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

The laser bending of near-alpha alloy Ti-6Al-2Sn-4Zr-2Mo sheets was investi gated 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 st resses 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 te mperature. 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 wa s 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 h eat flow. With a three-dimensional heat flow, significant thickening occurr ed and sheet bendability decreased rapidly with repeated scans. The forming response was different when heat how was more two dimensional. Although th e asymmetry of the yielded zone was significantly reduced, bending angles w ere as large as earlier ones because of wider yielded zones. Also, thickeni ng was barely observed, whereas bending rate continued to decrease. Causes of reduced bendability other than thickening are thus discussed. The expect ed contribution from transformations in microstructure was studied, but was not found to be significant. (C) 2000 Laser Institute of America. [S1042-3 46X(00)00304-1].