Acoustic emission from non-plasma sources at the laser weld site

This was an investigation into the laser weld pool and keyhole as possible sound sources or modifiers during the welding process. These structures were modeled as a vibrating piston and a resonant pipe, respectively and computer programs were written to predict their frequency response curves. The validity of the computer models was checked by building life size physical models (simulacra) of the structures in question and determining their frequency responses with a custom built ultrasonic acoustic driver. The weld pool simulacrum was a cone shaped hole drilled through a piece of metal with a Nd:YAG laser and filled with water to simulate the molten metal. The keyhole simulacrum was a cylindrical hole drilled through a piece of metal by conventional means. The frequency responses of the simulacra were then compared to the responses predicted by the computer models. This comparison indicated that the keyhole response was similar to the predicted response and was of sufficient magnitude to have an effect on the acoustic emission signature at the laser weld site. The weld pool response, however, was so low in magnitude as to prevent an absolute verification of the model. This suggests that the weld pool's contribution to the acoustic signature is negligible.