Mechanical Dynamics in Resistance and Solid State Welding
By Jerry Gould on Tuesday, August 17th, 2010
Engineers with expertise in the resistance and solid state welding processes come from many different backgrounds. A large number of experts come from an electrical engineering background. This is not surprising for the resistance welding processes, as managing electrical currents is key to successful implementation. This expertise is also useful in addressing the complexities of controls implicit in all the resistance and solid state welding processes. Engineers with a metallurgical background are also found among the ranks of resistance and solid welding experts. Metallurgy is a cornerstone to understanding the quality of any weld, including those within the resistance and solid state welding spectrum. Finally, engineers with a machine design background can also be found within this umbrella, largely addressing the complexity of the welding frames and motion systems themselves.
One area that is often overlooked with these processes is that of mechanical dynamics. Resistance and solid state welding processes are not mechanically static. Rather, nearly all of these process technologies require rapid mechanical motion of the hardware subcomponents in order to create high quality and reliable joints. In fact, a large range of defects, from expulsion in resistance processes to pin-holes in upset processes to bond line softening issues in forge processes (both resistance and friction based) can be directly traced to inadequate system mechanical dynamics. There have been some empirical efforts over the years to address these mechanical dynamic issues. Upset welding systems are often designed to specific forging speeds (the 600-kVA flash butt welder has a platen that has been timed at 400-mm/sec), and particularly resistance projection welding systems often incorporate fast follow-up heads. Understanding the specific mechanical dynamics requirements of a given application is still, however, an in-exact science. Over the last 20 years, EWI has done extensive research in this area, and has offered some guidelines on the basics of mechanical system design. However, a detailed understanding of the relationships between mechanical, electrical, and thermal dynamics, and how they effect the end joint metallurgy and weld quality of resistance and solid state welds still is in question. In this regard, the resistance and solid state welding community can benefit from those with a background in mechanical dynamics.