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Joo H.S.,KAIST | Hwang S.K.,Ultimate Manufacturing Technology Group | Kim Y.N.,KAIST | Im Y.-T.,KAIST
Journal of Materials Processing Technology | Year: 2017

In this study, a continuous hybrid (CH) process applied with newly designed dies was proposed to manufacture a high strength and high electrical conductivity rectangular copper wire in a continuous way. The 2nd pass CH process with different processing routes, A and C, was numerically and experimentally carried out to check the practicality of the process and to investigate the deformation behavior of the commercially pure copper wire. Electron backscatter diffraction, tension and Vickers micro-hardness tests were employed to study the changes in the microstructure and mechanical properties of the wire. Electrical conductivity was also measured by a four-point probe method. According to the current investigation, the CH process with the new concept dies could impose relatively high plastic deformation without die change during the process and promote the accumulation of dislocation, resulting in grain refinement of the wire compared to the conventional wire drawing (WD) process. The mechanical strength and hardness values of the processed rectangular pure copper wire by the CH process were increased, and the electrical conductivity was relatively maintained compared to the one processed by the WD process. In particular, route C could produce wire with relatively uniform strength distribution. Route A might be adequate for the manufacturing of one-sided hardened rectangular wire such as the contact wire for rail electrification. It is demonstrated that the CH process can be applied to the rectangular wire manufacturing process and might be beneficial to produce high strength and high electrical conductivity copper wire for various applications. © 2017 Elsevier B.V.

Park J.S.,Ultimate Manufacturing Technology Group | Lee M.-G.,Ultimate Manufacturing Technology Group | Cho Y.-J.,Ultimate Manufacturing Technology Group | Sung J.H.,Ultimate Manufacturing Technology Group | And 4 more authors.
Metals and Materials International | Year: 2016

The directed energy deposition process has been mainly applied to re-work and the restoration of damaged steel. Differences in material properties between the base and the newly deposited materials are unavoidable, which may affect the mechanical properties and durability of the part. We investigated the effect of heat treatment on the characteristics of tool steel deposited by the DED process. We prepared general tool steel materials of H13 and D2 that were deposited onto heat-treated substrates of H13 and D2, respectively, using a direct metal tooling process. The hardness and microstructure of the deposited steel before and after heat treatment were investigated. The hardness of the deposited H13 steel was higher than that of wrought H13 steel substrate, while that of the deposited D2 was lower than that of wrought D2. The evolution of the microstructures by deposition and heat treatment varied depending on the materials. In particular, the microstructure of the deposited D2 steel after heat treatment consisted of fine carbides in tempered martensite and it is expected that the deposited D2 steel will have isotropic properties and high hardness after heat treatment. © 2016, The Korean Institute of Metals and Materials and Springer Science+Business Media Dordrecht.

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