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自动 刀架 系统 设计

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8刀自动刀架系统设计,自动,刀架,系统,设计

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黑龙江工程学院本科生毕业设计附 录A对于手动挡的车型而言，离合器是汽车动力系统的重要部件，它担负着将动力与发动机之间进行切断与连接的工作。在城市道路或者复杂路段驾驶时，离合器成了我们最频繁使用的部件之一，而离合器运用的好坏，直接体现了驾驶水平的高低，也体现了对于车辆保护的好坏。正确使用离合器，掌握离合器的原理以在特殊情况下利用离合器来解决问题，是每个驾驶手动挡车型的车友应该掌握的。所谓离合器，顾名思义就是说利用“离”与“合”来传递适量的动力。离合器由摩擦片，弹簧片，压盘以及动力输出轴组成，布置在发动机与变速箱之间，用来将发动机飞轮上储存的力矩传递给变速箱，保证车辆在不同的行驶状况下传递给驱动轮适量的驱动力和扭矩，属于动力总成的范畴。在半联动的时候，离合器的动力输入端与动力输出端允许有转速差，也就是通过其转速差来实现传递适量的动力。离合器分为三个工作状态，即不踩下离合器的全连动，部分踩下离合器的半连动，以及踩下离合器的不连动。当车辆在正常行驶时，压盘是紧紧挤靠在飞轮的摩擦片上的，此时压盘与摩擦片之间的摩擦力最大，输入轴和输出轴之间保持相对静摩擦，二者转速相同。当车辆起步时，司机踩下离合器，离合器踏板的运动拉动压盘向后靠，也就是压盘与摩擦片分离，此时压盘与飞轮完全不接触，也就不存在相对摩擦。最后一种，也就是离合器的半连动状态。此时，压盘与摩擦片的摩擦力小于全连动状态。离合器压盘与飞轮上的摩擦片之间是滑动摩擦状态。飞轮的转速大于输出轴的转速，从飞轮传输出来的动力部分传递给变速箱。此时发动机与驱动轮之间相当于一种软连接状态。一般来说，离合器是在车辆起步和换挡的时候发挥作用，此时变速箱的一轴和二轴之间存在转速差，必须将发动机的动力与一轴切开以后，同步器才能很好的将一轴的转速保持与二轴同步，挡位挂进以后，再通过离合器将一轴与发动机动力结合，使动力继续得以传输。在离合器中，还有一个不可或缺的缓冲装置，它由两个类似于飞轮的圆盘对在一起，在圆盘上打有矩形凹槽，在凹槽内布置弹簧，在遇到激烈的冲击时，两个圆盘之间的弹簧相互发生弹性作用，缓冲外界刺激。有效的保护了发动机和离合器。在离合器的各个配件中，压盘弹簧的强度，摩擦片的摩擦系数，离合器直径，摩擦片位置以及离合器数目就是决定离合器性能的关键因素，弹簧的刚度越大，摩擦片的摩擦系数越高，离合器的直径越大，离合器性能也就越好。起步时需要有一定的半联动时间，以保证起步的平顺。坐新手开的车都有这样的体会，要么起步时熄火，要么是一颤一颤出去的，这些都是半联动技巧没有掌握好的表现。汽车在起步的时候，变速箱的二轴是静止的，当我们挂一挡以前，需要踩下离合器，此时变速箱的一轴与动力分开，通过同步器挂上一挡以后，一轴也同样变为静止。动力从飞轮出来是有一定转速的，此时与一轴存在巨大的转速差，这也就是为何起步时对于半联动的要求要比换挡时高得多的主要原因，离合器的前后部件一个静止一个运动。这样的转速差必须由半联动来消化，也就是动力开始的时候部分传递给一轴，使车辆能以较平稳的姿态起步，一旦车辆行驶起来，转速差就会变得很小，此时将离合器完全抬起，就不会有冲击了。坡道起步需要较高的半联动技巧。半联动可以消化发动机转速与车轮之间的转速差，也就是说可以有在动力已经传递到车轮上，但车轮并不运转的情况出现，这种情况常常发生在坡道。一般对于驾驶技术不熟练的驾驶员而言，在坡道起步时会拉起手刹，然后让离合器处于半联动状态，松下手刹，车辆保持静止，防溜车殃及后车。而车辆向后滑行的重力是由发动机提供的动力来抗衡的，而离合器则负责消除这里存在的转速差。车辆处于这种情况下，驾驶员就能很轻松的起步了，继续踩下油门踏板让转速进一步提升获得足够的扭力，车辆就顺利坡起了。此时对于半联动的技巧要求较高，如果半联动力度太弱，就可能在松开手刹时车辆向后滑动，容易造成新手的惊慌失措，如果半联动力度过强则容易是车辆加速过猛而撞到前车。所以对于新手而言，此时可以让发动机转速略高，并采用较大的半联动力度，使车辆有个向前走的趋势时，再松开手刹。新手驾驶的时候会存在一些离合器使用上的错误操作。作为新手，由于驾驶技术的不熟练，很难将油离很好的配合，导致在使用离合器的时候出现一些有损离合器的操作方法，而这些情况同样是出现在半联动的时候。避免离合器长时间处于半联动状态才能有效的保护离合器。有些新手刚上路时由于紧张，油离配合不好，害怕自己在起步时熄火灭车，于是就轰大油门而离合器却压得很低，半天也不全部抬起实现全联动，此时发动机的转速与一轴的转速存在巨大的转速差，而车辆则是慢慢起步的，这些巨大的转速差全部由离合器的半联动消化，这是非常毁离合器的做法。为了避免频繁的坡道起步，用脚半踩离合，这样能用半联动来控制车的行驶速度，也就是俗称闷着离合器走。整个过程离合器都是发生滑动摩擦的，这种长时间的滑动摩擦也会损害离合器。开车上路总喜欢把左脚放到离合器踏板上，从而导致不自觉的压下了离合器踏板，车辆长时间处于半联动状态。所有这些操作都会加速离合器片的磨损，对车辆的动力性和经济性都会造成损失。离合器是汽车上一个频繁摩擦的部件，它会随着使用时间和使用频率的增加而产生磨损，就会产生离合器打滑现象。对于有经验的驾驶员是可以提早发现的，比如判断离合器是否打滑我们可以在原地着车时挂入一挡，这时不要松手刹，然后慢慢抬离合器直至完全抬起，如果在离合器抬起时，发动机熄火这就证明你的离合器不打滑，反正如果离合器都完全抬起了而车还不熄火就证明你的离合器有问题了。还有就是在起步时明显感觉到离合器位置突然变高了，也是离合器打滑的前兆，再有就是我们在急加速时只是感觉发动机转速在不断升高，而车速却没有升高等等这些情况都是离合器打滑的征兆。当出现离合器磨损或打滑时我们要及时检查、更换，否则这会使发动机输出的动力不能有效的传递给输出轴上，而是将动力损失在离合器片与飞轮之间的滑动摩擦上，并将相互之间的摩擦转变为热能消耗掉，这样会导致动力传输下降，同时还会费油增加用车的成本。附 录BStick to the car, clutch is an important component of the auto power system, it bears will power and the engine cut and connection between the work. In urban road sections or complex, our most frequently used clutch became one of the components, and clutch, use directly reflects the driving of level, but also reflects the good protection for vehicles. Used correctly, principle of clutch clutch in special circumstances using clutch to solve problems, each block is driving the car manual should master enthusiasm.So-called clutch, just as its name implies is using from and close to deliver the amount of power. By friction clutch, shrapnal, pressure plate and dynamic output shaft, decorate in the engine and transmission between, used to be the flywheel storage engine torque to gearbox, ensure vehicles in different driving conditions apply to drive wheels, belong to the driving force and torque powertrain category. In half the time of the clutch, linkage power input and output power is allowed, namely through rotational speed to realize the amount of power transmission.The clutch is divided into three working condition, not on the clutch type on the part of the clutch, under half step down, and the type of clutch type. When the vehicle in normal operation, the pressure plate is tightly packed on the friction of friction, pressure plate and the friction between the biggest slice, input shaft and the output shaft remains relatively static friction between both speed and in the same. When the vehicle, the driver started on the clutch pedal, clutch platen movement by pulling back, also is the pressure plate and friction slices, pressure plate and the separation of the flywheel no contact will not exist relatively friction.Finally, also is a type of clutch. At this time, the pressure plate and the friction in small type. Clutch disc friction slices with flywheel is sliding friction between state. The flywheel speed than the output shaft speed, the power transmission from the flywheel part to the gearbox. This engine and driving wheel is equivalent to a soft connection between state.Generally speaking, the clutch is started and shift in vehicles, at the time of transmission shaft and a second shaft rotation difference exists between the power of the engine, must be with a shaft cut, can be very good synchronizer will keep a shaft speed and synchronous, block into later, again with a shaft through clutch of engine power, power continue to transmit.In the clutch, and an indispensable buffering device, it consists of two similar to the flywheel disc disc playing together, in rectangular groove is decorated in the slots in the spring, the impact of fierce encounter between the two disks, spring, mutual happen elastic cushion external stimuli. Effective protection of engine and clutch. In all parts of the clutch platen, intensity of spring, the friction coefficient, clutch friction, diameter and clutch position number is the key factor decision clutch performance, the stiffness of hydropneumatic spring, the friction coefficient is higher, the diameter of the clutch, clutch performance is better.When beginning to have time, to ensure the linkage of half started smoothly. Sit novice car have such experience, or remove, or started a quiver yishan, these are not good skills and linkage. The car at the start of the second shaft, gearbox, when we are still hang a block, need on the clutch, a transmission axis and power, through the synchronizer hang a block, a shaft also become motionless. Power is out from the flywheel, there must be a rotating shaft with great speed, which is why started to half of requirements than the shift much when the main reason, clutch before a stationary components, a movement.So the speed of the poor by half linkage to digest must, is at the beginning of the power transmission shaft, and give a part of the vehicle to a smooth start posture, once the vehicle, speed difference will become small, at this time will clutch, there wont be fully up the impact.Start to higher ramps and linkage skills. Half the speed and the engine can be digested linkage between the wheel speed difference, i.e., the power can be passed to the wheel, but not running wheel, which often occurred in the ramp. General for driving technology not skilled driver, start up the ramp when handbrake, then let the clutch is linkage, panasonic, vehicle handbrake stationary car after disaster prevention, slip. The gravity of the slide backwards and vehicle by the engine is the power to provide against, and clutch is responsible for eliminating the speed difference exists here.Vehicles in this kind of circumstance, the driver can easily start, continue to trample accelerator pedal to obtain enough to further improve speed of torsion, vehicle goes up the slope. Now the skills required for half a linkage, if half linkage too weak, might efforts in the open hand brake when slide backwards, easy to cause the vehicles panic, if half of a joint efforts, easy is accelerating and hit limber fast-drawing. So for beginners, can let the engine speed slightly tall, and the greater half linkage, make vehicles have a walk when the trend, and loosen the handbrake.When will the novice driving some mistakes on the use of the clutch. As a novice, due to driving technology, it will be difficult to unskilled oil from good coordination, resulting in use when the clutch of some beneath the clutch, and these operating methods are also appeared in the half of time.Avoid clutch at half time state can effectively protect the linkage of clutch. Some of the novice just when due to stress, oil from bad cooperation and started out in the car, then remove and clutch shot big throttle pressure very low, but also dont lift realize all along, the linkage of engine speed and a shaft rotational speed of the huge, and vehicle speed is slowly started, the great speed of all poor by clutch linkage, this is very destroyed digestion. Clutch, In order to avoid using the ramp frequent trample brake, so half feet in half the speed KongZhiChe linkage to, or a clutch. FrowstyThe whole process of sliding friction clutch occurs, the long time of sliding friction will damage the clutch. Driving on the left foot in general like the clutch not consciously, resulting in the clutch pedal under pressure for a long time, the vehicles at half linkage. All of these operations can accelerate the clutch disc wear, the dynamic performance and fuel economy of vehicle can cause damage.The clutch is a frequent automobile parts of the friction over time, it will be increased frequency of use and wear, and can produce clutch skid phenomenon. For experienced pilots can be found, such as advance whether we can judge the clutch in situ skidding car when a block, then hang soonly, and then slowly lift clutch brake up until completely, if the clutch lift, engine flameout this proof of your clutch not sliding, anyway if the clutch is completely lift and car is not leaving the clutch is proof that you.There is in start when suddenly felt clutch position, also the clutch, another is the precursor of sliding speed in urgent when we just feel engine speed in rising, and speed, but not all of these conditions are signs of sliding clutch. When the clutch when we want to wear or skid timely inspection, replacement, otherwise will make the engine output power can effectively to the output shaft, but will power loss in the clutch plate and the sliding friction between the flywheel, and the friction between energy consume, for it will cause power transmission, also dues increase the cost of oil transport. 9金刚石刀具钻探工程陶瓷的研究 摘要：使用金刚石刀具给工程陶瓷钻洞的方法已经被广泛应用。 用这种方法，金刚石刀具绕固定的研磨料旋转。 基于裂缝力学概念操练的机器加工机制被掌握，并且一个材料去除比率的新理论的模型被提出。 根据这个模型， 去除材料速度比率根据应用静载重的增加而增加， 钻削刀具的旋转的速度，以及研磨料的粒度。 选择99.5%的Al2O3陶器制法，因为这种工件材料已经进行过这样的实验。 结果显示金刚石刀具钻探工程陶瓷是机器加工工程陶瓷的一种有效的方法。关键字： 设计陶瓷； 钻石工具； 操练； 机器加工机制1.引言工程陶瓷有许多极好的物理和机械特性：高的硬度，高的热阻，化学稳定性和低的热和电传导性，还有很多,这里就不一一列举了。因为这些特别的性能，工程陶瓷预计使用越来越多的应用在从电子和光学设备到大范围内的许多高性能需求的加热并且穿抵抗部分. 直到今天，他们的申请几乎仅局限于电子和光学设备。 一个原因是发现将在粉末冶金之前 在对形成的过程的认识很局限， 保证复杂的几何尺寸并且保证足够的准确度完成相当困难。 还有一项相当多的赤字，在使用变硬的粉末冶金的国家后里，更复杂的几何学的生产或者机器加工，由于在当今的使用过程中的对性能或者形成的过程中的多数的能力的没有得到发挥。传统方法的对机器加工工程陶瓷极最后的尺寸保证极其艰苦和费时。近年来对进行研究有效率物质排除过程的更多的地区开始聚集冲力， 特别是在降低错误和在机械加工的陶器制法的附属表面里的裂缝的事件的方法和手段上。在前面的文章里研究了金刚石刀具钻探工程陶瓷这种加工方法，它可以提高材料去除率，并改善表面光洁度。 本文打算进一步作进一步的阐述金刚石刀具钻探的陶瓷的机理， 从而使预测中的材料去除率 条款适用于静态负荷，粒度的磨料和转速的钻井工具。2. 金刚石刀具的工作机制钻石刀具钻削的过程的机制如图1所示。 在加工的过程刀具旋转，工件是固定。 切除的材料机制已经被一般通过微小的对被磨损的表面的观察。在任何场合下，切除材料的过程都可看作类似于材料相对于刀具或者粒子或者骨除去工作表面的毛刺。 工件材料可以通过磨损的像谷粒一样的磨碎的很多微小的粒子就会形成 刺穿。可以断定工程陶器的切除主要靠钻石刀具的旋转得以实现。 理解这个过程， 研究机械表面就会像切除内部一样的脆的材料，因为得益于工件磨损的谷类的凹口。2.1刀具变形的研究刀具凹口在变形和骨折模式在洛氏硬度对陶器的正常接触下观察陶器的研究中发现的在图2 说明。 在直接变形的下一个区域是塑性变形的区域。 鉴定这两个区域主要靠裂缝。从塑性区流出： 中间/半径裂缝和横向裂缝。 裂缝的两种类型的的不同现象受有弹性/塑料里的不均匀的塑性变形被残余应力影响。 中间裂缝在装期间起源于一次楔块的冲击， 并且他们可能继续在装载期间受到断裂时的残余的抗拉的压力。 横向裂缝则是由残余应力引起并且可能会变形成锯齿形直到负荷被除去。 半径的大小和增减和横向裂缝是非常有助于材料切削过程。 如图2，这些半径和横向裂缝的开始和变大中后导致了脆的材料的碎裂。 开始时半径裂缝的关键的负荷Pc被给通过: 是一个与变形几何学有关的量纲， KIC是工件的裂缝坚韧， HV是工件材料的维氏硬度。 对中间或者半径裂缝铬Cr和横向裂缝CL的尺寸来说，公式如下: P是应用负荷， x1和x2是成比例常量。他们一般被看横向裂缝Ch的那最深处与eP=HVT1=1成正比。从中间/半径的尺寸或者横向裂缝用负荷的增加并且用减少增长的这些结果断定， 在工件材料的裂缝坚韧里。 迄今在描述的凹口上的调查为理解实际的钻头(操练陶器制法的过程)提供有用的信息。2.2物质移动比率和各种各样的参数之间的关系根据在凹口里的陶器制法的测验结果的在物质移动比率和各种各样的参数之间的关系， 因此发现了单个的研磨料引起的一个物质移动的模型，如图3中所示。 这个模型刀具沿着表面考虑到研磨料的线的切线的运动。 在额定负荷P下磨损的大小及除去的工件材料的体积与尺寸成正比 横向磨损和除去工件物质的V0向适合。V0 =2CLChd (4)CL是横向裂缝的长度，Ch是横向裂缝的最深度， d是磨损的距离然后材料的切削速度可以得到：MV0=4pCLChor (5) o 是工具的旋转的速度 r是预定轨迹的半径.假定有效钻削工件颗粒密度是l，在区域中A中的有效谷的数目:n= dA=2lprdr (6)此时刀具的移动速度：工件表面的有效切除量：其中A=00000000, R2是金刚石钻孔工具的外部半径 ,R1是金刚石钻孔工具 内部半径,K1是比例常数;ug研磨系数和d0是有研磨作用的最小直径. 然后:l作用在工件上的力：将 (2),(3),(9),(10) 带入公式(7):简化得：其中K是成比例常数.根据公式(12),材料切除速度MV将增加静止负担W，刀具o的旋转的速度随研磨最小直径的d0的大小地增加.3.试验的准备金刚石钻孔工具随着的外部半径R2是一个轮子旋转，另一齿轮的内圆半径10mm，准备三种类型的钻石钻孔工具,分别是80,120和160粗磨粉，他们的都集中在100%.一99.5% Al2O3。冷却液可以选择制陶艺术当工作部件材料或者水，准备一0.001毫米的英制千分表，用来准确测量。,然后转速能是精心设计(MRR是按照每分钟)钻孔的深度倍增钻孔工具的跨-组合家具的-区域.表面粗糙存在测量使用一5%的相对准确性地测量工具表面.4.实验结果和讨论4.1.静止负担试验r结果显示：材料的切削速度的关系如图5。表面粗糙受应用静止载荷负担影响，静止负担的增加而表面粗糙度增加.在下列情况下做试验: 0=720 rev/min, C=80, 当静止力分别为：25 35 45 55 65 N时，表面粗糙分别为：0.0040,0.0040,0.0042,0.0045和 0.0045毫米.4.2.钻孔刀具刀具的旋转的速度的影响钻孔工具的旋转的速度。钻孔工具的旋转的速度的增加造成一些其他的因子变动,例如在研磨作用下的流过的细铁屑会迅速而且变得锋利，并非和钻孔工具的旋转的速度成比例。随着材料的高速切削会使细铁屑变红是非常对重要的.随着钻孔工具的旋转的速度的增加,会形成许多细铁屑,和离开使它变红成为越来越更多困难.这个将也影响有研磨作用的谷的自我磨损.一般说来,研磨作用的谷包含两个成分，通过进步有研磨作用的谷碎裂自我锋利和通过进步债券侵蚀自我锋利.当细铁屑未被离开完全使变红的时候,债券侵蚀和有研磨作用的谷碎裂变得困难结果是钻孔工具的迟钝:因此转速将是受影响.此外,细铁屑变红把冷却液和压力的联系起来.在目前试验中,冷却液的压力在这状况下是104Pa.,当钻孔工具的旋转的速度是1200 rpm的时候就会产生。5.总结金刚石刀具钻探工程陶瓷的基本机械装研究，研究了金刚石刀具钻探工程陶瓷的影响，可以知道钻孔工具的旋转的速度和有研磨作用的谷的大小有关系的，随着谷的增加材料的切削速度的增加. 由完成的表面和每一参数的粗糙之间的关系得到:随着静压力的增加,刀具的旋转的速度减少，有研磨作用的谷大小的增加会使表面粗糙增加。参考资料 1 光碟戴维奇，机械性能的陶瓷，剑桥 大学出版社，剑桥， 1979年。 2 吨沃伦辽，抗折强度的地面陶瓷缓进给： 一般模式，韧脆转变和MLP建模，诠释。者 马赫。工具。 38 （ 4 ） （ 1998 ） 257-275 。 3 南雷什克，工程陶瓷：新观点 通过增值（多）的功能，重点工程。母校。 175-176 （ 1999年） 1月10日。 4 光铃木吨， ，一种新的研磨方法 陶瓷使用双向超声振动的工具， 人工神经网络。 CIRP 42 （ 1 ） （ 1993 ） 375-378 。 5 K.P. Rajurkar ， Z.Y.王答：，去除陶瓷微 材料（氧化铝）的高精度超声波加工，大意。杨永强。 23 （ 1999 ） 73-78 。 6 光田，吨杉阁下平，阿J积分办法材料 去除机制陶瓷，安子介。 CIRP 40 （ 1 ） （ 1991 ） 61-64 。 7 经济学家埃文斯， D.B.马歇尔在： D.A.里格尼（编辑） ，基本原理 摩擦磨损的材料，美国机械工程师协会，纽约， 1981年，页。 439 - 442 。 8 I.A.马尔可夫，加工性材料和超声波 声波振动， 1966年。 9 Komaraiah ， P.N.姆雷迪，研究的影响工件 物业超声波加工，诠释。学者马赫。工具。 33 （ 3 ） （ 1993 ） 495-505 。 10 美国国昭，东一仁，审判建设的超声波研磨 设备和加工技术的特点， JSPE 52 （ 1 ） （ 1986年） 107-113英文翻译Journal of Materials Processing Technology 122 (2002) 232-236 Study on the diamond tool drilling of engineering ceramics Q.H. Zhanga,*, J.H. Zhanga, D.M. Sunb, G.D. Wangc aCollege of Mechanical Engineering, Shandong University, No. 73, Jingshi Road, Jinan 250061, PR China bCollege of Material Engineering, Shandong University, Jinan, PR China cShandong Machine Design and Research Institute, Jinan, PR China Received 27 December 2000 Abstract A method for drilling holes in engineering ceramics by using a diamond tool has been developed. In this method, a drilling tool rotates with fixed abrasives. The machining mechanism of drilling based on the fracture mechanics concept is analyzed, and a new theoretical model of the material removal rate is proposed. According to this model, the material removal rate increases in accordance with the increase of the static load applied, the rotational speed of the drilling tool, and the grain size of the abrasive. Selecting 99.5% Al2O3 ceramics as the workpiece material, experiments have been carried out. The results show that diamond drilling is an effective method for machining engineering ceramics. # 2002 Published by Elsevier Science B.V. Keywords: Engineering ceramic; Diamond tool; Drilling; Machining mechanism1. IntroductionEngineering ceramics have numerous excellent physical and mechanical properties: high hardness, high thermal resi-stance, chemical stability, and low thermal and electricalconductivity, to name but a few. Because of these special qualities, engineering ceramics are expected to be used increasingly in a number of high-performance applicationsranging from electronic and optical devices to heat- and wear-resistant parts 1-3. Until today, their applications have mostly been limited to electronic and optical devices.One reason is to be found in the limitation on the forming process prior to sintering, which restricts the generation of complex geometry and makes it difficult to ensure adequateaccuracy and surface finish. There is also a considerable deficit in terms of the production or machining of more complex geometries in the hardened post-sintering state,with limitations on either the performance or the forming capacity of the majority of the processes in current use. Machining engineering ceramics to final dimensions byconventional methods is extremely laborious and time con-suming. Tight tolerances and dimensions with acceptable surface and sub-surface damage are something only attain-able at great cost. Thus research into the areas of more efficient material removal processes have been beginning to* Corresponding author.E-mail address: (Q.H. Zhang).0924-0136/02/$ - see front matter # 2002 Published by Elsevier Science B.V. PII: S 0 9 2 4 - 0 1 3 6 ( 0 2 ) 0 0 0 1 6 - Xgather momentum in recent years, especially in the ways andmeans of reducing the occurrence of faults or cracks in the sub-surface of the machined ceramics 4-6. A kind of machining method for drilling holes in engi-neering ceramics by using a rotary diamond tool is proposed in this paper. It can increase the material removal rate, and improve the surface finish.This paper intends to further the understanding of the basic mechanisms the diamond tool drilling of ceramics and thus to enable the prediction of the material removal rate in terms of the static load applied, the grain size of the abrasive, and the rotational speed of the drilling tool.2. The mechanism of diamond tool drillingThe process of diamond tool drilling is shown schemati-cally in Fig. 1. The tool is rotating in the drilling process, the workpiece is stationary. The material removal mechanism has been investigated generally by microscopic observation of the abraded surface. The process of material removal is thought to be similar to that of a single tool cutting in that in all cases material is removed by an individual tool or particle displacing or fracture the work surface. The workpiece material is found to be stabbed off in the form of many minute particles by the abrasive grains grinding. It is concluded that the removal of engineering ceramic occurs primarily by brittle fracture in diamond tool drilling. To understandthis process, it ishelpful to studythe indentation Pc ? a K 4Cr ? x1 P1=2 ?HV=4 K 1=3Q.H. Zhang et al. / Journal of Materials Processing Technology 122 (2002) 232-236233to chipping of the brittle material. A critical load Pc for initiating a radial crack is given by 7:ICH3 V(1) where a is a dimensionless factor related to the indenter geometry, KIC is the fracture toughness of workpiece, and HV is the Vickers hardness of the workpiece material. For the size of the median or radial crack Cr and lateral crack CL, respectively, the following equations have been derived 8:Fig. 1. Schematic diagram of the diamond tool drilling process: (1) chuck,(2) water, (3) workpiece, (4) tool, (5) water jacket.IC ?CL ? x2P3=4KIC(2)of brittle materials, because the abrasive grains acting on theworkpiece surface are just like indenters.2.1. Investigation of indentation in ceramicswhere P is the load applied, and x1 and x2 are proportionalconstants.It is generally regarded that the depth of the lateral crack Ch is proportional to ?P=HV?1=2 :1=2PThe deformation and fracture pattern observed under thenormal contact of ceramics by a Vickers indenter is illu-strated in Fig. 2. Directly under the indenter is a zone of plastic deformation. Two principal crack systems have been identified, which emanate from the plastic zone: median/ radial cracks and lateral cracks. The behavior of both types of cracks is effected by residual stresses from the non-uniform plastic deformation in the elastic/plastic material. Radial cracks are initiated by a wedge-like action during loading, and they may continue to propagate during unload-ing due to residual tensile stresses acting on the crack-tip. Lateral cracks are observed to initiate and propagate by residual stresses only as the indenting load is removed. The initiation and propagation of radial as well as lateral cracks are considered to contribute greatly to the material removal process. As shown in Fig. 2, the initiation and propagation of these radial and lateral cracks at the end leadFig. 2. Localized deformation and fracture of ceramics due to indentation.Ch ? x3(3)HVwhere x3 is a proportionality constant 9.It is concluded from these results that the size of the median/radial or lateral crack grows with an increase in the load and with a decrease in the fracture toughness of the workpiece material. Investigations on indentation des-cribed so far provide useful information for understanding the practical diamond drilling process of ceramics.2.2. The relationship between the material removal rate and various parametersAccording to the test results of ceramics in indentation, a model of material removal caused by a single abrasive is proposed, as shown in Fig. 3. The model takes into account the linear tangential motion of the abrasive along the sur-face. Assuming that an individual abrasive grain follows a linear path with a constant depth of cut, the volume of workpiece material removed by an abrasive grain (indenter) under a normal load P is proportional to the dimensions of the lateral crack and the length of travel d. The volume ofFig. 3. Schematic model of chip formation. N ? W pd0234Q.H. Zhang et al. / Journal of Materials Processing Technology 122 (2002) 232-236Eq. (11) can be simplified to: MV ? Kd0=2 ug 1=6 KIC3=4 HV 1=2 oW 5=4(12)where K is a proportional constant. According to Eq. (12), the material removal rate MV will be increased with the increase of the applied static load W, the rotational speed of the tool o, and the size of the abrasive grains d0. Fig. 4. Schematic diagram of the terminal face of the drilling tool.removed workpiece material V0 for one grain is obtained as(see Fig. 4):V0 ? 2CLChd(4)where CL is the length of the lateral crack, Ch is the depth of the lateral crack, d is the acting distance of the grain. Then, the material removal rate for one grain is given by:MV0 ? 4pCLChor(5)where o is the rotational speed of the tool, and r is the radius of the grains track.Assuming that the density of the effective cutting grains is l, the number of effective grains in area dA (see Fig. 4) is:n ? l dA ? 2lpr dr(6)Then, the material removal rate of the tool is:Z R23. Experimental procedureExperiments were performed on a drilling machine. The diamond drilling tool, which was especially designed to accept coolant (see Fig. 1), was a special diamond wheel with a external radius of R2 ? 10 mm and an internal radius of R1 ? 6 mm. Three types of diamond drilling tool were prepared, their grits being 80, 120, and 160, and theirconcentrations were being 100%.A 99.5% Al2O3 ceramic was selected as the workpiece material and water was selected as the coolant. The MRR is measured through a dial gauge with an accuracy of 0.001 mm. The depth of drilling per minute can be measured with a dial gauge, and then the MRR can be calculated (The MRR is the cross-sectional area of the drilling tool multiplied by the depth of drilling per minute.). The surface roughness is measured using a Talysurf 40 (England) surface measuring instrument with a relativeMV ?R18p2 lCLChor2 dr ? 83 p2 lCLCho ?R2R1 ?accuracy of 5%.(7)The number of effective grains in the terminal face of thetool is 10:2=36ug4. Experimental results and discussion 4.1. The effect of the static loadN ? lA ? K1d0pwhere A ? p?R2p?R2R1 ?(8)R1 ?, R2 is the external radius of theTest results show that the material removal rate tends to increase with the increase of the static load, as shown indiamond drilling tool, R1 is the internal radius of thediamond drilling tool, K1 is proportionality constant; ug is the concentration of abrasive grains, and d0 the meandiameter of the abrasive grains. Then:2=36ugFig. 5, which is similar to Eq. (12).The surface roughness is found to be slightly affected by the applied static load, increasing with the increase of the static load. The present experiments were conducted underl ? K1d0pThe load acting on a single abrasive grain is:2=36ug(9)P ? WK1p?R2R1 ? 1(10) Substituting Eqs. (2), (3), (9), (10) into Eq. (7):1=4MV ? 83 p3=4 x1 x2 o K1KIC3=4 HV 1=2 W 5=41=66ugpR2R1(11) ?R2R1 ?5=4Fig. 5. The effect of the static load.Q.H. Zhang et al. / Journal of Materials Processing Technology 122 (2002) 232-236235Fig. 6. The effect of the rotational speed of the drilling tool.Fig. 7. The effect of grain size.the following conditions: o ? 720 rev/min, C ? 80. Whenthe static load W is 25,35,45,55,65 N, the surfaceroughness (Ra) is 0.0040, 0.0040, 0.0042, 0.0045, and0.0045 mm, respectively.4.2. The effect of the rotational speed of the drilling toolFig. 6 shows the effect of the rotational speed of the drilling tool on the MRR. An increase of the rotational speed of the drilling tool causes an increase in the MRR. As there are some other factors affecting the MRR, for example the flushing of swarf and the self-sharpening of abrasive grains, the MRR is not proportional to the rotational speed of the drilling tool. It is very important for high material removal rate to flush away the swarf. With the increase of the rotational speed of the drilling tool, a lot of swarf is formed, and flushing it away becomes increasingly more difficult. This will also affect the self-sharpening of the abrasive grains. Generally speak-ing, self-sharpening of abrasive grains include two compo-nents, self-sharpening through progressive abrasive grain fragmentation and self-sharpening through progressive bond erosion. When the swarf is not completely flushed away, bond erosion and abrasive grain fragmentation become difficult, resulting in the dulling of the drilling tool: thus the MRR will be affected. Additionally, the flushing of swarf is related to the pressure of the coolant. In the present experiments, the pressure of the coolant is 2:0 104 Pa.Under this condition, loading occurred when the rotational speed of the drilling tool was 1200 rpm.The surface roughness decreases with an increase of the rotational speed of the drilling tool. The present experiments were conducted under the following