An improved ductile fracture criterion for fine-blanking process

In order to accurately simulate the fine-blanking process, a suitable ductile fracture is significant.So an evaluation strategy based on experimental and corresponding simulation results of tensile, compression, torsion and fine-blanking test is designed to evaluate five typical ductile fracture criteria, which are widely-used in metal forming process.The stress triaxiality and ductile damage of each test specimen are analyzed.The results show that none of these five criteria is sufficient for all tests.Furthermore, an improved fracture criterion based on Rice and Tracey model, taking the influence of both volume change and shape change of voids into account, is proposed.The characterization of this model for fine-blanking process is easily done by the tensile test and the prediction result shows good.     

Finite Element Optimization of Vee-ring Factor in Fine-blanking Process

The vee-ring is one of the most characteristic features of the fine-blanking process which is derived from the conventional blanking. With the vee-ring, a counter plate and some other working parameters, a component with a precise geometry and smoothly blanked surface can be produced without any major secondary operations. However, these working parameters are always empirically determined or determined by trial-and-error method, which is time-consuming and expensive. In this study, a numerical simulation method was used to analyze the effect of vee-ring factors on product quality, such as distance between vee-ring and punch, vee-ring height and blank holder force, so as to obtain as high clean cut ratio as possible. During the simulation, the model was assumed as axisymmetric one and the workpiece was considered as rigid plastic material, meanwhile the tools were defined as rigid bodies so as to shorten the computational time. A damage model taking into account the influence of hydrostatic stress was used to simulate material fracture in fine-blanking. The result obtained from the simulation indicated that with the help of vee-ring, the metal material near the shear band does not flow with the punch penetration and high compressive stress in the shear band is generated. Consequently, higher clean cut ratio can be obtained with a vee-ring model than the one obtained with a plane blank holder model. Furthermore, the longer the distance between vee-ring and punch is, the higher the height of roll-over becomes.