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Research Papers

Role of Capillary and Thermocapillary Forces in Laser Polishing of Metals

[+] Author and Article Information
Chi Zhang

School of Mechanical Engineering,
Shanghai Jiao Tong University,
Shanghai 200240, China

Jing Zhou

College of Mechanical Engineering,
University of Shanghai for Science
and Technology,
Shanghai 200093, China

Hong Shen

School of Mechanical Engineering,
Shanghai Jiao Tong University,
Shanghai 200240, China;
State Key Laboratory of Mechanical System
and Vibration,
Shanghai 200240, China
e-mail: sh_0320@sjtu.edu.cn

Manuscript received June 20, 2016; final manuscript received December 2, 2016; published online January 30, 2017. Assoc. Editor: Hongqiang Chen.

J. Manuf. Sci. Eng 139(4), 041019 (Jan 30, 2017) (11 pages) Paper No: MANU-16-1343; doi: 10.1115/1.4035468 History: Received June 20, 2016; Revised December 02, 2016

As one of emerging novel surface treatment techniques, laser polishing offers a cost-effective and efficient solution to reduce surface roughness of precision components at micro-/mesoscale. Although it has been applied for industrial and biomedical purposes, the underlying mechanism has not been fully revealed. This paper presents a study to understand the basic fundamentals of continuous wave fiber laser polishing of Ti6Al4V samples. A two-dimensional numerical model that coupled heat transfer and fluid flow is developed to illustrate the molten flow behavior. The roles of capillary and thermocapillary flow in the process of laser polishing are investigated to assist the understanding of the contributions of surface tension (capillary force) and Marangoni effect (thermocapillary force) in the polishing process. Capillary force dominates the molten pool at the initial stage of melting, while thermocapillary force becomes predominant when the molten pool fully develops.

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Figures

Grahic Jump Location
Fig. 1

Initial surface of Ti6Al4V sample

Grahic Jump Location
Fig. 2

Experimental setup

Grahic Jump Location
Fig. 3

Optical microscopic images of characteristic laser polished linear tracks for various parameters (a) 12 W, 1.5 mm/s, (b) 20 W, 1.2 mm/s, (c) 26 W, 1.0 mm/s, (d) 26 W, 1.2 mm/s, (e) 26 W, 1.5 mm/s, (f) 26 W, 1.7 mm/s, (g) 35 W, 1.5 mm/s, and (h) 44 W, 1.7 mm/s

Grahic Jump Location
Fig. 4

Initial (above) and polished (below) surfaces

Grahic Jump Location
Fig. 5

Data plot of line profile extracted from Fig. 4

Grahic Jump Location
Fig. 6

The schematic of the computational domain (scaled)

Grahic Jump Location
Fig. 8

Temperature profile along the distance from the heating center

Grahic Jump Location
Fig. 9

Surface evolution during laser polishing: time (arrow scale factor): (a) 6.00 ms (12,000), (b) 8.00 ms (50), (c) 10.00 ms (10), and (d) 12.00 ms (8)

Grahic Jump Location
Fig. 10

Curvature evolution of the top surface

Grahic Jump Location
Fig. 11

Development of capillary pressure and thermocapillary pressure: (a) 6.00 ms, (b) 8.00 ms, (c) 10.00 ms, and (d) 12.00 ms

Grahic Jump Location
Fig. 12

Surface evolution in capillary regime (arrow scale factor): (a) 6.00 ms (12,000), (b) 8.00 ms (3500), (c) 10.00 ms (1300), and (d) 12.00 ms (8000)

Grahic Jump Location
Fig. 13

Curvature evolution of the top surface in capillary regime

Grahic Jump Location
Fig. 14

Surface evolution in thermocapillary regime (arrow scale factor): (a) 6.00 ms (8000), (b) 8.00 ms (7000), (c) 10.00 ms (4500), and (d) 12.00 ms (3500)

Grahic Jump Location
Fig. 15

Curvature of the top surface in thermocapillary regime

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