Pressure welding or solid phase bonding of aluminum is accomplished by applying high pressure on the surfaces to be joined, either with or without heat, in the complete absence of melting.

Pressure can be applied by aligning two punches or tapered rolls. Another method uses a shoulder punch on one side of the material and a flat plate or anvil on the other. A third method uses a single tapered roll and a flat surfaced roll. In some instances, punches with shoulders are employed to control the amount of punch penetration and flatten the deformation at the point of entry simultaneously.

Wire brushing is the most satisfactory method of surface preparation.

 

Pressure Gas Welding

Metal flow between clean interfaces is essential to a cold pressure weld. Simple pressure is not enough.  Once started, metal flow must be vigorous and continuous,  although speed seems to have little bearing on quality of weld. Pressure must be applied over a comparatively narrow strip, so that the metal can flow away from the weld at both sides. When continuous welds are to be used, the indentor should be of waved design, rather than straight, for maximum strength. Strip and sheet can also be butt welded, but as the width increases, the gripping problem for the dies also increases.

There are two basic methods of pressure gas welding: closed joint and open joint. Coalescence is produced simultaneously over the entire area of abutting surfaces by heating with oxyacetylene flames and then applying pressure. No filler metal is used.

In closed joint welding (also called solid phase and closed butt welding), weld faces are in contact during the complete welding cycle. Ends are carefully cleaned, butted, and heated to a high temperature, but not to the melting stage. Pressure is applied, thereby upsetting the weld zone in a plastic deformation. Various refinements are used in this method, particularly in pressure. Often a low initial pressure is applied, and the pressure is increased as the metal attains its plastic state. Maximum pressure can be applied throughout the welding process, or different pressures may be applied at regular or varying intervals.

In open joint welding, parts are spaced a short distance apart, and heated to the melting temperature. When melting temperature is reached, the parts are brought together rapidly, causing an upset, or partial fusion, weld. Most of the melted material is squeezed from the interface by the impact, and the resulting weld resembles a resistance flash weld.

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