Study On Friction Mechanism And Test In Micro Scale Forming

Recent years, as the demand of micro parts products increasing, micro formingtechnology, have got rapid development. However, in microscopic scales, because of thesize effect phenomena, traditional mature macroscopic theory and technology is difficultto be directly applied to micro forming process. Therefore, it is very important to studysize effect in microscopic scales.In this thesis, the size effect phenomenon of both materials deformation behavior andfriction behavior is studied through experiments, and the surface transitional layer modelis established. Based on the deformation mode of micro forming, a new friction testmethod is developed.The pure copper micro cylinder compression tests are conducted to study theinfluence of specimen size and grain size on deformed specimen surface morphology andmaterial flow stress. The results show that as the grain size increases and specimen sizereduces, the deformation of specimen surface material become more inhomogeneous. Thematerial flow stress presents a decreasing trend with the increase of grain size and thedecrease of the specimen size. Based on characteristics of the micro plastic forming,considering the interaction between grains deformation, by joining the transitional layer,the surface transitional layer model is established. Then the flow stress curves of differentgrains are calculated.Surface transitional layer model is adopted to simulate micro ring compressionprocess, combined with the experimental results, the friction factor under different frictionconditions are measured. It is found that, under lubricated condition, friction factorincreases with the increase of grain size and the decrease of specimen size. There is noobvious friction size effect phenomena while under dry friction condition.According to the characteristics of compounding upsetting and extrusion in the microforming, the T-shaped upsetting-extrusion friction test method is proposed. By simulation,the rib height and web width are found both sensitive to friction factor, and the ratio of ribheight to web width is chosen as a criterion of friction factor. Then the influences ofcorner radius, rib width and friction on different interfaces are investigated.