Abstract:
The railway industry wants to obtain structural welded joints that have optimum weld strength and fatigue life. Since the variance of welding parameters producing welding defects and weak structural integrity, there are uncertainties in the selecting the welding parameters that produce a good structural welded joint with the necessary weld quality. This necessitates the optimisation of the welding parameters to produce welded joints with improved mechanical properties.
The impact of various welding parameters (i.e. wire-feed speed (WFS), voltage and travel speed) on the ultimate tensile strength (UTS) and fatigue life of S355J2+N single V butt weld produced by metal inert gas (MIG) robotic welding was experimentally investigated. The design of experiments (DOE) approach was used to optimise the welding parameters to ensure the reliability of the experimental results. A removable ceramic weld backing bar was used to improve weld root penetration and minimise the risk of lack of fusion. To ensure weld quality and reliability of the experimental results the flush ground welded joints were used to minimise the geometric notch effect. A minimum number of two specimens for each number of experiments were tested to ensure the correct evaluation of welds. The magnetic particle testing (MT) technique was used to detect the welding defects that might have an impact on the material properties of the welded joints. Analysis of variance (ANOVA) was used to precisely demonstrate which welding parameters had the greatest impact on the performance output of the welded joint and to determine interactions between welding parameters.
It was observed that varying the welding parameters had an impact on the weld quality. An increase in voltage and travel speed at lower WFS are the primary contributing factors to weld defects. Only the defect-free specimens were tested to avoid making the experimental results inconclusive for statistical analysis. According to the ANOVA results, voltage and travel speed interact to affect the welded joint’s UTS. Increasing voltage increases the UTS of the welded joints at the higher ranges of travel speed, while decreasing the UTS in the lower and medium range of travel speed. The most influential welding parameter that affects the UTS of the welded joint is travel speed. The fatigue life of the welded joint is affected by interactions between WFS and travel speed, as well as the voltage and travel speed. Increasing WFS increases the fatigue life at the medium range of travel speed. When welding at lower speed, the fatigue life duration becomes longer as the voltage increases. The fatigue life of the welded joint is significantly influenced by the WFS. The optimal welding parameters for the welded joint is A2B1C1 (i.e. WFS at level 2, voltage at level 1 and travel speed at level 1) for better UTS and fatigue life.
This research reduces uncertainties in the selection of optimum settings of welding parameters of a MIG welded joint. The welding parameters that significantly affect the welded joint mechanical properties performance were identified. The optimum welding parameters selection for UTS and fatigue life can be developed. Undesirable welding defects that affect the structural integrity of the welded joint can be minimised by an improved selection of welding parameters.
