Engineering design in laser beam and explosion welding

It is important to note that the function of all lasers whether they are gas (carbon dioxide, helium neon, etc.) or other lasing sources is based on the principle of the excitation of atoms by means of intense light, electricity, electron beam, chemicals, etc., and the spontaneous and stimulated emission of photons.

Up to the point that the laser beam contacts the workpiece, all the components that direct it are either transparent, refractive or reflective, absorbing only small amounts of energy from the ultraviolet light. The laser power supply is capable of delivering a pulse of light that has accurate and repeatable energy and duration. When the pulse of laser energy is focused into a small spot onto the workpiece, the energy density becomes quite large. The light is absorbed by the workpiece, causing a “keyhole” effect as the focused beam drills into, vaporizes and melts some of the metal. As the pulse ends, the liquefied metal around the keyhole flows back in, solidifying and creating a small spot weld. The entire process takes only milliseconds. The laser has the ability to fire many pulses per second, and moving the workpiece or optics allows anything from separate spot welds to a series of overlapping spot welds to create a seam weld that can be structural and/or hermetic.

In explosion welding the resultant composite system is joined with a high-quality metallurgical bond. The time duration involved in the explosion welding event is so short, that the reaction zone between the constituent metals is microscopic. During the bonding process, several atomic layers on the surface of each metal become plasma. The collision angle between the two surfaces (typically less than 30°) forces the plasma to jet ahead of the collision front, effectively scrubbing both surfaces and leaving virgin metal.

The remaining thickness remains near ambient temperature and acts as a huge heat sink. Therefore, the bond line is an abrupt transition from the clad metal to the base metal with virtually no degradation of their initial physical or mechanical properties. The obvious benefit from this process is the joining of metallurgically incompatible systems. Any conventional cladding method, which uses heat, may cause brittle intermetallic compounds to form.

In order to produce a quality weld, the variables affecting the weld formation must be tightly controlled. The amplitude and periodicity of the wave pattern formed during explosion welding can be controlled by adjusting three major parameters: detonation velocity, explosive load, and the interface spacing. The wave pattern formed at the bond line is most often described as resulting from a fluid-flow collision. The two constituent metals can be considered to act as viscous fluids in the reaction zone and, just as in laminar or turbulent flow.