Micro-Welding of Stainless Steel and Copper Foils Using a Nano -Second Pulsed Fiber Laser

Joining of materials is an essential process step in manufacturing industry. The need to weld dissimilar thin materials is growing lately with applications in MEMS devices involving different materials. Welding of thin dissimilar materials is a challenging task in comparison to their bulk counterparts as they are quite susceptible to damage. This paper is concerned with the feasibility of welding extremely thin stainless- steel foil (AISI 304) with pure copper foil of thickness of tens of microns in lap joint configuration using a single mode nano-second pulsed fiber laser. Welds were made in “weld brazing” mode as well as in “full fusion” mode with linear heat inputs of 0.1 J/mm and 0.145 J/mm respectively. Optical microscopy and electronic microscopy were used to evaluate the weld microstructure, X-ray radiography was employed to evaluate the integrity of the weld, while tensile testing and micro-hardness measurements of the welds were carried out to ascertain the mechanical properties the weld. Welds could be made without any defects, e.g. lack of fusion, cracks and porosities. Welds made in “weld brazing” mode was found to be mechanically superior to the welds performed in “full fusion” mode. The decided advantage of the usage of nanosecond single mode laser for this application is also elucidated.