Vertical Wall Formation and Material Flow Control for Incremental Sheet Forming by Revisiting Multistage Deformation Path Strategies

Abstract

In this article, multistage deformation path strategies for single point incremental forming (SPIF) are revisited with the purpose of controlling material flow (improving sheet thickness distribution) and forming a vertical wall surface for cylindrical cups. It is noted that stretching and thinning are two main deformation modes during SPIF. How to control material flow in an optimal way is a key point for successful forming. Multistage incremental forming shows more advantages than single-stage forming, especially dealing with shapes with steep walls. In this study, three basic multistage deformation path strategies have been proposed, that is: A. incremental part diameter; B. incremental draw angle; and C. incremental part height and draw angle. Those strategies and their combinations have been evaluated in terms of formability and compared in order to understand the material allocation mechanism and optimize the multistage forming process. In addition, approximate plane-strain analysis models have been given to provide formability predictions between single-stage and multistage strategies, and between strategies B and C, respectively. The prediction results show good agreement with the experimental results. It is demonstrated that the strategic combination A + B is the optimal way to achieve the forming target.