The Influence of Thermal Oxidation and Tool-Sheet Contact Conditions on the Formability and the Surface Quality of Incrementally Formed Grade 1 Titanium Thin Sheets

The incremental sheet metal forming process combines a series of characteristics, such as the capacity to produce large deformations, flexibility and low-cost tooling, making it preferable to conventional forming processes. One of the key factors in this process are the contact conditions between the forming tool and the sheet to be formed. The incremental forming process of titanium and its alloys is widely studied; on the other hand, the influence of some heat treatments that can induce superficial modifications is not fully known and understood yet. In this study, the influence of thermal oxidation and tool-sheet contact conditions on the formability and the surface quality of grade 1 titanium thin sheets manufactured by incremental forming was investigated by using both a sphere and a hemispherical head tool. The results of the experimental campaign, based on the production of conical and pyramid frusta, highlight the beneficial effects of the heat treatment on the process repeatability, reducing the occurrence of galling for all the contact conditions, and provide information on the quality of the worked surfaces.