Introduction to coextrusion welding

An advantage of extrusion welding in welding machine over other methods of deformation butt welding of tubes is that there is no flash or upset to remove following extrusion. The most common metals welded by the coextrusion process include low-carbon steel, aluminum, aluminum alloys, copper, and copper alloys.

COEXTRUSION WELDING (CEW)

  • COEXTRUSION WELDING (CEW) is a solid-state process that produces a weld by heating two or more workpieces to the welding temperature and forcing them through an extrusion die.
  • The process typically is conducted at elevated temperatures not only to improve welding but also to lower extrusion pressures.
  • Some cold coextrusion welding of aluminum and copper has been performed.
  • For hot coextrusion, the parts to be welded are often assembled in a can or retort that is designed with the appropriate leading taper and wall thickness to promote initiation of extrusion.
  • For reactive metals, such as zirconium, titanium, and tantalum, the retort may be evacuated and sealed.
  • Both forward and back coextrusion has been employed, but forward coextrusion is the usual mode.
  • A principal advantage of coextrusion welding is that the high isostatic pressures associated with the process are favorable to the deformation welding of lowductility alloys.

In a similar process, extrusion welding has been used to butt weld tubes. The ends of the tubes are prepared for extrusion by beveling at a 45 to 60° angle to produce an overlapping joint.

The leading tube contains the female portion of the beveled joint and is the stronger of the two metals in dissimilar metal joints. Extrusion press die angles of 30 to 35° are common. An advantage of extrusion welding over other methods of deformation butt welding of tubes is that there is no flash or upset to remove following extrusion.

Common Metals Welded  

  • The most common metals welded by the coextrusion process include low-carbon steel, aluminum, aluminum alloys, copper, and copper alloys.
  • Additional applicable materials include nickel, nickel-base alloys, zirconium, titanium, tantalum, and niobium.

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