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

We investigated two related topics as the first stage of our research: the characteristics of welding with multiple yttrium-aluminum-garnet (YAG) lase r beams transmitted through optical fibers and combined at the focal point; and the study of methods of combining YAG laser beams. Each laser beam mus t be inclined in such a combined system. The plume and the penetration chan ged their direction from the vertical direction of the specimen to the para llel one of an irradiated beam, if the peak power or energy of the irradiat ed 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 degrees an d at typical total power levels as those with a single and vertically irrad iated beam to the specimen surface, but were split above the angle of incli nation of 30 degrees and total average power of 3.3 kW. Two keyholes would be formed under the split penetration condition, The three split plumes wer e observed for irradiation by three combined beams. The second stage of our research was the development of an integration optics based on these exper iments, which could focus the laser beams transmitted through optical fiber s with a condensing lens. We studied all position welding characteristics u sing the developed integration optics and obtained the result that the over head welding has the maximum fusion volume among the three orientations-hor izontal, vertical, and overhead position welding. The result will be attrib uted to the direct reach of laser beam to the unfused bottom metal due to t he molten metal being pulled down from around the keyhole by gravity. The i ntegration optics is too heavy and large for an articulated robot to hand i t and move with high speed, This difficulty comes from combining laser beam s at the exit sides of optical fibers. Then, we developed a new launching o ptics of laser beams at an entrance side of an optical fiber in order to ov ercome the disadvantage. The development of the launching optics is describ ed. (C) 1999 Laser Institute of America.