In machining, numerical control, also called computer numerical control (CNC),is the automated control of tools by means of a computer. It is used to operate tools such as drills, lathes, mills, grinders, routers and 3D printers. CNC transforms a piece of material (metal, plastic, wood, ceramic, stone, or composite) into a specified shape by following coded programmed instructions and without a manual operator directly controlling the machining operation.

A CNC machine is a motorized maneuverable tool and often a motorized maneuverable platform, which are both controlled by a computer, according to specific input instructions. Instructions are delivered to a CNC machine in the form of a sequential program of machine control instructions such as G-code and M-code, and then executed. The program can be written by a person or, far more often, generated by graphical computer-aided design (CAD) or computer-aided manufacturing (CAM) software. In the case of 3D printers, the part to be printed is “sliced” before the instructions (or the program) are generated. 3D printers also use G-Code.

CNC offers greatly increased productivity over non-computerized machining for repetitive production, where the machine must be manually controlled (e.g. using devices such as hand wheels or levers) or mechanically controlled by pre-fabricated pattern guides (see pantograph mill). However, these advantages come at significant cost in terms of both capital expenditure and job setup time. For some prototyping and small batch jobs, a good machine operator can have parts finished to a high standard whilst a CNC workflow is still in setup.

In modern CNC systems, the design of a mechanical part and its manufacturing program are highly automated. The part’s mechanical dimensions are defined using CAD software and then translated into manufacturing directives by CAM software. The resulting directives are transformed (by “post processor” software) into the specific commands necessary for a particular machine to produce the component and then are loaded into the CNC machine.

Since any particular component might require the use of several different tools – drills, saws, touch probes etc. – modern machines often combine multiple tools into a single “cell”. In other installations, several different machines are used with an external controller and human or robotic operators that move the component from machine to machine. In either case, the series of steps needed to produce any part is highly automated and produces a part that meets every specification in the original CAD drawing, where each specification includes a tolerance.

Description
Motion is controlling multiple axes, normally at least two (X and Y), and a tool spindle that moves in the Z (depth). The position of the tool is driven by direct-drive stepper motors or servo motors to provide highly accurate movements, or in older designs, motors through a series of step-down gears. Open-loop control works as long as the forces are kept small enough and speeds are not too great. On commercial metalworking machines, closed-loop controls are standard and required to provide the accuracy, speed, and repeatability demanded.

Parts description

As the controller hardware evolved, the mills themselves also evolved. One change has been to enclose the entire mechanism in a large box as a safety measure (with safety glass in the doors to permit the operator to monitor the machine’s function), often with additional safety interlocks to ensure the operator is far enough from the working piece for safe operation. Most new CNC systems built today are 100% electronically controlled.

CNC-like systems are used for any process that can be described as movements and operations. These include laser cutting, welding, friction stir welding, ultrasonic welding, flame and plasma cutting, bending, spinning, hole-punching, pinning, gluing, fabric cutting, sewing, tape and fiber placement, routing, picking and placing, and sawing.

History
The first CNC machines were built in the 1940s and 1950s, based on existing tools that were modified with motors that moved the tool or part to follow points fed into the system on punched tape.These early servomechanisms were rapidly augmented with analog and digital computers, creating the modern CNC machine tools that have revolutionized machining processes.
Today
Now the CNC in the processing manufacturing field has been very extensive, not only the traditional milling and turning, other machines and equipment are also installed with the corresponding CNC, which makes the manufacturing industry in its support, greatly improving the quality and efficiency. Of course, the latest trend in CNC is to combine traditional subtractive manufacturing with additive manufacturing (3D printing) to create a new manufacturing method – hybrid additive subtractive manufacturing (HASM).Another trend is the combination of AI, using a large number of sensors, with the goal of achieving flexible manufacturing.