| In recent years,sheet metal and thin wall parts have been wildly used in microelectronics and micro-electro-mechanical systems,causing a sharp increase of demand for micro-stamping parts.The traditional plastic forming equipment and technology cannot meet the need when the micro-stamping parts are smaller,more complex of structure and higher requirements of forming quality.With the development and application of technology,such like numerical simulation,physical-assisted fields,new equipment and no mold or soft mold forming technology.Sheet metal micro-stamping technology gets fast and deep development.The purpose of this paper is to form spherical cap micro-array of T2 copper sheet covering parts through the tensile mechanical properties experiment,numerical simulation optimization,micro-bulging experiment and analyze its forming quality.Micro tensile tests of T2 copper thin sheet was conducted.The effects of heat treatment temperature and sheet thickness on the mechanical properties were studied.The samples with thickness of 20~100μm were heat treated at 350~750℃ respectively.The tensile tests results show that with the increase of heat treatment temperature,the yield ratio of T2 copper thin sheet decreased first and then increased.The thin sheet has a good plastic deformation when at 550℃.With the decrease of the thickness of the thin sheet,the yield ratio of T2 copper thin sheet increased.The sheet was better in plasticity when the thickness was 100μm and heat treatment temperature was 550℃.Numerical simulation analysis of micro spherical cap array part of T2 copper thin sheet was conducted.The effects of fillet,array shape and thin sheet thickness on microbulging were studied.The simulation results show that the R0.1 of the convex and concave die can reduce the stress concentration and improve the uniformity of the deformation.The microstructure of the spherical cap has a smaller degree of stress and strain and sheet reduction when the center distance is 2.5mm.The stress strain value of microstructure decreases with the increase of the sheet thickness.As a result,the intersection of the array and array edge of the convex and concave die should be rounded R0.1 and the center distance is 2.5mm.The micro-bulging experiments were carried out on the micro spherical cap array part of T2 copper thin sheet.The influence of heat treatment temperature and thickness of thin sheet on micro-bulging was studied.The results show that the most serious thinning happens in micro-bulge side wall,the intersection of the array is thinner than the array edge and the bottom of the crown is minimized.The thickness reduction of the part decreases first and then increases with the increase of the heat treatment temperature.The reduction of wall thickness is less,the distribution is uniform and the forming quality is higher when the heat treatment temperature is higher.The part is broken harder and the forming quality decreases with the decrease of the sheet thickness.The micro-bulging wall thickness distribution is the most uniform and the quality is highest when heat treatment temperature is 550℃ and the thickness is 100μm.The most serious thinning happens in fillet punching of micro-bulge side wall and prone to rupture,the maximum reduction rate is 56.5%.The ultrasonic vibration assisted micro-bulging experiments were carried out on the micro spherical cap array part of T2 copper thin sheet.The influence of soft mold,vibration holding time and sheet thickness on micro-bulging was studied.The experimental results show that the microstructure of the spherical cap micro-array is much clear and the wall thickness distribution is more uniform,the forming height increased by 11.66%,the forming limit of the T2 copper thin sheet is greatly improved and the quality is better than the traditional micro-bulging process.The quality of the micro spherical cap array part is best when the heat treatment temperature is 550 ℃,the thickness is 100μm,and the vibration holding time is 80s. |
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