Thermo-Mechanical Effect on Poly Crystalline Boron Nitride Tool Life During Friction Stir Welding (Dwell Period)

Abstract

Poly Crystalline Boron Nitride (PCBN) tool wear during the friction stir welding of high melting alloys is an obstacle to commercialize the process. This work simulates the friction stir welding process and tool wear during the plunge/dwell period of 14.8 mm EH46 thick plate steel. The Computational Fluid Dynamic (CFD) model was used for simulation and the wear of the tool is estimated from temperatures and shear stress profile on the tool surface. Two sets of tool rotational speeds were applied including 120 and 200 RPM. Seven plunge/dwell samples were prepared using PCBN FSW tool, six thermocouples were also embedded around each plunge/dwell case in order to record the temperatures during the welding process. Infinite focus microscopy technique was used to create macrographs for each case. The CFD result has been shown that a shear layer around the tool shoulder and probe-side denoted as thermo-mechanical affected zone (TMAZ) was formed and its size increase with tool rotational speed increase. Maximum peak temperature was also found to increase with tool rotational speed increase. PCBN tool wear under shoulder was found to increase with tool rotational speed increase as a result of tool's binder softening after reaching to a peak temperature exceeds 1250 °C. Tool wear also found to increase at probe-side bottom as a result of high shear stress associated with the decrease in the tool rotational speed. The amount of BN particles revealed by SEM in the TMAZ were compared with the CFD model.

Probing underlying mechanisms for PCBN tool decay during friction stir welding of nickel-based alloys

“…Ratschbacher and Luidold [41] noticed higher rate of oxidation in tungstenrhenium (W-Re) alloy in comparison with the pure tungsten (W) above 1073 K. Recently, Michel [42] showed the grain pullouts from the W-Re tool in FSW of X70 pipeline steel. All these above mentioned studies highlighted that W-Re binder phase tends to become weaker, and cBN grains are likely to disintegrate from the tool matrix above 1073 K. Almoussawi and Smith [36] argued that softening of the W-Re binder material at temperatures above 1500 K could be the main reason for pcBN tool wear. Their analysis considered the dwell stage of FSW with the tool moving at a constant rotational speed and at a fixed location.…”

Analysis of heat generation during friction stir welding of aluminum alloy 2024-T4 and its impact on joint characteristics

“…The fully sticking condition can recover when a→∞, while the sliding condition can be obtained when a = 0. Al-Moussawi and Smith [23] developed a CFD model based on a fully sticking condition for the analysis of the thermomechanical effect on tool life in the dwell stage. They observed the effect of tool rotation speed on peak temperature, tool wear, and the shear layer around the tool.…”

Friction Stir Welding Tool Life Assessment Through Fatigue Analysis

“…From the theoretical analysis and the past experimental results, a fatigue analysis of the tool needs to be done. The tool is not only affected by the stresses due to loads but also the temperature [12] . While joining the hightemperature and strength materials, the temperature at the stir zone is also maximum.…”