Research On Size Effects Of Plastic Micro Forming For Phosphor Bronze Thin Sheet

With the rapid development of MEMS, micro parts in the whole manufacturing industries of MEMS is becoming more and more important, the micro plastic forming technology as a new kind of micro processing methods is attaining the industry member’s attention. When the one dimension reduces to a certain extent, the mechanical properties of material exists size effects, and the parameters of forming technology also changes, it has a great influence on the development of micro plastic forming technology. Therefore, the systematically study of size effects of metal thin sheets during micro plastic forming is very meaningful.This paper adopted C5210 phosphor bronze as the research object for size effects of micro plastic forming. Tests of C5210 phosphor bronze thin sheets were performed to investigate the thickness and width, grain size effects on material’s yield stress, elasticity modulus and elongation and so on. Results show that:Yield strength shows “smaller is stronger” and increases with decreasing thickness from 800 μm to 50 μm, but work hardening exponent and elongation decreases as thickness decrease. Yield strength and elongation show “smaller is weaker” and decrease as section width decrease. Yield strength decreases as grain size increases and meets the relation of Hall-Petch, but work hardening exponent shows an increasing trend, elongation increases to a peak and then decreases. Sample thickness and grain size have little impact on material elasticity modulus.In order to research the size effects mechanism of elongation, fracture morphology of tensile specimens was observed by SEM. The results show that dimple intensity and size increases as specimen thickness increases from 50 μm to 100 μm, then elongation increases from 18.2% to 24.1%. The size of dimples and fracture area reduction increase as grain size increase, for the thickness of 100 μm, elongation increases to peak 29.2% when grain size increases to 28.72 μm. However, the dimples are less and smaller when the grain size continue to increasing, elongation decline.This paper adopted ABAQUS to simulate micro bending process and spring-back of C5210 phosphor bronze thin sheets based on the research on size effects of mechanical properties. The simulation results show that spring-back increases as the bending radius increases and decreases as the grain size increases. The spring-back increases with specimen thickness decreasing, and when the thickness is less than 100 μm, the trend gradually become clear with thinning of thickness, which shows size effects of the spring-back with the thinning of thickness. Among them, the specimen thickness is the greatest impact, which increases significantly with decrease of specimen thickness.The micro bending experimental of phosphor bronze thin sheets was carried out to investigate the different bending radius, different specimen thickness and different grain size effects on spring-back, which based on the simulation of micro bending process and spring-back. The experiment results show that the influence of bending radius, specimen thickness and grain sizes on the spring-back is consistent with simulation results, which indicates that the size effects on mechanical properties and micro bending spring-back which acquired through tests and simulation can provide a reference for micro plastic forming.