Effects Of Electro-hydraulic Chattering On The Grain Refinement Of Plastic Formed Parts In Metal Cold Extrusion

Cold extrusion forming technology as an advanced processing technology, it is wildly used in various types of machinery manufacturing industry due to its advantages of high-quality, high efficiency, low cost, etc. However, in the practices of production, the disadvantages of cold extrusion have been gradually revealed: high resistance to metal deformation, short life of die, high requirements on cold extrusion equipment, etc. To solve the above problems and product high-quality productions, our research group has proposed a cold extrusion processing with electro-hydraulic chattering and designed the experimental setup. Research results has shown that with the help of electro-hydraulic chattering,the extrusion load is decreased by about 10% and the distribution of metal flow line is more reasonable, metallic structure is more compacting. Previous studies showed that the refinement of metallic materials inside the grain structure can improve the mechanical properties of materials and quality of products. In this paper,we will discuss the effect of electro-hydraulic chattering on the metal grain structure.This paper selects a kind of forward extrusion cup part as research object, and the vibration signal is introduced in cold extrusion processing. The changes of internal grains and the microstructure evolution during the conventional extrusion processing and electro-hydraulic chattering assisted cold extrusion processing are compared and analyzed by experiments. The main research contents are as follows:1. The metal plastic deformation mechanism is explained by the microscopic mechanism, the plastic deformation methods and plastic deformation characteristics of polycrystalline. This paper introduces the vibration assisted metal forming mechanism by “volume effect” and grain refinement mechanism during the cold extrusion processing by the view of microscopic. The strengthening mechanism of grain boundaries of the polycrystalline during cold extrusion processing and the influence of vibration to it are discussed, laying a theoretical foundation for the subsequent study.2. A cold extrusion experimental setup includes the die structure, the electro-hydraulic chattering system and the experimental control and data acquisition system is put forward and the principle of it is introduced.3. The experimental platform is built and the experiments are designed. The deformed parts(axle sleeves) are deformed under conventional extrusion processing and electro-hydraulic chattering assisted extrusion processing(with different vibration parameters), and then the samples are prepared from the deformed parts. The changes and evolutions of the internal grains of the deformed parts(different regions) with and without electro-hydraulic chattering are compared and analyzed by optical microscopy and transmission electron microscopy(TEM), finally the grain refinement mechanism of vibration assisted plastic deformation is discussed from the view of dislocation. The results show that after the application of electro-hydraulic chattering, the internal grains of the deformed parts are refined and the grains become more slender, and within a certain frequency range, with increasing of chattering frequency, the level of refinement is increased. This indicates that the plastic deformation of metal become more intense under the function of electro-hydraulic chattering and the degree of metal grain refinement is increased.