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Research Papers

Simulation and Experimental Study of Nanosecond Laser Micromachining of Commercially Pure Titanium

[+] Author and Article Information
E. Williams

Cardiff School of Engineering,
Cardiff University,
Cardiff CF24 3AA, UK

E. B. Brousseau

Cardiff School of Engineering,
Cardiff University,
Cardiff CF24 3AA, UK
e-mail: BrousseauE@cf.ac.uk

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MICRO- AND NANO-MANUFACTURING. Manuscript received June 5, 2015; final manuscript received October 21, 2015; published online November 19, 2015. Assoc. Editor: Sangkee Min.

J. Micro Nano-Manuf 4(1), 011004 (Nov 19, 2015) (9 pages) Paper No: JMNM-15-1035; doi: 10.1115/1.4031892 History: Received June 05, 2015; Revised October 21, 2015

Nanosecond laser machining of titanium has gained increased interest in recent years for a number of potential applications where part functionalities depend on features or surface structures with microscale dimensions. In particular, titanium is one of the materials of choice to sustain the demand for advanced and miniaturized components in the biomedical and aerospace sectors for instance. This is due to its inherent properties of high strength-to-weight ratio, corrosion resistance, and biocompatibility. However, in the nanosecond laser processing regime, the resolidification and deposition of material expelled from the generated craters can be detrimental to the achieved machined quality at such small scale. Thus, this paper focuses on the investigation of the laser–material interaction process in this pulse length regime as a function of both the delivered laser beam energy and the pulse duration in order to optimize machining quality and throughput. To achieve this, a simple theoretical model for simulating single pulse processing was developed and validated first. The model was then used to relate (1) the temperature evolution inside commercially pure titanium targets with (2) the morphology of the obtained craters. Using a single fiber laser system with a wavelength of 1064 nm, this analysis was conducted for pulse durations comprised between 25 ns and 220 ns and a range of fluence values from 14 J cm−2 and 56 J cm−2. One of the main conclusions from the study is that the generation of relatively clean single craters could be best achieved with a pulse length in the range of 85–140 ns when the delivered fluence leads to the maximum crater temperature being above but still relatively close to the vaporization threshold of the cpTi substrate. In addition, the lowest surface roughness in the case of laser milling operations could be obtained when the delivered single pulses did not lead to the vaporization threshold being reached.

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Figures

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Fig. 5

Temporal temperature variations around 14 J cm−2 for different pulse durations. The horizontal lines show the melt and vaporization temperatures. The SEM images display the corresponding craters formed for 25 ns, 85 ns, and 140 ns pulses. Scale bars: 20 μm.

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Fig. 4

SEM images of single pulse craters machined at 140 ns. Scale bars: 20 μm.

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Fig. 3

Theoretical temperature variations for a 140 ns pulse at varying fluence values. The horizontal lines represent the melt and vaporization temperatures.

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Fig. 2

Comparison between predicted and measured (a) depths and (b) diameters of single craters formed at various fluence values for a pulse duration of 140 ns

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Fig. 11

Temporal temperature evolution at a fixed crater location during laser milling operations at a fluence of 14 J cm−2 for the pulse durations of (a) 140 ns and (b) 220 ns. The horizontal line shows the melt temperature of cpTi.

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Fig. 1

Illustration of the method used to evaluate the diameter of craters

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Fig. 6

Spatial temperature evolutions on the top surface of Ti for a fluence of 14 J cm−2 and for pulse durations of 140 ns and 25 ns

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Fig. 7

SEM micrographs of single craters machined in the cpTi specimens at varying fluence values for pulse durations of 25 ns, 85 ns, 140 ns, and 220 ns. Scale bars: 20 μm.

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Fig. 8

Measured crater (a) depth and (b) diameter for different pulse durations and fluence values

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Fig. 9

Maximum surface temperatures and the associated SEM micrographs of craters irradiated with three different fluence values. The horizontal lines show the melt and vaporization temperatures. Scale bars: 20 μm.

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Fig. 10

Surface roughness and machining efficiency during laser milling at various fluence values for pulse durations of (a) 140 ns and (b) 220 ns. The text boxes shown below the data points give the maximum temperature reached with a single pulse.

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