Definition

computer numerical control (CNC)

Contributor(s): David Essex

Computer numerical control (CNC) is a method for automating control of machine tools through the use of software embedded in a microcomputer attached to the tool. It is commonly used in manufacturing for machining metal and plastic parts.

With CNC, each object to be manufactured gets a custom computer program, usually written in an international standard language called G-code, stored in and executed by the machine control unit (MCU), a microcomputer attached to the machine. The program contains the instructions and parameters the machine tool will follow, such as the feed rate of materials and the positioning and speed of the tool's components. Mills, lathes, routers, grinders and lasers are common machine tools whose operations can be automated with CNC. It can also be used to control non-machine tools, such as welding, electronic assembly and filament-winding machines.

Early in the process, engineers create a computer-aided design (CAD) drawing of the part to be manufactured, then translate the drawing into G-code. The program is loaded onto the MCU and a human operator performs a test run without the raw material in place, to ensure proper positioning and performance. This step is important because incorrect speed or positioning can damage both the machine and the part.

CNC is considered to provide more precision, complexity and repeatability than is possible with manual machining. Other benefits include greater accuracy, speed and flexibility, as well as capabilities such as contour machining, which allows milling of contoured shapes, including those produced in 3D designs. On the other hand, CNC can be more expensive, require more maintenance than other production methods and compel companies to hire a skilled CNC programmer.

Some CNC systems are integrated with CAD and computer-aided manufacturing (CAM) software, which can speed the process of programming the MCU. Integration with ERP software and related applications, such as enterprise asset management software, can facilitate operational intelligence processes and help improve plant performance and maintenance.

This was last updated in September 2016

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