Research On Plastic Micro Formingand Size Effect Of Ultrafine Grained Pure Titanium

The traditional plastic forming technology in manufacturing of micro parts formed a new technology-plastic micro forming.Plastic micro forming is to use materials plastic deformation to production, at least in the direction of two-dimensional size in mm order of magnitude below the parts of technology.Plastic micro forming technology has become one of the many kinds of micro machining methods. With the decrease of micro parts size, the size effect which caused by the miniature components size reducing, has created under the macroscopic condition plastic forming technology and the microscopic condition micro plastic forming technology incompletely same.The micro plastic forming technology can not be regarded as the macroscopic condition plastic forming in the part geometry size reduction processing.The ECAP preparation of titanium and titanium alloy as a very promising material, has good resistance to corrosion, biological compatibility and room temperature mechanical properties, also has good plastic forming properties and has a broad development prospect in micro parts manufacturing, especially in MEMS, bio-medical, aerospace and other fields.In this paper, the micro compression and single cup micro extrusion experiments were carried out on the micro plastic forming machine at a constant speed, using the self-made micro forming die. After ECAP deformation of ultrafine grained commercially pure titanium and the corresponding coarse-grained titanium were used as experimental material.In the experiment of micro compression test, the diameter of the cylindrical specimen is 4mm, 2mm, 1mm, and the height to diameter ratio is 1.5. The diameter of the cylindrical sample is 4mm, 2mm, 1mm, and the height to diameter ratio is 0.5. The effects of sample size, grain size, temperature, extrusion speed and friction coefficient on the flow stress of plastic micro forming were investigated by two different micro forming techniques.The results show that in the micro compression experiments with decreasing specimen size, yield stress was a significant decreasing trend; the yield limit of ultrafine-grained titanium material specimen is much larger than the coarse grain titanium specimen; with increasing deformation temperature, the flow stress of ultrafine-grained titanium decreased significantly; flow stress with strain rate of increase of pure titanium ultrafine grain increases.With the decrease of the size of the material, the friction coefficient increases with the decrease of the size of the material during the single cup micro extrusion experiment. The flow stress of the material increases with the decrease of the size of the material; with the increase of extrusion speed, the flow of the same sample sizes should be tended to increase. Different grain sizes of the coarse-grained and ultrafine-grained samples, flow stress of ultrafine-grained titanium samples should be large.