Spatter reduction by using keyhole stir laser welding process

In high power laser welding, vigorous vaporization of the melt meal and fluctuation of the keyhole induce spatter formation. It is well known that for laser welding of thick plate, the keyhole opening can be enlarged and deepened if a sufficient gas pressure is provide by using a gas jet nozzle, and as a result, the keyhole can be kept stable and spatter can be greatly reduced. For thin plate laser welding, however, the high gas pressure provided by the gas jet may blow out the melt metal and even induce cutting through. Therefore, a stable low-spatter welding process should be developed for thin plate laser welding. In this paper, a keyhole stirring welding process was tried for eliminating spatter formation by using a high speed beam scanner. The high-speed beam scanner was combined with a 2 kW single mode fiber laser to conduct bead-on-plate welding. Type 304 Stainless steel plates were used as the test pieces. A high speed CMOS camera was used to observe the melt pool behaviour and spatter during welding. It was found that if the scanning frequency and beam rotation diameter are controlled at appropriate ranges, spatters can be significantly reduced. The mechanism of spatter reduction by using keyhole stirring process was discussed.