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Manufacturing Processes > Non-Traditional Machining > Laser Beam Machining

 

Laser Beam Machining

 

Process description

A pulsed beam of coherent monochromatic light of high power density, commonly known as a laser (Light Amplification by Stimulated Emission of Radiation), is focused on to the workpiece surface causing it to vaporize locally. The material then leaves the surface in the vaporized or liquid state at high velocity.

Materials

Most materials, but dependent on thermal diffusivity and to a lesser extent the optical characteristics of material, rather than chemical composition, electrical conductivity or hardness.

LMB

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.
  • High pressure gas streams are used to enhance the process by aiding the exothermic reaction process, keeping the surrounding material cool and blowing the vaporized or molten material and slag away from the workpiece surface.
  • Laser beam machines can also be used for cutting, surface hardening, welding (LBW), drilling, blanking, honing, engraving and trimming, by varying the power density.

Economic considerations

  • Production rates are moderate to high; 100 holes/s possible for drilling.
  • Higher material removal rate than conventional machining.
  • Material removal rates typically 5mm³/s and cutting speeds 70 mm/s.
  • High power consumption.
  • Lead times can be short, typically weeks.
  • Setup times short.
  • Material utilization good.
  • High degree of automation possible.
  • High flexibility. Integration with CNC punching machines is popular giving greater design freedom.
  • 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 very high.
  • Direct labor costs medium to high. Some skilled labor required.

Typical applications

  • For holes, profiling, scribing, engraving and trimming
  • Non-standard shaped holes, slots and profiling
  • Prototype parts
  • Small diameter lubrication holes
  • Features in silicon wafers in the electronics industry

Design aspects

  • Laser can be directed, shaped and focused by reflective optics permitting high spatial freedom in 2-dimensions and 3-dimensions with special equipment.
  • Suitable for small diameter, deep holes with length to diameter ratios up to 50:1.
  • Special techniques required to drill blind and stepped holes, but not accurate.
  • Minimal work holding fixtures required.
  • Sharp corners possible, but radii should be provided for in the design.
  • Maximum thicknesses: mild steel =25 mm, stainless steel =13 mm, aluminum =10 mm.
  • Maximum hole size (not profiled) =1.3 mm.
  • Minimum hole size =Ø0.005 mm.

Quality issues

  • Difficulty of material processing is dictated by how close the material’s boiling and vaporization points are.
  • Localized thermal stresses, heat affected zones, recast layers and distortion of very thin parts may be produced. Recast layers can be removed if undesirable.
  • No cutting forces, so simple fixtures can be used.
  • It is possible to machine thin and delicate sections due to no mechanical contact.
  • The cutting of flammable materials is usually inert gas assisted. Metals are usually oxygen assisted.
  • Control of the pulse duration is important to minimize the heat-affected zone, depth and size of molten metal pool surrounding the cut.
  • The reflectivity of the workpiece surface is important. Dull and unpolished surfaces are preferred.
  • Hole wall geometry can be irregular. Deep holes can cause beam divergence.
  • Surface detail is fair.
  • Surface roughness values ranging 0.4–6.3 µm Ra.
  • Achievable tolerances ranging ±0.015–±0.125 mm. (Process capability charts have not been included. Capability is not primarily driven by characteristic dimension.)

costing