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핫스탬핑강의 너트 프로젝션 용접시 너트 재질이 용접부 파단모드 변화에 미치는 영향
임성상(Sung-Sang Lim),김영태(Young-Tae Kim),천은준(Eun-Joon Chun),남기성(Ki-Sung Nam),박영환(Young-Wan Park),김재완(Jae-Wan Kim),이선영(Sun-Young Lee),최일동(Il-dong Choi),박영도(Yeong-Do Park) 대한용접·접합학회 2016 대한용접·접합학회지 Vol.34 No.2
The use of materials for modern lightweight auto-bodies is becoming more complex than hitherto assemblies. The high strength materials nowadays frequently used for more specific fields such as the front and rear sub frames, seat belts and seats are mounted to the assembled body structure using bolt joints. It is desirable to use nuts attached to the assembled sheets by projection welding to decrease the number of loose parts which improves the quality. In this study, nut projection welding was carried out between a nut of both boron steel and carbon steel and ultra-high strength hot-stamped steel sheets. Then, the joints were characterized by optical and scanning electron microscope. The mechanical properties of the joints were evaluated by microhardness measurements and pullout tests. An indigenously designed sample fixture set-up was used for the pull-out tests to induce a tensile load in the weld. The fractography analysis revealed the dominant interfacial fracture between boron steel nut weld which is related to the shrinkage cavity and small size fusion zone. A non-interfacial fracture was observed in carbon steel nut weld, the lower hardness of HAZ caused the initiation of failure and allowed the pull-out failure which have higher in tensile strengths and superior weldability. Hence, the fracture load and failure mode characteristics can be considered as an indication of the weldability of materials in nut projection welding.
프로젝션용접 FE 해석을 통한 재료강도에 따른 적정용접구간 도출
하상언(Sang Un Ha),최완섭(Wan Sub Choi),임성상(Sung Sang Lim),박영도(Yeong Do Park),이형일(Hyungyil Lee) 대한기계학회 2018 大韓機械學會論文集A Vol.42 No.2
프로젝션용접이란 국부적인 열발생을 유도해 원하는 위치에 재료를 접합시키는 용접법이다. 돌출부는 스탬핑 공정을 통해 제작되므로 돌출부 주변 잔류응력은 재료에 따라 변한다. 최근 다양한 고강도강의 개발로 재료특성이 저항용접에 미치는 영향에 대한 관심이 높아졌다. 그러나 고강도강의 적정용접구강은 기존의 강과 다르며 이는 많은 용접문제를 유발한다. 이에 본 연구에서는 Abaqus (6.13ver)로 전기-열-응력이 3중 연계된 3차원 프로젝션용접 전산모사를 수행하며 가압력, 전류, 통전시간, 돌출부 높이, 재료강도에 따라 얻은 해석 너깃크기를 토대로 적정 용접변수 구간을 제시한다. 고강도강 중 하나인 DP780강에 대한 실험과 해석 간 너깃크기의 평균오차는 6.8 %이다. The resistance projection welding is a welding method for inducing local heat generation to join a material to a desired position. As the projection is formed through the stamping process, the residual stresses around the projection varies with the material. Recent developments of various high-strength steels have kindled interest in the effect of material properties on resistance welding. However the acceptable welding domain of high-strength steel differs from that of conventional steels, resulting in various welding problem. In this study, we perform a fully coupled electricalthermal-mechanical finite element analyses (FE) of a 3-dimensional resistance projection welding model using Abaqus(6.13ver). The acceptable welding domains are obtained by using nugget size from FE analyses for various welding parameters such as electrode force, current, welding time, height of projection and material strength. For DP780 steel, one of the high-strength steels, the average error of the nugget size between the experiment and the analysis is 6.8 %.