A contribution to adaptively controlled robotic arc welding

Mathematical models have been devised expressing the levels of controllable welding factors as a function of the joint geometry, such that acceptable weld beads are produced. Weld beads were required to be both geometrically acceptable and mechanically sound despite changes in the root face thickness (0.5 mm - 2.5 mm) and root gap (0 - 1.5 mm). The equations are intended to form part of an adaptively controlled robotic arc welding system. Simulation was used to develop the adaptive expressions. The study was applied to the root weld bead of the closing seam of railway bogie side frames fabricated from structural steel. The self shielding flux cored electrode arc welding process was used to weld single J preparations orientated in the horizontal-vertical position. Single sided full penetration welds with underbeads were required. The weld bead geometry was defined in terms of ten responses. Mathematical models derived from factorially designed experiments were used to relate the weld bead geometry, incidence of porosity and the occurrence of electrode stubbing to a function of upto seven factors. A data base of almost 1000 test welds was generated, in which each test was characterised by 76 pieces of information. Analysis of variance was used to determine which factors most influenced each of the responses. Multiple regression enabled an expression for each response to be derived as a function of the welding factor levels. The weld bead geometry model consisted of ten equations, each a function of upto six factors, whilst the soundness model related the optimum welding voltage to a function of three factors so that porosity and electrode stubbing would not be encountered.