Computer numerical control (CNC) is a system for automating machine tools. It allows machinery to be operated using commands programmed on a computer and is increasingly used in machine shops because of its precision and speed, which reduce production costs and times.
CNC in metalworking
CNC dates back to the '40s and '50s and grew out of machines that worked with manual numerical control, following commands encoded on punched cards. Over the years, with the arrival of analogue and digital technology, CNC evolved to become one of the most widely used methods today.
Thanks to developments in processors, computer numerical control was created, that is to say, CNC. Today CNC is a real revolution for industry because, besides its many advantages, it has also made microprocessors cheaper.
Computer numerical control (CNC) relies on a computer to control and monitor the movements of a machine tool, whether stationary or portable.
CNC machines
More and more machine tools incorporate this technology; examples include lathes, milling machines, grinding machines, laser and waterjet cutting machines, and presses. The versatility of CNC means it can be fitted to many types of equipment that make the workshop's job easier, reduce production costs, increase speed and require minimal human intervention.
Machines with this technology have an integrated computer that forms part of the machine; most of them have a highly sophisticated feedback system that can automate the work and adjust speed, pressure, workpiece position, and so on, without an operator having to be present constantly.
CNC also works with a sophisticated system of motors and drive components that move the machine's axes along the workpiece. Machines that run on CNC follow a series of commands and instructions entered into the computer in CNC alphanumeric language. With these instructions, and depending on the machine, it can switch between cutting tools to carry out the work on the part.
How do CNC machines work?
The operating principle of these machines is very simple: they need a coordinate system (commands) that defines the path the cutting tool must follow, as well as the tilt angle of the workpiece (some machines can reposition the part by themselves). The movements take place along the machine's coordinate axes.
How does the tool know where to go? This is achieved through the prior programming the operator has to do in alphanumeric language. The machine receives its instructions from the computer through G and M codes; the computer's software then converts these codes into electrical signals that activate the motors and, in turn, the cutting tools.
Components of a CNC machine
A machine tool that works with CNC has six basic parts or elements:
- Machine tool (the machine itself, adapted to the technology: lathe, milling machine, etc.).
- Input device.
- Controller.
- Drive systems.
- Computer.
- Feedback device, available only on some types of machine tool.
CNC programming language
To run a CNC machine tool, it has to be programmed using a specific language. Programming can be manual or automatic. In manual programming, the operator works out the reasoning and calculations to be applied to the part and enters them into the computer.
Automatic programming, on the other hand, is distinguished by the fact that the computer performs the calculations from a series of data and parameters supplied by the operator; the result is an APT data exchange.
CNC language is made up of sets of instructions covering a single machining phase, called blocks or sequences. These blocks must contain all the geometric, technological and machine functions needed for machining. The characters used by CNC follow standards DIN 66024 and 66025, which include the following codes:
- N, the address for the block or sequence number, with up to 1000 programmable (N000 to N999).
- X, Y, Z: axis addresses of the machine.
- G, the address followed by the preparatory machining functions. It describes the machine's motion functions.
- M, address of auxiliary or complementary functions (rotation, stop, etc.)
- F, feed rate.
- S, rotational speed of the main spindle.