High forming force is often needed when high-strength and low-plasticity materials are processed by fine blanking. Too high forming force increases the load of the die and greatly increases the risk of die failure. If the forming force is reduced, the material will fracture prematurely, which will lead to poor quality parts. Aiming at this problem, a new force variation load fine-blanking technology is proposed in this paper. During the loading process, the forming force does not remain constant but changes with the blanking stroke. A 2D finite element fine-blanking model was established for the TC4 material. The mechanism of force variation fine blanking is also revealed. This paper proposes a method to design the loading route of the forming force with variable load. This method combines finite element simulation with neural network and a multi-objective genetic algorithm. Finally, the application of variable load fine blanking production and the application of traditional fine blanking production parts are verified by the experimental method. The same results are obtained from both simulation and experiment. It is found that the variable load fine blanking process can greatly reduce the load of the die on the premise of ensuring the quality of fine-blanking parts.
At room temperature, the hollow shaft of AISI 304 stainless steel tubes was produced by a hydraulic bulging process. The behavior of strain-induced austenite to martensite transformation and the twin crystallographic nature of AISI 304 stainless steel tubes at different positions after hydraulic bulging were discussed. The results have demonstrated that strain-induced austenite to martensite transformation occurred in AISI 304 stainless steel tubes during hydraulic bulging, resulting in the formation of the α′-martensite phase, and the volume fraction of martensite gradually increased with an increase in strain. The austenite and α′-martensite phases maintained lattice coherency throughout and followed the Kurdjumov–Sachs (K-S) relationship in terms of lattice coherency. During the deformation process, de-twinning occurred in the austenite and the deformation twins were formed in α′-martensite. With the increase in strain, the volume fraction of the annealing twins gradually reduced until complete disappearance in the austenite. The volume fraction of the deformation twins increased in the martensite with an increase in strain, and finally reached saturation.
Fine blanking is a kind of metal forming process with the advantages of high precision, good surface quality and low cost. Influenced by the concept of lightweight, a large number of metal materials with high strength are widely used in various fields. High strength materials are prone to be cracked during plastic deformation due to their poor plasticity, which limits the application range of them. This paper proposed a force variation fine blanking process for high-strength and low-plasticity materials. At the same time, a method to find the curve of forming force for this novel process was presented. A 2D finite element fine blanking model was established for the TC4 material. Combining genetic algorithm and neural network methods, a model was built up to find the optimal forming force loading curve. The parts fabricated by force variation loading and constant loading fine blanking process were compared through experiments. The mechanism of force variation fine blanking is also revealed. The forming force mainly affects the length of clean cutting surface by affecting hydrostatic stress. According to the ultimate optimal loading curve, the forming force should be kept at a low level in the early stage of blanking stroke, and increased gradually in the ending stage. In the application of force variation fine blanking, the part with long length of clean cutting surface can be obtained with lower die load.
As the increase in demand for microparts of metal foil, the micro-blanking process with many advantages of plastic deformation has been widely applied on microparts manufacturing area. But the fracture zone of shearing surface is always present and affects the service life of the part. This paper proposes a new micro-blanking die based on fine blanking technology. In this die, the rubber as the power transmission device is selected to provide a blank holder force and counter force. In the FEM simulation, the influence of a few key die parameters is considered such as punching clearance and fillet radius of female die and punch. And the fine micro-blanking experiments for superalloy foils were conducted to evaluate the feasibility of the die designs. The results had shown the fine micro-blanking die proposed was able to be used for micro-blanking and obtain metal microparts.
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