High speed fusion weld bead defects

Abstract

A comprehensive survey of high speed weld bead defects is presented with strong emphasis on the formation of humping and undercutting in autogenous and non-autogenous fusion welding processes. Blowhole and overlap weld defects are also discussed. Although experimental results from previous studies are informative, they do not always reveal the physical mechanisms responsible for the formation of these high speed weld bead defects. In addition, these experimental results do not reveal the complex relationships between welding process parameters and the onset of high speed weld bead defects. Various phenomenological models of humping and undercutting have been proposed that were based on observations of events in different regions within the weld pool or the final weld bead profile. The ability of these models to predict the onset of humping or undercutting has not been satisfactorily demonstrated. Furthermore, the proposed formation mechanisms of these high speed weld bead defects are still being questioned. Recent welding techniques and processes have, however, been shown to be very effective in suppressing humping and undercutting by slowing the backward flow of molten metal in the weld pool. This backward flow of molten weld metal may be the principal physical phenomenon responsible for the formation of humping and undercutting during high speed fusion welding.

Undercuts in Laser Arc Hybrid Welding

“…by LBW and LAHW, undercuts have become a more severe issue, Kaplan, et al (2007). In fusion welding the speed is often limited by the occurrence of undercuts, coupled with high power the speed can be further limited by other imperfections such as humping, Nguyen, et al (2006), Soderstrom and Mendez (2006). Undercut formation is generated by solidification (dependent on heat conduction) and melt flows, which is dependent on chemistry-and temperature-dependent viscosity and surface tension.…”

A Review on Melt‐Pool Characteristics in Laser Welding of Metals

“…e travel angle between the laser beam and the welding direction has been found to affect the onset of humping. Forehand welding has been shown to suppress hump formation to higher welding speeds [101,102]. Gratzke et al [103] defined a critical ratio of the width to the length of the melt-pool, which determined the likelihood of hump formation, such that maximizing this ratio during welding decreases the possibility of hump formation.…”

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.…”