CNC machines are electro-mechanical devices that manipulate machine shop tools using computer programming inputs. The name “CNC” actually stands for Computer Numerical Control and it represents one of two common methods (3D printing technology like SLA, SLS/SLM, and FDM being the other) to generate prototypes from a digital software file.
How it Works
Machining in general is a way to transform a stock piece of material such as a block of plastic and arrive at a finished product (typically a prototype part) by means of a controlled material removal process. Similar to the other prototype development technology, FDM (3D printing), CNC relies on digital instructions from a Computer Aided Manufacturing (CAM) or Computer Aided Design (CAD) file like Solidworks 3D. The CNC machine interprets the design as instructions for cutting prototype parts. The ability to program computer devices to control machine tools rapidly advances shop productivity by automating the highly technical and labor intensive processes. Automated cuts improve both the speed and the accuracy with which prototype parts can be created - especially when the material is critical (such as is the case with polypropylene - read more about polypropylene).
Types of CNC Machines
CNC machines typically fall into one the two general categories: conventional machining technologies and novel machining technology:
Drills: Drills work by spinning a drill bit and moving the bit about and into contact with a stationary block of stock material.
Lathes: Lathes, very much the inverse of drills, spin the block of material against the drill bit (instead of spinning the drill bit and putting it into contact with the material). Lathes typically make contact with the material by laterally moving a cutting tool until it progressively touches the spinning material.
Milling Machines: milling machines are probably the most common CNC machine in use today. They involve the use of rotary cutting tools to remove material from the stock unit.
Electrical and/or Chemical Machining: There are a number of novel technologies that use specialized techniques to cut material. Examples include Electron Beam Machining, Electrochemical machining, Electrical Discharge Machining (EDM), Photochemical machining, and Ultrasonic machining. Most of these technologies are highly specialized and are used in special cases for mass-production involving a particular type of material.
Other Cutting Mediums: There are a number of other novel technologies that use different mediums to cut material. Examples include laser cutting machines, oxy-fuel cutting machines, plasma cutting machines, and water-jet cutting technology.
Application For Rapid Prototyping
CNC machines were the first major break-through in the field of rapid-prototyping. Before numerical control (in the case of punched tape technology) and computer numerical control (with analog and digital computing), parts had to be machined by hand. This invariably led to larger margins of error in end prototype products and even more so if/when machines were manually used for larger scale manufacturing.