Particle Ejection by Jetting and Related Effects in Impact Welding Processes

Abstract

Collision welding processes are accompanied by the ejection of a metal jet, a cloud of particles (CoP), or both phenomena, respectively. The purpose of this study is to investigate the formation, the characteristics as well as the influence of the CoP on weld formation. Impact welding experiments on three different setups in normal ambient atmosphere and under vacuum-like conditions are performed and monitored using a high-speed camera, accompanied by long-term exposures, recordings of the emission spectrum, and an evaluation of the CoP interaction with witness pins made of different materials. It was found that the CoP formed during the collision of the joining partners is compressed by the closing joining gap and particularly at small collision angles it can reach temperatures sufficient to melt the surfaces to be joined. This effect was proved using a tracer material that is detectable on the witness pins after welding. The formation of the CoP is reduced with increasing yield strength of the material and the escape of the CoP is hindered with increasing surface roughness. Both effects make welding with low-impact velocities difficult, whereas weld formation is facilitated using smooth surfaces and a reduced ambient pressure under vacuum-like conditions. Furthermore, the absence of surrounding air eases the process observation since exothermic oxidation reactions and shock compression of the gas are avoided. This also enables an estimation of the temperature in the joining gap, which was found to be more than 5600 K under normal ambient pressure.

The Energy Balance in Aluminum–Copper High-Speed Collision Welding

“…However, the formation of large intermetallic phases at the weld interface in Figure 5b and the porous structure indicate excessive melting, which partially prevented bond formation. Recently, a correlation between the extent of the emitted light of the CoP and the temperature in the joining gap was shown [8]. Comparing the conditions in the welding gap close to the lower collision angle boundary, the CoP at the Cu-Cu and the Al-Cu configuration emitted a bright glow, which is not visible for Al-Al at the high-speed images, see Figure 7.…”

“…Furthermore, brittle layers of oxides and other surface contaminations are spalled from the strongly deformed surfaces and form a dispersed cloud of particles (CoP) ahead of the collision front [4]. Both phenomena can interact with each other, with the colliding surfaces and also with the ambient gas in the welding gap by entrapment and the stored thermal and chemical energy, as discussed in the literature [5][6][7][8][9]. This interaction determines the possible joining mechanism (solid-state, solid-liquid coexisting state or liquid-state bonding) and depends not only on the selected material and geometry of the joining partners, but on the collision kinetics, which are often described by welding windows [9,10].…”

Improving and monitoring the magnetic pulse welding process between dissimilar metals

“…It is attributed to the compression of the CoP itself, since the estimated temperatures based on the color temperature increase for smaller collision angles β [18]. It can exceed the vaporization temperature of the involved materials since temperatures in the range of 5600 K were measured [19]. Thus, the thermal interaction of the CoP with the surfaces of the joining partners contributes to the surface activation before being pressed together.…”

Impact Welding of Materials

“…Bellmann et al [10] studied the formation of a cloud of particles during impact welding, its characteristics, and its influence on weld formation. A detailed experimental plan was implemented by the authors, who carried out impact welding tests on different setups.…”