Search Results (2)

In this study, the GMAW welding torch was controlled by a stepping motor to achieve a periodic swing. By controlling the swing speed, a micro-variable deposition path was obtained, which was called the micro-control deposition trajectory. The influence of the micro-control deposition trajectory on the arc characteristics, microstructure, and mechanical properties of 304 steel wire arc additive manufacturing was studied. The results showed that the micro-control deposition process was affected by the swing arc and the deposition trajectory and that the arc force was dispersed over the whole deposition layer, which effectively reduced the welding heat input. However, the arc centrifugal force increased with the increase in the swing speed, which easily caused instability of the arc and large spatter. Compared with common thin-walled deposition, the deposition width of micro-control thin-walled deposition components was increased. In addition, the swinging arc had a certain stirring effect on the molten pool, which was conducive to the escape of the molten pool gas and refinement of the microstructure. Below, the interface of the deposition layer, the microstructure of the common thin-walled deposition components, and the micro-control thin-walled deposition components were composed of lathy ferrite and austenite. Compared with the common deposition, when the swing speed increased to 800 °/s, the microstructure consisted of vermicular ferrite and austenite. The tensile strength and elongation of the micro-control thin-walled deposition components are higher than those of the common thin-walled deposition components. The tensile fracture mechanism of the common thin-walled deposition components and the micro-control thin-walled deposition components was the ductile fracture mechanism. Full article

Pipe girth welds are prone to incomplete fusion problems in the automatic welding process of long-distance pipelines, which is often related to temperature inhomogeneity in the weld bead. The narrow gap and micro-swing welding technique was applied in pipeline construction to improve welding quality. The manuscript provides a detailed investigation of the micro-swing welding technique with a combination of welding experiments and numerical simulation. A swing welding strategy was proposed according to the actual welding condition in pipeline construction to study the formation mechanism of weld joints. The swing width grew to 1.25–1.35 times from the 3 to 6 o’clock position in the same filling layer. It also increased with filling layers, and filling layer 5 had the biggest swing width, almost two times that of filling layer 2. “Middle concave” morphology appeared at the 3 o’clock position, which could effectively avoid the occurrence of incomplete fusion, while “hump” morphology may appear at the 6 o’clock position, and incomplete fusion defects occurred if the next pass failed to eliminate the influence of the “hump”. The temperature field presented an obvious “sawtooth” shape at small swing frequencies, which could cause temperature inhomogeneity. It could be effectively eliminated when swing frequency reached over 5 Hz. Full article