Kenichi Kamimuki

Prevention of welding defect by side gas flow and its monitoring method in continuous wave Nd:YAG laser welding

In the Nd:yttrium–aluminum–garnet (YAG) laser welding of thick plates, reduction of porosity and monitoring the keyhole/molten metal behavior are very important issues to assure the high quality welding. The authors applied a side gas flow to prevent the porosity in the bead on plate welding with 6 kW Nd:YAG laser equipment. At the same time, a reflected Ar+ laser in the same axis as the Nd:YAG laser beam and the light emission from the weld were measured as monitoring signals. Under the optimum side gas condition, pores in the weld metal could significantly decrease, the penetration depth increased slightly, and the bead width became narrower. Under that condition, moreover, the generation of spatters was quite few. An acceptable limit of the transverse misalignment of the side gas nozzle position was about 1 mm. The misalignment could be detected by using the above mentioned monitoring signals.

Development of in-process monitoring technique in YAG laser welding

We have studied in-process monitoring technique in Nd:YAG laser welding. We used a CCD camera and a photodiode as the monitoring sensor, and observed laser processing coaxially with the laser beam. There were differences in the image of the CCD camera between full and partial penetration welding and the detection for full and partial welding was achieved by the image processing of the detected image data. And, it was suggested that a change in the focal position could be detected because a change in the luminescence intensity could be caught with the photodiode when the deviation of the focal position occurred.

Refill Friction Stir Spot Joining for aerospace aluminum alloys

Refill Friction Stir Spot Joining (RFSJ) developed by Kawasaki Heavy Industries (KHI) is a derivative technology of friction stir spot welding for joining aerospace aluminum alloys. The aerospace aluminum alloys were previously considered not weldable using conventional fusion welding methods. RFSJ does not consume any filler materials so that no additional weight is introduced to the assembly. As the solid-to-liquid phase transition is not involved in RFSJ in general, there is no lack of fusion or material deterioration caused by liquefaction and solidification. Unlike the conventional friction stir spot welding, RFSJ produces a spot joint with a perfectly flush surface finish without a key/exit hole. KHI has advanced the original friction stir spot welding concept and developed a robotic system that is capable of producing refill friction stir spot joints. The goal of this study is to demonstrate process parameter optimization of RFSJ for baseline aerospace aluminum alloys.

Detection of transition from keyhole-type to heat conduction-type welding in CO2 laser welding of metals

In welding of metals, there are two welding types: keyhole-type welding and heat conduction-type welding. In this paper, we propose a technique to detect the transition between these two welding types in CO2 laser welding by monitoring optical emission of a laser-induced plasma and acoustic emission from a laser irradiated point.SUS304, SS400 and A15083 were used for workpiece. Frequency analysis of the optical emission and acoustic emission was carried out using FFT program. When the welding is the keyhole-type, the frequency components of the acoustic signal at around 2 - 4 kHz appear strongly. When the welding changes to the heat conduction-type, the main frequency components appear at higher frequency range. Main frequency components of the signal shifts from lower frequency range to higher frequency range according to the decrease in the penetration depth. This phenomenon is observed for all three materials examined. Ratio of emission intensity at the lower frequency range to that at the higher frequency range is correlated to the aspect ratio. From this, we can evaluate the transition between the keyhole-type welding and heat conduction-type welding. The similar shift of the main frequency components is observed for the optical signal.In welding of metals, there are two welding types: keyhole-type welding and heat conduction-type welding. In this paper, we propose a technique to detect the transition between these two welding types in CO2 laser welding by monitoring optical emission of a laser-induced plasma and acoustic emission from a laser irradiated point.SUS304, SS400 and A15083 were used for workpiece. Frequency analysis of the optical emission and acoustic emission was carried out using FFT program. When the welding is the keyhole-type, the frequency components of the acoustic signal at around 2 - 4 kHz appear strongly. When the welding changes to the heat conduction-type, the main frequency components appear at higher frequency range. Main frequency components of the signal shifts from lower frequency range to higher frequency range according to the decrease in the penetration depth. This phenomenon is observed for all three materials examined. Ratio of emission intensity at the lower frequency range to that at the higher frequ...