Theoretical approach to the humping phenomenon in welding processes

Abstract

The conjecture which explains the humping phenomenon in terms of Marangoni convection is discussed and rejected. Instead, Rayleigh's theory of the instability of a free liquid cylinder due to surface tension is applied. The width-to-length ratio of the weld pool has to exceed 1/2 pi to avoid humping. The growth time of a disturbance is found to be approximately the same as the growth time of a hump. The analysis of a bounded cylinder provides a new stability criterion which allows the introduction of a bounding function to distinguish between arc and laser welding. The weld pool dimensions are estimated in terms of a simple heat conduction model. The threshold value predicted theoretically for the travel speed above which humping commences agrees well with the experimental value. It decreases with increasing power, which is in qualitative agreement with experimental results.

Research on Humping Tendency in High Speed Laser Welding of SUS304 Austenitic Stainless Steel

“…In general, the forces acting on the weld pool are surface tension and gravity. Gratzke [12] analyzed the influence of gravity on weld pool and considered that gravity was negligible in laser welding. We assume that molten metal forms a liquid cylinder and suspend freely in space under the effect of surface tension.…”

Quality assessment in laser welding: a critical review

“…It can be noticed at high speeds, while the weld pool shape plays a significant role in the formation of humping. As it was explained in [21], the governing quantity of the humping phenomenon is the width-to-length ratio of the weld pool. It has to remain below the critical value for the occurrence of humping while the increase in the ratio can prevent humping.…”

Physical Mechanisms and Mathematical Models of Bead Defects Formation During Arc Welding

“…Kelvin-Helmholtz instability Gratzke et al, 1992 Capillary instability model for humping Lin & Eagar, 1983 Explained humping using vortex theory Mendez & Eagar, 2003 Simple model for force balance between the gouged region and trailing region inside weld pool Nguyen et al, 2005Nguyen et al, , 2006 Experimental study of hump formation by the instrumentality of LaserStrobe video imaging system; hump bead as a series of periodic fluctuation of swellings is one of dominating defect in high speed welding Soderstrom & Mendez, 2006 Two types of humping formation: gouging region and beaded cylinder Kumar & DebRoy, 2006 Unified mathematical model of humping in GTAW with KelvinHelmholtz instability Thermohydrodynamic mathematical model and numeric analysis of hybrid process for prevention of weld bead hump formation Chen & Wu, 2009 Thermohydrostatic mathematical model and numerical analysis of forming mechanism of hump bead in high speed GMAW Table 2. Selected papers on the study of the humps formation and the creation of the correspondent models.…”

“…He has established that the hump defect was observed only at a high travel speed, that a leading ("push") weld gun travel angle suppressed hump formation, and that oxygen in the shielding gas exacerbated hump formation. He proposed a liquid instability theory that was later modified by Gratzke et al, 1992 explaining humping during GMAW. Shimada, 1975 andHoshinouchi, 1982 used the theory of hydraulic jump to account not only for an undercut, but also for the humping phenomenon, Fig.…”