CNC has been in use since the 1970s, prior to that Numerical control (NC) was in use for manufacturing since the 1940s. The introduction of computers significantly increased the speed and reproducibility of manufactured parts.
Before the introduction of CNC manufacturing.
CNC milling machines are typically used to replace several manual manufacturing operations with a single programmed routine, which involves less manual intervention than the individual manual steps would previously have required.
Prior to the introduction of CNC manufacturing, individual manufacturing operations such as drilling were quite dependent on the experience, skill and judgment of the individual operator. In the case of a drilling process the operator needs to select the correct drill, insert it into the drill press, chose the rotation speed and then turn a handle to drive the rotating drill into the workpiece. If a series of holes are required then the operator must manually move the work piece to new location and perhaps change the drill bit if the next hole is a different size.
This is a large number of manual steps and increases the opportunity for error, variation and scrap as well as the amount of time taken to perform each step. In practical terms, manual manufacturing like this becomes quite unacceptable as both the complexity and number of pieces of the manufactured components increases.
Alternatively, a CNC machining center can be programmed to perform all the steps involved in manual drilling, placing the drill in the spindle, activating the spindle, positioning the workpiece under the drill, machining the hole, and turning off the spindle. In addition, the CNC machining center can be programmed to perform many other steps in the process, with result that high volumes of sophisticated components can be manufactured with minimal operator intervention.
A CNC machine is a computer driven machine tool in which the both the workpiece and the cutting tool are moved. Like a drill press the tool is moved axially into the workpiece, unlike a drill press the workpiece is also moved radially against the rotating milling cutter.
Features of a CNC Manufacturing Center
The most important operation in using a CNC manufacturing center is the initial programming. Every operation that was previously performed manually can be programmed into the CNC machine. Once the correct program is installed and the machine is started the operator is only required to monitor the machine in the unlikely event that something goes wrong.
Often the machine will load workpieces automatically, so the operator has little to do to keep the machine running. This frees operators to perform other tasks such quality or statistical process measurements.
CNC machine types
There are two basic classifications of CNC machines, vertical and horizontal. Within these classifications there are numerous sub classifications that describe the size and speed of the operation. Both vertical and horizontal CNC milling centers can use X-Y tables to move the workpiece to the desired location, the vertical milling machine has the tool mounted above the work piece and is most suited for work such as machining a mold into a block of metal.
Horizontal CNC machining centers tend to used on heavier and longer workpieces and workpieces that require work on an angle.
CNC Milling centers can perform a vast number of operations, from simple (slot and keyway cutting, planing, drilling) to complex (contouring, die sinking). Cutting fluid is often pumped to the cutting site to cool and lubricate the cut and to wash away the resulting swarf.
CNC manufacturing machines have several common features:
All CNC machines allow for the controlled movement in at least 2 directions (X and Y) or axis of motion. A CNC machines level of complexity is partially defined by the number of axis is which it can be programmed, the more axis of motion the more complex the machine.
An axis of motion can be both linear (X,Y,Z) and also rotational (A,B,C). A simple operation such as drilling would require movement of the workpiece in the X and Y axis and movement of the tool in the Z axis.