The first CNC machines were developed in the 1940s and 1950s and relied on a common telecommunication data storage technology known as “punched tape” or “perforated paper tape.” Punched tape technology is long obsolete as the data medium quickly transitioned to analog and then digital computer processing in the 1950s and 1960s. As new technologies and improved digital processing power get introduced, CNC machines continue to improve their efficiency.
How it Works
In general, machining 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) utilizing a controlled material removal process. Similar to another 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. While the CAM or CAD does not run the CNC machine itself, they provide the roadmap for the CNC to fabricate the designs. 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).
Frequently machining processes require the use of multiple tools to make the desired cuts (e.g., different sized drill bits). CNC machines commonly combine tools into common units or cells from which the machine can draw. Basic machines move in one or two axes, while advanced machines move laterally in the x, y-axis, longitudinally in the z-axis, and often rotationally about one or more axes. Multi-axis machines are capable of flipping parts over automatically, allowing you to remove material that was previously “underneath.” This eliminates the need for workers to flip the prototype stock material and enables you to cut all sides without the need for manual intervention. Entirely automated cuts are generally more accurate than what is possible with manual inputs. That said, sometimes finishing work like etching is better accomplished by hand and simple cuts that would require extensive design work to program the machine for automation.
Types of CNC Machines
As you decide which CNC machines to add to your operation, there are some considerations you need to take into account. CNC machines typically fall into one of the two general categories: conventional machining technologies and novel machining technology. Each type provides you with advantages and disadvantages. You need to factor in your project’s particular needs when selecting the type of CNC machine to add to your workshop. The following infographic covers some of the similarities and differences between conventional and novel CNC machines:
Drills: Drills work by spinning a drill bit and moving the bit about and into contact with a stationary block of stock material. CNC drills help make precision holes where you need them.
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. Primarily used with metals and wood, lathes remove the unwanted excess material and leave behind a beautiful and ultimately more useful component.
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. They can perform various functions, including drilling, boring, cutting gears, and producing slots within a given piece of material.
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. These machines have gained popularity in different industries in recent years; however, they are still highly specialized pieces of equipment.
Almost any material can be used in a CNC machine — it all depends on the application. CNC machines offer production a degree of versatility to benefit a variety of projects. Common materials include metals such as aluminum, brass, copper, steel, titanium, wood, foam, fiberglass, and plastics such as polypropylene.
Application For Rapid Prototyping
CNC machines were the first significant 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 and when machines were manually used for larger-scale manufacturing. CNC machines helped revolutionize the manufacturing world’s ability to rapidly prototype different materials, parts, and other machines through the increased precision it offers.
Application For Manufacturing
Many novel CNC specialty machines are built specifically for niche manufacturing processes. For example, electrochemical machining is used to cut highly durable metal products not otherwise feasible. Conventional CNC machines are more adept at and typically used for prototype development than manufacturing.
Which is better? CNC or 3D Printing?
The honest truth is that it depends on the material, the complexity of the part, and the economic factors at play. 3D printing technology like FDM machines builds parts from the bottom-up. They can create complex shapes and internal components somewhat more quickly than a CNC machine. 3D printing provides product designers and manufacturers a degree of flexibility and creativity that CNC machines cannot offer through conventional means.
By contrast, conventional CNC machines are somewhat limited by the tools available and the axes of rotation the machine can utilize. While they can still be used with a variety of materials, these machines are locked into a relatively strict set of confines and restrictions regarding how they can interact with the different materials.
On the flip side, FDM prototyping is much more limited by materials than is a machined block of material. FDM prototyping requires specific materials that can be used in 3D printing. CNC machines offer greater variety in the types of materials they can manipulate and work with to create specific parts. For example, if you need a living hinge prototype, you would want to use CNC and polypropylene. Want to learn more? Read here.
Just about anything can be machined, while by contrast, only certain materials have been adapted into filaments suitable for 3D printing.