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1、Numerical Control System The numerical control system is the digital control system abbreviation. By early is composed of hardware circuit is called hardware numerical control (Hard NC), after 1970, hardware circuit components gradually instead by the computer called for computer numerical control

2、system. Computerized numerical control system is a system that is use computer control processing function to achieve numerical control system. CNC system according to the computer memory stored in the control program execution part or all, numerical control function, and is equipped with inte

3、rface circuit and servo drive the special computer system. CNC system consists of NC program, input devices; output devices, computer numerical control equipment (CNC equipment), programmable logic controllers (PLC), the spindle and feed drive (servo) drive (including detection devices) and so

4、 on. The core of CNC system is equipment. By using the computer system with the function of software and PLC instead of the traditional machine electric device to make the system logic control more compact, its flexibility and versatility, reliability become more better, easy to implement compl

5、ex numerical control function, use and maintenance can be more convenient, and it also has connected and super ordination machine and the remote communication function. At present, the numerical control system has variety of different forms; composition structure has its own characteristics. T

6、hese structural features from the basic requirements of the initial system design and engineering design ideas. For example, the control system of point and continuous path control systems have different requirements. For the T system and the M system, there are also very different, the former appli

7、es to rotary part processing, the latter suitable for special-shaped the axially symmetrical parts processing. For different manufacturers, based on historical development factors and vary their complex factors, may also be thinking in the design is different. For example, the United States Dynapath

8、 system uses a small plate for easy replacement and flexible combination of the board; while Japan FANUC system is a large plate structure tends to make the system work in favor of reliability, make the system MTBF rate continues to increase. However, no matter what kind of system, their basic princ

9、iple and structure are very similar. The numerical control system generally consists of three major components, namely the control system, servo system and position measuring system. Control procedures by interpolation operation work piece, issue control instructions to the servo drive system;

10、servo drive system control instructions amplified by the servo motor-driven mechanical movement required; measurement system detects the movement of mechanical position or speed, and feedback to the control system, to modify the control instructions. These three parts combine to form a complete clos

11、ed-loop control of the CNC system. Control system mainly consists of bus, CPU, power supply, memory, operating panel and display, position control unit, programmable logic controller control unit and data input / output interface and so on. The latest generation of CNC system also includes a c

12、ommunication unit; it can complete the CNC, PLCs internal data communications and external high-order networks. Servo drive system including servo drives and motors. Position measuring system is mainly used grating, or circular grating incremental displacement encoder. CNC system hardware from

13、 the NC device, input / output devices, drives and machine logic control devices, electrical components, between the four parts through the I / O interface to interconnect. Numerical control device is the core of CNC system, its software and hardware to control the implementation of various CNC

14、 functions. The hardware structure of no device by CNC installations in the printed circuit board with infixing pattern can be divided into the big board structure and function module (small board) structure; Press CNC apparatus hardware manufacturing mode, can be divided into special structure

15、 and personal computer type structure; Press CNC apparatus in the number of microprocessor can be divided into single microprocessor structure and many microprocessor structure. (1)Large panel structure and function templates structure 1) Large panel structure Panel structures CNC system CNC

16、 equipment from the main circuit board, position control panels, PC boards, graphics control panel, additional I / O board and power supply unit and other components. The main circuit board printed circuit board is big; the other circuit board is a small plate, inserted in the large printed circuit

17、board slot. This structure is similar to the structure of micro-computer. 2) Function templates structure (2)Single-microprocessor structure and mulct-microprocessor structure 1) Single-microprocessor structure In a single-microprocessor structure, only a microprocessor to focus on control

18、, time-sharing deals with the various tasks of CNC equipment. 2) melt-microprocessor structure With the increase in numerical control system functions, CNC machine tools to improve the processing speed of a single microprocessor CNC system can not meet the requirement; therefore, many CNC syste

19、ms uses a multi-microprocessor structure. If a numerical control system has two or more microprocessors, each microprocessor via the data bus or communication to connect, share system memory and common I / O interfaces, each processor sharing system Part of the work, which is multi-processor systems

20、. CNC software is divided into application software and system software. CNC system software for the realization of various functions of the CNC system, the preparation of special software, also known as control software, stored in the computer EPROM memory. CNC Systems feature a variety of setting

21、s and different control schemes, and their system software in the structure and size vary widely, but generally include input data processing procedures, computing interpolation procedures, speed control procedures, management procedures and diagnostic procedures. (1)Input data processing procedure

22、s It receives input part program, the standard code, said processing instructions and data decoding, data processing, according to the prescribed format for storage. Some systems also calculated to compensate, or interpolation operation and speed control for pre-computation. Typically, the input da

23、ta processing program, including input, decoding and data processing three elements. (2)Computing interpolation procedures CNC work piece processing system according to the data provided, such as curve type, start, end, etc. operations. According to the results of operations were sent to each axis

24、 feed pulse. This process is called interpolation operation. Feed drive servo system Impulsive table or by a corresponding movement of the tool to complete the procedural requirements of the processing tasks. Interpolation for CNC system is the side of the operation, while processing, is a typical

25、real-time control, so the interpolation directly affects the speed of operation the machine feed rate, and should therefore be possible to shorten computation time, which is the preparation of interpolation Complements the key to the program. (3)Speed control procedures Speed control program accor

26、ding to the given value control the speed of operation of the frequency interpolation, in order to maintain a predetermined feed rate. Changes in speed is large, the need for automatic control of acceleration and deceleration to avoid speed drive system caused by mutations in step. (4)Management pr

27、ocedures Management procedures responsible for data input, data processing, interpolation processing services operations as the various procedures for regulation and management. Management process but also on the panel command, the clock signal, the interrupt caused by fault signals for processing

28、. (5)Diagnostic procedures Diagnostic features are found in the running system failure in a timely manner, and that the type of failure. You can also run before or after the failure, check the system main components (CPU, memory, interfaces, switches, servo systems, etc.) function is normal, and t

29、hat the site of failure. Machining Any machining must have three basic conditions: machining tools, work piece and machining sports. Machining tool edge should be, the material must be rigid than the work piece. Different forms of tool structure and cutting movements constitute different cutti

30、ng methods. Blade with a blade-shaped and have a fixed number of methods for cutting tools for turning, drilling, boring, milling, planning, broaching, and sawing, etc.; edge shape and edge with no fixed number of abrasive or abrasive Cutting methods are grinding, grinding, honing and polishing.

31、 Machining is the most important machinery manufacturing processing methods. Although the rough improve manufacturing precision, casting, forging, extrusion, powder metallurgy processing applications on widely, but to adapt to a wide range of machining, and can achieve high accuracy and low surface

32、 roughness, in Manufacturing still plays an important role in the process. Cutting metal materials have many classifications. Common are the following three kinds. By cutting process feature distinguishing characteristics of the decision process on the structure of cutting tools and cutting too

33、ls and work piece relative motion form. According to the technical characteristics of cutting can be divided into: turning, milling, drilling, boring, reaming, planning, shaping, slotting, broaching, sawing, grinding, grinding, honing, super finishing, polishing, gear Processing, the worm process, t

34、hread processing, ultra-precision machining, bench and scrapers and so on. By material removal rate and machining accuracy distinction can be divided into: ① rough: with large depth of cut, one or a few times by the knife away from the work cut out most or all allowances, such as rough turning, roug

35、h planning, Rough milling, drilling and sawing, etc., rough machining precision high efficiency low, generally used as a pre-processing, and sometimes also for final processing. ② Semi-finishing: General roughing and finishing as the middle between the process, but the work piece accuracy and surfac

36、e roughness on the less demanding position, but also can be used as the final processing. ③ finishing: cutting with a fine way to achieve higher machining surface accuracy and surface quality, such as fine cars, fine planning, precision hinges, grinding and so on. General is the final finishing proc

37、ess. ④ Finishing process: after the finish, the aim is to obtain a smaller surface roughness and to slightly improve the accuracy. Finishing processing allowance is small, such as honing, grinding, ultra-precision grinding and super finishing and so on. ⑤ Modification process: the aim is to reduce t

38、he surface roughness, to improve the corrosion, dust properties and improve appearance, but does not require higher precision, such as polishing, sanding, etc. ⑥ ultra-precision machining: aerospace, lasers, electronics, nuclear energy and other cutting-edge technologies that need some special preci

39、sion parts, high accuracy over IT4, surface roughness less than Ra 0.01 microns. This need to take special measures to ultra-precision machining, such as turning mirror, mirror grinding, chemical mechanical polishing of soft abrasive. Distinguished by method of surface machining, the work piece

40、 is to rely on the machined surface for cutting tool and the work piece to obtain the relative motion. By surface methods, cutting can be divided into three categories. ① tip trajectory method: relying on the tip relative to the trajectory of the surface to obtain the required work piece surface geo

41、metry, such as cylindrical turning, planning surface, cylindrical grinding, with the forming surface, such as by turning mode. The trajectory depends on the tool tip provided by the cutting tool and work piece relative motion. ② forming tool method: short forming method, with the final work piece su

42、rface profile that matches the shape forming cutter or grinding wheel, such as processing a shaped surface. At this time forming part of the machine movement was replaced by the blade geometry, such as the shape of turning, milling and forming grinding forming and so on. The more difficult the manuf

43、acture of forming cutter, machine - clamp - work piece - tool formed by the process system can withstand the cutting force is limited, forming method is generally used for processing short shaped surface. ③ generating method: also known as rotary cutting method, cutting tool and work piece during pr

44、ocessing as a relatively developed into a campaign tool (or wheel) and the work piece instantaneous center line of pure rolling interaction between the two maintain a certain ratio between Is obtained by processing the surface of the blade in this movement in the envelope. Gear machining hobbling, g

45、ear shaping, shaving, honing, and grinding teeth (not including form grinding teeth), etc. are generating method processing. PLC Early called the programmable logic controller PLC (Programmable Logic Controller, PLC), which is mainly used to replace the logic control relays. With the technolog

46、y, which uses micro-computer technology, industrial control device function has been greatly exceeded the scope of logic control, therefore, such a device today called programmable logic controller, referred to as the PC. However, in order to avoid personal computer (Personal Computer) in the short

47、confusion, it will be referred to as programmable logic controller PLC, plc since 1966, the U.S. Digital Equipment Corporation (DEC) developed there, the current United States, Japan, Germany, PLC Good quality and powerful. The basic structure of Programmable Logic Controller A. Power PLC

48、s power in the whole system plays a very important role. If you do not have a good, reliable power system is not working, so the PLC manufacturers design and manufacture of power very seriously. General AC voltage fluctuations of +10% (+15%) range, you can not take other measures to PLC to connect d

49、irectly to the AC line. B.Central processing unit (CPU) Central processing unit (CPU) is the central PLC control. It is given by the function of PLC system program from the programmer receives and stores the user program and data type; check the power supply, memory, I / O and timer alert statu

50、s, and to diagnose syntax errors in the user program. When the PLC into run-time, first it scans the scene to receive the status of various input devices and data, respectively, into I / O image area, and then one by one from the user program reads the user program memory, after a shell and press Pr

51、ovisions of the Directive the result of logic or arithmetic operations into the I / O image area or data register. And the entire user program is finished, and finally I / O image area of the state or the output of the output register data to the appropriate output device, and so on to run until sto

52、pped. To further improve the reliability of PLC, PLC is also large in recent years constitutes a redundant dual-CPU system, or by three voting systems CPU. Thus, even if a CPU fails, the whole system can still work properly. C.Memory Storage system software of memory called system program m

53、emory. Storage application software of memory called the user program memory. D.Input and output interface circuit 1, the live input interface circuit by the optical coupling circuit and the computer input interface circuit, the role of PLC and field control of an interface for input channels.

54、 2, Field output interface circuit by the output data registers, interrupt request strobe circuit and integrated circuit, the role of PLC output interface circuit through the on-site implementation of parts of the output to the field corresponding control signal. E.Function module Such as co

55、unting, positioning modules. F.Communication module Such as Ethernet, RS485, Prefab’s-DP communication module. 數(shù)控系統(tǒng) 　　數(shù)控系統(tǒng)是數(shù)字控制系統(tǒng)簡(jiǎn)稱(chēng)，英文名稱(chēng)為Numerical Control System，早期是由硬件電路構(gòu)成的稱(chēng)為硬件數(shù)控（Har

56、d NC），1970年代以后，硬件電路元件逐步由專(zhuān)用的計(jì)算機(jī)代替稱(chēng)為計(jì)算機(jī)數(shù)控系統(tǒng)。 　　計(jì)算機(jī)數(shù)控（Computerized numerical control,簡(jiǎn)稱(chēng)CNC）系統(tǒng)是用計(jì)算機(jī)控制加工功能，實(shí)現(xiàn)數(shù)值控制的系統(tǒng)。CNC系統(tǒng)根據(jù)計(jì)算機(jī)存儲(chǔ)器中存儲(chǔ)的控制程序，執(zhí)行部分或全部數(shù)值控制功能，并配有接口電路和伺服驅(qū)動(dòng)裝置的專(zhuān)用計(jì)算機(jī)系統(tǒng)。 　　CNC系統(tǒng)由數(shù)控程序、輸入裝置、輸出裝置、計(jì)算機(jī)數(shù)控裝置（CNC裝置）、可編程邏輯控制器（PLC）、主軸驅(qū)動(dòng)裝置和進(jìn)給（伺服）驅(qū)動(dòng)裝置（包括檢測(cè)裝置）等組成。 　　CNC系統(tǒng)的核心是CNC裝置。由于使用了計(jì)算機(jī)，系統(tǒng)具有了軟件功能，又用PL

57、C代替了傳統(tǒng)的機(jī)床電器邏輯控制裝置，使系統(tǒng)更小巧，其靈活性、通用性、可靠性更好，易于實(shí)現(xiàn)復(fù)雜的數(shù)控功能，使用、維護(hù)也方便，并具有與上位機(jī)連接及進(jìn)行遠(yuǎn)程通信的功能。 　　目前世界上的數(shù)控系統(tǒng)種類(lèi)繁多，形式各異，組成結(jié)構(gòu)上都有各自的特點(diǎn)。這些結(jié)構(gòu)特點(diǎn)來(lái)源于系統(tǒng)初始設(shè)計(jì)的基本要求和工程設(shè)計(jì)的思路。例如對(duì)點(diǎn)位控制系統(tǒng)和連續(xù)軌跡控制系統(tǒng)就有截然不同的要求。對(duì)于T系統(tǒng)和M系統(tǒng)，同樣也有很大的區(qū)別，前者適用于回轉(zhuǎn)體零件加工，后者適合于異形非回轉(zhuǎn)體的零件加工。對(duì)于不同的生產(chǎn)廠家來(lái)說(shuō)，基于歷史發(fā)展因素以及各自因地而異的復(fù)雜因素的影響，在設(shè)計(jì)思想上也可能各有千秋。例如，美國(guó)Dynapath系統(tǒng)采用小板結(jié)構(gòu)，便

58、于板子更換和靈活結(jié)合，而日本FANUC系統(tǒng)則趨向大板結(jié)構(gòu)，使之有利于系統(tǒng)工作的可靠性，促使系統(tǒng)的平均無(wú)故障率不斷提高。然而無(wú)論哪種系統(tǒng)，它們的基本原理和構(gòu)成是十分相似的。 一般整個(gè)數(shù)控系統(tǒng)由三大部分組成，即控制系統(tǒng)，伺服系統(tǒng)和位置測(cè)量系統(tǒng)?？刂葡到y(tǒng)按加工工件程序進(jìn)行插補(bǔ)運(yùn)算，發(fā)出控制指令到伺服驅(qū)動(dòng)系統(tǒng)；伺服驅(qū)動(dòng)系統(tǒng)將控制指令放大，由伺服電機(jī)驅(qū)動(dòng)機(jī)械按要求運(yùn)動(dòng)；測(cè)量系統(tǒng)檢測(cè)機(jī)械的運(yùn)動(dòng)位置或速度，并反饋到控制系統(tǒng)，來(lái)修正控制指令。這三部分有機(jī)結(jié)合，組成完整的閉環(huán)控制的數(shù)控系統(tǒng)。 　　控制系統(tǒng)主要由總線、CPU、電源、存貯器、操作面板和顯示屏、位控單元、可編程序控制器邏輯控制單元以及數(shù)據(jù)輸入

59、/輸出接口等組成。最新一代的數(shù)控系統(tǒng)還包括一個(gè)通訊單元，它可完成CNC、PLC的內(nèi)部數(shù)據(jù)通訊和外部高次網(wǎng)絡(luò)的連接。伺服驅(qū)動(dòng)系統(tǒng)主要包括伺服驅(qū)動(dòng)裝置和電機(jī)。位置測(cè)量系統(tǒng)主要是采用長(zhǎng)光柵或圓光柵的增量式位移編碼器。 　　數(shù)控系統(tǒng)的硬件由數(shù)控裝置、輸入/輸出裝置、驅(qū)動(dòng)裝置和機(jī)床電器邏輯控制裝置等組成，這四部分之間通過(guò)I/O接口互連。 　　數(shù)控裝置是數(shù)控系統(tǒng)的核心，其軟件和硬件來(lái)控制各種數(shù)控功能的實(shí)現(xiàn)。 　　數(shù)控裝置的硬件結(jié)構(gòu)按CNC裝置中的印制電路板的插接方式可以分為大板結(jié)構(gòu)和功能模塊（小板）結(jié)構(gòu)；按CNC裝置硬件的制造方式，可以分為專(zhuān)用型結(jié)構(gòu)和個(gè)人計(jì)算機(jī)式結(jié)構(gòu)；按CNC裝置中微處理器的

60、個(gè)數(shù)可以分為單微處理器結(jié)構(gòu)和多微處理器結(jié)構(gòu)。 　　（1）大板結(jié)構(gòu)和功能模板結(jié)構(gòu) 1）大板結(jié)構(gòu) 　　大板結(jié)構(gòu)CNC系統(tǒng)的CNC裝置由主電路板、位置控制板、PC板、圖形控制板、附加I/O板和電源單元等組成。主電路板是大印制電路版，其它電路板是小板，插在大印制電路板上的插槽內(nèi)。這種結(jié)構(gòu)類(lèi)似于微型計(jì)算機(jī)的結(jié)構(gòu)。 　　2）功能模塊結(jié)構(gòu) 　?。?）單微處理器結(jié)構(gòu)和多微處理器結(jié)構(gòu) 　　1）單微處理器結(jié)構(gòu) 　　在單微處理器結(jié)構(gòu)中，只有一個(gè)微處理器，以集中控制、分時(shí)處理數(shù)控裝置的各個(gè)任務(wù)。 　　2）多微處理器結(jié)構(gòu) 　　隨著數(shù)控系統(tǒng)功能的增加、數(shù)控機(jī)床的加工速度的提高，單微處理

61、器數(shù)控系統(tǒng)已不能滿足要求，因此，許多數(shù)控系統(tǒng)采用了多微處理器的結(jié)構(gòu)。若在一個(gè)數(shù)控系統(tǒng)中有兩個(gè)或兩個(gè)以上的微處理器，每個(gè)微處理器通過(guò)數(shù)據(jù)總線或通信方式進(jìn)行連接，共享系統(tǒng)的公用存儲(chǔ)器與I/O接口，每個(gè)微處理器分擔(dān)系統(tǒng)的一部分工作，這就是多微處理器系統(tǒng)。 　　CNC軟件分為應(yīng)用軟件和系統(tǒng)軟件。CNC系統(tǒng)軟件是為實(shí)現(xiàn)CNC系統(tǒng)各項(xiàng)功能所編制的專(zhuān)用軟件，也叫控制軟件，存放在計(jì)算機(jī)EPROM內(nèi)存中。各種CNC系統(tǒng)的功能設(shè)置和控制方案各不相同，它們的系統(tǒng)軟件在結(jié)構(gòu)上和規(guī)模上差別很大，但是一般都包括輸入數(shù)據(jù)處理程序、插補(bǔ)運(yùn)算程序、速度控制程序、管理程序和診斷程序。 　?。?）輸入數(shù)據(jù)處理程序 　　

62、它接收輸入的零件加工程序，將標(biāo)準(zhǔn)代碼表示的加工指令和數(shù)據(jù)進(jìn)行譯碼、數(shù)據(jù)處理，并按規(guī)定的格式存放。有的系統(tǒng)還要進(jìn)行補(bǔ)償計(jì)算，或?yàn)椴逖a(bǔ)運(yùn)算和速度控制等進(jìn)行預(yù)計(jì)算。通常，輸入數(shù)據(jù)處理程序包括輸入、譯碼和數(shù)據(jù)處理三項(xiàng)內(nèi)容。 　?。?）插補(bǔ)計(jì)算程序 　　CNC系統(tǒng)根據(jù)工件加工程序中提供的數(shù)據(jù)，如曲線的種類(lèi)、起點(diǎn)、終點(diǎn)等進(jìn)行運(yùn)算。根據(jù)運(yùn)算結(jié)果，分別向各坐標(biāo)軸發(fā)出進(jìn)給脈沖。這個(gè)過(guò)程稱(chēng)為插補(bǔ)運(yùn)算。進(jìn)給脈沖通過(guò)伺服系統(tǒng)驅(qū)動(dòng)工作臺(tái)或刀具作相應(yīng)的運(yùn)動(dòng)，完成程序規(guī)定的加工任務(wù)。 　　CNC系統(tǒng)是一邊插補(bǔ)進(jìn)行運(yùn)算，一邊進(jìn)行加工，是一種典型的實(shí)時(shí)控制方式，所以，插補(bǔ)運(yùn)算的快慢直接影響機(jī)床的進(jìn)給速度，因此應(yīng)該盡

63、可能地縮短運(yùn)算時(shí)間，這是編制插補(bǔ)運(yùn)算程序的關(guān)鍵。 　　(3)速度控制程序 　　速度控制程序根據(jù)給定的速度值控制插補(bǔ)運(yùn)算的頻率，以保預(yù)定的進(jìn)給速度。在速度變化較大時(shí)，需要進(jìn)行自動(dòng)加減速控制，以避免因速度突變而造成驅(qū)動(dòng)系統(tǒng)失步。 　　(4)管理程序 　　管理程序負(fù)責(zé)對(duì)數(shù)據(jù)輸入、數(shù)據(jù)處理、插補(bǔ)運(yùn)算等為加工過(guò)程服務(wù)的各種程序進(jìn)行調(diào)度管理。管理程序還要對(duì)面板命令、時(shí)鐘信號(hào)、故障信號(hào)等引起的中斷進(jìn)行處理。 　　(5)診斷程序 診斷程序的功能是在程序運(yùn)行中及時(shí)發(fā)現(xiàn)系統(tǒng)的故障，并指出故障的類(lèi)型。也可以在運(yùn)行前或故障發(fā)生后，檢查系統(tǒng)各主要部件（CPU、存儲(chǔ)器、接口、開(kāi)關(guān)、伺服系統(tǒng)等）的功

64、能是否正常，并指出發(fā)生故障的部位。 切削加工 　 任何切削加工都必須具備3個(gè)基本條件:切削工具、工件和切削運(yùn)動(dòng)。切削工具應(yīng)有刃口，其材質(zhì)必須比工件堅(jiān)硬。不同的刀具結(jié)構(gòu)和切削運(yùn)動(dòng)形式構(gòu)成不同的切削方法。用刃形和刃數(shù)都固定的刀具進(jìn)行切削的方法有車(chē)削、鉆削、鏜削、銑削、刨削、拉削和鋸切等；用刃形和刃數(shù)都不固定的磨具或 磨料進(jìn)行切削的方法有磨削、研磨、珩磨和拋光等。 　　切削加工是機(jī)械制造中最主要的加工方法。雖然毛坯制造精度不斷提高，精鑄、精鍛、擠壓、粉末冶金等加工工藝應(yīng)用日廣，但由于切削加工的適應(yīng)范圍廣，且能達(dá)到很高的精度和很低的表面

65、粗糙度，在機(jī)械制造工藝中仍占有重要地位。　金屬材料的切削加工有許多分類(lèi)方法。常見(jiàn)的有以下3種。 按工藝特征區(qū)分 切削加工的工藝特征決定于切削工具的結(jié)構(gòu)以及切削工具與工件的相對(duì)運(yùn)動(dòng)形式。按工藝特征，切削加工一般可分為：車(chē)削、銑削、鉆削、鏜削、鉸削、刨削、插削、拉削、鋸切、磨削、研磨、珩磨、超精加工、拋光、齒輪加工、蝸輪加工、螺紋加工、超精密加工。按材料切除率和加工精度區(qū)分 可分為：①粗加工：用大的切削深度，經(jīng)一次或少數(shù)幾次走刀從工件上切去大部分或全部加工余量，如粗車(chē)、粗刨、粗銑、鉆削和鋸切等，粗加工加工效率高而加工精度較低，一般用作預(yù)先加工，有時(shí)也可作最終加工。②半精加工：一般作為粗加工與精

66、加工之間的中間工序，但對(duì)工件上精度和表面粗糙度要求不高的部位，也可以作為最終加工。③精加工：用精細(xì)切削的方式使加工表面達(dá)到較高的精度和表面質(zhì)量，如精車(chē)、精刨、精鉸、精磨等。精加工一般是最終加工。④精整加工：在精加工后 進(jìn)行，其目的是為了獲得更小的表面粗糙度，并稍微提高精度。精整加工的加工余量小，如珩磨、研磨、超精磨削和超精加工等。⑤修飾加工：目的是為了減小表面粗糙度，以提高防蝕、防塵性能和改善外觀,而并不要求提高精度,如拋光、砂光等。⑥超精密加工：航天、激光、電子、核能等尖端技術(shù)領(lǐng)域中需要某些特別精密的零件，其精度高達(dá)IT4以上，表面粗糙度不大于 Ra 0.01微米。這就需要采取特殊措施進(jìn)行超精密加工，如鏡面車(chē)削、鏡面磨削、軟磨粒機(jī)械化學(xué)拋光等。 按表面形成方法區(qū)分切削加工時(shí)，工件的已加工表面是依靠切削工具和工件作相對(duì)運(yùn)動(dòng)來(lái)獲得的。按表面形成方法，切削加工可分為 3類(lèi)。①刀尖軌跡法：依靠刀尖相對(duì)于工件表面的運(yùn)動(dòng)軌跡來(lái)獲得工件所要求的表面幾何形狀，如車(chē)削外圓、刨削平面、磨削外圓、用靠模車(chē)削成形面等。刀尖的運(yùn)動(dòng)軌跡取決于機(jī)床所提供的切削工具與工件的相對(duì)運(yùn)動(dòng)。②成形刀具法：簡(jiǎn)稱(chēng)成形法