Investigation of the Influence Factors on Distortion in Induction-Hardened Steel Shafts Manufactured from Cold-Drawn Rod
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TRODUCTION
COILED steel wires are frequently taken as semi-finished materials to produce machine components, for example automotive shafts. A typical manufacturing process can consist of uncoiling, pre-straitening, cold forming, fine cross-roll straightening, machining as well as heat treatment processes.[1,2] The heat treatment at the end of the manufacturing cycle is generally used to enhance the material properties. However, in nearly all cases, the heat treatment also leads to an undesirable change in dimensions and shapes, i.e., ‘‘distortion,’’ of the component. If the alterations exceed the tolerances, an additional corrective operation, such as straightening and/or final grinding, has to be carried out, high costs occur.[1] Nowadays, it is well-known that the heat treatment is not the only reason for causing the distortion of components, but it can release the distortion potential, which has been accumulated in the components during a manufacturing process, which constituted the series of operations.[2] Cold forming processes are used increasingly in the industry production because of its energy efficiency, cleanness, no loss of material in the form of chips, improvement of dimensional accuracy, and surface JUAN DONG, Research Engineer, JEREMY EPP, Research Group Leader, and HANS WERNER ZOCH, Professor and Director, are with the Division of Materials Science, Foundation Institute for Materials Science, Badgasteiner Str. 3, 28359 Bremen, Germany. Contact e-mail: [email protected] ALEXANDRE DA SILVA ROCHA, Professor, is with the PPGEM, Metal Forming Laboratory, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil. RAFAEL MENEZES NUNES, Postdoctoral Researcher, is with the LAMEF, Physical Metallurgy Laboratory, Federal University of Rio Grande do Sul, Porto Alegre, Brazil. Manuscript submitted July 7, 2015. Article published online November 25, 2015 METALLURGICAL AND MATERIALS TRANSACTIONS A
finish. Cold forming is defined as a forming process or plastic deformation operation carried out at temperatures below the recrystallization temperature of the workpiece material, but more often it is simply referred to as the forming process at room or ambient temperature.[3] Cold drawing is counted among the most commonly used cold forming operations. Large quantities of metal or alloy products such as rods, tubes, and wires with various special sections can be produced by cold drawing process. Bars are frequently given a light sizing pass, reducing the diameter slightly to improve surface finish, and dimensional tolerance. The plastic deformation in cold drawing is not uniform, causing inhomogeneous hardness distribution and residual stresses. This depends essentially on the die angle used in the process and is more pronounced for higher angles.[3] The changes in the material’s properties by one process step can influence the following manufacturing step. Particularly, if cold-formed components need to be heat treated (hardened) a broad range of distortions can occur.[4,5] It has been demonstrated that the distortion
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