Scaling of spiking and humping in keyhole welding

Abstract

Spiking, rippling and humping seriously reduce the strength of welds. The effects of beam focusing, volatile alloying element concentration and welding velocity on spiking, coarse rippling and humping in keyhole mode electron-beam welding are examined through scale analysis. Although these defects have been studied in the past, the mechanisms for their formation are not fully understood. This work relates the average amplitudes of spikes to fusion zone depth for the welding of Al 6061, SS 304 and carbon steel, and Al 5083. The scale analysis introduces welding and melting efficiencies and an appropriate power distribution to account for the focusing effects, and the energy which is reflected and escapes through the keyhole opening to the surroundings. The frequency of humping and spiking can also be predicted from the scale analysis. The analysis also reveals the interrelation between coarse rippling and humping. The data and the mechanistic findings reported in this study are useful for understanding and preventing spiking and humping during keyhole mode electron and laser beam welding.

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][21][22][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 u s and u e , associated with widths w and w e 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]…”

“…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.…”

Incapability of Drilling With a High-Power-Density Beam

“…In view of dimensionless and fundamental analysis, the results are generally valid for different materials. For any given dimensionless parameters Q, M cB , J eB , U * , and p 2 , efficiency can be improved by choosing surrounding gas or shield gas with small ionization to reduce energy absorption [51], reducing the strength of the Knudsen layer on the keyhole base [52], [53] and intensity of the incident flux [54], and increasing the surrounding pressure to avoid occurrence of the shock wave in the keyhole [49], respectively.…”

Understanding of humping formation and suppression mechanisms using the numerical simulation

“…Chen [5] developed a mathematic model to quantitatively analyze the formation mechanism of humping, the momentum and heat content of the backward flowing molten metal were considered. The humping formation in high speed laser welding and gas tungsten arc welding was also researched [6][7][8][9] . Many methods have been proposed to inhibit the formation of humping, such as laser +GMAW hybrid welding process [10][11] , DE-GMAW [12] , twin wire GMAW process [13] .…”