Investigation of the dynamic strength of weld beads applied by robot mechanisms

Welded joints are common in machine construction, shipbuilding, bridge and some other production. Design, manufacturing and operating conditions are some determinants that affect fatigue life of these joints. There are design codes, standards, and guidelines for the service of welded joints safely throughout the life designated. Numbers of determiners that affect fatigue life of welded joints complicate calculation of fatigue strength of weld. For the sake of simplicity, factors are wide in use for calculation. Excessive resistant weld bead causes over-costing of joint due to amount of filler metal, process time required for filling, and labor. Hence, adequate bead thickness and geometry should be specified considering both safety and cost. Welding robots are widely used in industrial applications because of the fact that they can apply weld beads qualitatively and repetitively. In this study, the factors were investigated experimentally and numerically. A linear fatigue testing machine that subjects dynamic variable load was designed and manufactured. An electromechanical cylinder was utilized for testing and programmed for force control. Single and double bevel T-joints with concave, convex and fillet weld beads were tested. Finite element analysis and test results were assessed and dynamic loading factors were proposed.