Experimental Investigation on the Spatial-temporal Evolution of the hole formation during Laser Helical Drilling

Abstract

In order to study the influence of process parameters of femtosecond laser helical machining on the formation of micro-holes, we selected main parameters of the femtosecond laser helical drilling process, used 304 stainless steel as the target material, designed a 5-factor and 5-level orthogonal experiment based on the L 25 (56) orthogonal table, and analyzed the significance levels of the impacts of single pulse energy, repetition rate, rotation rate, rate of focus downward movement, and air-blowing pressure on the ablation depth. Based on back propagation (BP) neural network, we established the relationship model between five factors and the material ablation depth, and trained the network with orthogonal experiment data. We used the data of the additional drilling experiments to test the generalization ability of the established network, and the results show that the prediction error of the model is within 3%. We designed a single-factor experiment for the characteristic parameter of the helical drilling--the rate of focus downward movement--and obtained the effect of the rate of focus downward movement on the formation of the micro-holes during the process of femtosecond laser helical drilling.

Effect of defocused plane on entrance and exit hole geometry of high grade steel 18CrNi8 during percussion drilling by Nd:YAG millisecond laser system

“…Quality of hole in laser drilling is largely dependent upon the operating parameters, such as laser beam wavelength, pulse repetition rate, intensity, pulse duration and operational current, etc and their combinations thereof. In general, the cracks, debris, major tapering effect, HAZ, shapes defects, are the main concerns [8][9][10][11]. Therefore, laser drilling has extensively studied theoretically and experimentally.…”