam power and a higher rotational speed allowed higher maximum weld strengths to be achieved at the expense of longer cycle time and higher energy consumption. Simulation of the temperature demonstrated that varying of the rotational speed at constant laser power does not change the overall temperature rise trend.