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TECHNICAL PAPERS: Heat Transfer in Manufacturing

Porosity Formation and Prevention in Pulsed Laser Welding

[+] Author and Article Information
Jun Zhou

Department of Mechanical and Electrical Engineering Technology, Georgia Southern University, Engineering Technology Bldg., Room 1126, 232 Forest Drive, Statesboro, GA 30460jzhou@georgiasouthern.edu

Hai-Lung Tsai

Department of Mechanical and Aerospace Engineering, University of Missouri-Rolla, 207 Mechanical Engineering, 1870 Miner Circle, Rolla, MO 65409tsai@umr.edu

J. Heat Transfer 129(8), 1014-1024 (Sep 05, 2006) (11 pages) doi:10.1115/1.2724846 History: Received January 19, 2006; Revised September 05, 2006

Porosity has been frequently observed in solidified, deep penetration pulsed laser welds. Porosity is detrimental to weld quality. Our previous study shows that porosity formation in laser welding is associated with the weld pool dynamics, keyhole collapse, and solidification processes. The objective of this paper is to use mathematical models to systematically investigate the transport phenomena leading to the formation of porosity and to find possible solutions to reduce or eliminate porosity formation in laser welding. The results indicate that the formation of porosity in pulsed laser welding is caused by two competing factors: one is the solidification rate of the molten metal and the other is the backfilling speed of the molten metal during the keyhole collapse process. Porosity will be formed in the final weld if the solidification rate of the molten metal exceeds the backfilling speed of liquid metal during the keyhole collapse and solidification processes. Porosity formation was found to be strongly related with the depth-to-width aspect ratio of the keyhole. The larger the ratio, the easier porosity will be formed, and the larger the size of the voids. Based on these studies, controlling the laser pulse profile is proposed to prevent/eliminate porosity formation in laser welding. Its effectiveness and limitations are demonstrated in the current studies. The model predictions are qualitatively consistent with reported experimental results.

Copyright © 2007 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematic sketch of a pulsed laser welding process

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Figure 2

A sequence of liquid metal evolution showing porosity formation

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Figure 3

The corresponding temperature distributions for the case as shown in Fig. 2

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Figure 4

The corresponding velocity distributions for the case as shown in Fig. 2

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Figure 5

Laser pulse profile used to generate (a) a small depth-to-width ratio keyhole; (b) a medium depth-to-width ratio keyhole; and (c) a large depth-to-width ratio keyhole

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Figure 6

A sequence of liquid metal evolution during the keyhole collapse and solidification in a small depth-to-width ratio keyhole welding process

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Figure 7

The corresponding temperature distributions for the case as shown in Fig. 6

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Figure 8

The corresponding velocity distributions for the case as shown in Fig. 6

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Figure 9

A sequence of liquid metal evolution during the keyhole collapse and solidification in a large depth-to-width ratio keyhole welding process

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Figure 10

The corresponding temperature distributions for the case as shown in Fig. 9

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Figure 11

The corresponding velocity distributions for the case as shown in Fig. 9

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Figure 12

The effect of depth-to-width ratio on pore formation for constant keyhole depth

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Figure 13

Laser pulse profiles used to reduce/eliminate pore/void formation for a keyhole with (a) a medium depth-to-width ratio and (b) a large depth-to-width ratio

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Figure 14

A sequence of liquid metal evolution during pore/void reduction/elimination for a medium depth-to-width ratio keyhole welding process by using the pulse profile in Fig. 1

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Figure 15

The corresponding temperature distributions for the case as shown in Fig. 1

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Figure 16

The corresponding velocity distributions for the case as shown in Fig. 1

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Figure 17

A sequence of liquid metal evolution during pore reducing/elimination for a large depth-to-width ratio keyhole welding process by using the pulse profile in Fig. 1

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Figure 18

The corresponding temperature distributions for the case as shown in Fig. 1

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Figure 19

The corresponding velocity distributions for the case as shown in Fig. 1

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