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Research Papers: Heat Transfer in Manufacturing

The Effects of Entrainment on Pore Shape in Keyhole Mode Welding

[+] Author and Article Information
P. S. Wei

Professor
Department of Mechanical
and Electro-Mechanical Engineering,
National Sun Yat-Sen University,
Kaohsiung 80424, Taiwan, ROC
e-mail: pswei@mail.nsysu.edu.tw

T. C. Chao

Department of Mechanical
and Electro-Mechanical Engineering,
National Sun Yat-Sen University,
Kaohsiung 80424, Taiwan, ROC
e-mail: m993020071@student.nsysu.edu.tw

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received July 23, 2014; final manuscript received November 5, 2014; published online April 16, 2015. Assoc. Editor: Zhixiong Guo.

J. Heat Transfer 137(8), 082102 (Aug 01, 2015) (9 pages) Paper No: HT-14-1488; doi: 10.1115/1.4029039 History: Received July 23, 2014; Revised November 05, 2014; Online April 16, 2015

This study theoretically investigates the effects of the entrainment accompanying mass, momentum, and energy transport on pore size during high power density laser and electron beam welding processes. The physics of macroporosity formation is not well understood, even though macroporosity often occurs and limits the widespread industrial application of keyhole mode welding. This work is an extension of a previous work dealing with collapses of keyholes induced by high intensity beam drilling. In order to determine the pore shape, this study, however, introduces the equations of state at the times when the keyhole is about to be enclosed and when the temperature drops to melting temperature. The gas pressure required at the time when keyhole collapses is determined by calculating the compressible flow of the two-phase, vapor–liquid dispersion in a vertical keyhole with varying cross sections, paying particular attention to the transition between annular and slug flows. It is found that the pore size increases as entrainment fluxes decrease in the lower and upper regions of the keyhole containing a supersonic mixture. The pore size also increases with decreasing total energy of entrainment and an increasing axial velocity component ratio between entrainment and mixture through the core region. With a subsonic mixture in the keyhole, the final pore size increases with entrainment fluxes in the lower and upper regions. This work provides an exploratory and systematical investigation of pore size induced by entrainment accompanied by mass, momentum, and energy transport during keyhole mode welding.

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References

Figures

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Fig. 1

Porosity occurs in the welding of Al 5083 [26]

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Fig. 2

(a) The physical model and coordinate system and (b) pore formation from the enclosure of the keyhole

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Fig. 3

Comparison of axial variations in dimensionless mixture temperature, pressure, Mach number, and keyhole radius for (a) different grid systems, and between (b) exact closed-form and numerical results for a supersonic flow, and (c) exact closed-form and numerical results for a subsonic flow subject to different ejected mass fluxes at the base

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Fig. 4

The effects of dimensionless ejected mass flux at the base on (a) dimensionless final pore size, maximum length, radius, and volume and (b) dimensionless average temperature and pressure when the keyhole containing a supersonic mixture is about to be closed

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Fig. 5

The effects of dimensionless ejected mass flux at the base on (a) dimensionless final pore size, maximum length, radius, and volume and (b) dimensionless average temperature and pressure when the keyhole containing a subsonic mixture is about to be closed

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Fig. 6

The effects of entrainment flux in the lower region of the keyhole on (a) dimensionless final pore size, maximum length, radius, and volume and (b) dimensionless average temperature and pressure when the keyhole containing a supersonic mixture is about to be closed

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Fig. 7

The effects of entrainment flux in the lower region of the keyhole on (a) dimensionless final pore size, maximum length, radius, and volume and (b) dimensionless average temperature and pressure when the keyhole containing a subsonic mixture is about to be closed

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Fig. 8

The effects of entrainment and deposition fluxes in the upper region of the keyhole on (a) dimensionless final pore size, maximum length, radius, and volume and (b) dimensionless average temperature and pressure when the keyhole containing a supersonic mixture is about to be closed

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Fig. 9

The effects of entrainment flux in the upper region of the keyhole on (a) dimensionless final pore size, maximum length, radius, and volume and (b) dimensionless average temperature and pressure when the keyhole containing a subsonic mixture is about to be closed

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Fig. 10

The effects of dimensionless total energy of entrainment on (a) dimensionless final pore size, maximum length, radius, and volume and (b) dimensionless average temperature and pressure when the keyhole containing a supersonic mixture is about to be closed

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Fig. 11

The effects of axial velocity ratio between entrainment and mixture flow through the keyhole on (a) dimensionless final pore size, maximum length, radius, and volume and (b) dimensionless average temperature and pressure when the keyhole containing a supersonic mixture is about to be closed

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