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TECHNICAL ARTICLE—PEER-REVIEWED

Investigation on the Crack and Thinning Behavior of Aluminum Alloy 5052 Sheet in Stretch Flanging Process Surendra Kumar . M. Ahmed . S. K. Panthi

Submitted: 5 October 2019 / in revised form: 28 February 2020 Ó ASM International 2020

Abstract Stretch flanging is the important sheet metalforming process which is widely used in automobile and aerospace sectors. The formability of sheet metal depends on various parameters such as material properties, geometry of the tool setup and process parameters. In the present work, effects of different die radius and sheet width on deformation behavior of sheet are studied by FEM simulation and experiments. The predicted FEM results are presented in the form of edge crack location and its propagation, crack length, forming load and strain distribution in sheet along the die profile radius. This study indicates that crack length increases with increase in the sheet width, while the crack length decreases with increase in the die radius. It is found that the crack propagation in stretch flanging process is affected by the strain distribution in sheet and this distribution of strain depends on many parameters. The crack initiates during deformation of the sheet at the die corner edge and propagates toward the center of the sheet along the die profile radius. Simulation results are compared with the experimental one in terms of crack length and variation in sheet thickness. FE simulation results are found in very good agreement with experimental results. Fractography study is also presented in terms of size, shape of the dimples along with their distribution on the fractured surface.

S. Kumar Academy of Scientific and Innovative Research (AcSIR), Bhopal 462026, India S. Kumar  M. Ahmed  S. K. Panthi (&) Council of Scientific and Industrial Research (CSIR)-Advanced Materials and Processes Research Institute (AMPRI), Bhopal 462026, India e-mail: [email protected]

Keywords Stretch flanging process  Finite element simulation  Edge crack  Crack length  Forming load  Strain and thickness distribution  Fractography

Introduction Flanging is one type of bending process which is used in automotive, aerospace and household appliance industries to manufacture the various components. In the stretch flanging process, a definite part of the sheet is fixed between the die and the blank-holder and the free part of sheet is bend to 90° to form the concave shaped flange. In this process, sheet material is stretched circumferentially along a bend line [1, 2]. The flanged portion is generally used to provide the stiffness to a component, smoothens the sharp edges of the part and to assemble the different parts [3, 4]. In this process, optimization of tensile or hoop stress is a major challenge that is responsible for the satisfactorily deformation of the sheet during flange formation. If this tensile stress exceeds beyond a certain limit, generation of cracks takes place in the sheet that is undesirable. Necking, localized thinning and localized frac