Milling machines are machine tools that perform chip-removal machining; the process relies on the movement of a rotating tool called a milling cutter, which has multiple cutting edges. Invented in the nineteenth century, milling machines are highly versatile thanks to the range of work they can carry out. This work would not be possible without the movements and axes of a CNC milling machine.
Milling machine movements
Before discussing the axes of a CNC milling machine, it is essential to look at the movements it makes, as the two are closely linked. On traditional milling machines, it is the workpiece that moves towards the cutter for machining; however, with the integration of computer numerical control (CNC), milling machines became more versatile and capable of machining very complex parts.
A movement common to all milling machines, CNC or not, is that of the cutter or cutting tool rotating about its own axis.
In addition, the worktable can move at different speeds and in different ways. The table makes a longitudinal movement along the X axis. The table can also move crosswise along the Y axis; this movement is used to place the tool in the correct position. The table also moves vertically along the Z axis; this movement determines the depth of cut.
There are other rotary movements, but they depend on the type of milling machine. For example, the table can rotate about the longitudinal axis or about the vertical axis, depending on its rotational degrees of freedom.
Movements between cutter and workpiece
The movements between the cutter and the workpiece are undoubtedly crucial in determining the type of work carried out on the part to shape it. The movements between tool and workpiece fall into three categories:
- Cutting. This movement is made by the tip of the cutter around the axis of the tool holder.
- Feed. An approach movement made by the tool from an area already cut towards an uncut area.
- Plunging. A feed movement that increases the depth of cut in the workpiece.
CNC milling machine axes
What is the relationship between the movements and the axes of a CNC milling machine? As you have seen, the milling machine’s movements are made along the various axes of the machine tool, hence their importance. On a CNC milling machine, it is precisely CNC technology that makes it possible to move three or more axes simultaneously, using computer technology. And it is the software, once properly programmed, that executes the tasks, movements and axes along which the various components of the milling machine must travel to carry out the machining.
A CNC milling machine has three axes:
- X axis, for longitudinal movement
- Y axis, for crosswise movement
- Z axis, for the vertical movement of the spindle towards the floor
2.5-axis machining
One machining operation that CNC milling machines can perform is 2.5-axis machining. This type of machining produces parts by moving the tool along the X and Y coordinates simultaneously while removing chips or cutting material. Its defining feature is that the tool can move along all three axes of the milling machine, but can never move along all three coordinates at once while cutting.
3-axis machining
The axes of a CNC milling machine make it possible to carry out three-axis machining operations, in which all three axes are controlled simultaneously during cutting. In these operations, the cutting paths follow the surface to be produced. Three-axis machining is used, for example, to mill 3D contours, surfaces or profiles. These operations are known as “copy milling”.
5-axis machining
Machines capable of five-axis machining are also available on the market. CNC milling machines usually have three axes, but there are also five-axis models. These machines carry out extremely complex work. They can perform linear movements along the X, Y and Z axes while rotating about two other axes, A and B, either on the table or on the tool head.
In this type of process, all five axes of the CNC milling machine can move simultaneously in order to reduce machining time and give the part an almost perfect finish. These machines can also work in a 3+2 cycle, in which the fourth and fifth axes remain fixed and only move between operations, while the other three axes move simultaneously.