Process Optimization in Single Point Incremental Forming in Particular Reference to Tool size and Sheet Thickness

Abstract

Many new manufacturing processes, such as hydroforming, laser forming, water jet forming and incremental forming, and were introduced in the last decade. However, owing to high flexibility, the single-point incremental forming (SPIF) process has attained a great attention. Single-point incremental forming (SPIF) is relatively a novel sheet forming process to produce small lots with low cost. It has potential to replace conventional sheet forming processes in order to produce small batches at low cost and in short delivery time. This study is focused on the formability in SPIF. A new test to evaluate maximum wall angle, a formability measure, in SPIF was used. This test makes use of geometry whose wall angle continuously increases from 0o to 90o along the depth. Therefore, the test specimen, depending upon the thinning limit of sheet, fractures somewhere between 0o and 90o. This enables the new test to provide maximum wall angle using single specimen and renders it promising over the existing test in which a series of specimen is required to be formed. In this thesis guidelines for tool size selection to maximize the spif-ability (i.e., formability in SPIF) of an aerospace grade alloy (AA-2024) are presented. The role of tool size, with respect to sheet thickness employed, on the formability in SPIF (i.e., spifability) is clarified. The response surface method is employed in order to study the significance of sheet thickness (to) and tool radius (r) on the spifability. The results of analysis of variance (ANOVA) show that the sheet thickness and tool radius are not significant individually, however, a strong interaction between these parameters exists. Moreover, for a particular sheet thickness, there exists only one r/to value at which the spifability can be maximized under a given set of conditions. Furthermore, for a given sheet thickness, if a tool with radius lesser than a particular value is used (i.e., r/to≤2) the material squeezes out from the tool/sheet interface. And, such a condition adversely affects the material spifability. In order to know facts behind experimental findings, FEA using LS-DYNA has also been carried out.