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

Abstract

Modern manufacturing industries prefer laser drilling processes owing to the adequate controlled drilling in comparison with existing alternatives. The presented experimental study mainly accounts defocusing impact along with other technical parameters and optimization of Nd:YAG millisecond pulsed laser drilling; and finally their influence on the entrance and exit holes profile. The key technical parameters such as pulse frequency, pulse width and assisting gas pressure with respect to different defocused focal plane are explored experimentally for the percussion laser drilling of high grade steel 18CrNi8. Experiment results revealed that increase in defocusing distance has caused an increment in hole entrance diameter; however, with different defocusing distance, the entrance diameter increasing rate keep changing. Different trends of increasing and decreasing diameter at entrance and exit are recorded and investigated with respect to work-piece defocusing positions. The defocusing variation of laser beam has been investigated with the hole profile, changing from straight hole to tapered blind hole. Which leads to conclusive and optimized results for obtaining optimal hole profile (at entrance and exit). The optimum parametric combinations for attaining lower heat treatment effects are also discussed for superior hole quality.

An integrated analysis of productivity, hole quality and cost estimation of single-pulse laser drilling process

“…Moreover, an increase in pressure does not permit the molten metal to set down inside the hole cavity. Thus, hole taper reduces when higher gas pressure is used which is in accordance with the findings of Chatterjee et al 42 A similar trend has been observed with the increase in gas flow rate because higher compressed air flow rate increases the localised temperature due to its combustible supportability and results in efficient removal of the material from the hole exits which results in lower hole taper, as stated by Nawaz et al 20 Influence of pulse energy and pulse duration on drilling cost. Figure 9 illustrates the response of pulse energy and pulse duration on drilling costs.…”

“…The laser processing parameters which affect hole taper include laser pulse duration/ width, pulse energy, assist gas pressure, beam focal position and gas flow rate. [12][13][14][15][16][17][18][19][20] In previous research studies, several authors have explored the effects of these process parameters for single-pulse drilling. Yilbas and Yilbas 21 used the full factorial method to evaluate the impacts of focal position and material thickness on the quality of laser-drilled holes in Nimonic 75.…”