Research On Mechanism Of Multi-stage Cold Forging And Optimum Structure Of Machine

Multi-stage cold forging machine have many production characteristics with high speed, high quality and high precision, as well as the application of high strength cold forging steel and the development of new process, so that more and more people select multi- stage cold forging machine to product high comprehensive performance parts in the modern manufacturing industry. Such as fasteners and special-shaped parts which are used in aviation, aerospace, shipbuilding, machinery manufacturing and other fields. However, with the rapid development of market economy, production demand towards to diversity, complex structure, high comprehensive performance requirements. While the domestic high-speed multi-stage cold forging machine existing die changing structure, unable to cope with the production trend of product diversification; the old stage cold forging process with less than four stages can not guarantee the forming accuracy of complex part, and the forming mechanism of multi-stage cold forging need for more in-depth research. the above problems greatly limits the development of multi-stage cold forging technology.In this paper the high-speed multi-stage cold forging technology was taken as the main line, around the high-speed cold forging mechanism, the process of multi-stage cold forging and the quick die change structure of multi-stage cold forging machine were discussed. The high-speed cold forging mechanism was discussed by the physical simulation experiment; the multi-stage cold forging process optimization was discussed by finite element simulation analysis and process optimization mathematical model; according to solve the quick die change problem for multi-stage cold forging machine, a off-line die exchange unit was developed. Finally the productive practice of typical parts by multi-stage cold forging machine was used to verify the above discussion. The important research content as follows.(1) Multi-stage high-speed cold forging mechanismFirst of all, the strain rate of multi-stage cold forging were determined by the velocity of machine and the displacement of slid platform, the multi-stage high speed cold forging is divided into the low dynamic forming category. Secondly, the deformation mechanism of high strength steel with multi-stage cold forging(low dynamic strain rate 100~101s-1) were researched by Gleeble testing machine. There are stress wave propagation,the positive strain rate effect, and the weak thermal insulation effect during multi-stage cold forging process. The number of stages and the deformation effect on microstructure refinement significantly, while the strain rate has less effect.(2) Multi-stage cold forging processBecause the combination property of complex cold forging parts were required severely, the design methods which include choice of materials, the number of cold forging stage selecting and the new cold forging process were presented. During multi-stage cold forging process with the finite element simulation, the problem which include the exchange and localization of multi-unit dies and the continuous of each stage simulation parameters were solved.In process optimization, the process optimization mathematical model was built. The optimal process was selected by which minimum value of the model, and the distribution of damage and equivalent stress-strain.(3) Structure optimization of multi-stage cold forging machine--- off-line die exchangeThe changeover times of multi-stage cold forging machine was reduced down, where internal activities are converted to external ones; the die block achieved rapid clamping and hanging with hydraulic cylinders and skewbacks; the movable and fixed dies were positioned precisely by square pins.(4) Multi-stage cold forging parts experimentThe typical cold forging parts were produced by multi-stage cold forging machine with optimized forming process, the forming force, forming process and the change of microstructure were studied. As a result, the parts had fine microstructure and high performance by multi-stage cold forging, as well as the productivity will be increased with development of off-line die exchange unite. The simulation result was verified by productive practice, which include physical simulation of multi-stage cold forging mechanism and the finite element simulation of parts process optimization.Based on the results above, the foreign monopoly about technological upgrading is broke, and achieve the fabrication techniques innovation of multi-stage cold forging machine in our country, and the status quo which has low added value of technology and high precision parts seriously shortage is improved, the study content has important theoretical value and practical significance.