PLCs are not the only control systems used for machines. Machine tools such as lathes, grinding machines, and machining centers are used to produce precisely machined parts. Machine tools typically combine a PLC control system with a computer numerical control (CNC). CNC-controlled machine tools allow parts to be machined to complex and exacting specifications. A gear, similar to the one illustrated, is one example of a part that might be made with a CNC-controlled machine tool.
Siemens offers a range of SINUMERIK CNC models such as the 810D, 840Di, 840D, and the compact FM357-2 positioning and path control module. These products provide the coordinated multi-axis control needed for milling, drilling, turning, and grinding applications. SINUMERIK CNCs also interconnect operator panels and SIMODRIVE servo and spindle drives and associated motors to form a complete control system for the machine tool.
Typically, machine tools are designed to perform a specific task, such as grinding, drilling, or cutting. Machine tools can be programmed to a predetermined pattern or model to obtain the desired shape of the finished piece. In the following example a SINUMERIK CNC controls a rotary grinding machine. The rotary grinding machines takes a piece of stock that has already been cut and shaped on another machine tool, removes any burrs or high spots, and grinds the material to a fine finish.