Three-dimensional numerical simulation of arc and metal transport in arc welding based additive manufacturing

The metal transfer is a fundamental process in gas metal arc welding, which substantially determines the shape of the weld seam and strongly influences arc formation and stability. In this investigation the material transfer from the wire electrode (anode) to the workpiece (cathode) is analysed experimentally with high accuracy using various innovative diagnostic techniques for a pulsed gas metal arc welding (PGMAW) process. A high-speed two-colour pyrometer, a calorimeter, thermocouples, a stereo optical setup and a droplet oscillation technique are used to analyse a precisely defined PGMAW process. Thus, results obtained are verified by different measurement techniques and enable a comprehensive description of the material transfer procedure.The surface temperature of both electrodes as well as the droplet temperature, enthalpy and surface tension were determined. Furthermore, the geometry of the arc, wire, droplets and weld pool were extracted in three dimensions in order to describe the interaction between the material transfer and the formation of the weld seam. The experiments are performed using argon as shielding gas and pure iron as filler and base material to reduce complex chemical processes. It turned out that the wire feed rate has the biggest influence on droplet temperature and detachment. A correlation between weld pool formation and weld pool surface temperature gradient was observed, which is mainly a function of welding speed and wire feed rate. The experimental results obtained provide a detailed data pool for use in modelling.

https://iopscience.iop.org/article/10.1088/0022-3727/46/22/224008/pdf

Determination of enthalpy, temperature, surface tension and geometry of the material transfer in PGMAW for the system argon-iron

Numerical investigation of weld pool behaviors and ripple formation for a moving GTA welding under pulsed currents

Hybrid welding, which is the integration of laser beam welding (LBW) and gas metal arc welding (GMAW), may minimise the disadvantages while retaining the advantages for each of the two welding technologies and, hence, has recently received increasing interest in the welding industry. However, the hybrid welding involves very complex transport phenomena which are inherited from each of LBW and GMAW and their interactions. The development of hybrid welding has been based on the trial and error procedure and so far rather limited numerical modelling on hybrid welding is available. This paper presents an up to date literature review on modelling of the hybrid welding including LBW and GMAW. Issues and challenges for a comprehensive hybrid welding model are discussed. With the advances of numerical techniques and computers, a comprehensive hybrid welding model can be developed as a useful tool for determining key process parameters and helping the elimination/reduction of possible weld defects.

Modelling of hybrid laser–GMA welding: review and challenges

Various kinds of multi-electrode welding processes are used to ensure high productivity in industrial fields such as shipbuilding, automotive manufacturing and pipe fabrication. However, it is difficult to obtain the optimum welding conditions for a specific product, because there are many operating parameters, and because welding phenomena are very complicated. In the present research, the heat source characteristics of a two-electrode TIG arc were numerically investigated using a 3D arc plasma model with a focus on the distance between the two electrodes. The arc plasma shape changed significantly, depending on the electrode spacing. The heat source characteristics, such as the heat input density and the arc pressure distribution, changed significantly when the electrode separation was varied. The maximum arc pressure of the two-electrode TIG arc was much lower than that of a single-electrode TIG. However, the total heat input of the two-electrode TIG arc was nearly constant and was independent of the electrode spacing. These heat source characteristics of the two-electrode TIG arc are useful for controlling the heat input distribution at a low arc pressure. Therefore, these results indicate the possibility of a heat source based on a two-electrode TIG arc that is capable of high heat input at low pressures.

https://iopscience.iop.org/article/10.1088/0022-3727/44/21/215202/pdf

Numerical analysis of the heat source characteristics of a two-electrode TIG arc

Distinct, periodic arc-shaped ripples are observed on the surface of the weld bead in almost any welded components which have a significant effect on weld quality. This article presents the complex transport phenomena and their effect on the formation of ripples in three-dimensional moving gas metal arc welding. The transient distributions of the melt flow velocity and temperature in the weld pool, weld pool shape and dynamics, and solidified weld bead are calculated. It is found that the surface ripples are formed by the interplay between the up-and-down weld pool dynamics, caused mainly by the periodic droplet impingements, and the rate of weld pool solidification. The effects of various welding parameters, including the welding current, droplet size, droplet frequency, droplet impinging velocity, and travel speed on the pitch (distance between two ripples) and height of the ripple are investigated. This study provides fundamental understanding to the underlying physics that cause the formation of ripples with different pitches and heights.

/pdf/three-dimensional-modeling-of-transport-phenomena-and-their-17uyt5z2qr.pdf

Three-dimensional modeling of transport phenomena and their effect on the formation of ripples in gas metal arc welding

This article presents the effects of shielding gas compositions on the transient transport phenomena, including the distributions of temperature, flow velocity, current density, and electromagnetic force in the arc and the metal, and arc pressure in gas metal arc welding of mild steel at a constant current input. The shielding gas considered includes pure argon, 75% Ar, 50% Ar, and 25% Ar with the balance of helium. It is found that the shielding gas composition has significant influences on the arc characteristics; droplet formation, detachment, transfer, and impingement onto the workpiece; and weld pool dynamics and weld bead profile. As helium increases in the shielding gas, the droplet size increases but the droplet detachment frequency decreases. For helium-rich gases, the current converges at the workpiece with a “ring” shape which produces non-Gaussian-like distributions of arc pressure and temperature along the workpiece surface. Detailed explanations to the physics of the very complex but interesting transport phenomena are given.

/pdf/effects-of-shielding-gas-compositions-on-arc-plasma-and-4ye8fsp0ef.pdf

Z. H. Rao

Papers

Three-dimensional modeling of transport phenomena and their effect on the formation of ripples in gas metal arc welding

Effects of shielding gas compositions on arc plasma and metal transfer in gas metal arc welding