CNC machines ( Computerized Numerical Control ) are machine tools which, through the use of control technology, are able to automatically manufacture workpieces with high precision, even for complex shapes .
When using a CAM system , the data from the CAD program, with which the components are usually designed, can be converted into a CNC program with the help of a postprocessor , taking into account a number of other factors such as the geometry of the tools , speeds, feed rates . In addition to the manual input of the control information, there is also the so-called teach-in method, which is available for a few suitable CNC machines, and workshop programming with input masks.
A distinction is made between machines with point control ( PTP control ), line control and path control . Modern CNC machines can already have more than six machining axes, whereby the fourth to sixth axes (A, B, C) each represent a rotation around the main axis (X, Y, Z) and are referred to as auxiliary axes.
When using CNC machines, it is often possible to dispense with the constant supervision of production by auxiliary personnel; in many series production only a few people are employed directly on the machines, as the controls offer sufficient options to even integrate quality control fully automatically into the production process . The monitoring of tool wear and breakage is also fully automatic. In principle, any conventional machine can be expanded to a CNC machine by using standardized components. However, it should be noted that in conventional milling machines, the backlash between the machine spindle and the spindle nut has been compensated by the operator and / or by counter-rotation milling . The drive systems of modern CNC milling machines are equipped with ball screws or linear drives , which are almost backlash-free and thus, among other things, synchronous milling is also possible. There are two ways in which the CNC machine measures the path it has covered: With the direct path measuring system, the position is measured directly on the moving axis using a glass scale . With the indirect position measuring system, the angle of rotation of the motor or the recirculating ball screw is measured and converted into the linear axis position. Both can be implemented both absolutely and incrementally.
A PLC works as the connection between the motion control (CNC) and the machine . There a program written by the machine manufacturer ensures that the operating modes, protective doors, coolant, lubrication and other units work. This linking program largely determines the possibilities and comfort of a machine and remains unchanged after the machine has been delivered. It is not directly visible to the end user of the machine.
Predecessor of CNC machines were the NC machines , ie machine tools with numerical control (Numerical Control) , z. B. by punched strips or punch cards.