During laser drilling, a short laser pulse with a high power density delivers the energy to the workpiece in a very short time. This melts and vaporises the material. The greater the pulse energy, the more material melts and vaporises. During vaporisation, the volume of material in the drilled hole increases abruptly, generating high pressure. This vapour pressure forces the molten material out of the drilled hole. Laser processing with ultrashort pulse lasers in the picosecond range is a unique feature. In this process, the material is vaporised directly from the solid state by sublimation without melting the material – the component is not heated in the process Over time, several drilling methods have been developed from this basic principle.
Drilling
During laser drilling, the laser beam generates very fine to large holes in a variety of materials in a non-contact procedure.
Single pulse drilling and percussion drilling
In the simplest instance, a single laser pulse with comparatively high pulse energy drills the hole. Multiple holes can be created very quickly using this technique. In percussion drilling, the hole is created by several laser pulses with a shorter pulse duration and pulse energy. This drilling method produces deeper and more precise holes than single pulse drilling. Percussion drilling also enables smaller bore hole diameters.
Trepan drilling
In trepan drilling, the hole is also created by multiple laser pulses. First, the laser drills a start hole using percussion drilling. It then enlarges the start hole by travelling over the workpiece in several, increasingly larger circular paths. Most of the molten material is driven downwards out of the drilled hole.
Helical drilling
Unlike trepan drilling, helical drilling does not create a start hole. The laser travels in a circular path over the material from the very first pulses, causing a lot of material to escape upwards. The laser works its way downwards in a spiral shape. The focus can be adjusted so that it is always directed at the bottom of the hole. Once the laser has penetrated the material, a few more rounds can be added. These are used to widen the underside and smooth the edges of the drilled hole. Helical drilling can be used to create very large and deep drilled holes of high quality.