A study on the plasma-augmented laser welding for small-diameter STS tubes

Laser welding is an effective method to join small, thin parts, such as small stainless steel tubes. Laser power can be precisely adjusted to melt only a small part of the tubes, and the heat-affected zone can be controlled accurately. But laser welding systems are generally expensive; therefore, the welding speed is restricted by the maximal laser power capacity. Also, the laser welding method is very sensitive to the joint clearance and tolerance, and this makes laser welding difficult to obtain consistent welding qualities over time. Recently, solutions of these problems are being tried by introducing another heat source, such as a plasma arc. Additional plasma arc energy can make the overall welding speed faster, and sensitivity to the joint clearance can be reduced by the plasma arc. Plasma-augmented laser welding (PALW) is one of this kind of welding method, where a plasma arc is used to augment the laser welding. In this study, plasma arc welding (PAW) was added to the existing single-laser heat source to join the conventional V-grooved butt joint of thin stainless steel strips for manufacturing small-diameter stainless steel tubes. The effect of the welding speed enhancement was investigated by experiments and simulations. Finite element (FE) thermal analysis considering multiple reflections of a laser beam in the V-groove was conducted and verified.