In-process Monitoring and Adaptive Control during Micro Welding with CW Fiber Laser

Abstract

A fiber laser has excellent beam quality enough to be applied for micro welding of electronics or automobile parts, and thus is regarded as a promising heat source for adaptive control since the laser peak power can be changed within sub-micro-second period. Laser micro welding of sheets can be influenced by the surrounding heat transfer conditions. This study was therefore undertaken with the objective of developing a new laser system with in-process monitoring and adaptive control for the stable production of sound welds in thin sheets. The bead-on-plate welding of 0.1-mm-thick stainless steels was performed with a 75-W fiber laser beam of 1,090 nm in wavelength. The stability of bead widths of laser welds made with or without monitoring and adaptive control was investigated in welding the sheet with or without a heat sink plate. It was revealed that the heat radiation signal was sensitive to the increase in the bead width when the heat transfer process was changed to the heat-insulated process. Moreover, the peak power was controlled in the minimum 2-ms-short period in order to produce stable bead width regardless of the existence of the heat sink plate, and the limit cycle of the adaptive control was investigated by comparison with the bead width of the weld made without adaptive control. It was consequently confirmed that a fiber laser was an excellent oscillator for the adaptive control in laser micro welding.