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Research Papers

Modeling of Cold Metal Transfer Spot Welding of AA6061-T6 Aluminum Alloy and Galvanized Mild Steel

[+] Author and Article Information
Zhenghua Rao

School of Energy Science and Engineering,
Central South University,
Changsha, Hunan 410083, China
e-mail: raoz@csu.edu.cn

Jiangwei Liu

School of Energy Science and Engineering,
Central South University,
Changsha, Hunan 410083, China
e-mail: liujiangwei1988@gmail.com

Pei-Chung Wang

Global Research and Development Center,
General Motors Corporation,
Warren, MI 48090
e-mail: pei-chung.wang@gm.com

Yunxiao Li

School of Energy Science and Engineering,
Central South University,
Changsha, Hunan 410083, China
e-mail: yunxiao546823810@gmail.com

Shengming Liao

School of Energy Science and Engineering,
Central South University,
Changsha, Hunan 410083, China
e-mail: smliao@csu.edu.cn

1Corresponding author.

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING. Manuscript received February 3, 2013; final manuscript received May 7, 2014; published online August 6, 2014. Assoc. Editor: Wei Li.

J. Manuf. Sci. Eng 136(5), 051001 (Aug 06, 2014) (11 pages) Paper No: MANU-13-1046; doi: 10.1115/1.4027673 History: Received February 03, 2013; Revised May 07, 2014

In this article, a three-dimensional (3D) transient unified model is developed to simulate the transport phenomena during the cold metal transfer (CMT) spot welding process of 1 mm thick aluminum AA6061-T6 and 1 mm thick galvanized mild steel (i.e., AISI 1009). The events of the CMT process are simulated, including arc generation and evolution; up-and-down movement of electrode, droplet formation and dipping into the weld pool; weld pool dynamics; zinc evaporation, and zinc vapor diffusion in the arc. The effects of the gap between the two workpieces and effects of zinc vapor evaporated from the steel surface on CMT process are studied. The results show that the arc temperature, velocity, and pressure keep changing during the CMT process, which is related to the variations of welding current, arc length, and zinc evaporation. It is found that the zinc evaporation leads to the extremely high arc pressure and the upward flow of zinc vapor near the steel surface, which would induce the arc instability and provide the drag force for the droplet impingement. The presence of the gap between the two workpieces can improve the expansion of the arc plasma, resulting in the smaller arc pressure and the more intensive upward flow of zinc vapor from the steel surface. The phenomena observed in the experiment are in agreement with the modeling results.

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Figures

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Fig. 1

Schematic sketch of the CMT joining process and the fixed 3D x–y–z coordinate system; the hole is perforated in the center of the workpiece 1.

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Fig. 2

The welding current (I) and voltage (U) waveforms used in CMT joining of 1 mm thick aluminum AA6061-T6 and 1 mm thick galvanized AISI 1009 steel

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Fig. 3

The physical properties for mixture of zinc vapor and argon: (a) density, (b) electric conductivity, (c) thermal conductivity, and (d) dynamic viscosity

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Fig. 4

The sequence of temperature distribution in plasma arcs at various instants in CMT joining of 1 mm thick aluminum AA6061-T6 and 1 mm thick galvanized AISI 1009 steel without the gap

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Fig. 5

The sequence of velocity distribution in plasma arcs at various instants in CMT joining of 1 mm thick aluminum AA6061-T6 and 1 mm thick galvanized AISI 1009 steel without the gap

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Fig. 6

The sequence of concentration distribution of zinc vapor in plasma arcs at various instants in CMT joining of 1 mm thick aluminum AA6061-T6 and 1 mm thick galvanized AISI 1009 steel without the gap

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Fig. 7

The sequence of arc pressure distribution at various instants in CMT joining of 1 mm thick aluminum AA6061-T6 and 1 mm thick galvanized AISI 1009 steel without the gap

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Fig. 8

The distributions of the main physical variables at various instants in CMT joining of 1 mm thick aluminum AA6061-T6 and 1 mm thick AISI 1009 steel with a gap of 0.2 mm: (a) arc temperature, (b) plasma velocity, (c) zinc vapor concentration, and (d) arc pressure

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Fig. 9

The comparison of arc pressure distribution between the cases with and without gap at the different instants: (a) inside the hole (at z = −0.5 mm), and (b) along the surface of workpiece 1 (at z = 0)

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Fig. 10

The distributions of the main physical variables at various instants in CMT joining of 1 mm thick aluminum AA6061-T6 and 1 mm thick AISI 1009 steel without zinc coating: (a) arc temperature, (b) plasma velocity, and (c) arc pressure

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Fig. 11

The comparison of arc pressure distribution between the cases with and without zinc coating at the different instants: (a) inside the hole (at z = −0.5 mm), and (b) along the surface of workpiece 1 (at z = 0)

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Fig. 12

Schematic of CMT welding system in the experiment (Dimensions in mm)

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Fig. 13

Images for the CMT spot welding process of 1 mm thick AA6061-T6 aluminum alloy and 1 mm thick galvanized AISI 1009 steel

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Fig. 14

Weld joint for the CMT spot welding of 1 mm thick AA6061-T6 aluminum alloy and 1 mm thick galvanized AISI 1009 steel

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