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┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ 裝 ┊ ┊ ┊ ┊ ┊ 訂 ┊ ┊ ┊ ┊ ┊ 線 ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ 長 春 大 學 畢業(yè)設(shè)計（論文）報告紙 開題報告 一、 設(shè)計題目： 電動扳手設(shè)計 二、 課題研究的目的和意義： 在生產(chǎn)生活中，螺栓連接是一種普遍可靠的鏈接方式。并且在大型鋼結(jié)構(gòu)建筑中，廣泛使用高強度螺栓鏈接。這種螺栓連接，在施工中要求用規(guī)定的擰緊力矩鎖緊螺母，以保證鏈接的可靠性。 由于高強度螺栓的材料和熱處理是嚴格控制和檢查的，因此螺栓定力矩切口處的扭剪斷裂力矩能夠控制在一個比較準確的范圍，從而能保證螺栓連接的可靠性。 另外，電動扳手以220V交流電源為動力進行工作，對于作業(yè)通常以螺栓群的方式出現(xiàn)高強度螺栓，可以大大提高螺栓擰緊的速度，并且可以改善工人的勞動強度。 三、 國內(nèi)外狀況和發(fā)展趨勢： 電動扳手自1980年研制成功并投入批量生產(chǎn)以來，至今已經(jīng)有20余載，生產(chǎn)了幾千臺，廣泛應(yīng)用于寶鋼自備電廠、寶鋼煉鋼廠房、天津無縫鋼管廠、包鋼等幾十項大型鋼結(jié)構(gòu)工程中，為我國推廣使用扭剪型高強度螺栓新技術(shù)提供了有力保證。 在長期的使用中，電動扳手充分發(fā)揮了它的設(shè)計有點——體積小、重量輕、操作方便快捷、安全可靠，從而使電動扳手成為施工現(xiàn)場不可缺少、不可替代的專用工具。從總體上看，電動扳手基本上可在設(shè)計壽命范圍正常工作，無需大修，施工現(xiàn)場也未發(fā)生任何由于漏電等原因引起的安全事故，從而得到使用單位的好評。 個別的電動扳手，在使用中曾發(fā)生柔輪筒體底部斷裂失效的現(xiàn)象，這一事實驗證了柔輪光彈性試驗得到的結(jié)論——柔輪工作時的切應(yīng)力及殼壁內(nèi)的正應(yīng)力的最大值均發(fā)生在柔輪的根部（并有應(yīng)力集中的影響），根部是最危險的截面。因此，改善柔輪根部的結(jié)構(gòu)和加工品質(zhì)是提高強度和使用壽命的關(guān)鍵措施。 多年的生產(chǎn)實踐表明，自行研制的電動扳手成功替代了進口產(chǎn)品，為國家節(jié)省了大量外匯，也為生產(chǎn)研制單位帶來了可觀的經(jīng)濟效益。 四 畢業(yè)設(shè)計方案的擬定 電動扳手與機床、汽車等大型機器比較起來雖然比較小巧簡單，但也是一種完整的機器，它應(yīng)該由動力機、傳動機構(gòu)和工作機構(gòu)組成。 根據(jù)前述設(shè)計任務(wù)要求，動力機應(yīng)選用電源為220V的交流電機。 由于電動扳手為人工操作，因此電動機應(yīng)該體積小、重量輕、絕緣好，以便于操作，并保證人身安全。大功率高轉(zhuǎn)速防護式串激電機能基本滿足這個要求。這種電機在制造中采用滴浸泡轉(zhuǎn)子，電焊整流子等新工藝，外殼采用熱固性工程塑料，電樞為接軸，從而形成雙重絕緣結(jié)構(gòu)，使用電安全有保證。 a) b) c) 圖2 扳手使用方法示意圖 1-12角夾緊頭 2-定力矩切口 3-螺栓部分 4-螺母 5-墊片 6-被緊固體 7-內(nèi)套筒 8-外套筒 9-頂桿 電動扳手的工作機構(gòu)為擰緊螺母的外套筒8和擰斷螺栓（在定力矩切口處）的內(nèi)套筒7，如圖2所示。工作時這兩個套筒的力矩相等，方向相反。如果利用這個特點，將傳動機構(gòu)設(shè)計成封閉系統(tǒng)，兩個相反的力矩就可以在電動扳手內(nèi)部平衡，操作者不受外力的作用，從而使操作變得輕便、簡單。 由于動力機采用了高轉(zhuǎn)速、小轉(zhuǎn)矩的電動機，因此動力機與工作機構(gòu)（套筒）之間就需要采用大傳動比傳動機構(gòu)。行星齒輪傳動（NGW型單機傳動比i=3~12）、漸開線少齒差齒輪傳動（單機傳動比i=10~100）、擺線少齒差齒輪傳動（單級傳動比i=11~87）和活齒少齒差齒輪傳動（單級傳動比i=20~80）等如果用語電動扳手，均需多級串聯(lián)使用，其結(jié)構(gòu)復(fù)雜，力線較長，會引起系統(tǒng)剛度下降、運動鏈累計誤差較大，這是不利的。因此，少齒差齒輪傳動，其行星輪的軸線做圓周運動，他們都需要一個運動輸出機構(gòu)，因此結(jié)構(gòu)復(fù)雜，這也是不足之處。 諧波齒輪傳動通過柔輪的彈性變形，利用了內(nèi)嚙合少齒差傳動可獲得大速比的原理，將行星輪系的運動輸出機構(gòu)簡化為低速構(gòu)件具有固定的轉(zhuǎn)動軸線，不需要等角速比機構(gòu)，運動直接輸出。因此諧波傳動具有速比大（i可達500），機構(gòu)件數(shù)量少，體積小重量輕，運轉(zhuǎn)平衡，效率高，無沖擊等優(yōu)點。電動扳手斷續(xù)、短時的工作特點恰好克服了柔輪由于變形而易產(chǎn)生疲勞斷裂的不足。諧波齒輪傳動機構(gòu)作為動力傳遞時其輸出轉(zhuǎn)矩的大小受柔輪尺寸的限制，故不宜將其設(shè)計為電動扳手的最終輸出。 綜合上述的分析，采用諧波齒輪傳動與行星輪系傳動串聯(lián)的設(shè)計是一種比較全面地、最大限度地滿足電動扳手工藝要求的最佳選擇。 從上述電動扳手的發(fā)展趨勢來看，電動扳手的設(shè)計要點集中在電動機的選擇和傳動形式的確定。在滿足輸出力矩（1010N.m）要求的前提下，盡量使整機體積小，重量輕，運轉(zhuǎn)平穩(wěn)，安全可靠。據(jù)此，初步確定電動扳手機構(gòu)方案簡圖如圖1所示。電動扳手整機由電動機1、定軸齒輪傳動2、諧波齒輪傳動3、NGW行星齒輪傳動4、外套筒5和內(nèi)套筒6組成。外套筒5用來把住螺母4，內(nèi)套筒用來把住高強度螺栓尾部的梅花頭，如圖2所示。圖1中的、、是 圖1 電動扳手機構(gòu)方案簡圖 1-電動機 2-定軸齒輪傳動 3-諧波齒輪傳動4-NGW行星齒輪傳動 5-外套筒6-內(nèi)套筒 定軸齒輪傳動的齒數(shù)；和是諧波傳動剛輪和柔輪的齒數(shù)；是諧波發(fā)生 器；a、g、b和H是NGW行星齒輪傳動的太陽輪、行星輪、內(nèi)齒輪和轉(zhuǎn)臂。這是一種行星輪系與諧波輪系雙差動串聯(lián)機構(gòu)方案，其原理可作如下分析： 諧波齒輪傳動輪系的自由度F可用下式計算： 式中 ——平面機構(gòu)的構(gòu)件數(shù)： ——機構(gòu)中的低副數(shù)； ——機構(gòu)中的高副數(shù)。 鑒于圖2電動扳手機構(gòu)中各構(gòu)件的回轉(zhuǎn)軸均互相平行，因此該機構(gòu)可視為平面機構(gòu)。 對于諧波齒輪傳動：=4，=3，=1，其自由度為 對于行星輪系，其自由度也為2。因此在無任何約束條件下，兩機構(gòu)均為自由度等于2的差動機構(gòu)。由此機構(gòu)組成的電動扳手擰緊螺栓的過程分兩階段： 階段1：在螺栓、螺母與扳手處于松動狀態(tài)時，系統(tǒng)實現(xiàn)自由度為2的差動運動，即內(nèi)外套筒同時反向旋轉(zhuǎn)。 階段2：當夾緊力增大到一定值后，系統(tǒng)實現(xiàn)自由度為1的NGW型行星傳動，即外套筒固定，內(nèi)套筒繼續(xù)旋轉(zhuǎn)，直到擰斷螺栓的梅花頭。 采用差動機構(gòu)的目的： （1）、為消除內(nèi)套筒與螺栓梅花頭、外套筒與螺母之間的安裝角度誤差，電動扳手必須具備可手動調(diào)節(jié)內(nèi)、外套筒產(chǎn)生相對角位移，確保內(nèi)、外套筒順利地進入工作的準備位置。 （2）設(shè)計時，為讓出中心頂桿的位置，電機與傳動系統(tǒng)不可“一”字布置。實際中采用的并列布置造成機殼形狀復(fù)雜。因此設(shè)計中將剛輪與內(nèi)齒輪聯(lián)接成整體，構(gòu)成差動機構(gòu)，可使內(nèi)、外套筒及相關(guān)輪系結(jié)構(gòu)之間形成封閉力線，從而機殼不承受外力矩，則機殼的加工性能大大改善。 按上述機構(gòu)方案設(shè)計的電動扳手，其操作步驟（圖1）如下： 1） 高強度螺栓預(yù)緊在被緊固件上，如圖1a所示； 2） 將內(nèi)套筒插人螺栓尾部的梅花頭，然后微轉(zhuǎn)外套筒，使其與螺母套正，并推到螺母根部，如圖1b所示； 3） 接通電源開關(guān)，內(nèi)外套筒背向旋轉(zhuǎn)將螺栓緊固，待緊固到螺栓達到設(shè)計力矩時，將梅花頭切口扭斷； 4） 關(guān)閉電源，將外套筒脫離螺母，用手推動開關(guān)上前方的彈射頂桿觸頭9，將梅花頭從內(nèi)套筒彈出，緊固完畢，如圖1c所示。 五 課題研究的時間分配： 3月 1 日 - 3 月15日 調(diào)研、閱讀分析資料、譯文 3月16日 - 3月30 日 開題報告、制定合理方案 4月 1 日 - 4月20 日 理論計算、繪制總裝配圖 4月21日 - 6月 1日 零件圖、修改裝配圖 6月 2 日 - 6月12 日 撰寫設(shè)計說明書 6月13日 - 6月25 日 設(shè)計評審、準備答辯 六 參考文獻： [1] 錢中主編.列車牽引計算.第一版.北京：中國鐵道出版社，1996 [2] 張文質(zhì)等主編.起重機設(shè)計手冊.第一版.北京：中國鐵道出版社，1998 [3] 馬鞍山鋼鐵設(shè)計院等編.中小型軋鋼機設(shè)計計算.北京：冶金出版社，1979 [4] 陳立周.飛剪機剪切機構(gòu)的合理設(shè)計.北京：北京鋼鐵學院學報 1980，（1） [5] Simon，J.M.Computerized Synthesis of Straight Line Four-Bar Linkages from Inflection Circle Properties . 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August 1977:610-614 [6] R.Strawertron .Flying Shears for Bars and Beams.Journal of the Iron and steel Institute .1958,(3),181 [7] 李克涵.應(yīng)用鮑爾點（Ball Point）理論設(shè)計連桿直移機構(gòu).機械設(shè)計.1982 [8] 李克涵.新型150kN曲柄連桿式鋼坯飛剪機的研制.冶金設(shè)備.1991，（1） [9] 李克涵.工業(yè)機械手運動參數(shù)的分析與綜合.機械設(shè)計.1993，（4） [10] 沈允文，葉慶泰.諧波齒輪傳動的理論和設(shè)計.北京：機械工業(yè)出版社，1985 [11] 許洪基主編.現(xiàn)代機械傳動手冊.北京：機械工業(yè)出版社，1995 [12] 沃爾闊夫等主編.諧波齒輪傳動.項其權(quán)等譯.北京：電子工業(yè)出版社，1985 [13] 雷廷權(quán)等主編.30CrMnSiA鋼調(diào)質(zhì)-旋壓-時效工藝研究.黑龍江機械.1981，No.3 [14] M.Frocht.光測彈性力學.陳森譯.北京：科學出版社，1994 [15] 羅祖道.吳連元.彈性圓柱薄殼的一般穩(wěn)定性.力學學報.1962，Vol.5,No.1 [16] 徐灝.機械設(shè)計手冊.機械工業(yè)出版社.1995年12月 共 5 頁 第 5 頁 序號（學號）： 010640502 長 春 大 學 畢 業(yè) 設(shè) 計（論 文）開題報告 電動扳手設(shè)計 姓 名 李楠 學 院 機械工程學院 專 業(yè) 機械工程及自動化 班 級 0106405 指導(dǎo)教師 李占國 教授 20** 年 ** 月 ** 日 序號（學號）： 010640502 長 春 大 學 畢 業(yè) 設(shè) 計（論 文）譯文 An Advanced Ultraprecision Face Grinding Machine 姓 名 李楠 學 院 機械工程學院 專 業(yè) 機械工程及自動化 班 級 0106405 指導(dǎo)教師 李占國 教授 20** 年 ** 月 ** 日 序號（學號）： 010640502 長 春 大 學 畢 業(yè) 設(shè) 計（論 文）說明書 電動扳手設(shè)計 姓 名 李楠 學 院 機械工程學院 專 業(yè) 機械工程及自動化 班 級 0106405 指導(dǎo)教師 李占國 教授 20** 年 ** 月 ** 日 Int J Adv Manuf Technol (2002) 20:639648 Ownership and Copyright 2002 Springer-Verlag London Limited An Advanced Ultraprecision Face Grinding Machine J. Corbett 1 , P. Morantz 1 , D. J. Stephenson 1 and R. F. Read 2 1 School of Industrial 2 Cranfield Precision, Division of Landis Lund, Cranfield University, Cranfield, Bedford, UK Cranfield Precision, Division of Landis Lund, has recently developed an ultraprecision face grinding machine which incor- porates several automatic supervision features. The company supplied the machine to Cranfield Universitys Precision Engin- eering Group in order that the group can undertake research, particularly in the area of damage-free grinding with high surface and subsurface integrity. The paper discusses the design of the machine, initial machining trials and potential research projects. Such projects will benefit from the avail- ability of such an advanced machine system which incorporates many state-of-the-art features for the automatic supervision and control of the machining process. Keywords: Automatic supervision; Grinding; Machine tool design; Precision machining 1. Introduction Cranfield Precision, which is a UNOVA Company, specialises in the design and manufacture of machines for cost-effective production of components in advanced materials including ceramics, glasses, intermetallics and hard alloy steels. The School of Industrial and Manufacturing Science (SIMS), Cran- field University, places great importance on developing close collaborative links with industry and is currently undertaking a range of ultraprecision and high-speed machining research projects including superabrasive machining, ductile machining of brittle materials and precision machining for the automotive industry. The complementary research interests of the two organisations have resulted in Cranfield Precision developing and supplying an advanced ultraprecision face grinding machine to the Precision Engineering Research Group within SIMS. This will enable the group to undertake a wide range of research programmes, particularly in the area of damage-free grinding with high surface and sub surface integrity. Correspondence and offprint requests to: Prof. J. Corbett, School of Industrial and Manufacturing Science, Cranfield University, Bedford MK43 0AL, UK. E-mail: j.corbettL50560cranfield.ac.uk. Materials processing with nanometric resolution and control is viewed as a mid- to long-term solution to the cost and time problems that plague the manufacturing of electro-optics and other precision components. For example, ductile grinding of brittle materials can provide surfaces, as ground, to nanometre smoothness and figure accuracy at higher production rates than usually encountered 1. More significantly, a ductile ground surface experiences little or no subsurface damage, thereby eliminating the need for the subsequent polishing step associa- ted with conventional grinding. The performance of many “microfeatured” products (e.g. semiconductor, optical communi- cations systems, computer peripherals, etc.), as well as larger components for aerospace and automotive applications, depends increasingly on higher geometric accuracies and micro- and nanostructured surfaces. Recently, the automotive industry has indicated a future requirement for the surfaces of certain key transmission components to be of “optical” quality, with targets of 10 nm Ra surface finish to be economically produced on hardened steel by direct machining, without polishing. The conditions under which damage-free surfaces can be produced on glasses and ceramics, and “optical” surfaces can be produced on hardened steel, are exacting, requiring (a) the use of a class of machine tool not normally found in even the best production facilities, e.g. high accuracy, smoothness of motion, loop stiffness 2, (b) the incorporation of ancillary features specially developed to suit the particular application (e.g. grinding wheel truing and conditioning), and (c) the use of the correct grinding technology for the application (many variables wheel type, coolant, speeds, feeds, etc). All the conditions must be satisfied and the wafer face grinding machine has been developed to meet them. 2. Objectives In order to meet the demands of surface integrity and pro- ductivity mentioned above, for a wide range of components, the principal objectives include the development of: 1. A machining process capability for the manufacture of sizeable components with high levels of surface/subsurface integrity. 640 J. Corbett et al. 2. Optimised “ductile mode” machining processes for brittle materials (glasses and ceramics). 3. A single process, with only one set-up, to replace the typical three-stage lapping, etching and polishing process, resulting in much higher productivity. 3. The Process A prime requirement of the process is that it should be capable of machining extremely flat surfaces on workpieces up to 350 mm diameter. Further, the surfaces should be smooth (50 nm Ra) and have minimum subsurface damage. Ideally the surface should be close to the quality obtained by polishing. In order to meet these demanding requirements rotation grinding is utilised. A feature of rotation grinding is that unlike conven- tional surface grinding, it has a constant contact length and constant cutting force. Figure 1 illustrates the grinding prin- ciple. Both the cup grinding wheel and workpiece rotate and the axial feed of the grinding wheel removes stock from the surface of the workpiece until it reaches its final thickness/geometry. 4. The Machine The demanding requirements of the process and component quality necessitate a machine of extremely high loop stiffness. The design targets for the face grinding machine (Fig. 2) are: 1. Loop stiffness better than 200 N H9262m H110021 with good dynamic damping, required to achieve submicron subsurface damage. 2. Control of pitch (wheel to component surface) to better than 0.333 arc seconds, required to achieve a total thickness variation (TTV) tolerance of 0.5 H9262m. 3. Control of cut-depth to better than 0.1 H9262m, required to achieve submicron subsurface damage. 4. Axial error motions of spindles better than 0.1 H9262m, required to achieve submicron subsurface damage. 5. Measurement and feedback of component thickness to 0.5 H9262m, required to achieve micron thickness tolerance. Fig. 1. Face grinding operation. The geometry of the ground flat surface is determined by the relative position of the rotary axes of the grinding wheel and workpiece. Figure 3 indicates the relative machine motions and axes. There are 11 axes, plus three automatic robot loading motions (not shown), all driven under servo control. These are: S1 Grinding spindle C Workhead spindle Z Infeed X Crossfeed S2 Truing spindle W Dressing axis A Tilt pitch B Tilt yaw S3 Chuck wash brush P Probe thickness Wash arm As described below, the flatness accuracy can be achieved by the superimposed rotations of the rotary axes coupled with an appropriate spindle alignment strategy. Further, this prototype research machine benefits from the incorporation of the following state-of-the-art features for the automatic supervision and control of the machining process. 4.1 Adjustment of the Workpiece and Grinding Wheel Planarity The relative alignment of the two rotary spindles S1 and C (Fig. 3) is simplified because the geometry of the ground surface can be described by geometrical equations. The grind- ing process requires a specific angle between the plane of the grinding wheel and the plane of the workpiece to be maintained as the Z-axis infeed is applied. This angle is typically much less than a degree, so that the workpiece and wheel are nearly parallel. This angle is monitored by three gauging LVDT sensors which measure the displacement between the grinding spindle housing, and a precision-machined surface on the work- spindle housing. The gauging sensors are placed around the grinding spindle housing, roughly equidistant from the centre of the wheel spindle axis in the plane of the wheel, at a known separation. The information from these sensors is fed back into the control system to amend the control for the A- (pitch), B- (yaw) and Z- (infeed) axes. This is a unique feature of the machine, to maintain workpiece flatness because, as the workpiece subsurface damage reduces and the surface finish improves the grinding forces increase significantly. This has the effect of distorting the grinding spindle to workhead align- ment, which then produces non-flat surfaces. On conventional machines this alignment is adjusted by mechanical trial-and- error adjustment, and relies on the force and deflection always being uniform. However, on this machine if the process con- ditions are changed, the alignment is automatically compensated for. This can then be optimised to suit the material and wheel conditions by changes in the software of the control system. A functional block diagram for the servo control of the Z-axis is illustrated in Fig. 4. Ultraprecision Face Grinding Machine 641 Fig. 2. Face grinding machine. Fig. 3. Axes nomenclature. 4.2 Grinding Wheels The roughing and finishing wheels are concentrically mounted on one spindle via a patented system which incorporates an advance/retract mechanism for the roughing wheel, as shown in Fig. 5. In order to maximise component throughput, a coarse- grained wheel is first used to obtain a high material removal rate. The fine-grained finishing wheel is then used to obtain the finished size and surface integrity. 4.3 Detecting Grinding Wheel Contact Acoustic emission (AE) sensors are used to establish the initial touch between the grinding wheel and component. Because of the importance of establishing first touch to very fine limits, when finish grinding, ring sensors are used on the workhead and grinding spindles. These are extremely sensitive and are located at the front of the spindles, close to the signal source. An on-machine grinding wheel truing spindle is also fitted with AE sensors which enables “touch dressing” of the grind- ing wheel. 4.4 Automatic Measurement of Grinding Forces Grinding forces are measured via sensors placed within the force loop away from external forces, such as lead screw nuts and their associated friction. Measurement of the grinding forces gives a good indication of grinding wheel wear. 4.5 Measurement of Grinding Wheel Wear and Component Thickness Grinding wheel wear is monitored together with component thickness. A specially designed anvil and LVDT probe assembly are used to measure component thickness. This is done by initially datuming the anvil and probe on to the porous ceramic vacuum chuck face to which the component is fixed. When measuring the component thickness, the anvil, which is on the same slideway as the probe, contacts the chuck datum and the LVDT probe makes contact with the face of the component, thus giving a measurement of thickness. Grinding wheel wear can be found by reading directly the position of the Z-axis, and relating this to the chuck face datum position. Thermal growth is measured by pairs of eddy current probes mounted on the workhead and grinding spindles. Any growth is automatically compensated by adjusting the relative positions of the two spindles. 642 J. Corbett et al. Fig. 4. Z-axis functional block diagram. Fig. 5. Single axis dual wheel system. 4.6 Ancillary Features The machine also has facilities for on machine component and chuck washing and also a robotic loading and unloading capa- bility to load and unload automatically components onto and from the workhead spindle. 5. Machine Commissioning Machine services consist of an air supply, grinding coolant supply and motor coolant supply, as well as three-phase electri- cal power. Air is provided by a high performance supply and conditioning system, which delivers clean dry air at 13 bar at over 5000 l min H110021 . The air consumption within the face grinder machine is around 2000 l min H110021 in the air bearings, the remain- der being for the various air purge and cleansing systems. The air is filtered to 0.1 H9262m and dried to a pressure dewpoint of H1100240C as required for the operation of ultraprecision air bear- ings. Coolant supply is by recirculating water. This is pumped at 4.5 bar at a flow rate of up to 100 l min H110021 . Coolant is distributed to various coolant nozzles, under individual control, as required by the machine process. Used coolant is returned to the collection tank, and then fed to the main coolant tank by a scavenge pump. Some water-borne debris (workpiece and grinding wheel residues) settles out here; the remainder is removed by filtration on the machine in various stages down to 0.01 H9262m. Services provision requires a multiplicity of controlled pro- cess fluid distribution points, together with appropriate safety interlock and performance monitoring systems. 5.1 The Control System The control system is in two parts, based on an industry standard Isagraph PLC, and a Cranfield Precision CNC system. Machine I/O is on a distributed Interbus S system and servo control is implemented by a Sercos fibre-optic ring. The PLC program required only minor modification during commissioning, most effort being concentrated in further devel- opment of the CNC program, particularly in grinding touch sensing, and in the truing and grinding operations. 5.2 Machine Preparation In preparation for grinding operations, an assessment of several areas was critical: 1. Machine alignments. 2. Balance of spindles. 3. Condition of wheels. 4. Application of coolant. 5. Control of machine motions. Ultraprecision Face Grinding Machine 643 Fig. 6. Grinding spindle horizontal amplitude response to out-of-balance forces. These are the major determinants of grinding surface quality, and were tackled in order. 5.3 Machine Alignments The machine tool builders had set most machine alignments accurately; metrology checks confirmed these to be in order. However, the critical alignment datum (alignment between workspindle axis and grinding spindle axis) had been lost, since the grinding spindle had to be removed, prior to relocating the machine in the Precision Engineering Laboratory. This alignment datum had to be re-established by using a miniature eddy current probe (with a measurement range of around 6 H9262m) mounted on the grinding spindle faceplate. A special purpose alignment jig was mounted on the workspindle faceplate. Measuring the variation of distance of the probe from features on the alignment jig, as the two spindles were independently rotated, allowed the angular alignment of the two spindle axes to be determined, using a multiparameter least squares fit. Fig. 7. Grinding spindle horizontal phase response to out-of-balance forces. 5.4 Wheel Balance The machine is configured to enable automatic balancing on the grinding spindle. This is included on the machine to accommodate the automatic selection of grinding wheels. The grinding spindle carries two concentric segmented cup wheels, rough and fine grit; the rough wheel is of slightly larger diameter. The roughing wheel can be selected automatically by sliding it parallel to the spindle axis, under air piston control, to engage in one of two face tooth couplings, so that it either projects or is just below the face of the fine wheel. These two configurations, with rough or fine wheel selected, have marginally different out-of-balance moments, and the automatic balancing is included to compensate for this. Figures 6 and 7 show the amplitude and phase response for a balance (displacement) sensor in a horizontal orientation, located at the grinding spindle nose, over a range of revolutions per minute (rpm) shown along the x-axis of the figure. The y- axis represents a nominal peak-to-peak displacement at that rotation rate of the grinding spindle. These data were obtained subsequent to fine (single plane) balancing of the grinding 644 J. Corbett et al. Fig. 8. Grinding spindle vertical amplitude response to out-of-balance forces. spindle. A strong resonant response can be seen at around 1200 rpm (or 20 Hz). Figure 8 shows the amplitude response for the balance (displacement) sensor in a vertical orientation. The resonant behaviour is entirely absent. Subsequent investi- gation has revealed that the source of the resonance is com- pliance in the “B” grinding wheel tilt axis (a vertical axis), as shown in Fig. 3, which is why this is only apparent to a horizontally oriented sensor. The truing wheel balance is also critical. Figure 9 shows the horizontal response of the truing spindle, subsequent to fine balancing. Again a small resonance is apparent in the horizontal direction, at around 4000 rpm (67 Hz). The truing spindle is mounted on the X-axis carriage, and this horizontal resonance is in the direction of the X-axis motion. Once more this is due to the compliance of the motion system in its drive direction. This has a lower impact on grinding performance than grinding spindle balance, although truing the spindle out- Fig. 9. Truing spindle horizontal amplitude response to out-of-balance forces. of-balance motion will impart a small-scale cyclic topography on to grinding wheels, which in turn affects grinding quality. 5.5 Wheel Condition On this machine, wheel form is imparted through a truing operation, and wheel condition is maintained through sub- sequent dressing, in between relatively infrequent truing oper- ations. The truing (forming) operation specified in the machine design involves a plunge “grind” similar to the wafer grinding operation, although in this case the cup grinding wheel and parallel truing wheel make contact at their periphery. The grinding wheel form was found to be in error by 0.2 (12 minutes of arc). The truing operation was amended to rectify this. Truing is now accomplished by a plunge and a subsequent traverse of the X-axis. Correctly applied, this can produce the Ultraprecision Face Grinding Machine 645 correct (planar) wheel form, since the grinding spindle axis had previously been set accurately to be perpendicular to the X-axis motion. 5.6 Coolant Application Considerable effort was concentrated in the alignment of the coolant nozzles, in order to deliver sufficient coolant into the grinding interface. This is particularly important here where the grinding arc of contact is so long, at approximately 200 mm for a 200 mm wafer. 5.7 Motion Control New grinding routines and complex motion profiles were developed for the grinding. A full wafer grinding cycle consists of an initial rough grind, followed by a finish grind. In each grinding phase, the work and grinding spindles are set to rotate, coolant is then applied, and the grinding spindle is fed into the work rapidly until the acoustic emission sensor detects a touch. Following rapid deceleration, the spindle is fed in further, in three stages, at successively lower feedrates, and for successively smaller feed depths. Finally, after a dwell (spark out) time, the grinding spindle is retracted. This in-feed motion sequence is complicated by the simul- taneous slaved motion of the A and B tilt axes. Completely coplanar plunge grinding is likely to result in non-planar grinding results. In order to achieve planarity in the finished surface, a slight angle must be maintained between spindle axes at first contact, and this angle is gradually reduced to zero (nominally) at the conclusion of grinding. A further modification to the infeed motion is imposed by the results of the three-point gauging, which monitors, in-process, the deflec- tion of the machine due to the high static grinding forces. The measurements of the gauges modify the demanded angle between spindle axes throughout the grinding process. 6. Initial Grinding Trials Initial grinding trials were conducted on monocrystalline sili- con, using 200 mm wafers. Initial grinding trials were conduc- ted, using parameters selected