An experimental study of twist phenomena in single point incremental forming

Knowledge of the twist, induced during Single Point Incremental Forming is of importance for understanding asymmetric behaviour when using unidirectional toolpaths. In order to correctly position cut-outs and pre-formed features in the undeformed sheets, insight in the magnitude and direction of the induced twist during incremental forming is required. The resulting twist direction, reported by different research groups in both single and two point incremental forming, typically corresponds to the toolpath direction as a result of the friction between tool and work piece when using a unidirectional toolpath. However a twist in opposite direction can be observed when processing parts with high drawing angles. Detailed analysis of twist phenomena provides insight in the forming mechanics of single point incremental forming. The purpose of this paper is to study the occurrence of twist by means of strain measurements and document its influence on the thickness distribution in parts characterised by stiff semi-vertical rib features.