数控机床与原理外文翻译文献

数控机床与原理外文翻译文献(文档含中英文对照即英文原文和中文翻译)

Fundamentals Numbercal Control of machine tools

Machine Tools

Machine tools are machines for cutting metals. The most important of metal used in industry are lathes, drilling machines and milling machines. Other kinds of metal working machines are not so widely used in machining metals as these three.

Drilling is perfurmed with a rotating tool called a drill. Most drilling in metal done with a twist drill. The machine used for drilling is called a drill press. Operations such as reaming and tapping, are also classified as drilling. Reaming consists of removing a small amount of metal from a hole already drilled.

Tapping is the process of cutting a thread inside a hole so that a cap screw or bolt may be threaded into it.

The lathe is commonly called the father of the entire machine tool family. For turning operations, the lathe used a single-point-cutting tool, which remove metal as it travels past the revolving workpiece. Turning operations are required to make many

different cylindrical shapes, such as axes, gear blanks, pulleys, and threaded shafts.

Boring operations are performed to enlarge, finish, and accurately locate holes.

Miling removes metal with a revolving, multiple cutting edge tools called miling cutter. Miling cutter are made in many styles and sizes. Some have as few as two cutting edges and others have 30 or more. Miling can produce flat or angled surfaces, grooves, slots, gear teeth, and other profile, depending on the shape of the cutters being used.

Shaping and planning produce flat surfaces with a single-point-cutting tool. In shaping, the cutting tool on a shaper reciprocates or moves back and forth while the work is fed automatically towards the tool. In planning, the workpiece is attached to a worktable that reciprocates past the cutting tool. The cutting tool is automatically fed into the workpiece a small amount on each stroke.

Grinding makes use of abrasive particles to do the cutting. Grinding operations may be classified as precision or non-precision, depending on the purpose. Precision grinding is concerned with grinding to close tolerances and very smooth finish. Non-precision grinding involves the removal of metal where accuracy is not important.

Fundamentals Number Control

Controlling a machine tool by means of a prepared program is known as numerical control, or NC. NC equipment has been defined the Electronic Industries Association (EIA) as “A system in which actions are controlled by the direct insertion of numerical data at some point. The system must automatically interpret at leastsome portion of this data.”

In a typical NC system the numerical data which is required for producing a part is maintained on a punched tape and is called the part program. The part program is arranged in the form of block of information, where each block contains the numerical data required to produce one segment of the workpiece. The punched tape is moved forward by one block each time the cutting of a segment is completed. The punched contains, in coded form, all the information needed for processing a segment of the workpiece: the segment length, its cutting speed, feed, etc .. Dimensional information

(lenth, width, and radii of circles) and the contour form (linear, circular, or other ) are taken form an engineering drawing. Dimensions are given separately for each axis of motion (x,y ,etc.). Cutting speed, feedrate, and auxiliary function (coolant on and off, spindle direction, clamp, gear change, etc.) are programmed according to surface finish and tolerace requirements.

Preparing the part program for a NC machine tool requires a part programmer. The part programmer must possess knowledge and experiences in mechanical engineering. PartProgrammers must be familiar with the function of NC machine tools and machining process and have to decide on the optimal sequence of operations.

In NC machine tools each axis of motion is equipped with a separate driving device which replaces the handwheel of the conventional machine. The driving device may be a direct current (DC) motor, a hydraulic actuator, or a stepping motor. The type selected is determined mainly by the power requirement of the machine.

The NC machine tool system contains the machine control unit(MCU) and the machine tool itself. The MCU has to read and decode the part program, to provide the decoded instructions to the control loops of the machine axes of motion, and to control the machine tool operation.

The MCU consists of two main units: the data processing unit(DPU) and the control loops unti(CLU) .The function of the DPU is to decode the information received form the tape, process it and provide data to the DLU. Such data contains the new required position of each axis, its direction of motion and velocity, and auxiliary control signals to relays. On the other hand, the CLU provides a signal announcing that the previous is completed and that the DPU can read a new block of the part program. The CLU operates the drives attached of the machine lead-screws and receives feedback signals on the actual position and velocity of each one of the axes. Each lead-screw is equipped with a separate driving device anf a separate feedback device, but the latter exists only in a closed-loop system.

In CNC system, the DPU functions are performed by the control program contained in the CNC computer. The major part of the CLU, however, is always

implemented in the most sophisticated CNC system.

Numberical Control of Machining Process

Numberical control of machine tools by computers has great advance in recent years. Generally, automatic machine tools are efficient and accurate when large quantities of parts of the same shape are required, but changing from one automatic cycle to another is a long and expensive process and would only be carried out for a long run. But there are many examples when only a few parts are required and it is in such work that the computer-controlled machine is valuable.

There are two types of computers-digital and analogue. A digital computer works with numbers given in digital form, a digit being one of a certain set of symbols used to show numbers. It is the digital computer which is used in electronic data processing. The analogue computer is based on an analogy of quantity. It deals with physical quantities and not numbers.

In a digital control system information form a drawing is put on a disc which is put into a computer which computers from the information to the continuous motion of the cutting tool. The output is put on a disc which is put into the machine tool control until when required. One computer services a number of machines. Disc can be stored and used any number of times in future cases, simply by replaying them if the same parts are wanted again. For best result, the electronic equipment and the machine tool must be designed together.

This method has also been applied to the control of oxygen cutting of steel plates. When irregular shapes are required, as in ship building, it has been the practice to make a model and to follow its outline by hand control, a method which does not always give accuate results. Again, information is processed by a special computer which then prepares a disc for use in the control console of the cutting machine. With this disc the machine can automatically cut plates of complicated shapes very accurately. This development has particular importance for making steel plates and is a good example of automation applied to batch production.

Programming for NC

A program for numerical consists of a sequence of directions that caused a NC

machine to carry out a certain operation, machining being the most commonly used process. Programming for NC may be done by an internal programming department, on the shop floor, or purchased from an outside source. Also, programming may be done manually or with computer assistance.

The program contains instructions and commands. Geometic instructions pertain to relative movement between the tool and the workpiece. Processing instructions pertain to spindle speeds, feed, tools, and so on. Travel instructions pertain to the type of interpolation and slow or rapid movements of the tool or worktable. Switching commands pertain to on/off position for coolant supplies, spindle rotation, direction of spindle rotation, tool change, workpiece feeding, clamping, and so on.

(1) Manual programming. Manual part programming consists of first calculating dimensional relationships of the tool, workpiece, and work table, based on the engineering drawings of the part, and manufacturing operations to be performed and their sequence. A program sheet is then prepared, which consists of the necessary information to carry out the operation, such as cutting tools, spindle speeds, feeds, depth of cut, cutting fluids, power, and tool or workpiece relative positions and movements. Based on this information, the part program is prepared. Usually a paper tape is first prepared for trying out and debugging the program. Depending on how often it is to be used, the tape may be made of more durable mylar.

Someone konledgeable about the particar process and able to understand, read, and change part programs can do manual programming. Because they are familiar with machine tool and process capabilities, skilled machinists can do manual programming with some training in programming, however, the work is tedious, and time consuming, and uneconomical and is used mostly in simple point to-point applications.

(2) Computer-Aided Programming. Computer-aided part programming involves special symbolic programming languages that determine the coordinate points of corners, edges, and surfaces of the part. Because numerical control involves the insertion of data concerning workpiece materials and processing parame ters, programming must be done by operators or programmers who are knowledgeable

about the relevant aspects of the manufacturing processes being used. Before production begins, programs should be verified, either by viewing a simulation of the procession on a CRT screen or by making the part from an inexpensive material, such as aluminum, wood, or plastic, rather than the material specified for the finished part.

Machining Center

The flexibility and versatility of numberial control have led to the development of a new type of machine tool called the machining center. Using simpler work holding fixtures and fewer cutting tools, this machine dose the work formerly done on several machines.

The machining center is provided with an automatic tool changer. On a command from the NC system, the tool change arm located above the spindle rotates clockwise, simultane-ously gripping the tool in the spindle and another tool in an interchange station located on the face of the machine which is used to store the tool temporarily. The arm them moves forward, removing the tools from the spindle and from the interchange station. After rotating clockwise 180 degrees, the arm retracts, insert the new tool in the spindle, and places the used tool in the interchange system, the arm then returns to the original position. A mechanical hand inside the drum removes the tool from the interchange station and stores it in the tool drum. The machanical hand removed the next tool to be used from the drum and places it in the interchange station in preparation for the next operation. The tool change operation may be completed in 5 seconds. The tool drum can hold a large number of different tools. Each tool holder being coded, the tools can be selected in a random order and in any sequence.

Machining centers can also be available without NC, however, provided with numerical control, the potential of these machines can be fully realized.

So a new generation of ?exible intelligent NC machines is a current machine manufacturing industry to develop number control process of tool machine principle. New challenges for intelligent recon?gurable manufacturing systems are on the agenda for the next generation of machine tool centres. Zero defect workpieces and just-in-time production are some of the objectives to be reached for better quality and high performance production. Sustainability requires a holistic approach to cover not only ?exible intelligent manufacture but also product and services activities. New

routes philosophy of possible machine architecture with characteristics such as hybrid processes with in-process inspection and self-healing will be presented with great features as well as challenges related to various aspects of the next generation of intelligent machine tool centres.

数控机床及其基本原理

机床

机床是用于切削金属的机器。工业上使用的机床要属数控车、钻床和铣床最为重要。其它类型的金属切削机床在金属切削加工方面应用不及这三种机床广泛。

钻削是由旋转的钻头完成的。大多数金属的钻削有麻花钻来完成。用来进行钻削加工的机床成为钻床，扩孔和攻螺纹也归为钻削，扩孔是从已经钻好的孔上在切除少量的金属。

攻螺纹实在内孔上加工出螺纹以使螺杆和螺栓拧进孔内。

车床通常被称为所有类型车床的始祖。为了进行车削，当工件旋转时，车床用一把单刃刀具切除金属。用车削可以加工各种圆柱体形状的工件，如轴、齿轮坯、带轮和四杆轴。

镗削可以将孔扩大，提高孔的表面质量和加工定位精度高的孔。

铣削由旋转的，多切削刃的铣刀来完成，铣刀有多种类型和尺寸。有些铣刀只有两个切削刃，而有些则多达三十或者更多的切削刃。铣刀根据使用的刀具不同能形成平面、斜面、沟槽、狭槽、齿轮和其它外形轮廓。

牛头刨床和龙门刨床用单刃刀具来加工平面。用牛头刨床进行加工时，工件朝向刀具自动进给，刀具往复运动；而在用龙门刨床进行加工时，工件安装在工作台上，工作台往复经过刀具切除金属。刀具

每完成一个行程则自动向工件进给一个小的进给量。

磨削利用磨粒来完成切削工作。根据加工要求，磨削可分为精密磨削和非精密磨削。精密磨削用于公差小河非常光洁的表面，非精密磨削用于在精度要求不高的地方切除多余的金属。

数字控制基本原理

用准备好的程序控制机床，这种工作方式被称为数字控制或NC。美国电子工业协会把数控设备定义为：“采用在某些点直接插入数字数据来控制操作的系统，此系统必须能够自动解释翻译这些信息中的一部分。”

在典型的数控系统中，加工零件所需的数控数据是保存在穿孔带上的，被称为零件程序。零件程序是以信息模块的方式排布的，每一模块中包含了对工件局部进行加工所需的数字信息。当一部分切削完之后，穿孔带移动一个程序块。代码形式的程序块包含了零件分段加工所需的所有信息如分段加工部分长度、切削速度、进给量等。尺寸信息（长、宽及圆半径）和轮廓形状（直线、圆弧或者其它）可以工程图上得到。分别给出每个轴（X、Y等）的运动尺寸，根据表面粗糙度及所需公差对切削速度、进给率及辅助功能（切削液的开、关，主轴的转向、夹紧、换齿轮等）进行编程。

要有一个零件编程人员为数控机床准备程序。零件编程人员必须具有机械工程的知识和经验。零件编程人员要熟悉数控机床的功能及加工工艺，并决定最佳加工工序。

在数控机床中，，每个轴的运动都要有单独的驱动设备代替普通

机床中的手轮来驱动。驱动设备可以是直流电动机、液压发动机或步进电动机，所选的设备的类型主要取决于机床所需的动力。

数控机床系统包括有机床控制单元和加工主机本身。机床控制单元（MCU）必须对零件程序读和译码，提供译码指令以控制机床轴的运动并控制机床操作。MCU有两个主要单元：数据处理单元（DPU）和控制回路单元（CLU）。DPU的主要功能是对从穿孔带得到的信息进行译码、处理并给CLU提供数据。这些数据包括每个轴所需要的新位置，运动方向和速度，传递的辅助控制信号。另一方面，CLU提供说明前一部分已经加工完的信号，DPU可以读入新的一段零件程序。CLU 操纵连在丝杠上的驱动设备，并接收每个轴的实际位置及速度的反馈信号。每个丝杠都有一个单独的驱动设备和反馈设备，不过后者只出现在闭环系统中。

在计算机数控系统中，DPU的功能总是由CNC计算机的控制程序来执行。而CLU的主要部分是在最复杂的CNC系统中实现的。

加工过程的数控

今年来，基础的计算机数控已经取得了重大的进展。通常形状相同的零件大批量生产时，自动检查显得有效率，加工的精度也高，但由一个自动循环变为另一个自动是一个时间长而又花费高的过程，只能长期运行。但是，又是同一个零件只需要价格几个，这种工作用计算机数控机床进行加工时非常值得的。

有计算机数字控制和模拟控制两种类型。数字计算机已数字形式显示数码来工作，一个数字就是一套用以表示数码的符号中的一个符