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NUMERICAL CONTROL Numerical control 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 work part 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 Number control lather main use to carry on a car to pare towards revolving body spare parts, the Tang pare, drill to pare, the Jiao pare, offend silk etc. process of work preface. General ability auto inside completion outside cylinder noodles, conic surface, surface of sphere, cylinder thread, slot and carry noodles etc. the slice of work preface pare to process. The host is the topic that the number control lather and include a tool machine body, sign pillar, principal axis and enter etc. is to the organization machine parts. Number control equip, is number control tool machine of core, include hardware and correspond of software, used for an importation numeral turn of spare parts procedure, and completion importation information of saving, the transformation of data, put to repair operation and realization various control function. Drive to equip, he is number control the drive of organization of the tool machine performance parts, include a principal axis to drive unit and enter to the unit, principal axis electrical engineering and enter etc. to electrical engineering. He under the control that number control to equip pass electricity or electricity liquid servo system realization principal axis with enters give drive. When several enter to give allied move, can completion fixed position, straight line, process of flat surface curve and space curve. Assistance equips the index number control tool machine of some necessity of 西北工業(yè)大學(xué)明德學(xué)院本科畢業(yè)設(shè)計(jì)論文 1 kit parts, in order to assurance number control tool machine of circulate, such as cool off, row scraps, lubricate, illuminate, monitor etc. It include a liquid to press friendly move equip, row scraps equip, exchange work set, number control to turn Taiwan and number control cent degree head. Plait distance and other subsidiary equipments, can use to carry on the procedure of spare parts to draw up outside machine, saving. Modern number control lather to all have X, Z two stalk of allied move function, knife position and point of a knife arc radius of compensate function, and process fix circulation function. The number control the structure of lather 1. The number control a lather brief introduction The number control constitute of lather: Number control system, bed body, principal axis and enter to the system, turn round a knife, operation front-panel and assistance system etc. (1) The economy number control lather: Adoption step enter electric motor and list slice machine to common the car of the lather pare into to the system carry on reformation behind formation of the simple number control lather. The cost is lower, automation degree and function be all more bad, the car pare to process accuracy also not high, be applicable to request not high of turn round type spare parts of the car pare to process. The economy number control lather (2) Common number control lather: Pare to process a request to carry on the structure according to the car specialized design, equipment in general use number control system but formation of number control lather. Number control system function strong, automation degree with process accuracy also more Ago, be applicable to general turn round type spare parts of the car pare to process. This kind of number control lather can control 2 sit a mark stalk in the meantime, namely x stalk and z stalk. Common number control lather (3)the car pare to process center: At common number control the 西北工業(yè)大學(xué)明德學(xué)院本科畢業(yè)設(shè)計(jì)論文 2 foundation of lather up, increment C stalk and motive head, more high class of the tool machine still take a knife database, can control X, Z and C 3 sit mark stalk, allied move control stalk can BE(X, Z),(X, C) or(Z, C).Because increment C stalk and Xian pare a motive head, this kind of number control process of lather function consumedly strengthen, in addition to carry on general the car pare, also can carry on path to pare with stalk toward the Xian, the curved face Xian pare, the center line dont turn round in the spare parts center of bore and path pare toward the drill of bore etc. process. 2. The liquid press card dish and liquid to press a tail The liquid press card dish is number control a car to pare to process clip tight work piece of importance enclosure, rightness general turn round type spare parts can adoption common the liquid press card dish; To the spare parts be clip hold the part isnt the spare parts of cylinder form, demand adoption appropriation card dish; With the stick anticipate direct process spare parts demand adoption spring coil card dish. To stalk to the size and the path is to the specific value bigger spare parts of size, demand adoption install press a tail in the liquid up of live top carry on prop up to the spare parts end tip, then can assurance carry on to the spare parts exactitude of process. The tail has a common liquid to press tail and programmable liquid to press a tail. 3. The number control the knife of lather Number control lather can equipment two kinds of knife: (1) Appropriation knife from lather produce manufacturer oneself development, haft for use is also appropriation of. This kind of the advantage be that the manufacturing cost is low, but lack in general use. (2)in general use knife according to certain in general use standard(like VDI, Germany engineers association) but produce of knife, number control lather production manufacturer can according to number control the function of lather request to carry on a choice allocation. In general use knife 西北工業(yè)大學(xué)明德學(xué)院本科畢業(yè)設(shè)計(jì)論文 3 4. The Xian pare a motive head Number control lather knife top to install Xian after pare the motive head can consumedly expand number to control process of lather ability. Such as :Make use of the Xian pare a motive head to carry on stalk to drill a hole to pare stalk toward the slot with Xian. The N C system consists of the following components: data input, the tape reader with the control unit, feedback devices, and the metalcutting machine tool or other type of N C equipment Data input, also called “mantocontrol 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 Eightchannel 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 西北工業(yè)大學(xué)明德學(xué)院本科畢業(yè)設(shè)計(jì)論文 4 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 tapepunching 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 西北工業(yè)大學(xué)明德學(xué)院本科畢業(yè)設(shè)計(jì)論文 5 signal The signals are then sent to registers in 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 machinetool 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 openloop 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 西北工業(yè)大學(xué)明德學(xué)院本科畢業(yè)設(shè)計(jì)論文 6 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 西北工業(yè)大學(xué)明德學(xué)院本科畢業(yè)設(shè)計(jì)論文 7 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 is 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 the mechanical system, ale designed with special hightorque stepping motors In this case, the motors have sufficient capacity to “overpower the system in the event of almost any contingency 西北工業(yè)大學(xué)明德學(xué)院本科畢業(yè)設(shè)計(jì)論文 8 數(shù)控 數(shù)控是可編程自動(dòng)化技術(shù)的一種形式,通過數(shù)字、字母和其他符號(hào)來控制加工設(shè)備。數(shù)字、字母和符號(hào)用適當(dāng)?shù)母袷骄幋a為一個(gè)特定工件定義指令程序。當(dāng)工件改變時(shí),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(duì)加工設(shè)備做大的改動(dòng)容易得多。 數(shù)控車床主要用來對(duì)旋轉(zhuǎn)體零件進(jìn)行車削、鏜削、鉆削、鉸削、攻絲等工序的加工。一般能自動(dòng)完成內(nèi)外圓柱面、圓錐面、球面、圓柱螺紋、槽及端面等工序的切削加工。 主機(jī)是數(shù)控車床的主題,包括 機(jī)床身、立柱、主軸、進(jìn)給機(jī)構(gòu)等機(jī)械部件。數(shù)控裝置,是數(shù)控機(jī)床的核心,包括硬件以及相應(yīng)的軟件,用于輸入數(shù)字化的零件程序,并完成輸入信息的存儲(chǔ)、數(shù)據(jù)的變換、插補(bǔ)運(yùn)算以及實(shí)現(xiàn)各種控制功能。驅(qū)動(dòng)裝置,他是數(shù)控機(jī)床執(zhí)行機(jī)構(gòu)的驅(qū)動(dòng)部件,包括主軸驅(qū)動(dòng)單元、進(jìn)給單元、主軸電機(jī)及進(jìn)給電機(jī)等。他在數(shù)控裝置的控制下通過電氣或電液伺服系統(tǒng)實(shí)現(xiàn)主軸和進(jìn)給驅(qū)動(dòng)。當(dāng)幾個(gè)進(jìn)給聯(lián)動(dòng)時(shí),可以完成定位、直線、平面曲線和空間曲線的加工。輔助裝置,指數(shù)控機(jī)床的一些必要的配套部件,用以保證數(shù)控機(jī)床的運(yùn)行,如冷卻、排屑、潤滑、照明、監(jiān)測等。它包括液壓和 氣動(dòng)裝置、排屑裝置、交換工作臺(tái)、數(shù)控轉(zhuǎn)臺(tái)和數(shù)控分度頭。編程及其他附屬設(shè)備,可用來在機(jī)外進(jìn)行零件的程序編制、存儲(chǔ)等。 現(xiàn)代數(shù)控車床都具有 X、 Z兩軸的聯(lián)動(dòng)功能、刀具位置和刀尖圓弧半徑的補(bǔ)償功能、以及加工固定循環(huán)功能。 數(shù)控車床的結(jié)構(gòu) 1.數(shù)控車床簡介 數(shù)控車床的組成:數(shù)控系統(tǒng)、床身、主軸、進(jìn)給系統(tǒng)、回轉(zhuǎn)刀架、操作面板和輔助系統(tǒng)等。 (1)經(jīng)濟(jì)型數(shù)控車床:采用步進(jìn)電動(dòng)機(jī)和單片機(jī)對(duì)普通車床的車削進(jìn)給系統(tǒng)進(jìn)行改造后形成的簡易型數(shù)控車床。成本較低,自動(dòng)化程度和功能都比較差,車削加工精度也不高,適用于要求不高的回轉(zhuǎn)類零件 的車削加工。 西北工業(yè)大學(xué)明德學(xué)院本科畢業(yè)設(shè)計(jì)論文 9 經(jīng)濟(jì)型數(shù)控車床 (2)普通數(shù)控車床:根據(jù)車削加工要求在結(jié)構(gòu)上進(jìn)行專門設(shè)計(jì),配備通用數(shù)控系統(tǒng)而形成的數(shù)控車床。數(shù)控系統(tǒng)功能強(qiáng),自動(dòng)化程度和加工精度也比較高,適用于一般回轉(zhuǎn)類零件的車削加工。這種數(shù)控車床可同時(shí)控制兩個(gè)坐標(biāo)軸,即 x軸和 z軸。 普通數(shù)控車床 (3)車削加工中心:在普通數(shù)控車床的基礎(chǔ)上,增加了 C軸和動(dòng)力頭,更高級(jí)的機(jī)床還帶有刀庫,可控制 X、 Z和 C三個(gè)坐標(biāo)軸,聯(lián)動(dòng)控制軸可以是 (X、 Z)、 (X、C)或 (Z、 C)。由于增加了 C軸和銑削動(dòng)力頭,這種數(shù)控車床的加工功能大大增強(qiáng),除可以進(jìn)行一般車削外 ,還可以進(jìn)行徑向和軸向銑削、曲面銑削、中心線不在零件回轉(zhuǎn)中心的孔和徑向孔的鉆削等加工。 2.液壓卡盤和液壓尾架 液壓卡盤是數(shù)控車削加工時(shí)夾緊工件的重要附件,對(duì)一般回轉(zhuǎn)類零件可采用普通液壓卡盤;對(duì)零件被夾持部位不是圓柱形的零件,則需要采用專用卡盤;用棒料直接加工零件時(shí)需要采用彈簧卡盤。 對(duì)軸向尺寸和徑向尺寸的比值較大的零件,需要采用安裝在液壓尾架上的活頂尖對(duì)零件尾端進(jìn)行支撐,才能保證對(duì)零件進(jìn)行正確的加工。尾架有普通液壓尾架和可編程液壓尾架。 3.數(shù)控車床的刀架 數(shù)控車床可以配備兩種刀架: (1)專用刀架 由車 床生產(chǎn)廠商自己開發(fā),所使用的刀柄也是專用的。這種刀架的優(yōu)點(diǎn)是制造成本低,但缺乏通用性。 (2)通用刀架 根據(jù)一定的通用標(biāo)準(zhǔn) (如 VDI,德國工程師協(xié)會(huì) )而生產(chǎn)的刀架,數(shù)控車床生產(chǎn)廠商可以根據(jù)數(shù)控車床的功能要求進(jìn)行選擇配置。 4.銑削動(dòng)力頭 數(shù)控車床刀架上安裝銑削動(dòng)力頭后可以大大擴(kuò)展數(shù)控車床的加工能力。如:利用銑削動(dòng)力頭進(jìn)
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