Research On The Dimensional Accuracy Of Composite Forming Of Fine-blanking And Bending

Fine-blanking and bending composite forming process combines fine-blanking technology with bending technology,is used to form three-dimensional multi-functional parts in a pair of mold.It can ensure the geometric characteristics of the parts,meanwhile obtain a very smooth surface quality.When unloading,dimensional accuracy of parts become worse,will seriously affect the assembly of the parts and other parts,and cause a large assembled residual stress.It also affects the reliability and service life of the final products.Spring-back is one of the main reasons why the accuracy gets worse.Spring-back is the cumulative effect of the whole deformation process,including the loading process and unloading process.Spring-back problem is very complex and difficult to control accurately,because the spring-back value is influenced by many parameters.Therefore,in order to improve the dimensional accuracy of the parts,further investigation into the laws of spring-back is of great significance.In this paper,based on the fork part of the car,firstly aiming at the spring-back problem of four-angel bending parts and fine-blanking parts,through combining theoretical analysis and finite element numerical simulation and experimental methods,study the influence laws of various factors on the spring-back value of the parts.Then,making a comparison of the forming accuracy of parts formed from fine-blanking and bending composite forming process and bending process,study the influence of the fine-blanking stage on the forming accuracy of the final part in the composite forming process.The main research works is as follows:As whether the FEM model is accurate or not have a great impact on the final shape of the parts.In order to improve the simulation accuracy of rebound model,in this paper,two methods were used to establish the models.By combining the finite element numerical simulation and experimental research,comparing the finite element numerical simulation results and data from the V-shaped bending experiments,theveracity of dieless method was verified.Based on the fine-blanking model and rebound model.The influence laws of the process parameters,such as the blank holder force,the back top force,the punch fillet radius,the die radius and blanking clearance on the radial dimension precision and cross-section quality of the parts were researched.Research shows that increasing the mean stress has opposite effect on the dimensional accuracy and cross-section quality.Through FEM simulations,the material flow,effective stress and hydrostatic stress distributions of the four-angle bending forming process were analyzed.The regions where the dimensional accuracy changed after spring-back were found and the reason why the dimensions changed was indicated.Through study how the straight edge area of the workpiece contacted the punch and the die,elaborating the formation mechanism of spring-go phenomenon further.Based on the four-angle bending model,the influence laws of plate thickness,bending depth,die clearance,punch radius and die fillet radius on the planeness of the part in the four-angle bending process of middle thick plate were researched,and influence degree of the process parameters on the forming precision is comprehensively assessed by lateral comparing the difference of the maximum and minimum planeness.The orthogonal test of the Taguchi method is combined with the finite element numerical method,with minimum spring-back value as the optimization objective and plate thickness,bending depth,die clearance,punch radius and die fillet radius are chosen as the variables for optimal design.The degree of importance of the process parameters are examined through S/N analysis and optimal parameters of minimum spring-back value are obtained.By making a comparison of the effective stress,mean stress and material flow distributions of fine-blanking and bending composite forming process and bending process,the influence of residual stress of fine-blanking parts on the dimensional accuracy of the final part was researched.Research shows that compared to the bending process,the part formed from composite forming process has better dimensional accuracy.