Product Code: ICAL07_1604

Study of the Phenomena of Fiber Laser-MAG Hybrid Welding
Authors:
Anna Fellman, Lappeenranta Univ. of Technology; Lappeenranta Finland
Antti Salminen, Lappeenranta Univ. of Technology; Lappeenranta Finland
Presented at ICALEO 2007

Laser hybrid welding processes are gaining more interest in many sectors of metal industry. The process is already in successful use for example in automotive, ship building and construction industry. The laser hybrid welding processes are traditionally a combination of CO2 or Nd:YAG laser together with MIG/MAG or TIG welding. The arc welding source is chosen depending on whether there is also need for extra material. The maximum powers available for these laser types are quite low and therefore the use of them for very deep penetration applications is limited. The development of high power fiber lasers has opened a new opportunity for laser hybrid welding for thick section welding. The aim of this study was to study the characteristics of laser hybrid welding with fiber laser. The maximum power of fiber laser used is 5 kW. The arc process used was MIG/MAG welding. Material used was mild steel S355 of thickness 6 mm and joint type was butt joint. Welding process phenomena is photographed with CCD camera to see the welding appearance. It seems obvious that the welding speed can be further increased when laser hybrid welding process is used instead of autogenous laser welding or not to mention arc welding. The welding speed of laser hybrid welding can be increased enormously if there is a minor airgap in the groove. If the airgap is increased the welding speed can be increased even more, the actual restriction being the capability of the arc welding process to melt the groove edges. Beyond the limit there will be undercut or even lack of fusion formed. The distance between the laser beam and arc welding process and torch direction play a big role in how wide airgaps can be tolerated. Leading torch tolerates longer distance between the processes than trailing torch, but if the processes are close enough to each other, there is no noticeable difference in gap bridgeability between these two arc positions. Whether we should use leading or trailing torch is always a question of debate among researchers. It seems that whether leading or trailing torch is better depends on many things, such as laser type, power level, material being welded, arc parameters and distance between the processes. With leading torch the gas shielding seems to be better, but trailing torch gives wider welds with smoother junction to the base metal. Wider weld is an advantage, when airgap is wide and important issue. Then the formation of undercut is decreased and the weld will have better junction to the base metal. With both trailing and leading torches good quality welds can be achieved, but they need their own optimized settings for arc welding. With trailing torch it is easier to use seam tracking or other external process observation devices, so that is in most cases probably the reason for using trailing torch.