Micro-joining of multi stainless steel sheets into mechanical element by low temperature diffusion process

Abstract

A new micro-joining system has been developed with use of the plasma surface activation and the intelligent heat induction processes. This micro-joining process consisted of two steps. Eight stainless steel sheets with a thickness of 0.5 mm had surfaces activated by argon and hydrogen plasmas for 600 s. The top and bottom surfaces of the eight sheets were subjected to physical bombardment by the argon plasma and to chemical reduction by the hydrogen plasma. The passivated oxide film thickness was reduced by this surface activation. This assembly of plasma cleaned stainless steel sheets was accurately stacked into a die set for joining. In this second step, the stack of eight stainless steel sheets was accurately hot stamped and joined into a mechanical element. The intelligent induction heating unit was utilized to make uniform heating of the whole stack up to 1073 K in short for 60 seconds. In parallel with heating, the stack was hot-stamped and held by 30 MPa for 1800 seconds. The miniature products and members such as a micro-pump are fabricated by this micro-joining process as an alternative process to lower the joining temperature, to shorten the duration time and to reduce the production cost for high qualification of metallic micro-pumps.