The Physics of Weld Bead Defects

Scaling of amplitude and pitch of surface ripples after welding solidification

“…A scale analysis confirmed by numerical results is valuable for a general, clear, quantitative and parametric study [20-23]. Extending previous scale analysis [3, 8, 15, 19], the present study scales average amplitude and pitches of ripples by further accounting for the effects of solid speed, solidification rate or scanning speed of energy beam, and oscillation frequency of liquid flow. Amplitude and space of surface ripples after solidification are found to be scaled by Equations (13) and (20) including transport variables of fluid velocities and , associated with widths w and of central and edge regions of the molten pool.…”

“…The Young–Laplace equation evaluated at the left side and edge of the pool, respectively, yield [3, 8, 15, 19] Subtracting between two equations in Equation (11) and scaling give …”

“…Productivity in different welding techniques can be enhanced by increasing welding speed and electric current. This strategy, however, is limited by the appearance of surface defects such as rippling, humping and undercutting [1-8], which are suffering from stress concentration, solute segregation, porosity and so on. Weld ripples exhibit rather regular, arc-shaped topographic features on a solidified surface.…”

“…Surface rippling can be resulting from solidification rate fluctuations, power source effects, thermocapillary instability, Kelvin–Helmholtz instability, Rayleigh–Taylor instability, thermocapillary edge flow, etc. [3, 8].…”

“…Provided that the scanning speed exceeded a critical velocity, insufficient time could avoid rippling formation. Recognising vertical displacement of the triple-phase line at the pool edge to be responsible for rippling formation, Wei et al [3, 8, 15, 19] provided a scale analysis [20-23] to predict surface roughness on pure metals and alloys affected by thermocapillary force balanced by shear stress and inertial force in the shear layer beneath the free surface subject to the incident flux. In view of change in pressure from the central to edge regions of the molten pool mechanical energy loss was accounted.…”