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Manufacturing Processes > Joining processes > Electron Beam Welding(EBW)

 

Electron Beam Welding(EBW)

 

Process description

A controlled high intensity beam of electrons (Ø0.5–Ø1 mm) is directed to the joint area of the work (anode) by an electron gun (cathode), where fusion of the base material takes place. The operation takes place in a vacuum, and the work is traversed under the electron beam typically.

Materials

  • Most metals and combination of metals weldable, including low to high carbon and alloy steels, aluminum, titanium, copper, refractory and precious metals.
  • Copper alloys and stainless steel difficult to weld. Cast iron, lead or zinc alloys are not weldable.
  • Metals that experience gas evolution or vaporization on welding difficult.
TIG

Process variations

  • High-vacuum (most common), semi-vacuum and atmospheric (out-of-vacuum) equipment available, depending on type of work, size and location.
  • Semi-vacuum setup used for transportable equipment. Only the area to be welded is surrounded by a vacuum using suction cups.
  • Joint advanced under beam for high-vacuumEBW, but for short weld lengths, the beam can bemoved along the joint using magnetic coils, rather than the work under the beam on a traversing system.
  • EBM : an electron gun is used to generate heat and evaporating the workpiece surface for fusion.
  • The electron beam process can also be used for cutting, profiling, slotting and surface hardening, using the same equipment by varying process parameters.

Economic considerations

  • Weld rates ranging 0.2–2.5 m/min.
  • Production rates range from 10–100/h using high-vacuum equipment.
  • Lead times can be several weeks.
  • Setup times can be short, but the time to create a vacuum in the chamber at each loading cycle an important consideration.
  • High flexibility. Possible to perform many operations on same machine by varying process parameters.
  • Full automation of process possible and gives best results.
  • Economical for low to moderate production runs.
  • Material utilization excellent.
  • High power consumption.
  • Tooling costs very high.
  • Equipment costs very high.
  • Direct labor varies depending on level of automation.
  • No finishing needed typically.

Typical applications

  • Aerospace assemblies (turbine vanes, filters, high pressure pump bodies)
  • Automotive assemblies (crankshaft, gears, valves, bearings)
  • Machine parts
  • Instrumentation devices
  • Pipes
  • Reactor shells
  • Hermetic sealing of assemblies
  • Medical implants
  • Bimetallic saw blades
  • Repair work

Design aspects

  • Typical joint designs possible using EBW: butt, fillet and lap (see Appendix B – Weld Joint Configurations). Horizontal welding position is the most suitable.
  • Path to joint area from the electron beam gun must be a straight line.
  • Beam and joint must be aligned precisely.
  • Depth to width ratio can exceed 20:1.
  • Balance the welds around the fabrication’s neutral axis.
  • Size limited by vacuum chamber dimensions unless semi-vacuum equipment used. Maximum height of work in a chamber is 1.2m typically.
  • Possible to weld thin and delicate sections due to no mechanical processing forces.
  • Maximum thickness (dependent on vacuum integrity):

    • Aluminum and magnesium alloys =450mm
    • Carbon, low alloy and stainless steels =300mm
    • Copper alloys =100 mm.
  • Minimum thickness =0.05 mm.
  • Single pass maximum =75 mm.
  • Highly dissimilar thicknesses commonly welded.

Quality issues

  • High quality welds possible with little or no distortion.
  • No flux or filler used.
  • Integrity of vacuum important. Beam dispersion occurs due to electron collision with air molecules.
  • Out-of-vacuum systems must overcome atmospheric pressures at weld area.
  • Beams can be generated up to 700mm from workpiece surface for high-vacuum systems; can be reduced to less than 40mm for out-of-vacuum.
  • Precise alignment of work required and held using jigs and fixtures.
  • Hazardous X-rays produced during processing which requires lead shielding.
  • Vacuum removes gases from weld area, e.g. hydrogen to minimize hydrogen embrittlement in hardened steels.
  • Localized thermal stresses leads to a very small heat affected zone. Distortion of thin parts may occur.
  • Surface finish excellent.
  • Fabrication tolerances a function of the accuracy of the component parts and the assembly/jigging method. Joints gaps less than 0.1mm required. Therefore, abutment faces should be machined to close tolerances.

costing