【作者】 沈学会；

【导师】 张建华；

【作者基本信息】 山东大学 ， 机械制造及其自动化， 2011， 博士

【摘要】 振动切削可以改善切削加工效果,振动车削、振动钻削、振动磨削等的研究较为广泛并已实际应用,但振动铣削的研究甚少。本文对单向超声振动辅助铣削加工技术及机理进行了系统的探索性研究。本文的主要研究内容包括：①单向超声振动辅助铣削运动学分析；②超声振动辅助铣削铣削力的实验研究；③超声振动辅助铣削温度场的有限元仿真分析；④超声振动辅助铣削对工件动态变化和加工尺寸精度的影响；⑤超声振动辅助铣削加工表面粗糙度研究；⑥超声振动辅助铣削加工表面的摩擦学性能研究。以立铣加工为研究对象,针对垂直于进给方向振动和进给方向振动两种单向振动模式,分别进行了刀尖轨迹的二维计算分析,建立了瞬时切削厚度的计算模型,探讨了不同振动方式下的切削力波形特点,分析得出了最佳的单向振动模式,并对理论分析结果进行了实验验证。研究结果表明：在匹配合理的切削和振动参数条件下,进给方向超声振动辅助铣削(下文简称超声振动辅助铣削)能够体现出超声振动切削的特征,将原来单个铣削周期内的连续铣削转变分离式的微细分割断续铣削,有效地改进传统铣削加工机理。实验研究分析了进给方向超声振动对铣削过程中各方向铣削分力峰值的影响,应用RSM方法和ANOVA方法对最大铣削力进行了数学统计建模和分析。研究结果表明：超声振动对进给方向铣削分力峰值变化影响显著,选用合理的超声振幅可有效降低进给方向铣削分力峰值；超声振动辅助铣削加工过程中,最大铣削力取决于主轴转速、每齿进给量以及超声振幅等因素的综合作用,合理匹配加工和振动参数可以获得理想的铣削力值。建立了超声振动辅助铣削二维有限元模型,对超声振动辅助铣削温度场进行了有限元仿真分析,获得了普通铣削和超声振动辅助铣削的变形区动态温度分布,并对仿真分析结果进行了实验验证。研究结果表明：超声振动辅助铣削可以明显改善切削温度场分布,降低刀具温度变化峰值,减小热变形和各种热效应对加工过程的影响。建立了刀具—工件振动系统模型,计算并分析了普通铣削和超声振动辅助铣削过程中工件在垂直于进给方向上的动态位移。研究结果表明：超声振动辅助铣削加工有助于提高工件在加工过程中的动态稳定性,有利于保证加工尺寸精度。实验研究分析了施加超声振动前后加工尺寸的变化,以及不同加工参数匹配对加工尺寸精度的影响规律。研究结果表明：在匹配合理的切削参数和振动参数条件下,断续铣削方式有助于减小加工过程中工艺系统的热变形和受力变形,减小加工尺寸偏差。其中,超声振幅对加工尺寸偏差的影响最为显著。系统研究了超声振动对立铣刀底刃和侧刃加工表面粗糙度的影响机理。研究结果表明：由于刀尖运动轨迹的复杂化,超声振动对底刃加工表面粗糙度产生不同程度的负面影响；由于超声振动辅助铣削的往复“熨压”效应,侧刃加工表面粗糙度明显改善。综合应用ANOVA方法和RSM方法对侧刃加工表面粗糙度进行了统计分析与建模。研究结果表明：侧刃加工表面粗糙度的大小取决于多个切削参数的综合作用,其中,主轴转速的影响最为显著。超声振动辅助铣削加工过程中,如果超声振幅一定,超声振动频率与主轴回转频率的比值越大越容易获得较好的加工表面质量；选用不同的主轴转速时,只有匹配合理的进给参数才能获得最小的表面粗糙度值。系统研究了超声振动辅助铣削加工表面的摩擦磨损特性,实验研究了不同加工参数条件下加工表面的摩擦系数、磨损率以及最大承载压力。研究结果表明：超声振动辅助铣削加工表面的摩擦系数变化曲线波动小,磨损率低,并且具有更好的极限承载能力。不同超声振动辅助铣削加工参数条件下获得的加工表面形貌不同,摩擦磨损过程中边界膜的具体形成方式和摩擦磨损机理也不相同。更多还原

【Abstract】 Vibration cutting can improve cutting effects. There have been many researches and practical applications about vibration turning, vibration drilling and vibration grinding. However, little research has been conducted in vibration milling. This paper presents an exploratory study on the technology and mechanism of one-direction ultrasonic vibration assisted milling.The main content of this research covers the following aspects:①Kinematic analysis of one-direction ultrasonic vibration assisted milling;②Experimental study on milling force in ultrasonic vibration assisted milling;③Study on the temperature field of ultrasonic vibration assisted milling by Finite element method;④Study on the dynamic characteristics of workpiece in ultrasonic vibration assisted milling and the effects of ultrasonic vibration on machining accuracy;⑤Study on machined surface roughness of ultrasonic vibration assisted milling;⑥Study on tribological properties of surfaces produced in ultrasonic vibration assisted milling.Regarding end milling as the research subject, two-dimensional calculation of the trajectory of tool tip was made by studying normal direction(i.e. direction perpendicular to feed direction) vibration mode and feed direction vibration mode respectively. A proposed chip thickness mathematic model was built. The characteristics of milling force under the two different vibration modes were also discussed. As a result, the optimal vibration mode was confirmed. A slot milling experiment was then carried out to prove theoretical analysis conclusions. Research results indicate that matching reasonable cutting parameters and vibration parameters, feed direction ultrasonic vibration assisted milling (hereinafter referred to as ultrasonic vibration assisted milling, UVAM) can embody the characteristics of ultrasonic vibration cutting, and change traditional continuous milling into micro-segmentation intermittent cutting in a milling cycle. Accordingly, UVAM can greatly improve the cutting mechanism of conventional milling (CM).The effects of ultrasonic vibration on the peak values of component forces in feed and normal direction were experimentally studied. Then a statistical model of the maximum resultant force was build, and detailed analysis was made by RSM and ANOVA method. Research results indicate that ultrasonic has a significant effect on milling force in feed direction, and the peak value of feed direction component force can be obviously decreased when choosing proper ultrasonic amplitude. The maximum resultant force is determined by the combined function of several parameters including spindle speed, feed and ultrasonic amplitude, and ideal milling force can be obtained when matching reasonable process parameters.A two-dimensional finite element model of UVAM was built, and FEM was used to analyze the temperature field of UVAM. As simulation results, the dynamic distribution of temperature at deformation zone in CM and UVAM was obtained. Simulation results were verified by experimental data. Research results show that UVAM can greatly improve the temperature distribution of cutting area, drop the max temperature of tool, decrease the influences of various heating effect on cutting process.A tool-workpiece vibration system model was built, and the dynamic displacements of the workpiece along normal direction in CM and UVAM were calculated respectively. Research results show that UVAM can make a great contribution to reducing the dynamic displacement of the workpiece and have a positive influence on machining accuracy.The effects of ultrasonic vibration on finish size and the influence of process parameters matching on machining accuracy were experimentally studied. Research results show that by matching rational process parameters, intermittent milling will help to reduce the deformation of process system caused by cutting heat and cutting force, decrease size deviation. Among all experiment factors, ultrasonic amplitude has a dominant influence on machining accuracy.The effects of assisted ultrasonic vibration on the roughnesses of surfaces produced by bottom edge and side edge of an end mill in UVAM were systematically investigated. Research results show that roughness of surface produced by bottom edge could increase to varying degrees because of ultrasonic vibration in most of the studied cases because of the complexity of tool tip. As for the surface produced by side edge,there is an obvious improvement of surface roughness when ultrasonic vibration is applied owning to the effect of reciprocating ironing.RSM and ANOVA were used to make statistic analysis for roughness of surface produced by side edge. Research results indicate that the surface roughness is determined by several key machining parameters in UVAM, and spindle speed is the most significant factor. It is also found that in most cases, at certain amplitude, higher ratio of vibration frequency to the gyro-frequency of spindle tends to produce better surface finish in UVAM. When spindle speed is selected, only matching proper feed can obtain small surface roughness.The tribological performance of surface produced in UVAM was studied. The friction coefficient, wear rate and carrying capacity of different surfaces obtained under different processing parameters were compared and studied. Research results show that the fluctuation of friction coefficient curve of surfaced produced in UVAM becomes less, the wear rate drops obviously, and the carrying capacity is greatly improved. In UVAM, the topographies of surfaces obtained at different parameters condition is dissimilar, and therefore their tribological performances and friction mechanisms are different.更多还原