Multiphysics modelling of Gas Tungsten Arc Welding on ultra-thin-walled titanium tubing

TL;DR

This thesis introduces gtawFoam, a novel multiphysics simulation tool for orbital Gas Tungsten Arc Welding on ultra-thin titanium tubing, validated against experiments and used to optimize welding parameters for different wall thicknesses.

Contribution

The paper develops and benchmarks a new open-source multiphysics solver, gtawFoam, for simulating orbital GTAW on ultra-thin titanium tubing, including additive manufacturing aspects.

Findings

A 'goldilocks' region for optimal welding identified

Heat input and gas pressure are critical for full penetration

Simulation results guide effective welding procedures for various wall thicknesses

Abstract

This thesis presents a novel multiphysics solver, named gtawFoam, for Gas Tungsten Arc Welding (GTAW) that is applied to simulate orbital GTAW on ultra-thin-walled titanium tubing. In this thesis, ultra-thin-walled tubing refers to tubing where the wall thicknesses are less than 500 $\mu m$. Orbital welding of tubing with this wall thickness requires both a sufficient heat input to weld the tubing and an internal buttressing gas flow to ensure the tube retains its geometrical integrity. The specific use case is for the commercially pure grade 2 titanium tubing used in the ATLAS ITk cooling system which is 2.275 $mm$ outer diameter and 300 $\mu m$ wall thickness at the weld. The solver is created using the open source computational fluid dynamics library OpenFOAM and each component of the solver is benchmarked against an appropriate case. With the solver established, it is used to simulate a series of welding procedures that were performed experimentally on the aforementioned titanium tubing. Both the experimental and simulation results show a `goldilocks' region where the weld heat input and inner buttressing gas flow are moderated to a level where a fully penetrating weld is created but the geometric integrity of the tube is not compromised. gtawFoam is then used to simulate hypothetical tubing with larger and smaller wall thicknesses between 250 $\mu m$ and 350 $\mu m$. The results suggest that the required buttressing gas pressure once achieved is relatively transferable between wall thickness changes but applying enough heat so as to achieve full penetration is critical. These results are then used to predict effective welding procedures for this hypothetical tubing. gtawFoam is subsequently applied to the welding of turbine blades. This includes the addition of multiple layers of filler metal to mimic additive manufacturing.