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数控技术

数控技术是现代制造技术的基础，它的广泛应用使普通机械被数控机械所代替，使全球制造业发生了根本变化。数控技术的水准、拥有和普及程度已经成为衡量一个国家综合国力和工业现代化水平的重要标志之一。为适应这种形势，需要大量培养数控专业技术人才。数控机床是一种用计算机来控制的机床，用来控制机床的计算机，不管是专用计算机、还是通用计算机都统称为数控系统。数控机床的运动和辅助动作均受控于数控系统发出的指令。而数控系统的指令是由程序员根据工件的材质、加工要求、机床的特性和系统所规定的指令格式编制的。数控系统根据程序指令向伺服装置和其它功能部件发出运行或终断信息来控制机床的各种运动。当零件的加工程序结束时，机床便会自动停止。任何一种数控机床，在其数控系统中若没有输入程序指令，数控机床就不能工作。

机床的受控动作大致包括机床的起动、停止；主轴的启停、旋转方向和转速的变换；进给运动的方向、速度、方式；刀具的选择、长度和半径的补偿；刀具的更换，冷却液的开起、关闭等。

CNC(数控机床)是计算机数字控制机床(Computer numerical control)的简称，是一种由程序控制的自动化机床。该控制系统能够逻辑地处理具有控制编码或其他符号指令规定的程序，通过计算机将其译码，从而使机床动作并加工零件。通过刀具切削将毛坯料加工成半成品成。

CNC加工（CNC Machining）数控加工是指用数控的加工工具进行的加工。CNC指数控机床由数控加工语言进行编程控制，通常为G代码。数控加工G 代码语言告诉数控机床的加工刀具采用何种笛卡尔位置坐标，并控制刀具的进给速度和主轴转速，以及工具变换器、冷却剂等功能。数控加工相对手动加工具有很大的优势，如数控加工生产出的零件非常精确并具有可重复性；数控加工可以生产手动加工无法完成的具有复杂外形的零件。数控加工技术现已普遍推广，大多数的机加工车间都具有数控加工能力，典型的机加工车间中最常见的数控加工方式有数控铣、数控车和数控EDM线切割（电火花线切割）。进行数控铣的工具叫做数控铣床或数控加工中心。进行数控车削加工的车床叫

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做数控车工中心。数控加工G代码可以人工编程，但通常机加工车间用CAM （计算机辅助制造）软件自动读取CAD（计算机辅助设计）文件并生成G代码程序，对数控机床进行控制。

数控机床能精确加工各种轮廓，而有些轮廓在普通机床上无法加工。数控机床特别适合以下场合：不许报废的零件、新产品研制、急需件的加工。

数控加工有下列优点：①大量减少工装数量，加工形状复杂的零件不需要复杂的工装。如要改变零件的形状和尺寸，只需要修改零件加工程序，适用于新产品研制和改型。②加工质量稳定，加工精度高，重复精度高，适应飞行器的加工要求。③多品种、小批量生产情况下生产效率较高，能减少生产准备、机床调整和工序检验的时间，而且由于使用最佳切削量而减少了切削时间。④可加工常规方法难于加工的复杂型面，甚至能加工一些无法观测的加工部位。数控加工的缺点是机床设备费用昂贵，要求维修人员具有较高水平。

为了提高生产自动化程度，缩短编程时间和降低数控加工成本，在航空航天工业中还发展和使用了一系列先进的数控加工技术。如计算机数控，即用小型或微型计算机代替数控系统中的控制器，并用存贮在计算机中的软件执行计算和控制功能，这种软连接的计算机数控系统正在逐步取代初始态的数控系统。直接数控是用一台计算机直接控制多台数控机床，很适合于飞行器的小批量短周期生产。理想的控制系统是可连续改变加工参数的自适应控制系统，虽然系统本身很复杂，造价昂贵，但可以提高加工效率和质量。数控的发展除在硬件方面对数控系统和机床的改善外，还有另一个重要方面就是软件的发展。计算机辅助编程（也叫自动编程）就是由程序员用数控语言写出程序后，将它输入到计算机中进行翻译，最后由计算机自动输出穿孔带或磁带。用得比较广泛的数控语言是APT语言。它大体上分为主处理程序和后置处理程序。前者对程序员书写的程序加以翻译，算出刀具轨迹；后者把刀具轨迹编成数控机床的零件加工程序。数控加工，是在对工件进行加工前事先在计算机上编写好程序，再将这些程序输入到使用计算机程序控制的机床进行指令性加工，或者直接在这种计算机程序控制的机床控制面板上编写指令进行加工。加工的过程包括：走刀，换刀，变速，变向，停车等，都是自动完成的。数控加工是现代模具制造加工的一种先进手段。当然，数控加工手段也一定不只用于模具零件加工，用途十分广泛。

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选择数控铣削用刀具，在数控加工中，铣削平面零件内外轮廓及铣削平面常用平底立铣刀，该刀具有关参数的经验数据如下：一是铣刀半径RD 应小于零件内轮廓面的最小曲率半径Rmin，一般取RD=(0.8一0.9）Rmin。二是零件的加工高度H< （1/4-1/6）RD，以保证刀具有足够的刚度。三是用平底立铣刀铣削内槽底部时，由于槽底两次走刀需要搭接，而刀具底刃起作用的半径Re=R-r，即直径为d=2Re=2(R-r），编程时取刀具半径为Re=0.95 (Rr）。对于一些立体型面和变斜角轮廓外形的加工，常用球形铣刀、环形铣刀、鼓形铣刀、锥形铣刀和盘铣刀。

目前，数控机床上大多使用系列化、标准化刀具，对可转位机夹外圆车刀、端面车刀等的刀柄和刀头都有国家标准及系列化型号对于加工中心及有自动换刀装置的机床，刀具的刀柄都已有系列化和标准化的规定.此外，对所选择的刀具，在使用前都需对刀具尺寸进行严格的测量以获得精确数据，并由操作者将这些数据输入数据系统，经程序调用而完成加工过程，从而加工出合格的工件。

加工原则

（1）上道工序的加工不能影响下道工序的定位与夹紧。

（2）先内后外，即先进行内部型腔（内孔）的加工，后进行外形的加工（3）以相同的安装或使用同一把刀具加工的工序，最好连续进行，以减少重新定位或换刀所引起的误荠．

（4）在同一次安装中，应先进行对工件刚性影响较小的工序。

加工路线的确定，数控车床进给加工路线指车刀从对刀点（或机床固定原点）开始运动起，直至返回该点并结束加工程序所经过的路径，包括切削加工的路径及刀具切人、切出等非切削空行程路径。精加工的进给路线基本上都是沿其零件轮廓顺序进行的，因此，确定进给路线的工作重点是确定粗加工及空行程的进给路线。

在数控车床加工中，加工路线的确定一般要遵循以下几方面原则。

①应能保证被加工工件的精度和表面粗糙度。

②使加工路线最短，减少空行程时间，提高加工效率。

③尽量简化数值计算的工作量，简化加工程序。

④对于某些重复使用的程序，应使用子程序。

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使加工程序具有最短的进给路线，不仅可以节省整个加工过程的执行时间，还能减少一些不必要的刀具消耗及机床进给机构滑动部件的磨损等。最短进给路线的类型及实现方法如下。

（1）最短的切削进给路线。切削进给路线最短，可有效提高生产效率，降低刀具损耗。安排最短切削进给路线时，还要保证工件的刚性和加工工艺性等要求。

（2）最短的空行程路线。

①巧用起刀点。采用矩形循环方式进行粗车的一般情况示例。其对刀点A的设定是考虑到精车等加工过程中需方便地换刀，故设置在离毛坯件较远的位置处，同时，将起刀点与其对刀点重合在一起

②巧设换刀点。为了考虑换刀的方便和安全，有时将换刀点也设置在离毛坯件较远的

位置处，那么，当换第二把刀后，进行精车时的空行程路线必然也较长；如果将第二把刀的换刀点也设置在中的毋点位置上，则可缩短空行程距离。

③合理安排“回零”路线。在手工编制复杂轮廓的加工程序时，为简化计算过程，便于校核，程序编制者有时将每一刀加工完后的刀具终点，通过执行“回零”操作指令，使其全部返回到对刀点位置，然后再执行后续程序。这样会增加进给路线的距离，降低生产效率。因此，在合理安排“回零”路线时，应使前一刀的终点与后一刀的起点间的距离尽量短．或者为零，以满足进给路线最短的要求。另外，在选择返回对刀点指令时，在不发生干涉的前提下，尽可能采用x、z轴双向同时“回零”指令，该功能“回零”路线是最短的。

（3）大余量毛坯的阶梯切削进给路线。列出了两种太余量毛坯的切削进给路线。是错误的阶梯切削路线，按1斗5的顺序切削，每次切削所留余量相等，是正确的阶梯切削进给路线。因为在同样的背吃刀量下。

（4）零件轮廓精加工的连续切削进给路线。零件轮廓的精加工可以安排一刀或几刀精加工工序．其完工轮廓应由最后一刀连续加工而成，此时，刀具的进、退位置要选择适当，尽量不要在连续的轮廓中安排切人和切出或换刀及停顿，以免因切削力突然变化而破坏工艺系统的平衡状态．致使零件轮廓上产生划伤、形状突变或滞留刀痕。

（5）特殊的进给路线。在数控车削加工中，一般情况下。刀具的纵向进

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给是沿着坐标的负方向进给的，但有时按其常规的负方向安排进给路线并不合理。甚至可能损坏工件。

Numerical control technology

Numerical control technology is the foundation of modern manufacturing technology, it is widely used to make general machinery replaced by CNC machinery, fundamental changes have taken place in the global manufacturing. Numerical control technology level, have and popularity, has become the measure of a national comprehensive national strength and an important symbol of industrial modernization level. In order to adapt to this kind of situation, need a lot of training nc professional and technical personnel. Nc machine tools is a use computer to control the machine tool, used to control the machine computer, whether it's a dedicated computer, or general-purpose computer called numerical control system. Numerical control machine tool movement and auxiliary movements are controlled by the directives issued by the CNC system. Instruction is by the programmer and nc system according to the workpiece material, processing requirements, the characteristics of machine tool and instruction format of the specified system. Numerical control system according to program instructions to the servo device and features other than running or end information to control the movement of the machine tool. When the parts at the end of the process, machine will stop automatically. Any kind of CNC machine tools, if there is no input in the numerical control system application instructions, numerical control machine can't work.

Machine tool control action is roughly including machine start and stop; Main shaft of the rev. Stop, rotating direction and rotating speed of transformation; Feed movement direction, speed, way; Cutting tool selection, the length and radius compensation; Tool change, cooling liquid of open, closed, etc.

CNC is a Computer numerical control machine tools (Computer numerical control) for short, is a kind of controlled by the application of automation machine tools. The control system is able to handle the with logic control code or other symbols in accordance with procedures prescribed by the instruction, through the computer to decode it, which makes the machine movement and machining parts. Through the tool cutting blank material processed into semi-finished products into.

CNC Machining (CNC) Machining nc Machining is refers to the use of CNC Machining tools for processing. Index of the CNC control machine tool controlled by nc programming language, usually in the form of G code. Nc machining G code language tells the CNC machine tool adopts what kind of cartesian coordinates, and controls the tool feed rate and spindle speed and tool changer, coolant, etc. Numerical

control processing relative to manual processing has great advantages, such as nc machining to produce the parts very precise and repeatability; Nc machining process can produce manual can't complete with complex shape parts. Nc machining technology has been widely adopted, most of the machining with CNC machining capabilities, the typical machining workshop, the most common way of nc machining with CNC milling, CNC and CNC EDM wire cutting, EDM wire cutting cut). For nc milling tool is called numerical control milling machine or numerical control machining center. To carry on the lathe of numerical control turning processing is called numerical control lathe work center. Nc machining G code programming can be artificial, but usually machining using CAM (computer-aided manufacturing) software automatically readCAD (computer-aided design) files and generate G code program, to control the CNC machine.

Nc machine tool can accurate processing of outline, and some outline on the ordinary machine tool will not be able to process. Numerical control machine is especially suitable for the following occasions: stop scrap parts, new product development, be badly in need of pieces of processing.

Numerical control processing has the following advantages:

(1) a large number of reducing number of tooling, processing complex shape parts don't need complicated tooling. If you want to change the shape and size of the parts, only need to modify the parts processing process, apply to new product development and modification.

(2) stable machining quality, machining accuracy is high, the repeat precision is high, the craft to meet the demand of the processing.

(3) many varieties, small batch production situations, high production efficiency, reduces the production preparation, machine tool adjustment and process inspection time, and due to the use of best cutting quantity, reduces the cutting time. Conventional methods difficult to processing the complexity of surface can be processed

(4) can even machining parts of some cannot be observed. Disadvantage is that the machine tool numerical control processing equipment is expensive, and require maintenance personnel with high level.

In order to improve the production automation degree, shorten the time and decrease the cost of the nc machining programming, in the aerospace industry development and the use of a series of advanced numerical control processing

technology. Such as computer numerical control, which USES small or micro computer instead of controller in the CNC system, and storage in the computer software to perform calculations and control function, this soft connection of computer numerical control system is gradually replacing the initial state of numerical control system. Direct numerical control is a control many sets of numerical control machine tool directly with a computer, very suitable for aircraft of small batch production short cycle. The ideal control system is can change the processing parameter adaptive control system continuously, while the system itself is complex, expensive, but can improve the machining efficiency and quality. In addition to the development of numerical control in hardware aspects of numerical control system and the improvement of the machine tool, there is another important aspect is the development of software. Computer aided programming (also called automatic programming) is by the programmers to write programs in numerical control language, will input it to the computer for translation, in the final output by computer automatic punch tape or tape. Is the APT language with more extensive numerical control language. It generally points to give priority to processing procedures and post processing. The former translation for programmers to write programs, calculate the tool path; Which the tool path into CNC machine tool parts processing program. Nc machining, the workpiece before processing is prior to write good program on a computer, then input the program to use the computer program control command processing machine tools, or directly in the computer program control of machine tool for processing writing instructions on the control panel. Machining process include: feeding, tool change, change, change to, parking, etc., are all done automatically. Nc machining is an advanced means of modern mold manufacturing processing. Nc machining means, of course, also must be not only used for mold parts processing, application is very extensive.

Choosing cutting tools for CNC milling, in CNC machining, milling plane parts inside and outside the outline and the milling plane commonly used flat end milling, the cutting tool related parameters of the empirical data is as follows: one is the radius of milling cutter RD should be less than the parts within the outline the minimum radius of curvature Rmin, generally take RD = Rmin (0.8 0.9). Machining high H 2 it is < RD (1/4 to 1/6), to ensure the stiffness of cutter has enough. Three is to use flat end milling cutter milling groove in the bottom, due to the bottom of the channel two feeding need to overlap, and the radius of the cutter blades work Re = R - R, the

diameter of d = 2 Re = 2 (R - R), programming for the tool radius are put to take Re = 0.95 (Rr). For some a multiple-layered surface and change the bevel contour shape processing, common spherical milling cutter, circular cutter, cylindrical milling cutter, taper milling cutters and milling cutter plate.

Now, mostly on nc machine tools, seriation, standardization tools being used for indexable mechanically-clamped turning tool, facing tool such as the handle and cutter are national standard and domestic model and automatic tool change device for machining center of machine tool, cutting tool shank for seriation and standardization of regulations. In addition, the choice of cutting tool, before use must be carried out on the cutter size strict measurements to gain accurate data, and by the operator input the data into data system, the program calls and complete machining process, so as to work out qualified artifacts.

The processing principle of

(1) the procedure of processing does not influence the positioning and clamping of next working procedure.

(2) after the first, the first internal cavity (hole) processing, after the shape of the processing

(3) in the same installation or use the same machining process, the cutting tool, had better undertake continuous to minimize repositioning or knife change caused by the mistake wil.

(4) installed at the same time, should look for smaller influence on rigidity workpiece process.

The determination of processing route, numerical control lathe feed processing route refers to turning tool from the knife point movement began fixed origin (or machine), until the return to that point and end the route processing program, including cutting paths and cutting and cut out the cutting spare travel path. Finishing of the feed line is basically along the contour of order, therefore, to determine the feed line focus is to determine the rough machining and empty trip feed line.

In the numerical control lathe processing, processing route determination of general should follow the principle of the following aspects.

(1) should be able to guarantee machining precision and surface roughness.

(2) reduce processing route, the shortest travel time, improve the efficiency of processing.

(3)Try to simplify the workload of numerical computation, simplify the processing procedure.

(4) for the repeated use of certain procedures, should use a subroutine.

Make process has the shortest feed line, not only can save the entire process of execution time, still can reduce some unnecessary tool consumption and machine tool feed mechanism sliding wear parts, etc. The shortest route of feed type and realization method are as follows.

(1) the shortest route of cutting feed. Cutting feed the shortest route, which can effectively improve the production efficiency, reduce the cutter wear and tear. When arrange the cutting feed shortest route, ensure the rigidity and the fabrication procedure of workpiece requirements.

(2) the shortest spare travel route.

①using a cutting point. Using rectangular circular manner to rough turning the general situation of the sample. Its set of knife point A is fine car considering the processing process to easily change, so the Settings from the blank remote location, at the same time, will the knife point instead of A knife point overlap together

②set in opportunely cutting point. For the tool change due to the convenience and safety, sometimes will change to a knife set in the blank more distant Location, so, when the first ErBaDao in pure car spare travel route is also relatively long; If will be the first ErBaDao tool change point is set at no point in the position, can shorten the empty travel distance.

③Arrange route back to zero. When complex contour machining program by hand, to simplify the calculation process, easy to check, will sometimes program makers every knife processing after the tooling finish, by performing a "zero" operation instruction, make its all return to the cutting point position, and then implement follow-up procedures. This will increase the feed line distance, reduce the production efficiency. Back to zero as a result, the reasonable arrangement of course, should be made before the end of a knife with a knife after the starting point of the distance between the short. As far as possible or to zero, in order to meet the requirements of feeding the shortest route. In addition, when choosing return instructions for cutting point, interference does not occur in the premise, as far as possible USES the x and z axis simultaneous two-way "zero" command, this feature is "zero" is the shortest route.

(3) large margin ladder of blank cutting feed line. Lists the two too slack cutting into the blank To route. Cutting route is the ladder error, press 1 5 order of cutting, cutting by each leave allowance is equal, is the right step cutting feed line. Because under the same amount of turning.

(4) parts contour finishing continuous cutting feed line. Parts contour of finishing can arrange for a knife or a few knife finishing process. The complete contour by the last knife should be continuous, at this point, the tool into position, should choose appropriate, try not to arrange cutting and cutting out the outline of the continuous or changing knife and pause, so as to avoid damage due to sudden changes in cutting force process system of the state of equilibrium. The parts on the contour cut, shape, mutations or retention tool marks.

(5) special feed line. In the numerical control turning processing, under normal circumstances. Longitudinal feed cutter feeding is along the negative direction of the coordinate, but sometimes arranged in the negative direction of the conventional feed line is not reasonable. Even may damage the workpiece.