A CNC milling machine is a milling machine equipped with computer numerical control (CNC) technology. This type of machine tool is one of the most advanced in the machining industry, as it can machine highly complex parts in a short time.
Features of the CNC milling machine
A CNC milling machine is simply a conventional milling machine that incorporates computer numerical control technology. Introducing this technology into various machine tools, such as lathes and milling machines, has brought automation to production processes. This technology also allows the machine to perform movements that would be impossible to execute manually.
Conventional milling machines are machine tools that use a single- or multi-edge cutting tool called a milling cutter. The cutter rotates as it reaches the surface of the workpiece in order to remove excess material from it. A CNC milling machine works on the same principle as conventional machines but also incorporates a computer. The computer automates the process, as it selects the various machining parameters such as speed and depth of cut. It also selects the cutting tool required for the operation and can even switch between different tools if necessary.
Parts of the CNC milling machine
A CNC milling machine is very similar to a conventional one and has the same moving parts: table, head, spindle and traverse slides. However, the difference between CNC and conventional milling machines is that the former do not have the handwheels or levers used to operate the moving parts. Instead, a CNC milling machine has a screen mounted on a control panel and a metal cabinet housing the machine's electrical and electronic components. These are what control the motors.
The combination of motors and CNC makes it possible to carry out multiple machining operations, including on highly complex parts. The parts of this machine are:
- Column.
- Worktable travelling along the Y and X axes.
- Milling cutter or cutting tool.
- Cutting head housing the spindle motor.
- Computer or CNC control panel.
- Hoses that deliver the coolant.
- Main travel axes (X, Y and Z).
- Complementary axes (A and B).
Milling axes
Conventional milling machines are classified according to the orientation of the cutting tool, but also according to the number of axes they have and on which the machine can work. A CNC milling machine has the three main axes, X, Y and Z, but can also include two complementary axes that make it even more sophisticated.
- The X axis is horizontal and parallel to the surface holding the workpiece.
- Y axis, which forms a right-handed trihedron with the X and Z axes. The table moves in the horizontal transverse plane.
- Z axis. The milling cutter is mounted on this axis, which provides the cutting power needed for machining. It moves vertically.
- A and B axes. On CNC milling machines, these axes allow rotation and tilting of the workpieces. Thanks to them, the cutter can reach areas of the workpiece that would be impossible to machine on conventional milling machines.
Thanks to CNC technology, there are various complementary axes that are controlled independently and depend on the movement of rotary tables and swivelling heads.
How a CNC milling machine works
The CNC controls the movements of the table, the cross and longitudinal slides and the spindle along the machine's various axes. However, for the machine to operate correctly, specific machining parameters must be followed. How does the machine's computer know along which axes to move the table? How does it know which tools to use and at what speed?
This requires a prior design of the part. The computer is controlled by software supplied with the machine itself, based on a CNC programming language, such as ISO, Fagor, Fanuc, and so on. This software uses numbers, letters and symbols to encode the appropriate format for machining. This is what gives the instructions to the machine.
But before the machine can operate with any of these alphanumeric languages, the design must be loaded into the main computer. It must be created on an external computer using specific programs. A CNC milling machine therefore requires:
- CAD. Software used to design the part.
- CAM. Computer-aided manufacturing software. It calculates the movements the axes must perform for machining and also adds parameters such as feed rate, spindle speed and the cutting tools required.
- Control software. It is built into the machine's computer and receives the CAM instructions when they are loaded into the machine. The software executes the design created in CAD according to the CAM instructions.