Laser drilling

Abstract

Since the first demonstrations of the ruby laser in 1960, the laser quickly took an important place in various domains of industry. This is mainly because of its concentrated and contactless energy supply. This has led to many applications in the domain of laser materials processing. The most important applications in this domain are cutting, welding and marking. Laser drilling, the topic of this article, is a niche application.

Laser percussion drilling (drilling by multiple shots) is for instance used in the process of gas turbine manufacturing, because of the fact that the components to be drilled are made of superalloys which are very hard to machine by conventional techniques. To fix ideas, the typical hole diameter, hole depth and pulse length are 0.5 : 1.0 mm, 3 : 10 mm and 1.0 ms, respectively. Laser percussion drilling is favoured over alternative drilling processes like spark erosion drilling and laser trepanning drilling because it is by far the fastest process.However, it suffers of problems with the quality of the hole. The main quality aspects are:

- Tapering (Decrease of hole diameter with depth)
- Recast layer (Re-solidified material at wall of hole)
- Bellow shape (Local increase of hole diameter)

The laser drilling process depends on the material properties and on the laser beam characteristics: wavelength and intensity as a function of space and time.

The main goal of the research being started at the study group is to come up with a simulation model based on a mathematical model which includes all relevant physical features. This model is needed to get a better understanding of the process and to be able to select proper settings of the process parameters. Once well validated, this model will be used to define the specification of the ideal laser used for drilling. The major problem will be to handle the different phases and in particular the modelling of the interaction of the beam with the vapour phase.