다구치 방법과 FE해석을 통한 너트프로젝션용접 사각너트 형상최적설계 = Optimal Design of Square Weld Nut by Taguchi Method and FE Analyses in Nut Projection Welding

다국어 초록 (Multilingual Abstract)

This study aims at optimizing the design of a square weld nut in nut projection welding by using Taguchi method. A three-dimensional (3D) fully coupled electrical-thermal-mechanical finite element (FE) model was constructed by considering temperature-dependent material properties. A preprocess code was written to create various geometries in the FE model. Weldability of square nut with metal sheet was then evaluated by using the concept of nut leg setdown for various nut shape and welding variables i.e. electrode force, current and welding time. The nugget does not penetrate into the vertical direction of the sheet when current is less than 10 kA. If the contact area between nut leg and plate is too small, the nugget size decreases owing to the early collapse of nut leg; consequently, the contact area increases. The maximum error of nut leg setdown between the welding experiments and FE analyses is 11.8%. An optimal nut geometry was then suggested to minimize the time required for 50 % setdown of nut leg. Maximization of the setdown was also considered with respect to the nut shape, and the optimized nut shape was compared with that of a standard geometry, which is proposed based on the experiment.

국문 초록 (Abstract)

본 연구에선 다구치 방법을 통해 너트프로젝션용접의 사각너트 형상최적화를 목적으로 한다. 온도 의존적 재료물성을 고려해 전기-열-응력 3중 연계된 유한요소모델을 구축했다. 다양한 너트형상에 대한 FE 모델을 생성하고자 전처리 코드를 개발했다. 이를 활용해 다양한 너트형상 및 용접변수(가압력, 전류, 통전시간)에 따른 사각너트/판재 간 용접성을 용착강도와 관련된 너트발 붕괴량으로 평가했다. 전류가 10kA 미만일 경우 너깃은 판재 수직방향으로 발달하지 못하며 만약 너트발/판재 간 접촉면적이 너무 작으면 너트발의 빠른 붕괴를 유발해 접촉면적이 증가하므로 너깃크기가 감소한다. 실험-해석 간 너트발 붕괴량의 최대오차는 11.8%이다. 너트발 붕괴량 50% 도달시간을 최소화하고 붕괴량이 최대화되는 너트모양을 다구치 방법으로 분석해 최적너트형상을 제시했으며 실험 기반으로 제시된 기존 규격과 비교했다.

참고문헌 (Reference)

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