한국산업융합학회 논문집 (Journal of the Korean Society of Industry Convergence)

한국산업융합학회 (The Korean Society of Industry Convergence)
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Failure Analysis and Countermeasures of SCM435 High-Tension Bolt of Three-Step Injection Mold

  • Yun, Seo-Hyun (Dept. of Marine Convergence Design Engineering, Pukyong National University) ;
  • Nam, Ki-Woo (Dept. of Materials Science and Engineering, Pukyong National University)
  • 투고 : 2020.05.27
  • 심사 : 2020.06.29
  • 발행 : 2020.08.31
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초록

When injection mold is repeatedly used for mass production, fatigue phenomenon due to cyclic stress may occur. The surface and interior of structure might be damaged due to cyclic stress or strain. The objective of this study was to analyze failure of SCM435 high-tension bolts connecting upper and lower parts of a three-stage injection molding machine. These bolts have to undergo an accurate heat treatment to prevent the formation of chromium carbide and the action of dynamic stresses. Bolts were fractured by cyclic bending stress in the observation of ratchet marks and beach marks. Damaged specimen showed an acicular microstructure. Impurity was observed. Chromium carbide was observed near the crack origin. Both shape parameters of the Vickers hardness were similar. However, the scale parameter of the damaged specimen was about 20% smaller than that of the as-received specimen. Much degradation occurred in the damaged specimen. Bolts should undergo an accurate heat treatment to prevent the formation of chromium carbide. They must prevent the action of dynamic stresses. Bolts need accurate tightening and accuracy of heat treatment and screws need compression residual stress due to peening.

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