Explosive welding (EXW) has been used since the 1940s for solid-state joining of widely dissimilar metals. The method is used commercially for shipbuilding and pressure-vessel construction. Explosive welding impacts a flyer sheet with a target sheet at an appropriate velocity (ranging from 200 m/s to 5000 m/s) with a low oblique impact angle. The impact ejects the surface impurities from the flyer and target as a jet and brings clean metal surfaces into atomic bonding distance.
Smaller scale collision welding has also seen limited commercial development using electromagnetic Lorentz force as the driver, in a process known as magnetic pulse welding (MPW). Two new methods that rely on similar physics have been developed at The Ohio State University.
Vaporizing foil actuator welding, Laser Impact welding...
two methods invented, and only available, at The Ohio State University (Watch Video!)
Vaporizing foil actuator welding (VFAW) uses a high-voltage capacitor bank to provide an energetic electrical pulse to an aluminum foil or wire, which vaporizes it to hot plasma in a time period on the order of micro-seconds. The expanding plasma can almost instantly accelerate structural metal sheets (of thicknesses on the order of mm) to speeds over 500 m/s. This can be used to create large impact-welded patches of several cm^2 or larger, which can have exceptional strength in both shear and peel. The entire system is reusable with the exception of a small consumable laminate of aluminum foil and polymer insulation, which is inexpensive and easily replaced.
Laser impact welding (LIW) uses the optical energy from a pulsed laser to accelerate one thin metal foil toward another. Our system outputs 3 J of optical energy in about 8 ns at a frequency of 1060 nm, and can cycle at 10 Hz. This system is appropriate for foils or components under about 0.01” (250 micro-meter) and typically produces a weld patch with a diameter of about 5 mm. Rates of 10 welds/s are easily obtained and precise spatial control and regular arrays of hundreds of welds have been demonstrated.
Both VFAW and LIW can easily generate flyer speeds in excess of 1 km/s (for sheets ~1 mm thick with VFAW, and ~200 micro-meter thick with LIW), and both have been shown to be effective in joining a wide variety of dissimilar metals without melting the constituents. Because the surfaces do not melt, continuous regions of intermetallic phases can be eliminated, as in the VFAW interface shown to the right.
Both methods are in the early stages of development. So far, these methods have proven capable of bonding all dissimilar metal combinations attempted, including Al-Mg, Al-Fe, Al-Ti, Al-Ni, Al-Cu, Ti-Fe, Cu-Fe, and laminated series with three or more layers. Unlike explosive welding, these methods can be performed in a laboratory or factory; and unlike magnetic pulse welding, very high pressures are produced without damaging the tool.