Controlling Pillow Defect in Single Point Incremental Forming Through Varying Tool Geometry

Single point incremental forming (SPIF) is a new sheet forming process with much potential for application in industry and can be used in combination or in place of standard sheet forming processes. However, part accuracy is a major drawback in this process. Pillow formation in particular is a major defect in SPIF because it leads to early fracture and part inaccuracy. This study aims at understanding the effects of sheet thickness, tool geometry and radius on pillowing in SPIF. The study was carried out on aluminum 1060 alloy (commercial aluminum).The findings are determined based on practical work and simulations using Finite Element Analysis (FEA) on Abaqus 6.12. The temperature, machining conditions and material property are assumed to be same in FEA. Parameters that influence the formation of pillow were studied. It is observed that an increase in tool radius decreases pillow height due lower stresses and strains as revealed by FEA. Flats tools tend to form lower pillows than round tools due to lower bending angles and also the fact that flat tools may bend the sheet at two points along the profile. Pillow height was found to increase with sheet thickness. The ratio of the tool size to sheet thickness was proven to be a very important parameter as this determines the amount of bend severity. FEA was used to determine of the stress and strain states in SPIF and hence an explanation for pillowing mechanism. The results are expected to be a useful reference to designers and manufacturing enterprises. Keywords: Single Point Incremental Forming, Pillow Forming, Small batch production, Finite Element Analysis, Modeling, Part Accuracy.