Numerical And Experiment Investigation On Laminated Steel Sheet Forming Failure And Process Optimization

Vibration is one of the main sources of vehicle noise. The bump when the car is in motion, andthe high speed rotary and reciprocating motion of engine generate a large number of vibration. Inaddition, focus on energy saving and emission reduction, lightweight technology is applied to thecar body. A lot of high strength steel sheet is used. This type of steel sheet is easy to produce noise.At present, in order to reduce the internal noise, automobile manufacturers often use soundproofor sound absorption layer, coated sound-absorbing materials in car body etc. to alleviate vibration.Although some approach of vibration and noise reduction work well, they are very expensive.Vibration damping steel sheet is a typical laminated steel sheet. It is a functional material, inwhich metal sheet and polymer damping material is laminated through laminated process.Vibration damping steel sheet combines the properties of metal material and polymer material.Metal apply formability and polymer apply damping properties. It is an environmental friendlyproduct to alternative pure metal in vibration and noise conditions. To the automobile industry,this kind of material can satisfy the structural strength, vibration and noise reduction of car bodyand lightweight requirements. Therefore, application of this kind of steel sheet in the car body hasaroused wide concern and become a hot research point. Although laminated steel sheet have goodproperties to reduce vibration, the failure during drawing process is different from normal steelsheet. This paper focus on current theory and process, and drawing failure mechanism andprocessing optimization analysis is studied in deeply. Research achievement is obtained asfollows:An improved continuum model which accounts for nonlinear visco-elasticity has beendeveloped for polymer layer of laminated steel sheet to describe deformation behavior in sheetforming process. The physical meaning of this model is clear. Only simple test are required toobtain the parameters of the continuum model, including tensile test and stress relaxation test oflap-shear and T peeling test. Using the second development tools which is supplied by acommercial finite element program ABAUQS, this material model has been successfullyintegrated into this software.Two different methods, cohesive element and contact interface, were compared to characterize abetter method for modeling the polymer layer deformation. The comparative result indicates thatcohesive element is easy to convergence. When drawing part structure is complicated, aimed to 3D modeling issue, continuum shell element is used to discretize facial steel sheet. Simulationresult show that continuum shell element can save much compute time.Satisfaction function method is used to implemented multi-objective optimization duringlaminated steel sheet drawing process design, where Response surface is used to constructrelationship between design parameters and objective function. Simulation result shows that thismethod can obtain high calculate efficient and is simple. In the reliability analysis, first ordersecond moment method and Monte Carlo simulation is used, respectivly.Spring-back study of laminated steel sheet using numerical study is implemented and nonlinearvisco-elasticity is considered. V bending and U Bending experiment and numerical study resultshows that: forming speed, standing time after forming, initial yield stress and polymer thicknesshas a significant influence on Spring-back. In U bending process, blank hold force, forming speed,polymer thickness and initial yield stress also have significant influence on spring-back.Delamination failure is studied in laminated steel sheet forming process. U bending researchresult shows that increasing drawing speed can partly inhibit the trend of delamination. Increasingblank hold force can significantly eliminate delamination. Step bottom square box drawingresearch result shows that wrinkling often induce delamination. Increasing blank hold force andfriction coefficient can inhibit wrinkling, namely inhibit delamination. However, when wrinklingis inhibit future increasing blank hold force and frictional coefficient will increase the probabilityof delamination.Multi-objective optimization and reliability analysis for step shape bottom box drawing processis implemented. Based on Satisfaction function method, multi-objective optimization isconducted. Based on determined multi-objective optimal design result, step shape bottom boxdrawing process is evaluated using reliability. Firstly, only blank hold force and frictionalcoefficient is set to be stochastic variable and first order second moment method is used toconduct reliable analysis. Then, other three noise factor: blank thickness, normal and sheardelamination criterion is future considered. Those three variables are set to be stochastic variableand Monte Carlo method is used to calculate random model. Research result shows that afterreliability analysis, we can obtain a robust optimization design for laminated steel sheet drawingprocess.