Abstract
The purpose of this study is to analyze the differences between the effects of robot welding and manual welding on the low- and high-cycle fatigue lives of the weld zones for T-shaped weld structures fabricated from SM50A carbon steel using a CO2 gas arc welding method. Fatigue tests were conducted using a three-point bending method, and the S-N curves of the manual welding and robot welding crossed each other at approximately 3 × 104 cycles. The robot welding weld zone had better high-cycle fatigue lives than the manual welding. The results are attributable to the fact that the more uniform and higher welding speed of the robot welding leads to smaller weld zone area (i.e. ~12% smaller than the manual welding) and also smaller grain size than the manual welding. Because a smaller grain size in the robot welding weld zone results in a higher hardness than the manual welding and material brittleness increases with increasing hardness, the robot welding weld zone shows better high-cycle fatigue lives but poorer low-cycle fatigue lives than the manual welding.
Highlights
The area of the weld zone for the manual welding (MW) (180 mm2) was larger by approximately 12% compared with the robot welding (RW) (161 mm2), as shown in Figures 8 and 9
The results of the measurement showed that the weld bead widths of MW (WMW) were 15.68 6 0.28 mm (n = 63: 7 test specimens 3 9 points), and the weld bead widths of RW (WRW) were 13.16 6 0.24 mm (n = 63: 7 test specimens 3 9 points) indicating that the WMW values were larger by approximately 2.5 mm than the WRW
The RW and MW effects on the fatigue of SM50A carbon steel weld zones were analyzed in this study
Summary
In the fabrication of hull blocks or construction equipment, welding between metal pieces is one of the essential joining methods between individual structures.[1,2,3] The primary goals of any welding method are enhancing the reliability of welded structures by minimizing the weld defects and improving the welding productivity by reducing costs and manpower while completing the targeted structure within the set schedule, as well as enhancing the welding precision by minimizing the welding deformation of the fabricated structures.[4,5,6,7] welding operations are very sensitive and welding conditions, skill levels, weld defects, and heataffected zones (HAZ) created by the heat generated during welding cause changes in the mechanical properties.[8,9,10] Since such weld defects and HAZ may change the microstructures of metals and affect the material properties considerably, the fatigue strength of weld zones should be evaluated before the parts are applied to the actual products.[11,12,13,14,15] In particular, the weld zone strength highly relies on the welding method.
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