【作者】 王艳；

【导师】 袁林；

【作者基本信息】 哈尔滨工业大学 ， 材料工程（专业学位）， 2019， 硕士

【摘要】 在薄板微成形工艺中,材料易产生不均匀变形、应变集中和成形极限降低等问题,尺寸效应使传统的薄板成形极限预测模型和实验方法难以适用。而振动辅助薄板微成形技术能够提高薄板材料的成形性和表面质量。目前,超声振动软化效应的研究已经取得了一定的成果,但在振动辅助微成形韧性失效和成形极限的尺度效应问题、振动辅助软模成形极限和振动辅助微阵列的研究较为匮乏。本文从传统的成形极限实验方法出发,搭建了适用于板厚0.2mm以下的振动辅助薄板微成形极限实验平台,通过超声振动辅助微拉伸和微胀形实验,研究振动对薄板微成形极限和断裂的影响。发现,振动对拉—压区和拉—拉区极限应变值具有相反的影响规律,原因是由振动加载方式和超声能量不同引起的;随着振幅的增大,断裂形式由微孔聚集型断裂逐渐向疲劳断裂特征发展;振幅较小时,振动并没有改变成形极限曲线随晶粒度的变化趋势和断裂模式,但也具有明显的尺寸效应;晶粒尺寸的变化和振动对材料断口韧窝的数量和大小具有相反的影响。将软模应用到振动辅助双拉胀形中,对超声振动、柔性冲头和尺寸效应在微成形中的多重影响进行了探讨。软模成形后的极限胀形高度降低,极限应变值增加;振动后极限胀形高度增大,极限应变变化不明显。随着晶粒尺寸的变化,振动辅助软模作用尺寸效应明显。结果表明,振动提高了软模的流动性,使塑形变形更加均匀,增加了材料成形性能。开展振动辅助软模微胀形阵列实验,通过改变超声振幅、振动时间和作用力,分析工艺参数对球冠微结构阵列件表面质量和贴模性的影响,结果表明,一定程度的振动辅助软模成形可以提高球冠的表面质量和贴模性,有利于保证成形件的精度,提高板料的成形性能。获得了研究范围内的最佳工艺路线,成形出与凹模尺寸一致的球冠微结构阵列件,表明振动辅助软模胀形工艺非常适合制造薄壁微结构阵列件。更多还原

【Abstract】 In the sheet microforming process,the material is easily to cause uneven deformation,strain concentration and forming limit reduction.The size effect makes the traditional prediction model and experimental method of sheet metal forming limit difficult to apply.Ultrasonic vibration assisted sheet micro-forming technology can improve the formability of the metal sheet and enhance the surface quality of forming parts At present,the research on ultrasonic vibration of the softening effect have achieved certain results,but there are few research on the scale effect of the ductility failure and forming limit of ultrasonic vibration,the vibration assisted soft mold forming limit and the vibration assisted microarray.In this paper,based on the traditional forming limit experimental method,established an experimental platform for ultrasonic vibration-assisted micro-forming limit of sheet metal,which is suitable for materials below 0.2mm;The effects of vibration on the forming limit and fracture of were studied by ultrasonic vibration-assisted microstretching and micro-bulging experiments.It is found that vibration has opposite effect on the extreme strain values in tension-compression zone and tension-tension zone.,The reason for the analysis is due to the difference of vibration loading mode and ultrasonic energy.With the increase of amplitude,the fracture mode gradually develops from microporous aggregation fracture to fatigue fracture.When the amplitude is small,vibration does not change the trend of forming limit curve with grain size and fracture mode.But it also has obvious size effect.The change of grain size and vibration have opposite effect on the number and size of fracture dimples.Appling the soft mold to the vibration auxiliary etc double bulging,.Made a discussion about the multiple influences of ultrasonic vibration,flexible punch and size effect.The ultimate bulging height of the soft mold is reduced,but the ultimate strain value is increased.After vibration,the ultimate bulging height increases gradually,and the change of ultimate strain is not obvious.With the change of grain size,the size effect of vibration assisted soft mold is obvious.The results show that vibration improves the fluidity of the soft die,makes the plastic deformation more uniform and increases the formability of the material.Carried out the ultrasonic vibration assisted soft mode micro-bulging array experiment,the influence of process parameters on surface quality and die-insertion of spherical crown micro-structure array parts is analyzed by changing the amplitude,vibration time and force.The results show that a certain degree of vibration-assisted soft die forming can improve the surface quality of spherical crown and die-bonding property,which is beneficial to ensure the accuracy of forming parts and improve the forming performance of sheet metal.The optimum technological route was obtained and spherical crown microstructural arrays with the same die size were formed.The results show that the vibration-assisted soft die bulging process is very suitable for manufacturing thin-walled microstructural arrays.更多还原