Research On Size-effects In Micro-extrusion Of T2 Copper

With the rapidly development of micro-electro-mechanical systems (MEMS) and micro-system technology (MST), the demand for micro parts is increasing gradually. So it is urgent to develop a processing method of micro-components with efficient, low-cost, volume manufacturing. The plastic micro-forming technology inherits the advantages of the traditional plastic forming, such as high forming efficiency, high utilization ratio, low cost, simple process, as well as forming part with good performance and high precision, so it is very suitable to manufacture mass miniature components with low-cost .Effect of the die angle and extrusion speed on the extrusion process was simulated using the commercial software DEFORM-2D and custom material models, it reveals that the smaller the die angle is, the smaller extrusion pressure needed and the more homogeneous plastic flow is; Influence of extrusion speed on extrusion pressure is minor. Basing these results and combining with micro-forming characteristics, experimental program of this topic was designed, it is to study the effect of billet diameter, grain size and extrusion temperature on the micro-extrusion process. With the simulation results and taking micro-forming characteristics into account, the segmented extrusion die with the smaller angle was designed in order to removal of the small parts easily and experiments were carried by micro-forming system which was developed by our team.Experimental results reveal that, with the decrease of specimen diameter, the pressure reduces, it comes up for specimen diameter with 0.5mm unusually; With the decrease of the grain sizes, the pressure reduces except the specimen with 0.5mm in diameter, the main reason maybe is that little grains in the deforming area cause resistance to deformation to get higher resulted in deformation incompatibility. Then a micro-extrusion model of polycrystal was created to give a deep explanation. Surface morphology and microstructure of the extruded parts were observed and analysed by SEM, Confocal laser scanning microscope (CLSM) and Optical microscopy, results reveals that, the inner metal flows faster than the outer metal, when the sample size downscales, the inhomogeneity becomes worse; It is found that distribution of microstructure in the vertical and horizontal sections is inhomogeneous through analyzing microstructure of the formed parts, microstructure in the top and tail of part maintained original one , however in the central fibre microstructure appeared, also in the outer the microstructure is more meticulous than that in the inner. When increasing the temperature, the plastic flow of the material and microstructure distribution tend to be more uniform than what in the cold extrusion.