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research-article

Microhole Drilling by Double Laser Pulses with Different Pulse Energies

[+] Author and Article Information
Ze Liu

School of Mechanical Engineering, Purdue University, 585 Purdue Mall, West Lafayette, IN 47907, USA
liu1583@purdue.edu

Benxin Wu

Associate Professor, School of Mechanical Engineering, Purdue University, 585 Purdue Mall, West Lafayette, IN 47907, USA
wu65@purdue.edu

Rong Xu

School of Mechanical Engineering, Purdue University, 585 Purdue Mall, West Lafayette, IN 47907, USA
xu.r1968@gmail.com

Kejie Zhao

School of Mechanical Engineering, Purdue University, 585 Purdue Mall, West Lafayette, IN 47907, USA
kejiezz@gmail.com

Yung Shin

School of Mechanical Engineering, Purdue University, 585 Purdue Mall, West Lafayette, IN 47907, USA
shin@purdue.edu

1Corresponding author.

ASME doi:10.1115/1.4040483 History: Received December 09, 2017; Revised May 24, 2018

Abstract

Previous investigations on "double-pulse" nanosecond (ns) laser drilling reported in the literature typically utilize double pulses of equal or similar pulse energies. In this paper, "double-pulse" ns laser drilling using double pulses with energies differing by more than 10 times has been studied, where both post-process workpiece characterizations and in-situ time-resolved shadowgraph imaging observations have been performed. A very interesting physical phenomenon has been discovered under the studied conditions: the "double-pulse" ns laser ablation process, where the low-energy pulse precedes the high-energy pulse (called "low-high double-pulse" laser ablation) by a suitable amount of time, can produce significantly higher ablation rates than "high-low double-pulse" or "single-pulse" laser ablation under a similar laser energy input. In particular, "low-high double-pulse" laser ablation at a suitable inter-pulse separation time can drill through a ~0.93-mm thick aluminum 7075 workpiece in less than 200 pulse pairs, while "high-low double-pulse" or "single-pulse" laser ablation cannot drill through the workpiece even using 1000 pulse pairs or pulses, respectively. This indicates that "low-high double-pulse" laser ablation has led to a significantly enhanced average ablation rate that is more than 5 times those for "single-pulse" or "high-low double-pulse" laser ablation. The fundamental physical mechanism for the ablation rate enhancement has been discussed, and a hypothesized explanation has been given.

Copyright (c) 2018 by ASME
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