Burr grinder: Advanced & effective post weld toe treatment to optimize fatigue life of welded structures

Abstract

Earth-moving machines are exposed to the repeated fluctuating stresses which cause fatigue cracks at the toe and throat of welded joints due to the metallurgical imperfections. So welding joints is the weak region for the components of all earth-moving machines and acts as a determining factor of expected life of earth-moving machines. Also due to this, welded joints must be fully understood to improve the fatigue and service life of the earth-moving machines. Here failure at throat can be minimized by achieving optimum strength but problem of weld toe cracking only be eliminated by reducing stress concentration at weld toe. To do this, R & D work has been initiated by preparing set of five T-joint weld samples having 8mm (sample F to J) throat thickness with one as-welded sample i.e. J (without post weld toe treatment) for benchmarking purpose has been prepared using GMAW welding process. For the toe grinding of samples F to J post weld toe grinding treatment as per IIW guidelines with cylindrical & hemispherical burr tool, cutter (A24PBF) and flap disc grinder respectively has been applied to reduce the stress concentration at weld toe by making smooth transition at weld toe with undercut of 1mm. Using UG NX 7.5, solid models of T-Joint shaped with sample size of 170 × 192 × 8mm has been created from the images of etched weld toe profile. Post weld toe treated with hemispherical burr tool has given maximum optimization in fatigue life of 76% as compared to as-welded samples i.e. J and validated by hardness testing at Heat affected zone (HAZ) of etched samples which shows that graph of alternating stress and fatigue limit shows almost parallel trend and differs by proportionality constant.