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Research Papers

Sequential Laser Mechanical Microdrilling of Inconel 718 Alloy

[+] Author and Article Information
M. M. Okasha1

Manufacturing and Management Group, School of Mechanical, Aerospace and Civil Engineering, The University of Manchester, Manchester M60 1QD, UKmostafa.okasha@postgrad.manchester.ac.uk

P. T. Mativenga

Manufacturing and Management Group, School of Mechanical, Aerospace and Civil Engineering, The University of Manchester, Manchester M60 1QD, UKp.mativenga@manchester.ac.uk

L. Li

Manufacturing and Management Group, School of Mechanical, Aerospace and Civil Engineering, The University of Manchester, Manchester M60 1QD, UKlin.li@manchester.ac.uk

1

Corresponding author.

J. Manuf. Sci. Eng 133(1), 011008 (Jan 31, 2011) (8 pages) doi:10.1115/1.4003334 History: Received October 31, 2009; Revised November 29, 2010; Published January 31, 2011; Online January 31, 2011

Mechanical microdrilling of nickel-based aerospace alloys suffers from premature drill breakage due to the fragile nature of the microdrill. Additionally, burr size reduction in both macro- and microscales has become one of the key problems in the drilling process. This paper presents a new method to microdrill Inconel 718 alloy using laser followed by mechanical drilling (sequential drilling). The aim of this research was to understand and evaluate the capability of using sequential laser mechanical drilling method as an effective and efficient method in drilling difficult-to-cut metals. Two new approaches were developed, namely, a two-step process of laser pilot drilling followed by twist drilling and a three-step process of laser pilot hole drilling followed by mechanical pilot drilling and then twist drilling. The holes produced by the new approaches were compared with those by mechanical microdrilling (pilot drilling and then twisting drilling). The results show that mechanical drilling eliminates the laser drilling defects. Furthermore, while large nonuniform burrs with attached cap were found in pure mechanical drilling, 75% reduction in burr size was achieved with the complimentary sequential drilling technology. Additionally, when compared with purely mechanical microdrilling, the new drilling method resulted in 240–430% tool life increase. Thus, the new drilling method presents an opportunity for industry to extend tool life and decrease burr.

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Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Factor effect on (a) recast layer thickness, (b) HAZ thickness, and (c) hole taper angle

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Figure 2

Longitudinal cross section of laser-drilled hole: (a) run 1 at 1000 W, 2 ms, and 4 bar oxygen assist gas and (b) run 8 at 750 W, 5 ms, and 2 bar nitrogen assist gas

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Figure 3

Typical optical micrograph shows the recast layer and HAZ thickness (1000 W and oxygen at 4 bars)

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Figure 4

Mechanical-laser drilling alignment accuracy

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Figure 5

Illustration of combined laser and mechanical drilling steps (Laser-Pilot-Mech)

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Figure 6

Measured thrust (a) and torque (b) for mechanical and sequential Laser-Pilot-Mech (0.8 mm drill, 4.7 m/min, 28 mm/min, 0.8 mm peck, and mist coolant)

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Figure 7

Roundness error for different drilling methods

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Figure 8

Typical SEM micrographs showing the hole entry side of (a) mechanical, (b) Laser-Pilot-Mech, (c) Laser-Mech, and (d) Laser-Pilot-Mech with spatter extent

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Figure 9

Typical SEM micrographs showing the hole exit side of (a) mechanical, (b) mechanical after removing cap, (c) Laser-Mech, and (d) Laser-Pilot-Mech

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Figure 10

Effect of different drilling methods on tool life

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Figure 11

Optical photos showing the difference between the microchips from (a) mechanical and (b) Laser-Pilot-Mech

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