What Is CNC
CNC stands for Computer Numerical Control and has been around since the early 1970''s. Prior to this, it was called NC, for Numerical Control. (In the early 1970''s, computers were introduced in these controls, hence the name changed)While people in most walks of life have never heard of this term, CNC has touched almost every form of manufacturing process in one way or another. If you''ll be working in manufacturing, it''s likely that you''ll be dealing with CNC on a regular basis.
Before CNC
While there are exceptions to this statement, CNC machines typically replace (or work in conjunction with) some existing manufacturing process/es. Take one of the simplest manufacturing processes, drilling holes, for example.
A drill press can of course be used to machine holes. (It''s likely that almost everyone has seen some form of drill press, even if you don''t work in manufacturing.) A person can place a drill in the drill chuck that is secured in the spindle of the drill press. They can then (manually) select the desired speed for rotation (commonly by switching belt pulleys), and activate the spindle. Then they manually pull on the quill lever to drive the drill into the workpiece being machined.
As you can easily see, there is a lot of manual intervention required to use a drill press to drill holes. A person is required to do something almost every step along the way! While this manual intervention may be acceptable for manufacturing companies if but a small number of holes or workpieces must be machined, as quantities grow, so does the likelihood for fatigue due to the tediousness of the operation. And do note that we''ve used one of the simplest machining operations (drilling) for our example. There are more complicated machining operations that would require a much higher skill level (and increase the potential for mistakes resulting in scrap workpieces) of the person running the conventional machine tool. (We commonly refer to the style of machine that CNC is replacing as the conventional machine.)
By comparison, the CNC equivalent for a drill press (possibly a CNC machining center or CNC drilling & tapping center) can be programmed to perform this operation in a much more automatic fashion. Everything that the drill press operator was doing manually will now be done by the CNC machine, including: placing the drill in the spindle, activating the spindle, positioning the workpiece under the drill, machining the hole, and turning off the spindle.
How CNC works
There is another article included in this web site called The Basics of CNC that explains how to program, setup, and operate CNC machines in greater detail. Additionally, we offer a series of products aimed at helping you learn how to use CNC machines. Here we''re relating how CNC works in very general terms.
As you might already have guessed, everything that an operator would be required to do with conventional machine tools is programmable with CNC machines. Once the machine is setup and running, a CNC machine is quite simple to keep running. In fact CNC operators tend to get quite bored during lengthy production runs because there is so little to do. With some CNC machines, even the workpiece loading process has been automated. (We don''t mean to
over-simplify here. CNC operators are commonly required to do other things related to the CNC operation like measuring workpieces and making adjustments to keep the CNC machine running good workpieces.)
Let''s look at some of the specific programmable functions.
Motion control
All CNC machine types share this commonality: They all have two or more programmable directions of motion called axes. An axis of motion can be linear (along a straight line) or rotary (along a circular path). One of the first specifications that implies a CNC machine''s complexity is how many axes it has. Generally speaking, the more axes, the more complex the machine.
The axes of any CNC machine are required for the purpose of causing the motions needed for the manufacturing process. In the drilling example, these (3) axis would position the tool over the hole to be machined (in two axes) and machine the hole (with the third axis). Axes are named with letters. Common linear axis names are X, Y, and Z. Common rotary axis names are A, B, and C.
Programmable accessories
A CNC machine wouldn''t be very helpful if all it could only move the workpiece in two or more axes. Almost all CNC machines are programmable in several other ways. The specific CNC machine type has a lot to do with its appropriate programmable accessories. Again, any required function will be programmable on full-blown CNC machine tools. Here are some examples for one machine type.
Machining centers
Automatic tool changer
Most machining centers can hold many tools in a tool magazine. When required, the required tool can be automatically placed in the spindle for machining.
Spindle speed and activation
The spindle speed (in revolutions per minute) can be easily specified and the spindle can be turned on in a forward or reverse direction. It can also, of course, be turned off.
Coolant
Many machining operations require coolant for lubrication and cooling purposes. Coolant can be turned on and off from within the machine cycle.
The CNC program
Think of giving any series of step-by-step instructions. A CNC program is nothing more than another kind of instruction set. It''s written in sentence-like format and the control will execute it in sequential order, step by step.
A special series of CNC words are used to communicate what the machine is intended to do. CNC words begin with letter addresses (like F for feedrate（馈送率）, S for spindle speed, and X, Y & Z for axis motion). When placed together in a logical method, a group of CNC words make up a command that resemble a sentence.
For any given CNC machine type, there will only be about 40-50 words used on a regular basis. So if you compare learning to write CNC programs to learning a foreign language having only50 words, it shouldn''t seem overly difficult to learn CNC programming.
The CNC control
The CNC control will interpret a CNC program and activate the series of commands in sequential order. As it reads the program, the CNC control will activate the appropriate machine functions, cause axis motion, and in general, follow the instructions given in the program.
Along with interpreting the CNC program, the CNC control has several other purposes. All current model CNC controls allow programs to be modified (edited) if mistakes are found. The CNC control allows special verification functions (like dry run) to confirm the correctness of the CNC program. The CNC control allows certain important operator inputs to be specified separate from the program, like tool length values. In general, the CNC control allows all functions of the machine to be manipulated.
What is a CAM system?
For simple application (like drilling holes), the CNC program can be developed manually. That is, a programmer will sit down to write the program armed only with pencil, paper, and calculator. Again, for simple applications, this may be the very best way to develop CNC programs.
As applications get more complicated, and especially when new programs are required on a regular basis, writing programs manually becomes much more difficult. To simplify the programming process, a computer aided manufacturing (CAM) system can be used. A CAM system is a software program that runs on a computer (commonly a PC) that helps the CNC programmer with the programming process. Generally speaking, a CAM system will take the tediousness and drudgery out of programming.
What is a DNC system?
Once the program is developed(either manually or with a CAM system), it must be loaded into the CNC control. Though the setup person could type the program right into the control, this would be like using the CNC machine as a very expensive typewriter. If the CNC program is developed with the help of a CAM system, then it is already in the form of a text file . If the program is written manually, it can be typed into any computer using a common word processor (though most companies use a special CNC text editor for this purpose). Either way, the program is in the form of a text file that can be transferred right into the CNC machine. A distributive numerical control (DNC) system is used for this purpose.
A DNC system is nothing more than a computer that is networked with one or more CNC machines. Until only recently, rather crude serial communications protocol (RS-232c) had to be used for transferring programs. Newer controls have more current communications capabilities and can be networked in more conventional ways (Ethernet, etc.). Regardless of methods, the CNC program must of course be loaded into the CNC machine before it can be run.
中文翻译：
什么数控机床
数控机床代表计算机数字控制机床，并且从20世纪70年代以来一直受到人们的关注。在这之前它被叫做NC，也就是数字控制（20世纪70年代早期，电脑被引用到这些控制里面，然后就变成CNC了）。虽然大多数其他领域的人从来没有听说过这个词，但数控机床以一种或另一种几乎涉及每一种形式的制造过程。如果你从事的是制造业，你将会经常与数控机床打交道。
数控机床之前
尽管以上表述不尽如此，但数控机床显然替代（或参与）了现有的一些制造过程。举最简单的制造过程――钻孔为例。
台式钻床当然可以用于加工孔。人们可以将钻钻头装在钻夹中，钻夹固定在台钻的轴里；接着可以（手工）选择所需的转速（通常通过切换皮带改变主轴转速），并且启动主轴旋转，然后操作钻轴手柄，将钻头钻入被加工的工件。
显而易见，使用台式钻床钻孔，需要许多人为的干预。几乎全过程的每一步都需要人参与！如果只有数量不多的孔或工件要加工，这种人为干预对制造厂来说可能是可以接受的，但是，随着生产数量的增加，由于操作乏味而产生疲劳的可能性也增大了。务必注意我们只是举了最简单的操作之一（钻削）为例，还有更加复杂的加工方式，对普通机床操作员的技能水平要求非常高（技能要求高，意味着操作失误的可能性也增大，易导致废品的产生）。（我们通常称被数控机床替代的这种机床为普通机床。）
相比较起来，替代台式钻床的数控机床（可能是数控加工中心或数控钻削中心）可以通过编写程序完成这种操作，自动化程度极高。一度由台钻操作员做的各种操作现在都由数控机床完成，包括：将钻头装进主轴里、启动主轴、将工件定位在钻头下方、钻孔、停止主轴。数控机床是如何工作的
有另一个关于数控机床的网站解释了怎么编程，设置并且操作数控机床的每一个细节。实际上，我们列举了一系列产品就是为了帮助你学习如何使用数控机床，下面我们就举几个例子看看数控机床是如何效率的工作。
也许你已经做出猜想：普通机床需要操作员做的每一件工作，在数控机床上都是由程序控制。一旦机床装夹完毕并且运行，数控机床容易保持自动运行状态。实际上，由于无事可做，数控操作员在冗长的生产运行过程中会感到很无聊。在有些数控机床上，甚至工件装夹的过程都是自动化的（我们并不是说是在这是多余的。数控机床操作者要做一些其他有关数控机床的事情就像测量车间并且调整使数控机床机器更好效率的工作）。让我们来看一下具体的可编程功能。
运动控制
所有的数控机床都有一个共同点：它们都有两个或两个以上的可编程运动方向，称之为轴。轴运动可以是直线的（沿直线），也可以是旋转的（沿圆周轨迹）。表征数控机床复杂程度的首要指标之一是它有几个轴。一般说来，轴数越多，机床越复杂。
任何数控机床的轴是为了产生加工过程所的运动，在钻削的例子中，这些(三个)轴将刀具定位在待加工孔的上方两轴运动，然后加工孔。轴用字母命名，常用的直线轴名称为X，Y，
Z，常用的旋转轴名称为A，B，C，它们与坐标系相关。
可编程附件
如果数控机床只能进行两个方向以上的运动，则这种运动没有多少优势。几乎所的数控机床在很多方面都是可编程的，具体的数控机床与其配置的可编程附件很有关系。而且，在全数控机床上，任何需要的功能都是可编程的。下面是一种机床(加工中心)的一些可编程功能的例子。
组合加工中心机床
自动刀具交换装置
多数加工中心的刀库能够容纳很多刀具，需要时，刀具被自动装到主轴上，准备加工。
主轴转速选择和启动停止
主轴速度(转/分钟)的指定很简单。主轴可丄方向转动，也可反方向转动。当然，也可停止。
冷却液
很多加工操作需要冷却液，用于润滑和冷却，冷却液的开和关可在加工循环中进行。
数控机床程序
想一想逐步发指令的方式，数控(数控机床)加工程序只不过是另外一种指令的组合。其格式类似句子，数控系统按其编写顺序，一步一步地执行。
专门的数控机床字母用于表示机床将执行的操作。数控字以字母地址开头(如F表示进给速度，S表示主轴转速，X，Y，Z表示轴运动)。一组数控字以合理的方式写在一起，就构成了一个命令，命令很像句子。
对于任何给定的数控机床，通常只会有40到50个字符经常使用。所以你学习一门外语中50个蛋子就能学些编程，所以数控编程应该不是很难学习。
数控机床控制器(数控系统)
数控系统对数控程序进行翻译，按顺序激活一连串的命令。数控系统阅读程序时，会激活相应的机床，产生轴运动，总而言之，遵照执行程序中所给的指令。
除了翻译数控程序，数控系统还有其他的作用。目前所有的数控系统都允许程序有错时进行修改(编辑)数控系统提供了程序测试功能(如空运行)确保程序的正确性。数控系统允许指定独立于程序的一些重要的操作员输入，如刀具长度值。总之，数控系统使机床的所有功能都可控。
什么是CAM系统
对于简单的应用分（比如钻孔）数控程序可以手工编写。程序员只需要坐下用铅笔，图纸和计算器来编写程序。再一次提起，这也许是最好的方法来编写数控程序。
随着应用的越来越复杂，尤其是当新项目需要定期的基础上，人工编写程序显得就越来越困难。为了简化编程，就可以使用计算机辅助程序。CAM是一个在计算机上运行的程序（通常是电脑）来帮助数控编程者编程。一般来说。CAM程序编程将会很枯燥。
什么是DNC系统
一旦程序呗开发出来（无论是人工编写还是用CAM程序编写），他都必须被载入到数控机床控制中心。虽然设置人员能够键入程序，就好像把数控机床比作是一个比较昂贵的打印机一样。如果数控机床是用CAM编写的，那么他就以文本文件的格式存在。如果程序是由人工编写的，他能被同样的形式输入到任何一台电脑上（当然有些公司用一种特殊的数控机床形式）。无论是那种方式，该程序是一个文本文件并且能够被转换成数控机床识别的形式。DNC
系统就是用于这一目的。
一个DNC系统只不过是一个计算机网络与一个或多个数控机床相连。直到最近一段时间，RS-232c才用来改变程序方式。无论是什么方式，数控程序都必须要被加载到数控机床才能够运行。