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풀림방지 와셔 표면의 미세 패턴 성형을 위한 예비 성형체 적용 다단 프레스 공정 설계
전용준(Yongjun Jeon),최현석(Hyunseok Choi),고영배(Young Bae Ko),김동언(Dongearn Kim) 한국자동차공학회 2020 한국 자동차공학회논문집 Vol.28 No.12
The loosening of bolted joints, due to vibration or dynamic load while a vehicle is in motion, may lead to vehicle failures and accidents. Thus, the reliability of joint parts is critical in ensuring the safety of both motorists and pedestrians. The performance of anti-loosening washers, which are processed into the shape of densely serrated upper and lower sides along the circumferential direction, depends on the shape accuracy of the serrate profile. While forging is typically done to small joint components, such as washers, to improve productivity and maintain price competitiveness, it is quite challenging to secure the sharp profiles of anti-loosening washers through this process. In this study, the process of press forming was designed, based on finite-element analysis, to achieve fine double-serrated profiles on the upper and lower sides of a washer. Formability improved after limiting the circumferential spread, and the material flow was guided to the serrate portion of the mold. However, a forming load, which was too high to be applied in a typical progressive mold used by washer production plants, was observed. A precise serrate shape for the upper and lower sides of the anti-loosening washers can be formed by using a preforming process with wave patterns that reflected the serrate profile, and by optimizing the relative position of the preformed shape to reduce forming load.
핫스탬핑 소재의 열간 피어싱 공정에서 펀치 전단각에 따른 전단면 특성 평가
전용준(Yongjun Jeon),최현석(Hyunseok Choi),강정진(Jeongjin Kang),채보혜(Bohye Chae),김동언(Dongearn Kim) 한국자동차공학회 2020 한국 자동차공학회논문집 Vol.28 No.12
Although post-processing by using trimming dies has been continuously conducted to shorten the processing time of press-hardened steel, it is quite difficult to secure the life expectancy of the dies due to its high strength at 1.5 GPa. Therefore, in this study, hot piercing was performed at 550 °C during the quenching process of press-hardened steels. The characteristics of the pierced holes were analyzed after changing the shearing angle of the piercing punch. The specimen on which a flat punch with a shear angle of 0° was applied showed a 17 % rollover, 65 % burnish, and 18% fracture, all relative to depth. However, when a piercing punch with a shear angle of 2° was applied, the surface quality deteriorated considerably, with a 14 % rollover, 12 % burnish, and 74 % fracture. These results indicated that when a piercing punch with a shearing angle was applied, the diameter of the piercing hole increased above the target dimension. This can be attributed to the unbalanced load occurring in the radial direction of the piercing punch when the active surface of the punch failed to make contact with the material in the circumferential direction. Moreover, the application of the piercing punch also reduced the effect of the shear load. This can be explained by the temperature at which the piercing process was performed (i.e., 550 °C), which was higher than the martensitic transformation temperature of press-hardened steel. Therefore, the application of a piercing punch with a shearing angle is deemed unsuitable for the piercing process, which would be conducted during the quenching of press-hardened steel, for the following reasons: decreased quality of the processed surface, increased diameter of the processed hole, and reduced impact load.
자동차 크로스멤버 하판넬 제작용 금형 설계를 위한 스프링백 해석
장성호(Sungho Chang),허영무(Youngmoo Heo),신광호(Kwangho Shin),전용준(Yongjun Jeon) 한국자동차공학회 2010 한국자동차공학회 부문종합 학술대회 Vol.2010 No.5
In this study, the drawing process simulation and springback analysis through using PAM-STAMP, a commercial FEM code were conducted for the lower pannel of Rear cross-member in the sub-frame as a automobile part. And the predicted springback results were compared and checked with the CAD data of the product and the CMM data for the prototype product. As a stamping analysis results, a wrinkling problem was occurred in the side-wall of the lower pannel. As a solution for this wrinkling problem, it was recommanded that two drawing steps, which are 1st stamping and restriking process, is needed. And then as a springback analysis results, the result of deformed shape after springback compared with the CMM data for the prototype product was a little bit different as a quentity, but the springback trend is similar.