1、What Is CNC CNC stands for Computer Numerical Control and has been around since the early 1970s. Prior to this, it was called NC, for Numerical Control. (In the early 1970s, computers were introduced in these controls, hence the name changed)While people in most walks of life have never heard of thi
2、s term, CNC has touched almost every form of manufacturing process in one way or another. If youll be working in manufacturing, its likely that youll be dealing with CNC on a regular basis. Before CNC While there are exceptions to this statement, CNC machines typically replace (or work in conjunctio
3、n 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. (Its likely that almost everyone has seen some form of drill press, even if you dont work in manufacturing.) A person c
4、an 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
5、 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 w
6、orkpieces must be machined, as quantities grow, so does the likelihood for fatigue due to the tediousness of the operation. And do note that weve used one of the simplest machining operations (drilling) for our example. There are more complicated machining operations that would require a much higher
7、 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
8、 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, posi
9、tioning 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 produc
10、ts aimed at helping you learn how to use CNC machines. Here were 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 runni
11、ng, 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 dont mean to over-simplify here. CNC operators are comm
12、only required to do other things related to the CNC operation like measuring workpieces and making adjustments to keep the CNC machine running good workpieces.) Lets look at some of the specific programmable functions. Motion control All CNC machine types share this commonality: They all have two or
13、 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 machines complexity is how many axes it has. Generally speaking, the more axes, the more complex the mach
14、ine. 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 letter
15、s. Common linear axis names are X, Y, and Z. Common rotary axis names are A, B, and C. Programmable accessories A CNC machine wouldnt 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
16、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.
17、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. Coo
18、lant 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. Its writte
19、n 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).
20、 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 only 50 wor
21、ds, it shouldnt 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.
