Fundamentals of EMPT-Welding

Abstract

A well-suited solid state welding process for treatment of tubular structures is the electromagnetic pulse welding technique (EMPT): A pulsed magnetic pressure loads the structure to be welded within a few microseconds and accelerates one of the both contact partners (the so called "flyer" onto a stationary one. When the flyer strikes the stationary contact partner, contact normal stresses far above 1000 MPa act on the interfacial zone between flyer and stationary part. As a result of these high interfacial loads, a layer of several micrometers thickness next to the interface is severely plastically strained. Hence, the oxide layers covering both contact partners are cracked. These chipped oxide particles are blown out of the joining area by a so called "jet". This jet is caused by the air between the two joining partners being compressed and accelerated due to the movement of the flyer. The result of both phenomena - the oxide chipping by severe plastic deformation of the interfacial zone and the particle blow out caused by the jet - is a pure metallic interfacial zone, loaded by contact normal stresses. The conjunction of the highly reactive metallic surface and the contact normal stresses establishes a metallic bonding, whose strength equals at least the strength of the weaker contact partner. This report presents the results of a collaborative research project between the Institute for Production Engineering and Forming Machines (PtU) and PSTproducts GmbH. Experimental welding analysis is accompanied by numerical work for the study of the underlying mechanisms of solid state welding with respect to interfacial plastic deformation and contact loads. Additional metallographic work gives insight into the microscopical structure of the interfacial joint zone.