無摩擦球閥設(shè)計

無摩擦球閥設(shè)計,摩擦,磨擦,球閥,設(shè)計 NUMERICAL CONTROL Numerical control(N／C)is a form of programmable automation in which the processing equipment is controlled by means of numbers，letters，and other symbols．The numbers，letters，and symbols are coded in an appropriate format to define a program of instructions for a particular workpart or job．When the job changes，the program of instructions is changed．The capability to change the program is what makes N／C suitable for low-and medium-volume production．It is much easier to write programs than to make major alterations of the processing equipment． There are two basic types of numerically controlled machine tools：point—to—point and continuous—path(also called contouring)．Point—to—point machines use unsynchronized motors，with the result that the position of the machining head Can be assured only upon completion of a movement，or while only one motor is running．Machines of this type are principally used for straight—line cuts or for drilling or boring． The N／C system consists of the following components：data input，the tape reader with the control unit，feedback devices，and the metal—cutting machine tool or other type of N／C equipment． Data input，also called“man—to—control link”，may be provided to the machine tool manually，or entirely by automatic means．Manual methods when used as the sole source of input data are restricted to a relatively small number of inputs．Examples of manually operated devices are keyboard dials，pushbuttons，switches，or thumbwheel selectors．These are located on a console near the machine．Dials ale analog devices usually connected to a syn-chro-type resolver or potentiometer．In most cases，pushbuttons，switches，and other similar types of selectors aye digital input devices．Manual input requires that the operator set the controls for each operation．It is a slow and tedious process and is seldom justified except in elementary machining applications or in special cases． In practically all cases，information is automatically supplied to the control unit and the machine tool by cards，punched tapes，or by magnetic tape．Eight—channel punched paper tape is the most commonly used form of data input for conventional N／C systems．The coded instructions on the tape consist of sections of punched holes called blocks．Each block represents a machine function，a machining operation，or a combination of the two．The entire N／C program on a tape is made up of an accumulation of these successive data blocks．Programs resulting in long tapes all wound on reels like motion-picture film．Programs on relatively short tapes may be continuously repeated by joining the two ends of the tape to form a loop．Once installed，the tape is used again and again without further handling．In this case，the operator simply loads and unloads the parts．Punched tapes ale prepared on type writers with special tape—punching attachments or in tape punching units connected directly to a computer system．Tape production is rarely error-free．Errors may be initially caused by the part programmer，in card punching or compilation，or as a result of physical damage to the tape during handling，etc．Several trial runs are often necessary to remove all errors and produce an acceptable working tape． While the data on the tape is fed automatically，the actual programming steps ale done manually．Before the coded tape may be prepared，the programmer，often working with a planner or a process engineer, must select the appropriate N／C machine tool，determine the kind of material to be machined，calculate the speeds and feeds，and decide upon the type of tooling needed. The dimensions on the part print are closely examined to determine a suitable zero reference point from which to start the program．A program manuscript is then written which gives coded numerical instructions describing the sequence of operations that the machine tool is required to follow to cut the part to the drawing specifications． The control unit receives and stores all coded data until a complete block of information has been accumulated．It then interprets the coded instruction and directs the machine tool through the required motions． The function of the control unit may be better understood by comparing it to the action of a dial telephone，where，as each digit is dialed，it is stored．When the entire number has been dialed，the equipment becomes activated and the call is completed． Silicon photo diodes，located in the tape reader head on the control unit，detect light as it passes through the holes in the moving tape．The light beams are converted to electrical energy，which is amplified to further strengthen the signal．The signals are then sent to registersin the control unit, where actuation signals are relayed to the machine tool drives． Some photoelectric devices are capable of reading at rates up to 1000 characters per second．High reading rates are necessary to maintain continuous machine—tool motion；otherwise dwell marks may be generated by the cutter on the part during contouring operations．The reading device must be capable of reading data blocks at a rate faster than the control system can process the data． A feedback device is a safeguard used on some N／C installations to constantly compensate for errors between the commanded position and the actual location of the moving slides of the machine tool．An N／C machine equipped with this kind of a direct feedback checking device has what is known as a closed-loop system．Positioning control is accomplished by a sensor which，during the actual operation，records the position of the slides and relays this information back to the control unit．Signals thus received ale compared to input signals on the tape，and any discrepancy between them is automatically rectified． In an alternative system，called an open—loop system，the machine is positioned solely by stepping motor drives in response to commands by a controllers．There are three basic types of NC motions, as follows: Point-to-point or Positional Control In point-to-point control the machine tool elements ( tools,table,etc.) are moved to programmed locations and the machining operations performed after the motions are completed. The path or speed of movement between locations is unimportant; only the coordinates of the end points of the motions are accurately controlled. This type of control is suitable for drill presses and some boring machines, where drilling, tapping, or boring operations must be performed at various locations on the work piece. Straight-Line or Linear Control Straight-Line control systems are able to move the cutting tool parallel to one of the major axes of the machine tool at a controlled rate suitable for machining. It is normally only possible to move in one direction at a time, so angular cuts on the work piece are not possible, Consequently, for milling machines, only rectangular configurations can be machined or for lathes only surfaces parallel or perpendicular to the spindle axis can be machined. This type of controlled motion is often referred to as linear control or a half-axis of control. Machines with this form of control are also capable of point-to-point control. Continuous Path or Contouring Control In continuous path control the motions of two or more of the machine axes are controlled simultaneously, so that the position and velocity of the can be tool are changed continuously. In this way curves and surfaces can be machined at a controlled feed rate. It is the function of the interpolator in the controller to determine the increments of the individual controlled axes of the machines necessary to produce the desired motion. This type of control is referred to as continuous control or a full axis of control. Some terminology concerning controlled motions for NC machines has been introduced. For example, some machines are referred to as four-or five-or even six-axis machines. For a vertical milling machine three axes of control are fairly obvious, these being the usual X, Y, Z coordinate directions. A fourth or fifth axis of control would imply some form of rotary table to index the work piece or possibly to provide angular motion of the work head. Thus, in NC terminology an axis of control is any controlled motion of the machine elements ( spindles, tables, etc ). A further complication is use of the term half-axis of control; for example, many milling machines are referred to as 2.5-axis machine. This means that continuous control is possible for two motions (axes )and only linear control is possible for the third axis. Applied to vertical milling machines, 2.5axis control means contouring in the X, Y plane and linear motion only in the Z direction. With these machines three-dimensional objects have to be machined with water lines around the surface at different heights. With an alternative terminology the same machine could be called a 2CL machine (C for continuous, L for linear control ). Thus, a milling machine with continuous control in the X, Y, Z directions could be termed be a three-axis machine or a 3c machine, Similarly, lathes are usually two axis or 2C machines. The degree of work precision depends almost entirely upon the accuracy of the lead screw and the rigidity of the machine structure．With this system．there is no self-correcting action or feedback of information to the control unit．In the event of an unexpected malfunction，the control unit continues to put out pulses of electrical current．If，for example，the table on a N／C milling machine were suddenly to become overloaded，no response would be sent back to the controller．Because stepping motors are not sensitive to load variations，many N／C systems are designed to permit the motors to stall when the resisting torque exceeds the motor torque．Other systems are in use，however，which in spite of the possibility of damage to the machine structure or to themechanical system，ale designed with special high—torque stepping motors．In this case，the motors have sufficient capacity to“overpower’’the system in the event of almost any contingency． The original N／C used the closed—loop system．Of the two systems，closed and open loop，closed loop is more accurate and，as a consequence，is generally more expensive．Initially，open—loop systems were used almost entirely for light-duty applications because of inherent power limitations previously associated with conventional electric stepping motors．Recent advances in the development of electrohydraulic stepping motors have led to increasingly heavier machine load applications． MILLING Milling is a basic machining process in which the surface is generated by the progressive formation and removal of chips of material from the workpiece as it is fed to a rotatingcutter in a direction perpendicular to the axis of the cutter．In some cases the workpiece isstationary and the cutter is fed to the work．In most instances a multiple—tooth cutter is used so that the metal removal rate is high，and frequently the desired surface is obtained in a single pass ofthe work． The tool used in milling is known as a milling cutter．It usually consists of a cylindrical body which rotates on its axis and contains equally spaced peripheral teeth that intermittently engage and cut the workpiece．In some cases the teeth extend part way across one or both ends of the cylinder． Because the milling principle provides rapid metal removal and can produce good surface finish，it is particularly well—suited for mass-production work，and excellent milling machines have been developed for this purpose．However，very accurate and versatile milling of a general-purpose nature also have been developed that are widely used in job-shop and tool and die work．A shop that is equipped with a milling machine and an engine lathe can machine almost any type of product of suitable size． Types of Milling Operations．Milling operations can be classified into two broad categories，each of which has several variations： 1．In peripheral milling a surface is generated by teeth located in the periphery of the cutter body；the surface is parallel with the axis of rotation of the cutter．Both flat and formed surfaces san be produced by this method．The cross section of the resulting surface corresponds to the axial contour of the cutter．This procedure often is called slab milling． 2．In face milling the generated flat surface is at right angles to the cutter axis and is the combined result of the actions of the portions of the teeth located on both the periphery and the face of the cutter．The major portion of the cutting is done by the peripheral portions of the teeth with the face portions providing a finishing action．The basic concepts of peripheral and face milling are illustrated in Fig．16—1．Peripheral milling operations usually are performed on machines having horizontal spindles，whereas face milling is done on both horizontal—and vertical-spindle machines. Surface Generation in Milling．Surfaces can be generated in milling by two distinct1y different methods depicted in Fig．16-2．Note that in up milling the cutter rotates against the direction of feed the workpiece，whereas in down milling the rotation is in the same direction as the feed．As shown in Fig．16—2，the method of chip formation is quite different in the two cases．In up milling the chip is very thin at the beginning，where the tooth first contacts the work，and increases in thickness,becoming a maximum where the tooth leaves the work．The cutter tends to push the work along and lift it upward from the table．This action tends to eliminate any effect of looseness in the feed screw and nut of the milling machine table and results in a smooth cut．However，the action also tends to loosen the work from the clamping device so that greater clamping forcers must be employed. In addition the smoothness of the generated surface depends greatly on the sharpness of the cutting edges． In down milling，maximum chip thickness occurs close to the point at which the tooth contacts the work．Because the relative motion tends to pull the workpiece into the cutter，all possibility of looseness in the table feed screw must be eliminated if down milling is to be used．It should never be attempted on machines that are not designed for this type of milling．Inasmush as the material yields in approximately a tangential direction at the end of the tooth engagement，there is much less tendency for the machined surface to show tooth marks than when up milling is used．Another considerable advantage of down milling is that the cutting force tends to hold the work against the machine table，permitting lower clamping force to be employed．This is particularly advantageous when milling thin workpiece or when taking heavy cuts． Sometimes a disadvantage of down milling is that the cutter teeth strike against the surface of the work at the beginning of each chip．When the workpiece has a hard surface，such as castings do，this may cause the teeth to dull rapidly． Milling Cutters．Milling cutters Can be classified several ways．One method is to group them into two broad classes，based on tooth relief，as follows： 1．Profile-cutters have relief provided on each tooth by grinding a small land back of the cutting edge．The cutting edge may be straight or curved． 2．In form or cam-relieved cutters the cross section of each tooth is an eccentric curve behind the cutting edge，thus providing relief．All sections of the eccentric relief，parallel with the cutting edge，must have the same contour as the cutting edge．Cutters of this type are sharpened by grinding only the face of the teeth，with the contour of the cutting edge thus remaining unchanged． Another useful method of classification is according to the method of mounting the cutter．Arbor cutters are those that have a center hole so they can be mounted on an arbor．Shank cutters have either tapered or straight integral shank．Those with tapered shanks can be mounted directly in the milling machine spindle，whereas straight—shank cutters are held in a chuck．Facing cutters usually are bolted to the end of a stub arbor． Types of Milling Cutters．Plain milling cutters are cylindrical or disk—shaped，having straight or helical teeth on the periphery．They are used for milling flat surfaces．This type of operation is called plain or slab milling．Each tooth in a helical cutter engages the work gradually，and usually more than one tooth cuts at a given time．This reduces shock and chattering tendencies and promotes a smoother surface．Consequently, this type of cutter usually is preferred over one with straight teeth． Side milling cutters are similar to plain milling cutters except that the teeth extend radially part way across one or both ends of the cylinder toward the center．The teeth may be either straight or helical．Frequently these cutters are relatively narrow，being disklike in shape. Two or more side milling cutters often are spaced on an arbor to make simultaneous．parallel cuts，in an operation called straddle milling． Interlocking slotting cutters consist of two cutters similar to side mills，but made to operate as a unit for milling slots．The two cutters are adjusted to the desired width by inserting shims between them． Staggered-tooth milling cutters are narrow cylindrical cutters having staggered teeth，and with alternate teeth having opposite helix angles．They are ground to cut only on the periphery，but each tooth also has chip clearance ground on the protruding side．These cutters have a free cutting action that makes them particularly effective in milling deep slots． Metal-slitting saws are thin，plain milling cutters，usually from 1／32 to 3／16 inch thick，which have their sides slightly "dished” to provide clearance and prevent binding.They usually have more teeth per inch of diameter than ordinary plain milling cutters and are used for milling deep，narrow slots and for cutting-off operations． 數(shù)控技術(shù) 數(shù)控是可編程自動化技術(shù)的一種形式，通過數(shù)字、字母和其他符號來控制加工設(shè)備。數(shù)字、字母和符號用適當(dāng)?shù)母袷骄幋a為一個特定工件定義指令程序。當(dāng)工件改變時，指令程序就改變。這種改變程序的能力使數(shù)控適合于中、小批量生產(chǎn)，寫一段新程序遠(yuǎn)比對加工設(shè)備做大的改動容易得多。 數(shù)控機(jī)床有兩種基本形式：點(diǎn)位控制和連續(xù)控制(也稱為輪廓控制)。點(diǎn)位控制機(jī)床采用異步電動機(jī)，因此，主軸的定位只能通過完成一個運(yùn)動或一個電動機(jī)的轉(zhuǎn)動來實(shí)現(xiàn)。這種機(jī)床主要用于直線切削或鉆孔、鏜孔等場合。 數(shù)控系統(tǒng)由下列組件組成：數(shù)據(jù)輸入裝置，帶控制單元的磁帶閱讀機(jī)，反饋裝置和切削機(jī)床或其他形式的數(shù)控設(shè)備。 數(shù)據(jù)輸人裝置，也稱“人機(jī)聯(lián)系裝置”，可用人工或全自動方法向機(jī)床提供數(shù)據(jù)。人工方法作為輸人數(shù)據(jù)唯一方法時，只限于少量輸入。人工輸入裝置有鍵盤，撥號盤，按鈕，開關(guān)或撥輪選擇開關(guān)，這些都位于機(jī)床附近的一個控制臺上。撥號盤通常連到一個同步解析器或電位計的模擬裝置上。在大多數(shù)情況下，按鈕、開關(guān)和其他類似的旋鈕是數(shù)據(jù)輸入元件。人工輸入需要操作者控制每個操作，這是一個既慢又單調(diào)的過程，除了簡單加工場合或特殊情況，已很少使用。 幾乎所有情況下，信息都是通過卡片、穿孔紙帶或磁帶自動提供給控制單元。在傳統(tǒng)的數(shù)控系統(tǒng)中，八信道穿孔紙帶是最常用的數(shù)據(jù)輸入形式，紙帶上的編碼指令由一系列稱為程序塊的穿孔組成。每一個程序塊代表一種加工功能、一種操作或兩者的組合。紙帶上的整個數(shù)控程序由這些連續(xù)數(shù)據(jù)單元連接而成。帶有程序的長帶子像電影膠片一樣繞在盤子上，相對較短的帶子上的程序可通過將紙帶兩端連接形成一個循環(huán)而連續(xù)不斷地重復(fù)使用。帶子一旦安裝好，就可反復(fù)使用而無需進(jìn)一步處理。此時，操作者只是簡單地上、下工件。穿孔紙帶是在帶有特制穿孔附件的打字機(jī)或直接連到計算機(jī)上的紙帶穿孔裝置上做成的。紙帶制造很少不出錯，錯誤可能由編程、卡片穿孔或編碼、紙帶穿孔時的物理損害等形成。通常，必須要試走幾次來排除錯誤，才能得到一個可用的工作紙帶。 雖然紙帶上的數(shù)據(jù)是自動進(jìn)給的，但實(shí)際編程卻是手工完成的，在編碼紙帶做好前，編程者經(jīng)常要和一個計劃人員或工藝工程師一起工作，選擇合適的數(shù)控機(jī)床，決定加工材料，計算切削速度和進(jìn)給速度，決定所需刀具類型，仔細(xì)閱讀零件圖上尺寸，定下合適的程序開始的零參考點(diǎn)，然后寫出程序清單，其上記載有描述加工順序的編碼數(shù)控指令，機(jī)床按順序加工工件到圖樣要求。 控制單元接受和儲存編碼數(shù)據(jù)，直至形成一個完整的信息程序塊，然后解釋數(shù)控指令，并引導(dǎo)機(jī)床得到所需運(yùn)動。 為更好理解控制單元的作用，可將它與撥號電話進(jìn)行比較，即每撥一個數(shù)字，就儲存一個，當(dāng)整個數(shù)字撥好后，電話就被激活，也就完成了呼叫。 裝在控制單元里的紙帶閱讀機(jī)，通過其內(nèi)的硅光二極管，檢測到穿過移動紙帶上的孔漏過的光線，將光束轉(zhuǎn)變成電能，并通過放大來進(jìn)一步加強(qiáng)信號，然后將信號送到控制單元里的寄存器，由它將動作信號傳到機(jī)床驅(qū)動裝置。 有些光電裝置能以高達(dá)每秒1000個字節(jié)的速度閱讀，這對保持機(jī)床連續(xù)動作是必須的，否則，在輪廓加工時，刀具可能在工件上產(chǎn)生劃痕。閱讀裝置必須要能以比控制系統(tǒng)處理數(shù)據(jù)更快的速度來閱讀數(shù)據(jù)程序塊。 反饋裝置是用在一些數(shù)控設(shè)備上的安全裝置，它可連續(xù)補(bǔ)償控制位置與機(jī)床運(yùn)動滑臺的實(shí)際位置之間的誤差。裝有這種直接反饋檢查裝置的數(shù)控機(jī)床有一個閉環(huán)系統(tǒng)裝置。位置控制通過傳感器實(shí)現(xiàn)，在實(shí)際工作時，記錄下滑臺的位置，并將這些信息送回控制單元。接受到的信號與紙帶輸入的信號相比較，它們之間的任何偏差都可得到糾正。 在另一個稱為開環(huán)的系統(tǒng)中，機(jī)床僅由響應(yīng)控制器命令的步進(jìn)電動機(jī)驅(qū)動定位，工件的精度幾乎完全取決于絲杠的精度和機(jī)床結(jié)構(gòu)的剛度。有幾個理由可以說明步進(jìn)電機(jī)是一個自動化申請的非常有用的驅(qū)動裝置。對于一件事物，它被不連續(xù)直流電壓脈沖驅(qū)使,是來自數(shù)傳計算機(jī)和其他的自動化的非常方便的輸出控制系統(tǒng)。 當(dāng)多數(shù)是索引或其他的自動化申請所必備者的時候，步進(jìn)電機(jī)對運(yùn)行一個精確的有角進(jìn)步也是理想的。因為控制系統(tǒng)不需要監(jiān)聽就提供特定的輸出指令而且期待系統(tǒng)適當(dāng)?shù)胤磻?yīng)的公開- 環(huán)操作造成一個回應(yīng)環(huán)，步進(jìn)電機(jī)是理想的。 一些工業(yè)的機(jī)械手使用高抬腿運(yùn)步的馬乘汽車駕駛員，而且步進(jìn)電機(jī)是有用的在數(shù)字受約束的工作母機(jī)中。 這些申請的大部分是公開- 環(huán) ,但是雇用回應(yīng)環(huán)檢測受到驅(qū)策的成份位置是可能的。 環(huán)的一個分析者把真實(shí)的位置與需要的位置作比較，而且不同是考慮過的錯誤。 那然后駕駛員能發(fā)行對步進(jìn)電機(jī)的電脈沖，直到錯誤被減少對準(zhǔn)零位。在這個系統(tǒng)中，沒有信息反饋到控制單元的自矯正過程。出現(xiàn)誤動作時，控制單元繼續(xù)發(fā)出電脈沖。比如，一臺數(shù)控銑床的工作臺突