Application of high speed filming techniques to the study of rearwards melt ejection in laser drilling

Abstract

Melt ejection is the dominant material removal mechanism in long, ms, pulse laser drilling of metals, a process with applications such as the drilling of cooling holes in turbine blades. Droplets of molten material are ejected through the entrance hole and, after breakthrough, through the exit hole. High speed filming is used to study the ejected material in order to better understand how this debris may interact with material in the immediate vicinity of the drilled hole. Existing studies have quantified various aspects of melt ejection, however they usually focus on ejection through the entrance hole. This work concentrates on rear melt ejection and is relevant to issues such as rear wall impingement. A 2kW IPG 200S fibre laser is used to drill mild steel. High speed filming is combined with image analysis to characterise the rearward-ejected material. Particle size and velocity data is presented as a function of drilling parameters. It is concluded that high speed filming combined with image analysis and proper consideration of process limitations and optimisation strategies can be a powerful tool in understanding resultant debris distributions.

In situ thermography for laser powder bed fusion: Effects of layer temperature on porosity, microstructure and mechanical properties

“…Using the raw pixel intensity values, the melt pool is observed during processing and a qualitative assessment of the amount of spatter ejected during melting is made. Image processing and analysis was carried out on the intensity images using particle segmentation methods developed in [22]. The images were segmented using Otsu's method [23] combined with a Watershed Transform Function in order to distinguish spatter particles.…”

The influence of ultrasonic vibration amplitude and magnetic field intensity on microstructural characteristics in laser drilling of Ti6Al4V

“…By reviewing the conducted researches in the field of MFUV-Aided LD, 1–27 it has been found that limited studies have been performed on evaluating the effect of simultaneous application of magnetic field and ultrasonic vibration on the microstructure of the machined part. Therefore, in this paper, the simultaneous application of magnetic field (with various intensities) and ultrasonic vibrations (with different amplitudes) were studied on the formed phases, thickness of recast layer and thickness of HAZ in the LD of Ti6Al4V.…”

“…Nowadays, laser drilling (LD) has found a special place in various industries, including drilling parts in aerospace devices and cooling holes for turbine blades [1][2][3][4] as well as drilling parts of medical devices such as implants. 5 Despite the widespread applications, this process has encountered several restrictions such as low penetration depth, high thickness of recast layer, high thickness of HAZ, micro-cracks and spattering.…”