This thesis is focussed on shielding gas optimisation in gas shielded arc welding processes, and has been conducted along two themes; deriving conditions in which the shielding gas flow rate can be safely reduced, and through the highly novel process of alternating shielding gases.The correct shielding gas flow rate is essential for providing adequate protection to the weld metal during the heating, liquid and solidification stages. Hence, there is an optimum shielding gas flow rate, but this is difficult to define and is often decided on the basis of preference or experience.A multi-disciplined, systematic study has been conducted, which has shown that there is considerable scope to reduce the shielding gas flow rate. Experimental trials have shown that the shielding gas flow rate can be reduced, in a draft-free environment, to 6 l/min, with no degradation in weld quality for the worst draft conditions measured in a typical shipyard fabrication hall, at 10 l/min.This study has resulted in shielding gas flow controllers, preset at 12 l/min, being installed in a large shipyard environment, removing the welding operatives ability to increase the shielding gas flow rate.The application of alternating shielding gases offers clear manufacturing cost reduction benefits which arise from measurable increases in productivity, improved distortion control and re-work reduction, and overall improvements to the mechanical properties of the weld. Arc pressure measurements, and the subsequent derivation of forces acting on the liquid weld metal, have indicated that flow vectors for helium are opposite in direction to that produced by argon, creating a dynamic action within the weld pool.Schlieren visualisation has shown that there is a greater degree of helium entrainment in the primary jet due to a constriction of its flow in the secondary jet, influencing the arc's behaviour and inferring more of the associated benefits.
|Date of Award||27 May 2015|
- University Of Strathclyde
|Sponsors||EPSRC (Engineering and Physical Sciences Research Council)|
|Supervisor||Alexander Galloway (Supervisor) & James Wood (Supervisor)|