Magnetic pulse welding: Solutions for process monitoring within pulsed magnetic fields

For Magnetic Pulse Welding (MPW), Lorentz forces are utilized for the rapid acceleration and controlled high velocity collision of two metallic parts. Due to the absence of external heat, solid state weld seams can be produced without the formation of critical intermetallic phases. In order to adjust the process parameters for a sound weld, optical measuring techniques are preferred, since they are not influenced by the strong magnetic fields of the working coils. Unfortunately, existing technologies are either expensive, difficult to evaluate, or limited in their accessibility to the interesting areas. To overcome these drawbacks, a new method was applied taking advantage of the hypervelocity impact (HVI) flash that is characteristic for the process. Experiments were performed using phototransistors for the detection of the HVI flash and the established photonic Doppler velocimetry in parallel. The flash characteristic was found to be a reliable measure for the evaluation of the local impact time as well as the weld seam length. It has a great potential for both process development and monitoring. Furthermore, disturbances, which are unfavorable for the weld seam formation, e.g. oily contaminants on the surfaces of the parts to be joined, can be detected.