Factors affecting the laser bending of Ti–6Al–2Sn–4Zr–2Mo

The laser bending of near-α alloy Ti–6Al–2Sn–4Zr–2Mo sheets was investigated with a 1200 W Nd-YAG laser. The effect of scanning a material with a laser beam is to produce complex thermal cycles, which result in thermal stresses and angular deflections (bending angles). The conditions to promote large bending angles are first studied using an existing model of a moving Gaussian heat source. Analysis showed that bending could be explained from a characteristic temperature defined from material properties: the yield temperature. The morphology associated with its isotherm, which defines both the depth and the width of the yielded zone, adequately described bending. Optimal bending angles were observed when asymmetry of this yielded zone was maximum with respect to the neutral axis; i.e., before the yielded depth penetrated through the sheet thickness. The effects of repeated scans, such as the increases in bending angles, are also discussed together with the heat flow. With a three-dimensional heat flow, significant thickening occurred and sheet bendability decreased rapidly with repeated scans. The forming response was different when heat flow was more two dimensional. Although the asymmetry of the yielded zone was significantly reduced, bending angles were as large as earlier ones because of wider yielded zones. Also, thickening was barely observed, whereas bending rate continued to decrease. Causes of reduced bendability other than thickening are thus discussed. The expected contribution from transformations in microstructure was studied, but was not found to be significant.