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Information Sheets

Cutting & Drilling

Cutting

The cutting process can be split into two process types depending on whether the laser is the only source of energy or a gas is used to assist the process. High peak intensities are required with small focal spot sizes. Energy is delivered very rapidly due to the high peak intensity breaking down the reflectivity. The surface is vaporised and ejected from the surface. As the laser energy continues, more material is heated and vaporised. An assist gas may be necessary to eject vaporised material and prevent re-solidifying.

Most cutting is carried out using a gas. Oxygen is often used. However with pyrophoric materials which will continue burning in air, an inert gas may be necessary.

Using a gas may have two functions. Firstly the gas used to blow material away from the process zone. Secondly the gas provides additional energy to the cutting process increasing the overall thermal effect.

Where a pulsed laser is used, the cutting speed is mainly governed by the repetition rate. Using an active gas may mean that low power is required from the laser thus allowing a higher repetition rates to be used. The action of the gas becomes more important as the material thickness increases. Cutting requires sufficient laser energy and gas reaction to overcome the absorption of the materials and keep the material molten as it passes out of the cut area.

Assist gases

The assist gas is selected dependant on the material being processed. Oxygen, compressed air, argon and nitrogen are all used dependant on the application.

Process problems to be addressed include:

  • Taper across the cut width (often called “kerf width”)
  • Edge roughness
  • Dross usually adhering to the back surface
  • Consistency of cut width and roughness
  • Oxidisation of the cut edge

Drilling

Drilling uses one of two processes – trepanning or percussion drilling. Trepanning is very similar to cutting by initially percussion drilling a small hole and then cutting to produce a larger hole. Often this is completed by small movement of the laser beam (usually under computer control) rather than movement of the workpiece with the laser beam being static.

Percussion drilling uses one or more laser pulses at the same postion on the material to vaporise a hole. The size of the hole depends on the focus spot size, pewak power, pulse energy and any assist gas used. Perusiion drilling require good beam quality. In general the better the beam quality the better is he hole quality. A difficulty is getting perfectly round holes.

The choice of which process to use depends on the size of the holes to be produce and the rate at which they are to be produced.

Process problems associated with drilling include

  • Hole taper and barrelling
  • Hole shape and roundness
  • Spatter
  • Hole exit shape
  • Recasting within the hole
  • Cracking around the heat affected zone
  • Cracking in the material being drilled
  • Dross on the underside (exit) of the material


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