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Electron beam fabrication replaces casting

TWI collaborated with BAE Systems and the Ministry of Defence on a project to identify an alternative to high strength steel castings in the manufacture of a safety-critical hull penetrating valves.  This collaboration came up with the concept of employing the Electron Beam (EB) process to fabricate the valve components and developed the procedure for manufacture. 

As well as their expertise in EB welding, TWI were able to offer unrivalled knowledge in materials selection.EB welding offers a range of advantages over casting in the fabrication of the valve components.

Large valve body component fabricated using EB welding
Large valve body component fabricated using EB welding

These include:

  • Flexibility in design – patterns and moulds for the castings cannot be changed easily and cheaply
  • Rapid delivery times – production lead times are reduced significantly
  • Suited to small volume production – minimum melt for casting is in the region of 10-15 tonnes; individual castings <2 tonnes
  • Improved performance – higher product integrity and better material properties in wrought products

In addition to this, the numbers of foundries able to cast the high strength steel grade have dwindled.  There can be further complications encountered when the castings are clad using the hot wire TIG process.  These complications are largely avoided in the EB welded component.

The near net shape component parts are cut using oxy-fuel cutting.  These are then EB welded, with each join being made in a single pass, and inspected.  The fabrications are machined before heat treatment by a full quench and temper.  A final machining operation gives the component its final shape and they are then inspected again using dye penetrant inspection.  The component is then given a Ni-Cu or Inconel overlay by hot wire TIG cladding, after which the valve component is assembled.

Although the fabrication process has not been widely employed, the development has demonstrated the possibilities of adopting the EB welding process as an alternative to existing production methods.

For information about TWI’s capabilities please email contactus@twi.co.uk

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