Hot-pressure-welding

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Hot-pressure-welding

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Hot-pressure-welding is a solid state process that produces joints between the faying surfaces of two bodies.

It is done by application of heat and pressure.

Fusion temperature is not reached, filler metal is not needed, substantial plastic deformation is generated.

Heat is generally applied by flames of oxyfuel torches directed on the end surfaces of solid bars or hollow sections to be joined.

Alternatively, heat can be generated by eddy currents caused by electrical induction from a suitable inductor coil.

Hot-pressure-welding: Heat and Squeeze

As soon as the two bodies facing ends reach the correct temperature, the torches are suddenly removed, not to stand in the way.

The bodies are brought to contact and upset together under pressure, usually by hydraulic equipment.

This variant is properly called the open joint process.

If the parts are making contact under pressure before heat application from the outside, it is called the closed joint process.

In either case flash material is expelled and a bulge is formed at the joint.

Hot-pressure-welding is similar in a way to both friction welding (see Friction Welding Processes) and flash welding (see Flash Welding Process), although the source of heating is different.

For obtaining the best results the surfaces should be machined square and clean. Some beveling can be used to control the amount of upset.

The process as described is performed as a manual operation.

The materials to be welded must exhibit hot ductility or forgeability. Therefore cast iron cannot be Hot pressure welded.

The materials commonly joined by Hot pressure welding are carbon steels, low alloy steels, and certain nonferrous metals.

Certain dissimilar materials combinations are weldable by Hot pressure welding.

Materials that immediately form on the surface adherent oxides upon heating cannot be easily welded in air by this process.

Typically among them aluminum alloys and stainless steels. Tests were performed in a vacuum chamber.

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Advantages

  • Simple process
  • Simple joint preparation
  • Relatively low cost equipment
  • Quick weld production
  • High quality joints
  • No filler metal needed
  • Minimally skilled operators required

Limitations

  • Not all metals are weldable
  • Not easily automated
  • Length of cycle dependent on time for heating
  • Removal of flash and bulge required after welding.
  • Only simple sections readily butt weldable.

The most important parameter is the pressure sequence cycle, possibly being developed by trial and error.

Pressure in the range of 40 to 70 MPa (6 to 10 ksi) must be available.

Typical application reported, refer to butt Hot-pressure-welding of railroad rails sections and steel reinforcing bars, especially in Japan.

For use in the production of weldments for the aerospace industry with delicate materials Hot-pressure-welding can be carried out in closed chambers with vacuum or a shielding medium.

Mechanical properties tend to be near those of the base materials, but depend upon materials composition, cooling rate and quality.

Hot-pressure-welding can be an economic and successful process for performing butt joints of simple shapes if the materials are easily weldable.

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