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Prediction of Joining Torque for Bit Depth of Subminiature Bolt

초소형 볼트의 비트 깊이에 따른 체결 토크 예측

  • Lee, Hyun-Kyu (Dept. Mech. and Automotive Eng. Seoul Nat. Univ. of Sci. and Tech.) ;
  • Park, Keun (Dept. Mech. System and Design Eng. Seoul Nat. Univ. of Sci. and Tech.) ;
  • Ra, Seung-Woo (Technology Research Center, Seoul Metal) ;
  • Kim, Jong-Bong (Dept. Mech. and Automotive Eng. Seoul Nat. Univ. of Sci. and Tech.)
  • 이현규 (서울과학기술대학교 기계자동차공학과) ;
  • 박근 (서울과학기술대학교 기계시스템디자인공학과) ;
  • 나승우 (서울금속 기술연구소) ;
  • 김종봉 (서울과학기술대학교 기계자동차공학과)
  • Received : 2014.04.17
  • Accepted : 2014.05.27
  • Published : 2014.08.01

Abstract

Subminiature joining bolts are required for the electronic parts of gadgets such as mobile phones and watch phones. During the miniaturization of bolt heads, it is difficult to obtain sufficient joining force owing to the risk of shear fracture of the bolt head or severe plastic deformation on the bit region. In this study, the maximum joining torque for the bit depth was predicted using finite element analysis. A shear fracture test was conducted on a wire used in bolt forming. The results of this test were subjected to finite element analysis and a fracture criterion was obtained by comparing the experimental and analysis results. The shear fracture of the bolt head during joining was predicted based on the obtained criterion. Furthermore, the maximum joining torque was predicted for various bit depths. Fracture on the boundary between the bolt head and thread was found to occur in lower joining torque as bit depth increases.

휴대폰과 같은 전자제품의 소형화로 체결 부품도 소형화가 요구된다. 초소형 볼트의 머리부분 두께 감소 요구에 따라 체결시 볼트 머리부 파손으로 충분한 체결력을 확보하는데 어려움이 있다. 본 연구에서는 볼트 깊이에 따른 체결 토크를 해석적으로 예측하여 비트 형상 설계에 활용하고자 한다. 볼트 머리부는 주로 전단 파손이 발생하기 때문에, 볼트용 선재의 전단 실험을 통하여 파손 기준을 설정하였다. 그리고, 설정된 전단파손 기준을 바탕으로 체결시 파손 형상과 최대 체결 토크를 예측하였다. 또한, 머리부에 성형되는 비트의 깊이에 따른 최대 체결토크을 예측하였다. 비트 깊이가 깊을수록 볼트 머리와 나사부의 경계에서 응력 집중으로 파손이 빨리 발생하고, 최대 체결 토크도 작아짐을 알 수 있었다.

Keywords

References

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