What Is CNC Machining?

23/04/2020

So, we now know what CNC stands for and how CNC machines work. But not all CNC machines are used for CNC machining.

CNC machining refers to only a few of these automated processes. Namely milling, turning, grinding, routing, drilling, etc.

CNC Milling

It is an operation where the cutting tool rotates. When the milling tool comes into contact with the workpiece, it removes chips from it.

Milling operations include:

End milling
Chamfer milling
Face milling
Drilling, boring, tapping, etc.

It is a very universal fabrication method with great accuracy and tolerances. Milling is suitable for a variety of materials and is also very quick. The ability to manufacture a wide range of complex parts is a great advantage.

The disadvantages include a large amount of waste, need for a variety of tooling and high cost of equipment.

CNC Turning

While the two are often called just CNC machining, turning and milling have distinct differences. Turning, or lathing is pretty much the opposite of milling. This means that instead of the cutting tool, the workpiece is rotating.

A CNC lathe is commonly used for producing shafts, for example. The tool is brought against the rotating workpiece to cut off bits of metal, known as chips or swarf.

Turning is usable on the outside of a cylinder or on the inside. The latter operation is called boring.

CNC Grinding

CNC grinding machines are machine tools which use a rotating grinding wheel to achieve material removal on a metallic workpiece by means of cutting. Grinding machines are mostly used for the hard-fine machining of workpieces (parts). The surface quality which can be achieved is very high, and grinding machines thus almost always find application in modern industry as a finishing process. Furthermore, through the increased performance of the grinding tools, grinding machines can now be used to achieve high material removal rates (Q’w [mm³/(mm*s)] during production grinding
.

Besides the high machining performance possible with today’s CNC grinding machines during the actual grinding process, the loading and unloading of the workpieces is often also carried out fully automatically using automated loading facilities. This is referred to as an “unmanned operation”, where a sporadic check of the CNC grinding machine or the grinding process is all that is required. For the machining process itself, the continual presence of a worker at the CNC grinding machine is no longer necessary.

CNC Routing

A CNC router is similar to a CNC mill. It comes with the ability to use computer numerical control to route tool paths that enable the machine to function. CNC routers reduce waste and increase productivity, producing various items in a much shorter amount of time than using other machines.

CNC Drilling

Computer Numerical Control (CNC) Drilling is commonly implemented for mass production. The drilling machine, however, is often a multi-function machining center that also mills and sometimes turns. The largest time sink for CNC drilling is with tool changes, so for speed, variation of hole diameters should be minimized. The fastest machines for drilling varying hole sizes have multiple spindles in turrets with drills of varying diameters already mounted for drilling. The appropriate drill is brought into position through movement of the turret, so that bits do not need to be removed and replaced. A turret-type CNC drilling machine is shown below.

A variety of semi-automated drilling machines are also used. An example is a simple drill press which, on command, drills a hole of a set depth into a part set up beneath it.

In order to be cost-effective, the appropriate type of CNC drilling machine needs to be applied to a particular part geometry. For low-volume jobs, manual or semi-automated drilling may suffice. For hole patterns with large differences in sizes and high volume, a geared head is most appropriate. If holes are close to each other and high throughput is desired, a gearless head can locate spindles close together so that the hole pattern can be completed in one pass.

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Key: CNC drilling, cnc milling, cnc turning, cnc routing