Metalworking and fabrication was performed by numerical controlled or NC machines before the invention of CNC machining. These NC machines were created in the late 1940s by John T. Parsons, who worked closely with the Massachusetts Institute of Technology. The product being developed by them was commissioned by the United States Air Force. The goal of this work was to find a more cost effective way to manufacture aircraft parts that had intricate geometries. During this time period NC became the industry standard.
It was not till 1967 that the idea of computer-controlled machining started to circulate. The implementation of Computer Aided Design and Computer Aided Machining started developing in 1972 which lead to prominent developments in CNC machining. 1976 marked the first year 3D Computer Aided Design/Computer Aided Machining systems were available. By 1989, these CNC machines had become the industry standard.
Original NC machines had been controlled by punch cards that had a set of codes. These codes were called G-codes. The codes were designed to give the machine its positioning instructions. A large problem with these machines were that they were hardwired which made it impossible to change the pre-set parameters. As CNC machines took over G-codes were still used as a means of control. The difference was that they were now designed, controlled and conducted through computer systems. Today G –codes in CNC machines, along with logical commands have been combined to form a new programming language. This language is called parametric programs and the machines that feature it, allow the worker to make real time adjustments.
The advantage of CNC machining is represented in accuracy, productivity, efficiency and safety. Human interaction is significantly decreased when using a CNC machine, as a result the amount of errors are lower. Some large fabrication companies even leave the CNC running over an extended period of time unmanned. If there is a problem with the machine, the software automatically stops the machine and calls the operator.
When it comes to CNC milling, there has not been much change when it comes to the concept from the original model built at MIT in 1952. They typically consist of a table that moves in both the X and Y axes. In addition they include a tool spindle that moves in the Z. The actual position of the tool is driven by motors through multiple gears to provide high accurate positioning. On most commercial metalworking machines closed loop controls are used in order to provide the accuracy needed to complete the job.