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1、精选优质文档-倾情为你奉上Effect of Tool Rake Angle on Machining VibrationAbstract：Effect of tool rake angle on cutting vibration by experiments are done at different cutting speed in machining operation, and corresponding theoretical analysis is conducted. Result indicates, amplitude of machining vibration grad
2、ually decreases with tool rake angle increasing; while rake angle 00, the biggest unidirection amplitude occurs at V=5070m/min; While 00, it is at V=160180m/min. Moreover, quarding measures is presented on avoiding the biggest amplitude range so as to guarantee quanlity in precision machining at hig
3、h speed.Keywords: machining,vibration,amplitude,tool rake angleIn machining operation, tool character is not only decided by material, to a certain extent, it depends on resonable geometrical parameters. Tool rake angle is one of the specialest geometrical parameters, directly affects cutting zone d
4、eformation, chip morphology, chip break effection, cutting force, tool head strength and machined surface, quality it is researched by foreign scholars. Relative study points out1: tool rake angle also has considerable effect on machining vibration. But what is present situation about research of to
5、ol rake angle affecting machining vibration? What is the relation exsits between arke angle and amplitude of vibration at different cutting speed and what is the law ? These and others questions have not yet integrated coferences and exact data. For this reason, choose general machine tool, fairly u
6、sed workpiece and tool material in experimental research on the relation between rake angle and amplitude of machining vibration at different cutting speed, and theory analysis of the result is producted, in an attempt to get relevent datas and corresponding material, and then perfect relevent theor
7、y of relation between rake angle and amplitude of vibration. This research provides theorecial basis for adopting resonable rake angle in practice, avoiding largest maplitude zone and guaranteeing quality in practice.1 Experimental Material,Equipment and Instrument1.1 Workpiece MaterialDifferent met
8、al materials have different physical mechanical characters. In this experiment, choose general used workpiece material 45# steel in cylindrical machining.1.2 Tool MaterialAccording to piece material, choose YT14 hard alloy tool tip is choosen and drill weld it on to 45# steel tool. Precision and utr
9、aprecision machining are strict on quality of spare surface, while vibraltion affects is mostly. Therefore, the geometrical parameters and corresponding machining quality of six tools are selected in this experiment rake angle 0 is made:-20,-10,0,10,20and 30, tool cutting edge anglekris 45, tool min
10、or cutting edge angle kr is 15, tool orthogonal clearance0 is 8, tool cutting edge inclination 0 is 0, corner radius r is 1.52.0mm, cuting speed V is 2030mmin-1, feed per revolution 0.2mmr-1, and beck engage mentap is 0.5mm.1.3 Equipment and InstrumentIn experiment, choose CA6140 lathe (Shenyang Fir
11、st machine Tool Plant Made), electric eddy-current sensor and riameter WFC-. Electric eddy-current sensor can be used in dynamic untouched survey, survey range is 01500m, resolving power can reach 1m; Measure range of WFC-is 0.2300m (Unidirection vibration value), this viameter fairly resists interf
12、erance, measured data has quite accurate.2 Experiment Method and Measured DataConsidering up limit of vibration in machining opration, clamp wordpiece on lathe CA6140 with cantilever of three-jaw-chuck. Experiment test device sketch map in Fig.1indicates: Distance from sensor untouched testing point
13、 ( its surface roughnessRa=2.2m)to end surface of chuck is 200mm. Sensor is fixed on lathe tail stock, the measured amplitude (only measure the sensitive direction of work- piece in machining) is an absolute value of piece relative to lathe guide. Distance between cutting part and outter end of chuc
14、k is 50190mm. Relation between rake angle and amplitute of vibration measured in machining operation see table 1.With measured data in table 1, relation curve of tool rake angle and cutting speedaffecting amplitute of vibration is given in Fig.2.Fig.2 indicates: The measured amplitudes of vibration
15、differently correspond to dif-ferent tool rake angle; with rake angle changing, amplitude varies even at same rake angle, while 0 0, the biggest amplitute occurs at V=5070m/min; while 00, itis at V=160-180m/min. To each tool, three repeat experiments are done to verify thereliability of above testin
16、g data, its trend of vibration is roughly the same, only the amplitude of vibration changes a little all (relative error less 5%).3 Analysis of Experiment ResultOn the base of measured data and experiment curve in Fig.2, analysis is given asfellows: 3.1 Relation between Rake Angle and Biggest Amplit
17、udeIn compliance wity table 1, putting data in order, relation between rake angle and biggest amplitude of vibration see table 2. It indicates: With tool rake angle increasing, the biggest amplitude value progrssively decreases. It is because rake angle increasing lessens press of rake face to chip,
18、 plastic defrmation of chip reduced, then coefficient of chip frictiona force on tool rake face decreases, therefore, it lessens cutting force, results in amplitude of viberation in machining operation dropping.3.2 Effect of Rake Angle and Clearanec Angle Dynamic Changing on Amplitude of Vibration F
19、rom machining principle, tool work angle changes with tool movement properties, and it affects cutting force. Variation of work angle is decided by the situation of cutting edge plane in machining operation2,3.Variation of tool rake angle and clearance angle in machining operation is list in Fig.3.
20、In cutting process, tool vibrates at the direction of main vibration, formes vibrating , relative velocity changes not only at value, but also at direction. Namely, because of changes with time, it changes the situation of tool cutting edge plane, results in both tool working rake angleoeand working
21、 clearance angleoechanging cyclically, then form an alternating force. Variation of cutting force is decided by change quantity (strictly speaking, it also includes the change of clearance angle).Variation of rake angle can be get from Fig.3: Thus, variation of level compont of force Py can be discr
22、ibed as Where K is the effect coefficient of rake angle on level component of force. As mentioned above,Py decreases with 0 increasing, thus K 0 .Analysying force state in Fig.3, motion equation isStraigten out as fellows, There upon, condition of causing self driving vibration is : (C+K/v0) 0, Name
23、ly, at this time, change rate of K is fairly big, it causes considerable amplitude of vibration in machining opration.2) While 00, though working angle also changes, but oe increases relatively less than 0(change rate of K if small), thus Py changes a little, just small amplitude of vibration forms.
24、3.3 Effect of Tool Head Dynamic Stiffness on Amplitude In the condition of fixing others tool geometrical paramenters, just change rake angle, it will cause tool head dynmic stiffness changing, thus the intrinsic frequency of tool and compund rest is affected, when it approaches technological system
25、 frequency, considerable amplitude forms (even resonance forms). Relation of biggest amplitude caused by tool rake angle and corresponded cutting speed see table 3.Table 3 indicates:While 00, the corresponding cutting speed range of largest vibrating amplitude is V=5070m/min; While 00, the range is
26、V=160180m/min.Thus it can see, it is necessary to solve the problem of vibration to get high precision and high quality spares at high speed (over 120m/min). Otherwise, it is difficult to ensure machining high precision, high quality spares with high efficiency. According to equation (3): Amplitude
27、of vibration can be decreased by increasing coefficient of damper C. Namely, adopt dead pressure compound rest or set up auxiliary damper to increase C, or increase section of tool, reduce suspend quantity, polish tool reference plane and others measure to decrease of control effect of vibration, so
28、 as to get high precision, high quality spares at high speed.4 Conclusion1) With tool rake angle increasing, amplitude of machining vibration progressively reduces;2) At fixed rake angle, with cutting speed changing, amplitude of machining vibration changes continuonsly;3) At same cutting speed, wit
29、h rake angle changing, amplitude of machining vibration also changes;4) In the choosen condition of this experiment, while 0 0), namely, adopt damp and siffness etc.References1 Zhou Zehua. Metal cutting principles. Shanghai: Shanghai Science and Technology Press, 1984,1392 Yangdi. Machine tool dynam
30、ics. Beijing: Engineering Industry Press, 19933 Zheng Weizhong. machine tool vibration and prevention. Beijing: Science Press, 1981From: JOURNAL OF BASIC SCIENCE AND ENGINEERING Vol.7,No.2June 1999刀具前角对切削加工振动的影响摘 要 对机械加工中刀具前角对切削加工振动的影响进行系统的实验研究和相应的理论分析,结果表明:随着刀具前角增加切削加工振动的振幅逐渐减小，当刀具前角00时,最大振幅产生在V=50
31、-70m/min;而当00时,最大振幅产生在V=160-180m/min。这一结果为精密和超精密加工中有效地抑制或避免切削振动提供了理论与实验依据。关键词 机械加工 振动 振幅 刀具前角机械加工中，刀具的性能除了受材料的影响，在一定程度上取决于刀具集合参数的合理性。刀具前角是一种最特别的集合参数，它直接影响切削带形变，切屑形状，切屑强度，刀具头强度和加工表面质量，这些情况已经经过一些国外学者的调查研究。相关研究表明1：刀具前角对加工振动也有明显的影响。但刀具前角对切削加工中振动的影响的研究结果怎么样呢？在不同的切削速度下，刀具前角与振动振幅有什么关系？规律是什么呢？这些以及一些其它问题没有经过
32、整理且没有确切的数据。由于这方面的原因，在不同的切削速度下对刀具前角与加工振动相互关系的经验调查和理论分析与结果的产生中进行一般的刀具选择和合理的使用工件与刀具材料，目的是试图得到相关数据和相应材料。这个调查为实际中采用合理的刀具前角提供了理论依据。1. 实验材料.设备和仪器1.1 工件材料不同的金属材料有不同的物理机械性能。在这个实验中选择在柱面加工中用过的45#钢工件材料。1.2 刀具材料通过一部分材料，选择YT14硬质合金刀头并把它焊接于45#刀柄上。在大多数时候，精密和半精密机器对配件表面有严格要求。因此，实验中选择六种相应刀具集合参数和加工质量。它们前角0分别为：-20,-10,0,
33、10,20和30，刀具主偏角kr为45,刀具副偏角kr为15。刀具后角0为8，刃倾角0为 0，刀具圆角半径为1.52.0mm，切削速度V为2030m/min，进给量为0.2mm/r，啮合量间隙为0.5mm。1.3 设备与仪表实验中，选择CA6140型车床，电气涡流传感器和WFC-振。电器涡流传感器可用于动态非接触测量，它的测量范围为01500m，分辨率可达到1m；WFC-的测量范围为0.2300m（单行振动值），此振抗干扰能力很强，测量数据比较准确。2. 实验方法与测量数据考虑极限振动加工运行中，CA6140车床工件夹具与悬臂三爪卡盘。实验装置示意图如图1图1 实验装置示意图说明：真空传感器测
34、试点距离卡盘表面为200mm（表面粗糙度为Ra=2.2m），传感器固定于车床尾部，切削部分与卡盘外部底端的距离为50190mm。在机械加工中，前角与振动的关系如表1所示。表1 前角与振幅的关系如表1中的测量数据，刀具前角和切削速度对振动振幅的影响关系曲线如图2.图2.前角.速度与振幅之间的关系图2表明：不同的刀具前角对应不同的振幅：当前角0 0时，随着刀具前角的变化，即使前角相同，最大振幅会发生在V=5070m/min；当00时，最大振幅发生在V=160180m/min。对每个刀具都做了3次重复实验以验证测量数据的可靠性，它的趋势大致相同，只是振幅均有所变化（相对误差小于5%）。3.实验结果分
35、析以实验数据和实验曲线为依据，研究员分析如下：3.1 前角与最大振幅的关系按表1对数据进行有规律的排列，前角与最大振幅关系如表2所示。它表明：随着刀具前角的增大，最大振动幅度会逐步减小。这是因为刀具前角的增大会使前表面对切屑及切屑塑性变形减小从而使刀具表面摩擦系数降低，因此，它可以减小切削强度，从而使切削加工振动降低。表2 前角与最大振幅的关系3.2 前角和后角对振幅动态变化的影响通过加工原理，刀具工作角度随刀具运动性能而变化并影响切削强度。工作角度的变化情况取决于前角的加工操作2，3。刀具前角和后角的变化在机械加工中如图3所示。在切削进程中，刀具振动在主振动方向形成振动速度y.，相对速度不仅
36、数值变化，方向也变化。即由于y随时间变化而变化，它改变了刀具切削前刀面的情况，结果使刀具前角o 和后角o周期性变化，从而形成强度的交替变化。切削强度的变化取决于角度的变化量（严格的说，它也包括后角的变化），前角的变化可以通过图3得出： 图3 前角与后角动态变化因此，构件强度变化变化程度Py可表示为：其中K是影响组件强度的前角因素。如上所述，Py随前角的增大而减小，因此K0。如图3进行强度分析，相关方程为： 变形为： 通过以上可以得出引起自激振动的条件是：(C+K/v0) 0, 即如果这样，K的改变量比较大，它会在机械加工中带来不可预测的振动幅度。2）当00时，即便刀具工作角度变化，但是由于的增
37、加幅度小于0（假设K改变量较小），因此Py改变量较小，形成的振动幅度也较小。3.3 刀具头动态刚度对振动幅值的影响在刀具其它集合参数固定的情况下，仅改变刀具前角就会使刀具头动态刚度发生变化，刀具前角与切削速度引起对应最大振幅的关系如表3所示。表3 刀具前角与切削速度引起的最大振幅的关系表3表明：当0120m/min）切削下，为了得到高精度和高质量的备件，这些问题都必须要决，否则很难保证机械加工中的高精度，高质量和高效率。通过方程3可以看出：振动振幅的减小可以通过增加减振系数C来实现。也就是通过采用设置助减振系统来增加系数C或者暂时减少数量，这样就可以在高速切削情况下得到高的精度和高的质量。4. 结论1)随着刀具前角的增大，加工中的振动幅度会逐步减小；2)当前角一定时，随着切削速度的变化，加工中的幅度会持续变化；3)切削速度相同时，随着刀具前角的变化，加工中的振动幅度也变化；4)在实验所分析的几种情况下，当前角00），即采用合适的刚度和湿度等。专心-专注-专业