Research Papers

Thermal Science of Weld Bead Defects: A Review

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

Department of Mechanical and Electro-Mechanical Engineering, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan, China

J. Heat Transfer 133(3), 031005 (Nov 15, 2010) (22 pages) doi:10.1115/1.4002445 History: Received June 15, 2009; Revised March 15, 2010; Published November 15, 2010; Online November 15, 2010

Mechanisms for the formation of bead defects, such as humping, gouging, rippling, and other unexpected surface patterns, encountered in welding or drilling are interpreted and reviewed from thermal-fluid science viewpoint. These defects usually accompanying with porosity, undercut, segregation, stress concentration, etc., seriously reduce the properties and strength of the joint or solidification. Even though different mechanisms for formation of the defects have been extensively proposed in the past, more systematical understanding of pattern formations from thermal, fluid, physics, electromagnetic, pattern selections, and metallurgy sciences is still limited. The effects of working parameters and properties on humping and rippling, for example, can be systematically and quantitatively interpreted from scale analysis presented in this work. Good comparison with experimental results reveals mechanisms of different surface patterns. The mechanistic findings for bead defects are also useful for other manufacturing and materials processing.

Copyright © 2011 by American Society of Mechanical Engineers
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Figure 1

Photographs of rippling in welding Al 6061 for welding speeds of (a) 30 mm/s and (b) 15 mm/s (4)

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Figure 2

Photographs of (a) humps with gouged region and (b) parallel hump in GTAW (38), (c) cylinder beads in GMAW (19), and ((d) and (e)) humps in EBW for different welding speeds (4)

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Figure 3

(A) Morphologies affected by beam power and welding speed (39-40), and (B) molten pool changes with increasing welding speed in low pressure GTAW (39)

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Figure 4

Effects of fiber laser beam diameter and welding speed on weld penetration and welding defect formation (44)

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Figure 5

Scenario of Richtmyer–Meskhow environment in the laser spot on an indium target surface: (a) melted surface with slightly concave shape. The melted surface layer comprises high-temperature and velocity, low-density top layer, and a lower temperature, slow, high-density bottom layer, separated by the density interface (black curve); (b) the density perturbed by the blow-off during pulsed vaporization; (c) the shock wave generated in the center moves toward the periphery and strikes tilted and periodically perturbed interface, causing the vorticity deposition; (d) vorticity evolution and roll-up in the near field zone behind the shock. By the end of pulse, the ultrafast cooling wave generated at the periphery moves toward the center, causing that surface structures to stay frozen permanently in the wavy structures (88).

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Figure 6

Atomic force microscopy images of rippled structure (a) generated at near normal incidence with 400 pulses of a single beam of p-polarized light at a fluence of 0.8 J/cm2. The direction of the projected electric field of the electromagnetic wave is also indicated and (b) irradiated by 50 pulses at a laser fluence of 0.7 J/cm2, using a p-polarized single beam and incident angle of 38.5 deg. Notice tiny little “fingers” in lower rim of fringes and asymmetry in fringe profile taken in downward direction (104).

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Figure 7

Video observation of humping: (A) GMAW (58) and (B) LBW (44)

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Figure 8

Schematic sketch for two states in hydraulic jump (132)

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Figure 9

Photographs of a “starlike hole” in etching Mo films with an Ar+-laser in Cl2 atmosphere with powers (a) 10 mW, (b) 20 mW, (c) 50 mW, (d) 100 mW, (e) 500 mW, and (f) 150 mW (133-134)

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Figure 10

(a) Surface tension as a function of temperature for different surface active solute contents of sulfur and oxygen in iron (169,17) and (b) schematic sketch of Marangoni convection in the presence of a surface active solute (17)

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Figure 11

Comparison between measured and predicted amplitude of ripples in EBW of (a) Al 1100 (15) and (b) alloys containing a surface active solute (17)

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Figure 12

Comparison between scaled and measured average pitches of humps or coarse ripples versus dimensionless parameter governing incident flux and surface tension coefficient of alloys in the absence of volatile elements (4)

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Figure 13

(left) A two-dimensional steady state solution and (right) comparison of the centerline profile (solid curve), with the corresponding one-dimensional solution (dashed curve) (191)



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