Automatic Multi-pass Narrow-gap Laser Welding With Filler Wire And Seam Tracking

Traditionally, welding path planning mainly depends on man’s experiences and teaching methods. Human factors are not only influencing the quality of the joint but also in low welding efficiency. The aim of this paper is that the automatic multi-pass laser welding and seam tracking process are developed.To be the first, the process parameters of laser welding with filler wire should be explored. Experiment results showed that laser power, welding speed, wire feed rate, defocusing distance and shielding gas flow have big influences on the quality of the joint. The filling volume of single pass welding will decrease and the bead width will increase with the adding of laser power. As the wire feed rate grows, the filling volume and bead height all raise. The welding speed has a negative effect on filling volume and bead height. Because the heat input will decrease. The defocusing distance mainly affects the penetration of the bead. The quality of the joint will become terrible because of excessive shielding gas flow.Besides, statistical methods were applied to study the interactions between welding parameters and the geometry of single bead. By this method, the models between bead geometry and input welding parameters have been established. The responses include the transversal area, bead width, bead height of the added metals and the ratio of bead width to height. Verification experiments indicate that all these models can forecast the responses within the factors domain. These results will provide supports for automatic multi-pass laser welding.Finally, YLS-10 Kw Nd:YAG fiber laser system、KUKA robot and seam tracking sensor were used to study the automatic multi-pass and multi-layer laser welding. The number of filling pass was planned according to the ratio of gap width to the bead width. Then the algorithms of path planning were achieved by the robot programming. The laser point and wire tip position can be set automatically only by inputting bead parameters, groove sizes and welding parameters after teaching the weld line of the first pass.Verification experiments indicate that this method is valuable in automatic multi-pass laser welding. The practical filling passes and build-up sequence are accurately accord with the predicted results. Welding robot reached the planned position at precise coordinates and then finished the welding process successfully. Experiments about voids show that the heat input and the ratio of wire feed rate to the welding speed are the main factors affecting the joint qualities. The ratio of bead width to the width of the root layer also influences the forming of defects.