WHAT IS COLD WELDING?
Cold welding is a solid state process in which pressure is used at room temperature to produce coalescence of metals with substantial deformation at the weld. Both butt and lap joints can be cold welded.
Characteristics of Cold Welding
- At least one of the metals must be ductile without excessive work hardening.
- Total absence of applied heating.
- Dissimilar metals can be joined.
- Surface preparation is important.
Dies in Cold Welding
The dies play an important role in the cold weld process. Firstly, they must grip the material firmly and, therefore, the inside of the cavity is either etched with an electric pencil or, when the die is to be used for welding large pieces of aluminium, grip marks are put in the cavity before the die is heat treated.
Cold Welding Process
- The parts to be welded are first cleaned.
- A short section of the part is sheared
- The parts are clamped in a die with some initial extension.
- A forging force is applied to complete welding.
Cold Welding Machines
Stages of Cold Welding
Advantages and Disadvantages of Cold Welding
Advantages
- As the process is performed at ambient temperature, there are no thermal effects on the parts being joined.
- The process is fast.
- It is simple and inexpensive to operate once dies have been produced.
- The ends of the wire or rod need no preparation to welding and the alignment of the two butt ends is automatic as the material is placed in the die.
Disadvantages
- Highly specialized with respect to joint design and materials to be welded (soft iron that has no carbon content).
- welds are made in the ‘solid state’ they are difficult to inspect.
- With the exception of butt welds, or welds where the contact surfaces are sheared together, the thickness of the parts is reduced.
Applications of Cold Welding
- Cold welded butt joints are used in the manufacturing of aluminum, copper, gold, silver, and platinum wires with continuous drawing.
- Most commonly, used in sealing heat sensitive semiconductor devices.
- Sealing of heat sensitive containers such as containing explosives.
- Used in underground wire servicing due to hostile environments (explosive gasses).
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