Relationship of Optical and Acoustic Emissions to Laser Weld Penetration

摘要

Detection and analysis of optical, acoustic and plasma charge emissions from laser beam welds is a promising approach for quality monitoring. In this work, the airborne acoustic and optical-wavelength electromagnetic ("light") emissions from laser welds were studied. A matrix of travel speed and CO_2 laser power settings was used to generate bead-on-plate welds in cold-rolled low-carbon steel sheet metal. The power/travel matrix-generated welds having partial penetration, "moderate" full penetration (visually sound welds) and "excessive" penetration (relatively wide weld beads with undercut due to drop-through of the molten pool). The intensity of the light emitted from the weld area was found to vary with process parameters, exhibiting a local minimum for moderately full-penetration welds. The RMS amplitude of the acoustic energy was found to have a local maximum for these same moderate full-penetration conditions. The relationship between the optical and acoustic signals was investigated and it was found that the acoustic signal was approximately proportional to the time derivative of the optical signal. The front-side light emission signal was also found to vary inversely with backside light emission.