Tribology Size Effect And Lubrication In Micro Sheet Forming Of Copper T2 Thin Sheet

Micro sheet forming which is focused by researchers from home and abroad has great potential in micro electro mechanical systems, electron industries, medical, new energy and other fields, and has been rapidly developed because of its mass production, high efficiency, high precision, low cost and no pollution. However, it is not wise to apply macro sheet forming to micro sheet forming directly because of mechanical property size effect and tribology size effect with the miniaturization of specimen size.Friction between the billet and the mould is one of the most important factors affecting the whole process of metal forming, such as forming energy, forming limit, surface quality and geometry of the product, tool life and so on. Tribology size effect in micro sheet forming of copper T2 thin sheet was systematically studied in this paper, besides this, the lubrication method suit for micro sheet forming was also studied, both of which have great significance in promoting the development of micro forming process.A non-contact strain measurement device was developed based on the charge coupled device, and the error was decreased compared to the contact measurement method. Using this device, the mechanical property size effect of copper T2 thin sheet was investigated. The influence of mechanical property size effect on friction coefficient was studied by the pin-on-disk experiment. The results showed that the flow stress and elongation percentage were dramatically decreased with the decreasing of the specimen size. The friction coefficient was almost the same and was not affected by the mechanical property size effect.A strip drawing device suit for micro friction test was developed. The influence of different process parameters on friction coefficient of specimens with different sizes were studied by using this device. The surface of specimens after test was observed by the scanning electron microscope. The results showed that the friction coefficient was greatly increased with the increase of the mould surface roughness, decreased with the increased of the forming velocity, increased with the increase of the specimen surface roughness and normal pressure. The friction coefficient was almost the same for different specimens with different size at the same condition. The tribology size effect in micro forming under different lubrication conditions of copper T2 thin sheet was studied. The results showed that the friction coefficient increased dramatically with decreasing the specimen size with the lubrication of three liquid lubricants. The mechanism of tribology size effect in micro sheet forming was studied by SEM observation and theoretical analysis. A friction model was established based on the Coulomb theory and considering the ratio of nominal contact diameter and brim width. The friction coefficient obtained from the experiment was in accord with the friction model.Because tribology size effect occurred by using liquid lubricants, surface modification of micro sheet forming mould by solid lubrication film was chosen. TiN, DLC, and MoS₂ were fabricated on the dies by using plasma immersion ion implantation device. Structure and composition analysis were studied by atomic force microscope, Raman spectrum, and X-ray diffraction. Property analysis was investigated by ball-on-disk test, scratch test, and nano-indentation test. The results showed that DLC was superior to TiN and MoS₂, and can be chosen as a lubricant in micro sheet forming.A micro punching system based on servo motor and a micro blanking-deep drawing multiple operation mould were developed. By using these devices, micro deep drawing of copper T2 thin sheet under different lubrication conditions was studied. The results showed that the DLC coated mould greatly decreased the forming force, increased the limit drawing ratio, improved the surface quality, and keep the forming quality stable.