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17.8.3 Explosive Welding
Welding 335
In explosive welding, strong metallurgical bonds can be produced between metal combinations
which cannot be welded by other methods or processes. For example, tantalum can be
explosively welded to steel although the welding point of tantalum is higher than the
vaporization temperature of steel. Explosive welding process is shown in Fig. 17.28. It is
carried out by bringing together properly paired metal surfaces with high relative velocity at
a high pressure and a proper orientation to each other so that a large amount of plastic
interaction occurs between the surfaces. The work piece, held fixed is called the target plate
and the other called flyer plate. While a variety of procedures have been successfully employed,
the main techniques of explosive welding can be divided into contact techniques and impact
techniques. In critical space and nuclear application, explosive welding permits fabrication of
structures that cannot be made by any other means and, in some commercial applications,
explosive joining is the least costly method. The main advantage of explosive welding includes
the simplicity of the process, and the extremely large surface that can be welded. Incompatible
materials can also be bonded, and thin foils can be bonded to heavier plates.
Explosive
Detonator
Explosive
Detonator
Buffer
plate
Flyer
plate
Buffer
plate
Flyer
plate
α
Ta rg et
plate
Ta rg et
plate
Anvil
Anvil
(a) Parallel Stand Off
Fig. 17.28 Explosive welding process
(b) Ang ular Stand Off
17.9 THERMIT WELDING
It may be of forge or fusion kind of welding. Fusion welding requires no pressure. Thermit
welding process is depicted in Fig. 17.29. It is a process which uses a mixture of iron oxide
and granular aluminium. This mixture in superheat liquid state is poured around the parts
to be joined. The joint is equipped with the refractory mold structure all around. In case of
thermit pressure welding, only the heat of thermit reaction is utilized to bring the surface
of metal to be welded in plastic state and pressure is the applied to complete the weld. The
temperature produced in the thermit reaction is of the order of 3000°C. Thermit welding is
used for welding pipes, cables, conductors, shafts, and broken machinery frames, rails and
repair of large gear tooth.
17.10 RADIANT ENERGY WELDING PROCESSES
In radiant energy welding processes, heat is produced at the point of welding when a stream
of electrons or a beam of electro-magnetic radiations strikes on the workpiece. This welding
can be carried out in vacuum or at low pressures. Electron beam welding (EBW) and laser
welding are two main types of radiant energy welding processes.