Computerized Numerical Control (CNC) has exponentially lengthy industrial machines’ applications through the programmable automation of creation and the getting of actions impossible to automatically transfer, such as rounds, sloping lines, and other more difficult data on the construction of parts with too tricky shapes.
It also translates into the optimization of many essential variables of any manufacturing process: productivity, precision, safety, speed, repeatability, flexibility, and reduction of waste.
The diversity of milling machines that exist today has comfortably expanded into the proliferation of their CNC-equipped peers. There are also special kits to transform old mills into a CNC milling machine.
CNC milling machines are very similar to conventional ones and have the same moving parts: the table, the cutting head, the spindle, and the side and cross slide cars. However, they do not have levers or characters to operate these moving parts. Instead, a screen is a place full of controls and a metal box that houses the electrical and electronic machinery that controls motors’ operation designed to carry out the same work they did.
The levers and cranks of the old machines. Among these components is the CNC, a computer mainly responsible for milling machines’ movements through the corresponding software. The combination of electronics and drive motors or servomotors is capable of achieving all possible milling operations.
To understand the CNC’s movement control, we will briefly review how a conventional milling machine works.
The figure schematizes a typical milling machine. In this type of machine, the cranks actuate the moving parts manually so that the cutting tool (milling cutter) moves linearly in at least three axes, which remain call as main axes:
It is associated with movement in the longitudinal horizontal plane of the milling table.
Forms a direct direction trihedral with the X and also Z axes. It is associated with the movement in the horizontal transverse plane of the milling table.
Where the cutter is mounted, it is the one that has the cutting power and can adopt different positions according to the possibilities of the head. It is associated with the vertical displacement of the machine head.
If the milling machine has a fixed table, these three movements remain executed by the spindle.
However, the milling of more complex parts will require a more significant number of axes whose trajectory is linear and rotary. At this point, the CNC concept comes into play, giving rise to an assortment of complementary axes controlled independently and determined by the movement of rotary tables and adjustable heads.
It gives rise to various machine models that allow machining of the part in different planes and approach angles.
The following figure shows an example of a CNC milling machine with its essential components and main (X, Y, Z) and complementary (B, W) axes.
1 – Column
2 – Workpiece
3 – Milling table, with movement in the X and Y axes
4 – Strawberry
5 – Cutting head including a spindle motor
6 – CNC control panel
7 – Coolant hoses
X, Y, Z – Main axes of travel
B – Complementary axis of rotary movement of the cutting head
W – Complementary axis of longitudinal displacement of the cutting head
The CNC’s primary function is to control the table’s movements, the transverse. And longitudinal carriages, and the spindle along their respective axes using numerical data. However, this is not all, because the control of these movements to achieve the desired final result requires the perfect adjustment. And the correct synchronization between different devices and systems that are part of every CNC process. These include the principal and complementary axes, the transmission system, the workpiece clamping systems, and the tool changers. Each of them presents its modalities and variables that must also be adequately stipulated.
This rigorous control is carrying by software supplied with the milling machine and based on some of the CNC numerical programming languages. Such as ISO, HEIDENHAIN, Fagor, Fanuc, SINUMERIK, and Siemens.
This software contains numbers, letters, and other symbols. For example, the G and M codes – encoded in an appropriate format to define an instruction program capable of carrying out a specific task. G codes are machine motion functions (rapid moves, feeds, radial feeds, pauses, cycles), while M codes are miscellaneous functions required for machining parts, but are not machine motion.
From this, it follows that to function and programs this type of machine, basic knowledge in machining operations on conventional equipment, elementary knowledge of mathematics, technical drawing, and handling of measuring instruments are required.
Currently, the use of CAD (computer-aided design) and CAM (computer-aided manufacturing) programs is an almost obligatory complement to any CNC machine, which is why, generally, the manufacture of a part involves the combination of three types of software:
Makes the design of the part.
Calculates the axes’ displacements for the machining of the part. And adds the feed rates, rotation speeds, and different cutting tools.
Control software (included with the machine)
Receives the instructions from the CAM and executes the orders to move the milling machine’s moving parts according to these instructions.
The following video illustrates the manufacture of a part using CAD / CAM:
CNC milling machines specially adapted for milling profiles, cavities, surface contours, and die-cutting operations. In which two or three axes of the milling table must be skillful simultaneously. Although depending on the machine’s complexity and the programming carried out, CNC mills can operate automatically; an operator is usually required to change the cutters and mount and dismount the workpieces.
Industries that routinely use CNC milling machines include automotive (design of engine blocks, molds. And miscellaneous components), aerospace (aircraft turbines), and electronics (mold and prototyping). As well as manufacturing of machinery, instruments, and electrical components.