A study on the laser forming of near-alpha and metastable beta titanium alloy sheets

Abstract

Laser forming has been identified as a technique suitable for producing sheet metal products and for making on-site repairs. One application is the repair of titanium turbines for military airplanes, which consists of shaping distorted blades back to their original shape without removing them. This paper essentially analyzes the effects of consecutive scans at known beam parameters, and to a practical standpoint, it can help to select adequate forming conditions. Two titanium alloys were chosen: a near-alpha alloy, Ti–6Al–2Sn–4Zr–2Mo, and a metastable beta alloy, Ti–15V–3Cr–3Al–3Sn. Empirical equations for predicting bending and section thickening were derived so that series of experimental points could be reduced into two parameters. Effects of repeated scans on bending angle and thickening were first investigated. Second, these two geometric changes were correlated and the two materials compared. The reduced bending often observed after a few scans was related to the initial thickening. Alloy Ti–6Al–2Sn–4Zr–2Mo was found to bend more in the early stage of forming, but it also thickened more than alloy Ti–15V–3Cr–3Al–3Sn. It was concluded that gradual thickening reduced subsequent bendability. The greater initial bending in alloy Ti–6Al–2Sn–4Zr–2Mo was due to a lower yield temperature and a higher thermal expansion coefficient. Because lesser thickening occurred in Ti–15V–3Cr–3Al–3Sn, a better formability was found after many scans. It is also proposed that buckling could cause bending to decrease. As a result of this work, process parameters can be chosen to create the largest bending angles and minimize the number of scans.