Abstract
This paper presents an experimental investigation on the influences of laser trepanning drilling process parameters on the recast layer thickness and surface crack formation in CMSX-4 nickel-based superalloy angled holes. The effects of peak power, pulse frequency and the trepanning speed as input parameters were investigated in details by varying the laser drilling conditions using Taguchi orthogonal array-based design of experiment approach. Analysis of variance identifies the significant parameters affecting the output responses. It is found that the output responses are affected mainly by the peak power and trepanning speed. The experimental results reveal that the recast layer thickness increases with the increase of peak power and trepanning speed whereas the crack number density decreases with the increase of peak power only. Pulse frequency has no significant effect on both output responses within the range of values investigated. The knowledge gained in this parametric study could be used to improve the metallurgical characteristics of laser-drilled nickel-based acute angled holes.
Highlights
Pulsed Nd:YAG laser drilling is extensively used to produce holes of various sizes and shapes, in particular for the cooling film holes of hot section gas turbine components such as combustor liners, nozzle guide vanes and turbine blades
The ‘smaller is better’ (SB) quality characteristic was chosen for the analysis of the maximum of recast layer thickness (RLTmax) and transverse microcrack number density (TCNDmax) observed
In the laser trepanning drilling process, the molten material formed due to intense laser beam energy is ejected towards the exit hole by assist process gas
Summary
Pulsed Nd:YAG (neodymium-doped yttrium aluminium garnet) laser drilling is extensively used to produce holes of various sizes and shapes, in particular for the cooling film holes of hot section gas turbine components such as combustor liners, nozzle guide vanes and turbine blades. Laser drilling in millisecond regime induces surface damage such as spatter [6], oxide and recast layer formation [7], heat-affected zone (HAZ) [8] and burrs [9]. The recast layer is the most significant since it may contain oxide inclusions and microcracks [8] This is highly undesirable the presence of microcracks in the recast structure since the propagation of the cracks from the recast layer into the parent material could occur in service, leading to failure and compromising the integrity and lifetime of the drilled component. Pulsed Nd:YAG laser drilling is a non-contact and thermalbased process, in which a high-power, pulsed focused laser beam is irradiated onto the workpiece surface to melt and vaporise the material to form a hole [2]. In an attempt to understand the process better, some researchers have used observation techniques such as streak photography [11], field emission scanning electron microscope [12, 13] and high-speed cameras [14] to describe the material removal mechanism and surface characteristics during the laser drilling
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