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Manufacturing Processes > Joining processes > laser Beam Welding(TIG)

 

laser Beam Welding(TIG)

 

Process description

Heat for fusion is generated by the absorption of a high power density narrow beam of light, commonly known as a laser. Focusing of the laser is performed by mirrors or lense.

Materials

  • Dependent on thermal diffusivity and to a lesser extent the optical characteristics of material, rather than chemical composition, electrical conductivity or hardness.
  • Stainless steel and carbon steels typically.
  • Aluminum alloys and alloy steels difficult to weld. Not used for cast iron.
LBW

Process variations

  • Many types of laser are available, used for different applications. Common laser types available are: CO2, Nd:YAG, Nd:glass, ruby and excimer. Depending on economics of process, pulsed and continuous wave modes are used.
  • Shielding gas such as argon sometimes employed to reduce oxidation.
  • Laser beam machines can also be used for cutting, surface hardening, machining (LBM) , drilling, blanking, engraving and trimming, by varying the power density.
  • Laser beam spot and seam welding can also be performed on same equipment.
  • Laser soldering: provides very precise heat source for precision work.

Economic considerations

  • Weld rates ranging 0.25–13 m/min for thin sheet.
  • Production rates moderate.
  • High power consumption.
  • Lead times can be short, typically weeks.
  • Setup times short.
  • Material utilization excellent.
  • High degree of automation possible.
  • Possible to perform many operations on same machine by varying process parameters.
  • Economical for low to moderate production runs.
  • Tooling costs very high.
  • Equipment costs high.
  • Direct labor costs medium. Some skilled labor required depending on degree of automation.

Typical applications

  • Structural sections
  • Transmission casings
  • Hermetic sealing (pressure vessels, pumps)
  • Transformer lamination stacks
  • Instrumentation devices
  • Electronics fabrication
  • Medical implants

Design aspects

  • Laser can be directed, shaped and focused by reflective optics permitting high spatial freedom in 2-dimensions. Horizontal welding position is the most suitable.
  • Typical joint designs using LBW: lap, butt and fillet (see Appendix B – Weld Joint Configurations).
  • Mostly for horizontal welding.
  • Balance the welds around the fabrication’s neutral axis.
  • Path to joint area from the laser must be a straight line. Laser beam and joint must be aligned precisely.
  • Intimate contact of joint faces required.
  • Filler rod rarely utilized, but for thick sheets or requiring multi-pass welds, a wire-feed filler attachment can be used.
  • Minimal work holding fixtures required.
  • Minimum thickness =0.1 mm.
  • Maximum thickness =20 mm.
  • Multiple weld runs required on sheet thickness ≥13 mm.
  • Dissimilar thicknesses difficult.

Quality issues

  • Difficulty of material processing dictated by how close the material’s boiling and vaporization points are.
  • Localized thermal stresses lead to a very small heat affected zone. Distortion of thin parts may occur.
  • No cutting forces, so simple fixtures can be used.
  • Inert gas shielding, argon commonly, employed to reduce oxidation.
  • Control of the pulse duration important to minimize the heat affected zone, depth and size of molten metal pool surrounding the weld area.
  • The reflectivity of the workpiece surface important. Dull and unpolished surfaces are preferred and cleaning prior to welding is recommended.
  • Hole wall geometry can be irregular. Deep holes can cause beam divergence.
  • Surface finish good.
  • Fabrication tolerances a function of the accuracy of the component parts and the assembly/jigging method.

 

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