Formability analysis of polymers in incremental sheet forming process

Single point incremental forming (SPIF) being simple and flexible has potential to replace conventional process in order to produce customized cost-effective parts. It has found several applications in automobile, aerospace and biomedical industries. Traditional processing of polymers normally requires dedicated tools, long setup times and high investments. Therefore, there is a need to find an economical alternative of traditional processing. In this study, the ability of SPIF to process polymers is examined at room temperature. Two polymer materials, polyvinylchloride (PVC) and polyethylene (PE) are employed. The said objective is done through examining the formability of these polymer sheets by varying process parameters, namely tool radius, spindle rotation and step size. To do so, a frustum of cone with wall angle continuously varying along depth is used as test geometry. The formability is defined in two ways: maximum wall angle corresponding to commencement of wrinkling and maximum wall angle corresponding to fracture point. To examine the effect of temperature, if any, on sheet failure during SPIF, temperature rise is recorded in each test. The test plan following response surface method is prepared using a statistical package, Design Expert Dx-8. The tests results have shown that the formability of PVC is limited by sheet fracturing and the formability of PE is limited by sheet wrinkling. Moreover, the combination of parameters, instead of an individual one, is more meaningful to control formability in SPIF. Further, high-high combination (i.e., high values of parameters) is useful for improving formability of PVC, whereas low-low combination of parameters is useful to enhance formability of PE. Temperature rise during SPIF has been found to be the major reason behind the above findings, which have been detailed in the thesis. Finally, to predict the formability for both of PVC and PE material, empirical models as function of process parameter have been proposed. Keywords: Single point incremental forming, polymers, PVC, PE, formability, maximum wall angle, fracture, wrinkling.