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Research Papers

Hybrid CO2 Laser/Waterjet Machining of Polycrystalline Diamond Substrate: Material Separation Through Transformation Induced Controlled Fracture

[+] Author and Article Information
Dinesh Kalyanasundaram

Centre for Biomedical Engineering,
Indian Institute of Technology Delhi,
Hauz Khas, New Delhi 110016, India
Department of Mechanical Engineering,
Iowa State University,
Ames, IA 50011

Andrea Schmidt, Pal Molian

Department of Mechanical Engineering,
Iowa State University,
Ames, IA 50011

Pranav Shrotriya

Department of Mechanical Engineering,
Iowa State University,
Ames, IA 50011
e-mail: shrotriya@iastate.edu

1Corresponding author.

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING. Manuscript received June 23, 2011; final manuscript received February 28, 2014; published online May 21, 2014. Assoc. Editor: Allen Y. Yi.

J. Manuf. Sci. Eng 136(4), 041001 (May 21, 2014) (10 pages) Paper No: MANU-11-1222; doi: 10.1115/1.4027304 History: Received June 23, 2011; Revised February 28, 2014

This paper presents a combined experimental and computational investigation of a novel material separation mechanism in polycrystalline diamond (PCD) substrates. A hybrid CO2 laser/waterjet (CO2-LWJ) machining system that combines a CO2 laser for localized heating and an abrasive-free waterjet to rapidly quench the heated area is utilized for cutting experiments on PCD substrates. Scanning electron microscopy (SEM) and micro-Raman spectrometry characterization performed on the cut surfaces show that cut surfaces were divided into two zones—a thin transformed zone near the top where the PCD grains have transformed to graphite and diamond-like carbon; and a fracture zone with the same composition as-received substrate. The experimental results indicate that the PCD substrates were cut through a “score and snap” mechanism—laser heating leads to localized damage and phase transformation of surface layers; and subsequently, stress fields developed due to constrained expansion of transformed material and waterjet quenching act on the laser made “score” to propagate crack through the thickness. Analytical solutions for thermal diffusion and force equilibrium are used to determine the temperature and stress fields in the PCD substrate during CO2-LWJ cutting. Fracture mechanics analysis of crack propagation is performed to demonstrate the feasibility of the “score and snap” mechanism for cutting of PCD substrates.

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Figures

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Fig. 1

Schematic of the CO2-LWJ system

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Fig. 2

Effect of velocity on modes of material separation

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Fig. 3

SEM image of the cross section by Laser cutting at 1000 W and at a velocity of 42.32 mm/s (100 in./min) Below: Magnified images of region (a), (b), and (c)

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Fig. 4

Above: SEM image of the cross section by CO2-LWJ cutting at 1000 W and at a velocity of 42.32 mm/s (100 in./min) Below: Magnified images of region (a) and (b)

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Fig. 5

Raman spectroscopy of laser cutting of PCD

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Fig. 6

Crack orientations (a) plane strain cracking and (b) crack channeling

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Fig. 7

Temperature history at an arbitrary point on the surface at different time intervals (temp solution by error-function expansion is plotted by dotted lines and temp solution by trignometric function expansion is plotted by solid lines)

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Fig. 8

(a) Temperature and (b) stress distributions across the thickness of PCD substrate at the instant corresponding to maximum surface tensile stress during CO2-LWJ machining

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Fig. 9

Griffith energy for channeling crack (Gchan) versus a/w. Griffith energy calculated for CO2-LWJ cutting (presence of tensile thermal stresses).

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Fig. 10

Influence of laser irradiation induced transformation on crack propagation through thickness

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