Analysis of forces, accuracy and formability in positive die sheet incremental forming

Sheet Incremental Forming (IF) is a forming technology which consists of a sheet clamped along its edges by a suitable blank-holder while an hemispherical head punch is moved along a defined path and locally deforms the sheet. To improve the part geometrical accuracy, a die (which can be positive or negative) is placed behind the sheet with respect to the punch position. In this case, the process is called Two Point Incremental Forming (TPIF). In the present paper TPIF with positive die was studied through an experimental tests campaign using deep drawing steel sheets. The die geometry used in this research was chosen so to be representative of the process and it was tested using different tool paths. Forming forces were measured using self designed instrumented punch and table while the final workpiece geometry was detected using a coordinate measuring machine (CMM). The collected data allowed to study the effects of the different tool paths on the maximum forming forces, the geometry errors, the maximum reachable wall angle and the drawing depth during forming and after springback. The results were also compared with a previously performed experimental campaign where similar tests with negative die were conducted.