저자명 김세호 
년도 2002 
The sheet metal forming process has taken an important role in industries because of its various advantages. There have been remarkable advances in sheet metal forming analysis with the increasing need from industries although it is very difficult to determine process parameters before real manufacturing due to very complicated deformation. Deformation during the forming process is effected by many process parameters such as the die geometry, the blank shape, the blank holding force, the bead force, friction and so forth. In spite of its importance on the process parameter determination, the effect of process parameters is yet informed by the experience, the intuition or the time-consuming computer analysis such as incremental finite element methods for small modification during the process design. When the number of process parameters considered becomes larger, it becomes more difficult to determine the optimum values of parameters, which satisfy the design specifications without any problem during the forming process. As the number of parameters considered is increased, it requires more time to choose the optimum parameters by trial and error.
In this paper, a design methodology is proposed to overcome the deficit of the trial-and-error approach in the design stage before manufacturing. A process parameter design system is proposed to determine process parameters directly using the design sensitivity analysis and the optimization scheme. A design sensitivity analysis scheme proposed deals with an elasto-plastic finite element method with explicit time integration and a direct differentiation method. The direct differentiation is concerned with large deformation, the elasto-plastic constitutive relation considering the planar anisotropy, shell elements with reduced integration and complicated contact between the sheet and the dies. The design sensitivities with respect to the process parameter are obtained with the direct analytical differentiation of the equilibrium equation for the finite element analysis. The present result is compared with the result obtained with the finite differentiation method (FDM) in sheet metal forming processes such as a hemi-spherical punch stretching, a cylindrical cup drawing process and a U draw-bending process for the verification of its accuracy and the versatility. The analysis results obtained with the present study show good agreement with the results obtained by FDM. The analysis also provides useful information on the inspection of the failure such as fracture or wrinkling. The abrupt change of the sensitivity of the major strain inspects the initiation of the element necking. The sudden change of sensitivity of the blank holder displacement inspects the initiation of wrinkling. The analysis shows that the sensitivity of state variables provides useful information not only for the strain control but also for the inspection of fracture or wrinkle initiation.
The present algorithm has been implemented the process optimization code and applied to sheet metal forming processes for demonstration of its validity. A new control algorithm of the variable BHF is proposed in order to improve the maximum cup height and to control the strain distribution in the cylindrical cup drawing process. The blank holding force is controlled incrementally in the divided punch stroke interval in order to maximize the cup height and to achieve the desired principal strain distribution of the drawn cup. The objective function is constructed so that the principal strain can follows the desired path within the safe region. The constraint condition is imposed to suppress the sudden lifting of the blank holder, which causes severe wrinkling during the forming process. Other constraints prevent the fracture by excessive stretching, which is prevented by inspecting the principal strain distribution on the forming limit diagram. The numerical experiment confirms that the proposed control algorithm for the variable BHF guarantees the improvement of the cup height and the regularization of the strain level in the weak part of the drawn cup.
The optimization algorithm has been applied to the U draw-bending process in order to reduce the amount of springback and improve the shape accuracy. The bending dominated forming process often suffers difficulties of inaccurate shape after unloading, which is caused by the non-uniformity of the stress distribution along the sheet thickness. The amount of springback can be reduced by increasing the blank holding force. The blank holding force can control the amount of spingback with a limitation due to the excessive stretching in the cup wall. In this paper, a variable blank holding force is proposed in the U draw-bending process in order to reduce the springback amount. The blank holding force is increased in the last 15% of punch stroke interval. In the optimization procedure, the increasing blank holding force is calculated. The objective function is constructed so that the longitudinal stress components in the integration points along the shell thickness have the minimum deviation from the average value. The constraint condition prevents the fracture by excessive stretching, which is predicted by inspecting the principal strain distribution on the forming limit diagram. The other constraint condition suppresses the excessive wall stretching by controlling the effective plastic strain. The obtained optimum blank holding force ensures that the stress distributions have very small inherent deviation caused by bending and unbending in the punch shoulder region and the die shoulder region. The result also shows that higher blank holding force improves the stress deviation by a small amount but excessive stretching occurs during forming. The analysis result after springback simulation confirms that the present optimization algorithm improves that shape accuracy after unloading effectively.
The results demonstrate that the proposed design methodology is applicable to the complicated sheet metal forming analysis and design.


번호 제목 저자명 날짜 조회 수
27 Study on Dynamic Tensile Tests of Auto-body Steel Sheet at the Intermediate Strain Rate for Material Constitutive Equations (차체강판의 중변형률 속도에서의 동적 인장시험 및 물성 구성방정식에 관한 연구) 임지호  2005.11.29 25583
26 Analysis of Elasto-Plastic Stress Waves by a Time Discontinuous Variational Integrator of Hamiltonian with a Second-Order Integration Scheme of the Constitutive Model (해밀토니안의 시간 불연속 변분적분기와 구성방정식의 2차 정확도 적분법을 이용한 탄소 조상순  2008.12.15 21776
25 Forming Limit Diagram of Auto-body Steel Sheets at High Strain Rates for Sheet Metal Forming and Crashworthiness (박판성형 및 충돌성능 향상을 위한 고변형률속도에서의 차체강판 성형한계도) 김석봉  2010.07.13 21727
24 A New Ductile Fracture Criterion for the Formability Prediction of Steel Sheets and Its Application to Finite Element Analysis (강판의 성형성 예측을 위한 새로운 연성 파괴 조건 및 유한 요소 해석에의 응용) [1] Yanshan Lou  2012.12.10 21135
23 A Study on the Tension/Compression Hardening Behavior of Auto-body Steel Sheets Considering the Pre-strain and the Strain Rate (초기 변형률 및 변형률 속도를 고려한 차체 강판의 인장/압축 경화 거동에 관한 연구) [1] 배기현  2011.01.11 20408
22 A Study on Material Properties of OFHC Copper Film at High Strain Rates using High-Speed Micro Material Testing Machine (고속마이크로재료시험기를 이용한 무산소동 박판의 고변형률속도 재료물성치 연구) 김진성  2010.07.13 20308
21 Finite Element Inverse Approach and Initial Guess Generation for Sheet Metal Forming Analysis of Complicated Auto-body Members (복잡한 차체부재의 박판성형공정을 위한 유한요소 역해석 및 초기추측치 계산) 김승호  2005.11.29 19183
20 A Study on the Dynamic Failure Model of a Spot Weld under Combined Loading Conditions for Auto-body Crash Analyses (차체용 부재의 충돌해석을 위한 복합하중조건에서 점용접부의 동적 파단모델 연구) [1] 송정한  2008.07.24 18638
» Optimum Process Design in Sheet Metal Forming Processes using Finite Element Sensitivity Analysis (유한요소 민감도해석을 이용한 박판금속성형에서의 공정변수 최적설계) [1] 김세호  2005.11.29 18592
18 Strain-Rate Dependent Anisotropic Yield Criteria for Auto-body Steel Sheets (자동차용 강판의 변형률속도 의존 이방성 항복함수에 관한 연구) 허지향  2012.12.11 18138
17 Evaluation of a cast-joining process of dual metal crankshafts for heavy-duty engines with ductile cast iron and high strength forged steel(구상흑연주철과 고강도 단조강의 주조접합 이종금속을 이용한 중대형 엔진 크랭크샤프트의 평가) 한 신  2010.07.13 17969
16 Dynamic Formulation of Finite Element Limit Analysis for Impact Simulation of Structural Members (구조부재의 충돌해석을 위한 유한요소 극한해석의 동적 수식화) 김기풍  2005.11.29 17893
15 Measurement Uncertainty Evaluation for High Strain Rate Tensile Properties of Auto-body Steel Sheet (자동차용 강판 고속인장물성 데이터의 측정불확도 산출) 정세환  2012.12.10 17840
14 Development of a Nonlinear Degenerated Shell Element with the Drilling Degree of Freedom by the Cubic Polynomial Interpolation and the Assumed Strain Method (드릴링 자유도의 삼차 근사법과 대체변형률법을 이용한 비선형 감절점 쉘 요소의 개발) 이형욱  2005.11.29 17801
13 Rate Dependent Hardening Model for Pure Titanium Considering the Effect of Deformation Twinning (쌍정의 영향을 고려한 티타늄의 변형률속도 의존 경화 모델) 안광현  2012.12.12 17295
12 Finite Element Simulation of 3-dimensional Superplastic blow forming with diffusion bonding (유한요소법을 이용한 초소성 재료의 삼차원 확산 접합 및 압력 성형 해석) 이기석  2005.11.29 17048
11 Microscopic investigation of the strain rate hardening for auto-body steel sheet(차체강판 변형률속도 경화의 미시적 관찰) 윤종헌  2010.07.13 17036
10 Crash Analysis of Auto-body Structures with an Explicit Finite Element Method ( 외연적 유한요소법을 이용한 차체 구조물의 충돌해석 ) 강우종  2005.11.29 16783
9 Shell Element Formulation for Limit Analysis of Thin-Walled Structures ( 박판부재의 붕괴거동해석을 위한 극한해석의 쉘요소 수식화 ) 김현섭  2005.11.29 14789
8 A Study on a Continuum Damage Yield Function to Predict Ductile Fracture of Materials (재료의 연성파단을 예측하기 위한 연속체 손상 항복 함수에 관한 연구) 고윤기  2012.12.10 14688