In situ micro gas tungsten constricted arc welding of ultra-thin walled 2.275 mm outer diameter grade 2 commercially pure titanium tubing

Abstract

Ultra-thin walled cooling tubes for heat exchangers and condenser units have applications in multiple high-value manufacturing industries. Grade 2 commercially pure titanium (CP-2 Ti) requires far less mass to achieve the same mass flow handling abilities as stainless steel tubing yet it is more challenging to join, particularly at wall thicknesses less than 500 μm (termed ultra-thin walled tube). This paper presents a single-pass joinery method that produces reliable welds on 2.275 mm outer diameter (OD), 160 ± 10 μm wall thickness tubing with a service life of 20 of more years. This is achieved through an automated orbital gas tungsten constricted arc welding (GTCAW) process incorporating enveloping low-mass sleeves used in tandem with a buttressing internal gas pressure to support the molten metal and maintain consistent internal diameter inside the tube. The industrial applicability is demonstrated through the production of a 1:1 scale mock-up of a fixed geometry CO2 cooling circuit for a next-generation particle detector. The tensile strengths of the joints, 403.8 ± 4.2 MPa, exceed the tensile strength of the parent CP-2 Ti.

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

“…. 6.2 Produced part (a) and CAD model (b) of high-value cooling circuit for a two phase CO 2 cooling plant presented in [8]. The joints are highlighted green in (b).…”

“…This is undertaken through a combination of experimental and simulation work. The experimental work was undertaken as part of the development for the ATLAS ITK [8] and was performed with the goal of rapidly achieving production capabilities rather than for the purpose of investigating the physics of ultrathin-walled tube welding. The simulation work thus adapts to the available experimental data to benchmark against it before being extended to predict a general case.…”

“…Hence, this is an application of ultra-thin-walled tube welding. Figure 6.2 shows a demonstration two phase CO 2 cooling plant for the ATLAS ITk presented in [8]. Despite the attractive properties of titanium (high strength to weight ratio and excellent corrosion resistance), welding challenges have encumbered its industrial application in ultra-thin-walled tubing.…”

“…Finally, this general case is presented to answer to main research question of this thesis. Parts of the chapter are adapted from the paper 'In situ micro gas tungsten constricted arc welding of ultra-thin walled 2.275 mm outer diameter grade 2 commercially pure titanium tubing' principally written by the author [8]. The author was involved in the experimental welding trials although these were principally performed by Sam Edwards and Paul Kemp-Russell.…”