An Experimental Investigation on Thinning and Formability in Hybrid Incremental Sheet Forming Process

Abstract

Single point incremental forming (SPIF) has several advantages over conventional sheet forming process, but due to its inherent drawbacks such as localized thinning, poor formability of parts having steep walls and long processing time make it unsuitable in many industrial applications. In present experimental investigation, two-step hybrid incremental sheet forming (HISF) process is proposed which combines stretch forming (SF) and SPIF process. Stretch forming or preforming is done in order to get intermediate shape and desired thickness distribution. On the same setup final part shape is obtained using SPIF process. From the literature review it is found that sophisticated tooling is used for stretching process. In present experimental investigation simple tooling comprising wooden preforming tool is used for stretching followed by SPIF process to form final part shape. Full factorial design of experiments is used to quantify influence of wall angle, preforming and preform tool radius on minimum thickness. From the experimental results it is observed that wall angle has significant influence on thinning which is in good agreement with the previous literature. Further, from the same set of experiments, the influence of preforming depth and preform tool radius on minimum thickness is studied keeping wall angle as constant. It is found that preforming has significant influence on minimum thickness and formability. For conical frustum of 30o and 50o wall angle, 70 mm preform tool radius and 10 mm preforming results in minimum thinning. Also, improvement of 18% in minimum thickness is observed while forming parts with 50o wall angle. Using preform tool radius 70 mm and preforming depth 18 mm, an improvement of around 40 % in forming depth of part having 70o wall angle is achieved in HISF process as compared to SPIF process.