Experimental investigation of tool path strategies for incremental necking-in

Incremental necking-in is a forming process to achieve a diameter reduction of tubular parts. Conventionally an inside mandrel is used which gives its shape to the part. In order to increase the flexibility of the process, necking-in is performed without any mandrel in this investigation. The objective of this paper is to deliver a qualitative insight into the effects of the tool motion on the properties of the parts which are manufactured by this incremental forming process. Using a conventional spinning machine, tubular parts are necked by applying six different tool path strategies. The investigation is focused on determining the geometrical properties of the produced parts. With statistically planned screening experiments, including linear models for the process effects, the influence of several tool paths on the workpiece quality is analyzed. The results show a high dependency of the chosen tool path on the reached value of the inclined area as well as the parts elongation. All observed effects are explained in a qualitative manner. Additionally, undesired deformation of the part contour can be observed. Using the given results, a further tool path is developed, which allows a compensation of those effects.