By: Shinpei Oiwa
Remote welding has many advantages; very fast welding, flexibility of process designs, efficient production and so on. Now remote welding attracts much attention due to such advantages. In fact, remote welding has already been applied to many industries, especially automobile industries. Meanwhile, remote welding requires high beam quality. Although CO2 laser has been used for remote welding, fiber laser has also been increasing recently. Fiber laser is one of the most promising lasers. CO2 laser beam can only travel within a mirror system; however, fiber laser can be transmitted through an optical fiber. Therefore, remote welding with fiber laser is more flexible and can weld more complex objects compared with CO2 laser.
On the other hand, it is well known that a laser-induced plume comes out from a keyhole affects welding results greatly during laser welding. Generally, this plume is removed with a shielding gas. In remote welding, however, it is often difficult to remove the plume using such a gas due to its long focal length. Until now, the interaction between fiber laser and its plume has been revealed. However, phenomenon of the plume affecting welding results during remote welding are not fully understood.
Our research purpose is to reveal the phenomena during remote welding of zinc-coated steel sheets with fiber laser. This material is often used in automobile bodies. Fig. 1 shows the top and bottom appearances of a weld bead made with fiber laser remote welding under certain conditions. The appearances of bottom surface shows that a weld bead changed from full to partial penetration. Then we observed the plume during remote laser welding with a high-speed camera. As a result, the plume ascended to high as the welding proceeds. An observed plume is shown in Fig.2. From the observation results, the cause of the transition was interpreted by considering that the high plume heated the space above a specimen and then refractive index distributions were formed in the beam path due to its high temperature. This distribution affected laser beam to cause the change of weld bead geometry. In addition, it was found that air blowing between the laser head and specimen by a fan improved welding results by removing the high plume and heated air. Fig. 3 shows the appearances of a weld bead produced by using the fan. It is seen that full penetration bead was formed all over.
Fan blowing is very easy and low-cost improvement for remote welding bead and this method is efficient for real welding situation. Now we have succeeded in observing accurate refractive index distribution during welding by using an interferometer with a fiber laser.
The above brief overview was extracted from its original abstract and paper presented at The International Congress on Applications of Lasers & Electro-Optics (ICALEO) in Orlando, FL. To order a copy of the complete proceedings from this conference click here