【作者】 秦娜；

【导师】 郭东明；

【作者基本信息】 大连理工大学 ， 机械制造及其自动化， 2011， 博士

【摘要】 旋转超声波加工是固结金刚石磨料工具的磨削加工与普通超声振动加工为一体的复合加工。此加工方法采用固结金刚石磨料工具,通过工具超声振动产生的冲击、工具旋转使磨料在工件上产生的耕犁和划擦、超声振动和工具旋转共同形成的磨蚀,以及高频超声振动下工件表面层产生的疲劳等作用,在较小的切削力下去除工件材料。因此,旋转超声波加工的材料去除率远远高于传统超声波加工,在难加工材料中具有很高的应用价值,广泛应用于难加工材料的制孔。但是,目前对恒速进给式旋转超声波在韧性和脆性材料制孔技术上缺乏系统研究。国内由于缺乏试验设备,试验研究相对较少,在理论研究方面也未见报道,影响了恒速进给式旋转超声波加工技术的应用。本文建立了恒速进给式旋转超声波加工韧性和脆性材料的切削力模型,研究了输入参数对切削力和孔出口崩边的影响,为恒速进给式旋转超声波加工参数的合理选择及工具和机床设计提供了理论依据。主要研究内容和结论如下：1.基于如下假设和简化建立了恒速进给式旋转超声波加工韧性材料的切削力模型：被加工工件为理想的刚塑性材料；参与磨削的金刚石磨粒是具有相同直径的刚体；工具端面的金刚石具有相同的切削高度,且每个振动周期内参与磨削的金刚石数量相同；每个振动周期内,单颗金刚石磨粒在工件上去除的材料体积等于每个金刚石压入工件材料的体积。基于此模型,研究了恒速进给式旋转超声波加工韧性材料时各输入参数对切削力的影响。结果表明：当金刚石磨粒数量和粒度以及主轴进给速度减小时,切削力减小；当超声波振幅和主轴转速增大时,切削力减小；振频对切削力没有显著影响,并对模型结果进行了试验验证。2.建立了恒速进给式旋转超声波加工脆性材料的切削力模型。该模型的假设和简化条件为：工件材料以脆性断裂方式被去除；参与磨削的金刚石磨粒是具有相同直径的刚体；工具端面的金刚石具有相同的切削高度,且每个振动周期内参与磨削的金刚石数量相同。建模中采用压痕断裂力学理论计算了金刚石磨粒压入工件的深度。研究表明：当金刚石磨粒数量和粒径,超声波振幅和主轴转速增大时,切削力减小；主轴进给速度减小时,切削力减小；超声波振频对切削力没有显著影响,并通过试验验证了模型。3.采用全因素试验设计方法,系统研究了金刚石磨粒数量和粒度、超声波振频和幅度、主轴转速和进给速度对切削力的影响。揭示了恒速进给式旋转超声波加工韧性材料时,不存在显著的交互作用,而在脆性材料加工中交互作用影响明显,因此在恒速进给式旋转超声波加工脆性材料时,首先需要确定有交互作用的参数。4.针对在脆性材料上进行恒速进给式旋转超声波磨削制孔时易产生出口崩边的问题,提出了三种改进的工具结构设计,并结合切削力计算、有限元仿真和工艺试验,研究了金刚石工具结构参数和工艺参数对工件孔出口边崩边的影响规律,提出了减小孔出口崩边的有效方法。结果表明：主轴进给速度增大,工件出口崩边厚度和宽度增大；主轴转速和超声波振幅增大,出口崩边厚度和宽度减小；当工具端面倒角增大时,崩边厚度增大；当工具壁厚增大时,崩边厚度也相应的发生变化。在三种工具结构中,外倒角工具获得最小的出口崩边厚度和宽度,而目前普遍使用的无倒角工具加工后孔出口崩边厚度和宽度最大。更多还原

【Abstract】 Ultrasonic-vibration-assisted grinding (UVAG) is a hybrid machining process which combines diamond grinding and ultrasonic machining. With impact mode produced by ultrasonic vibration, grinding mode produced by tool rotation, erosion mode produced by both ultrasonic vibration and tool rotation, and the fatigue of workpiece surface layer produced by high-frequency ultrasonic vibration, the core drill with metal bonded diamond abrasives removes material from workpiece with lower cutting force. Therefore, UVAG gets much higher material removal rate than conventional ultrasonic machining, and attractive applications on hard-to-machining materials, especially the hole drilling on hard-to-machining materials. However, the hole drilling in UVAG of ductile and brittle materials under the condition of constant feed rate has not been systematically studied. In China, due to lack of equipment, not much experimental research has been done on hole drilling by constant-feedrate UVAG, especially no research on fundamental mechanisms under the drilling condition of constant feed rate has been reported in author’s knowledge, hindering the application of constant-feedrate UVAG. In this dissertation, two predictive cutting force models have been developed for constant-feedrate UVAG of ductile materials and brittle materials, respectively. The effects of input variables on cutting force and exit edge-chipping have been studied. The results in this dissertation could provide theoretical guidance for choosing reasonable process variables and designing diamond drilling tool and UVAG equipment.The main research contents and conclusions are as follows:1. A physics-based predictive cutting force model is developed for ductile materials with these assumptions and simplifications:workpiece material is rigid-plastic; diamond grains are rigid spheres of the same size; diamond grains located on the tool end surface have the same extrusion, and all of them take part in cutting during each ultrasonic vibration cycle; the volume of material removed by a diamond grain in one vibration cycle is approximately equal to the intersection volume between the diamond grain and the workpiece. With this developed model, the effect trends of input variables on cutting force are studied. It shows that in constant-feedrate UVAG, as diamond grain number, diamond grain size and feedrate decrease, cutting force decreases; as ultrasonic vibration amplitude and spindle speed increase, cutting force decreases; ultrasonic vibration frequency has no significant effects on cutting force. The model results are verified through experiments.2. A mechanistic predictive cutting force model is developed for brittle materials under these assumptions and simplifications:the workpiece material is an ideally brittle material; diamond grains were rigid spheres of same size; diamond grains located on the tool end surface had the same height of extrusion, and all of them took part in cutting during each ultrasonic vibration cycle. The maximum indentation depth is calculated with theory of fracture mechanics. It shows that as diamond grain number, diamond grain size, ultrasonic vibration amplitude, and spindle speed increase, cutting force decreases; as feedrate decreases, cutting force decreases; ultrasonic vibration frequency has no significant effects on cutting force. The model results are also verified through experiments.3. Based on these models, a full-factorial design of experiments is utilized to study the main effects and interaction effects of input variables on cutting force systematically. There are no significant interaction effects among these input variables in constant-feedrate UVAG of ductile materials. However, there are significant interaction effects among input variables in constant-feedrate UVAG of brittle materials. Therefore, in constant-feedrate UVAG of brittle materials, it is important to determine the input variables which have interaction effects.4. Three cutting tool designs are proposed to improve the exit edge-chipping since it is common in UVAG of brittle materials. Finite element analysis is utilized to study the effects of tool design and process variables on exit edge-chipping for brittle materials in constant-feedrate UVAG and the simulation results are verified by experiments. It shows that, with increase of feedrate, the edge-chipping thickness and size increase; with increase of spindle speed and ultrasonic vibration amplitude, edge-chipping thickness and size decrease; with increase of tool angle, the edge-chipping thickness increases; with increases of wall thickness of tool, the edge-chipping thickness varies. Among the three cutting tools, the outer tool gets the lowest exit edge-chipping thickness, followed by inner tool and normal tool.更多还原