Enhanced methods to get high average power by combining yttrium–aluminum–garnet laser beams and their characteristics in processing materials

Abstract

We investigated two related topics as the first stage of our research: the characteristics of welding with multiple yttrium–aluminum–garnet (YAG) laser beams transmitted through optical fibers and combined at the focal point; and the study of methods of combining YAG laser beams. Each laser beam must be inclined in such a combined system. The plume and the penetration changed their direction from the vertical direction of the specimen to the parallel one of an irradiated beam, if the peak power or energy of the irradiated YAG laser beam exceeds a threshold value. In the two continuous wave YAG laser beams irradiation the form of plume and welding penetration were the same at the average angle of inclination of the two beams of 15° and at typical total power levels as those with a single and vertically irradiated beam to the specimen surface, but were split above the angle of inclination of 30° and total average power of 3.3 kW. Two keyholes would be formed under the split penetration condition. The three split plumes were observed for irradiation by three combined beams. The second stage of our research was the development of an integration optics based on these experiments, which could focus the laser beams transmitted through optical fibers with a condensing lens. We studied all position welding characteristics using the developed integration optics and obtained the result that the overhead welding has the maximum fusion volume among the three orientations—horizontal, vertical, and overhead position welding. The result will be attributed to the direct reach of laser beam to the unfused bottom metal due to the molten metal being pulled down from around the keyhole by gravity. The integration optics is too heavy and large for an articulated robot to hand it and move with high speed. This difficulty comes from combining laser beams at the exit sides of optical fibers. Then, we developed a new launching optics of laser beams at an entrance side of an optical fiber in order to overcome the disadvantage. The development of the launching optics is described.