Investigation of precession laser machining of micro-holes in aerospace material

Sidewall tapering is one of the main limitations in ultrashort pulse (USP) laser machining and is associated with the beam shape and self-limiting effect. Laser processing with a precession beam is a potential solution to overcome this limitation. A study into the effects of precession parameters on the taper angle in micro-hole drilling of Nickel alloy is reported in this paper. The effects of three key precession parameters, i.e. incident angle, relative distance between the focuses of the precession and individual beams and scanning speed have been investigated in details. Experiments were performed to drill through holes with aspect ratios up to 20:1 and diameters ranging from 100 μm to 500 μm over 0.6 mm to 2 mm thick Nickel alloy substrates. Experiment results showed that all the considered parameters/factors were significant and affected the hole tapering in different ways. In addition, there were important interaction effects between two of the factors, i.e. incident angle and focus position, in some cases. The optimal parameters to minimise tapering effect are suggested and the mechanism is discussed in detail. The precession laser machining showed clear advantages in overcoming the limitations 1rocess1eed with the conventional USP laser machining. Fabricating micro- holes with high geometrical accuracy, i.e. with straight side walls and zero taper angles, is feasible with the use of precession beam. The results clearly show the potential of precession laser processing and the capabilities that the technology can offer for a range of laser micro- machining applications in different industries, such as microelectronics, automotive and aerospace.