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자동차 외판에 발생하는 미세변형에 대한 연구

Study on the Micro Deformation that Occurs on the Automobile Outside Plate

초록/요약 도움말

During the production process of an automobile, structure analysis technique was suggested to improve and predict occurrence of micro deformation in oven process of the roof. Firstly, in order to understand the stiffness of an automobile, material characteristics of mastic sealer in hood and roof were figured out through tensile test and shear test. Also equivalent elastic material was applied to analysis model and stiffness scanning was performed. After determining the hemming sealer and mastic sealer as equivalent elastic material, the hood was computed by changing the material constants. And analysis model was determined by comparing with measurement value. The pressure distribution that affects the hood during the dipping process was obtained from CFD analysis. Then the pressure distribution was applied according to time by dividing whole dipping process into 7 processes. In order to improve defects of the hood, stay locations which influences on the micro deformation was determined as the main factor. By computing optimal stay location, the supports which minimized defect during dipping process were determined. Also after understanding the characteristics of equivalent elastic material and mastic sealer, these were applied into the roof analysis model and were computed. Then analysis model was compared with measurement value to determine the final analysis model.. Determined analysis model showed same tendency of micro deformation when the real oven process conditions of time and temperature were applied. By applying the foam, driving force, elastic stress model of Hwang(2013), measured location of deformation and computed location of deformation could be compared, and the result was fairly accurate. The stiffness of hood and roof coincide with the actual model for more than 90%, and validity of computation was verified by comparing with measured value that were obtained from dipping process and oven process. Also the decrease in micro deformation by computing for optimal supports of the hood was confirmed.

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초록/요약 도움말

자동차 제작과정 중 후드의 디핑공정과 루프의 오븐공정에서 미세변형 발생에 대한 문제를 예측 및 개선하기 위한 구조해석기법을 제시했다. 먼저, 자동차의 강성을 파악하기 위해 인장시험과 전단시험을 통해 후드와 루프에 사용되는 mastic sealer의 물성을 파악하고, 등가 탄성재료를 해석모델에 적용하여 강성스캐닝을 하였다. 후드는 hemming sealer와 mastic sealer를 등가 탄성재료로 결정한 후 재료상수를 변화시켜 계산했고, 측정값과 비교를 통해 해석모델을 결정했다. 그리고 공정 중 후드에 영향을 주는 압력분포는 전산유체해석기법을 통해 확보하였으며, 입조부터 출조까지의 공정을 총7회로 분할하여 시간 별 압력분포를 적용했다. 후드에 발생하는 결함을 개선하기 위해 미세변형에 영향을 미치는 stay지점을 주요인자로 결정했다. 최적의 stay위치를 계산하여 디핑공정시 발생하는 결함이 최소가 되는 지지 점을 구축했다. 또한 등가 탄성재료와 mastic sealer에 대한 특성을 파악한 후 루프 해석모델에 적용하여 계산하였다. 그리고 측정값과 계산값을 비교를 통해 해석 모델을 결정했다. 결정된 해석모델로 실제 오븐공정과 동일한 시간 및 온도조건을 통해 루프의 미세변형을 파악했다. Hwang(2013)의 발포, 구동력, 탄성응력모델을 적용함으로써, 측정된 굴곡지점과 계산된 굴곡지점을 비교할 수 있었고, 그 결과는 상당히 일치하는 것을 확인하였다. 후드와 루프의 강성은 90%이상 실제모델과 일치하였고, 디핑공정과 오븐공정에서 발생한 측정값을 계산값과 비교를 통해 계산의 타당성을 검증하였다. 또한, 후드는 최적지지점에 대한 계산으로 미세변형에 대한 감소를 확인하였다.

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