Abstract

The mechanical properties and the operating life of a formed component are highly dependent on the residual stress state. There is always a high magnitude of residual stresses in the components formed by incremental sheet forming (ISF) due to the localized deformation mechanism. Hence, a thorough understanding of the generation of the residual stresses by ISF is necessary. This study investigates the residual stress generation mechanism for two process variants of ISF, i.e., Single Point Incremental Forming (SPIF) and Two Point Incremental Forming (TPIF). This understanding is used to control and targetedly generate the residual stresses to improve the part performance. In this regard, the residual stress state in a truncated cone geometry manufactured using SPIF and disc springs manufactured using TPIF was experimentally analyzed. Validated numerical models for both process variants were developed to study the residual stresses in detail. The residual stress state in SPIF is such that the tool contact side develops tensile residual stresses and the non-contact side undergoes compressive residual stresses. The tool step-down variation was used to control residual stresses and improve the fatigue strength of truncated cones manufactured using SPIF. For TPIF, two different forming strategies were used to analyze the residual stress generation mechanism and the role of major process parameters. The residual stresses for TPIF are pre-dominantly compressive in both directions of forming tool motion. For both process variants of the ISF process, it is shown that the residual stresses can be beneficially utilized to improve mechanical properties of the components.

Highlights

  • Incremental sheet forming (ISF) is a flexible sheet metal forming process for small batch production and rapid prototyping [1]

  • The disk springs of dimension 80/50/0.8 mm were incrementally formed from sheet blanks of AISI 304.The magnitude of the residual stresses is further aided by martensite transformation in the deformed zone, as the selected materials for disk spring manufacturing exhibit transformation-induced plasticity (TRIP) effect

  • The main aim of the current study was to provide an in-depth analysis of the targeted generation and utilization of the forming induced residual stresses by Single Point incremental forming (SPIF) and Two Point Incremental Forming (TPIF) variants of the ISF process

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Summary

Introduction

Incremental sheet forming (ISF) is a flexible sheet metal forming process for small batch production and rapid prototyping [1]. SPIF is characterized as the forming of a sheet blank by a CNC-controlled hemispherical forming tool with sheet blank clamped in non-workpiece specific tooling without any partial or full tooling. The lack of die ensures high flexibility of the SPIF variant. In the case of TPIF, a full or partial die is added to the opposite side of the forming tool. The full die can either have a positive or negative shape [2]

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