Without touching the workpiece, the laser beam produces holes – from ultrasmall to relatively large - in different materials.
In laser drilling, a short laser pulse with high power density feeds energy into the workpiece extremely quickly, causing the material to melt and vaporize. The greater the pulse energy is, the more material is melted and vaporized. Vaporization causes the material volume in the drilled hole to increase suddenly, creating high pressure. The vapor pressure expels the molten material from the hole.
Over the years, several drilling processes have developed from the basic method:
In the simplest case, a single laser pulse with comparatively high pulse energy is used to produced the hole. This method enables a large number of holes to be created in an extremely short amount of time. In percussion drilling, the hole is produced using multiple short-duration, low-energy laser pulses. This technique produces deeper, more precise holes than single-shot drilling and also enables smaller hole diameters.
Trepanning also uses multiple laser pulses to produce the hole. In this process, a pilot hole is first created using percussion drilling. Then the laser enlarges the pilot hole, moving over the workpiece in a series of increasingly larger circles. Most of the molten material is expelled downward through the hole.
Unlike trepanning, helical drilling does not involve the creation of a pilot hole. Right from the start, the laser begins moving in circles over the material as the pulses are delivered, with a large amount of material shooting upward in the process. The laser continues to work its way through the hole in a downward spiral. The focus, meanwhile, can be adjusted so that it is always at the base of the hole. Once the laser has pierced through the material, it can complete a few more revolutions to enlarge the base of the hole and smooth out the edges. Helical drilling makes it possible to produce very large and deep high-quality holes.