3D Printing vs CNC Machining

They difference between 3D printing and CNC machining is that 3D printing is a form of additive manufacturing, while CNC machining is subtractive. This means CNC machining starts with a block of material and cuts away material to create the finished part. To do this, cutters and spinning tools are used to shape the piece. Some advantages of CNC machining include great dimensional accuracy as well as many compatible materials, including wood, metals and, plastics.

3D printing is a rapidly growing technology with many advantages over traditional manufacturing methods. It however has its problems, including that 3D printing cannot be effectively used for mass production, and is limited in speed and accessibility. Another manufacturing technique for low-to-mid production is CNC machining (computer numerical control), a fairly common subtractive technique for part creation.

3D printing, or additive manufacturing, is the construction of a three-dimensional object from a CAD model or a digital 3D model. The term "3D printing" can refer to a variety of processes in which material is deposited, joined or solidified under computer control to create a three-dimensional object, with material being added together, typically layer by layer. using materials such as plastic filaments (FDM), resins (SLA/DLP), plastic or metal powders (SLS/DMLS/SLM). Using a source of energy such as a laser or heated extruder, layers of these materials are solidified to form the finished part. Advantages of 3D printing include its freedom of shape, applications in many sectors, accuracy, speed, and ability to cut costs and weight in parts.

There are however several machines that have sought to combine these two forms of manufacturing in one. Most notably of these, the ZMorph 2.0 SX, is marketed as a CNC mill which also functions as a 3D printer. This includes a CNC mill with 3 axes as well as a print head due to its interchangeable heads. Moreover, several companies have recently closed successful Kickstarter campaigns with these combined machines, such as Mooz’s 3-in-1 3D printer.

3D Printing vs CNC Machining: Materials

Both 3D printing and CNC machining are compatible with a wide variety of materials, including both plastics and metals. 3D printing however is more focused on plastics overall, though this is changing rapidly as better and more affordable ways of 3D printing metal are being developed by manufacturers such as 3D Systems, Arcam, Desktop Metal and Markforged.

The most commonly used plastics used in CNC include ABS, Nylon (PA66), Polycarbonate (PC), Acrylic (PMMA), Polypropylene (PP), POM and PEEK. A very commonly used metal in CNC machining is aluminium, used by prototyping companies to create high-quality prototypes in a variety of industries. Aluminium is recyclable, has good protective qualities, and can create effective prototypes for machining. Other commonly used metals include stainless steel, magnesium alloy, zinc alloy titanium, and brass.

3D printing is known to be simpler to use than CNC machining. This is because once the file is prepared, you just need to chose the part orientation, fill, and supports if needed. Then once printing has commenced, no supervisor is required and the printer can be left until the part is finished. Post-processing requirements depends on the technology.

However, CNC machining is a far more labour-intensive process. A skilled operator is required to choose between different tools, rotation speeds of tools, the cutting path, and any repositioning of the material the part is being created from. There are also post-processing techniques which can require more time.

Though on average 3D printing is cheaper, costs depend on how many parts are required and how quickly you need them. For larger quantities (higher double digits to 100s) CNC is likely to be more appropriate. For low volumes, 3D printing is more appropriate and lower-cost. 3D printing is also more appropriate if you need your prototypes or parts very quickly. There are additional factors however that make comparing the two technologies more difficult. These include materials varying in cost (from cheap materials like ABS to materials that can cost $500/kg like PEEK), and repairing and changing machinery (such as CNC heads).

Since CNC involves cutting material away from an original block, there is always going to be mess afterwards. These pieces of material need to be cleaned afterwards and disposed of, which isn’t required from 3D printing. Since additive manufacturing forms an object on the build platform from material fed into the machine, there is no mess except supports (if used). This makes 3D printing the more ethical of two methods as there is less unused waste.

Overall to conclude, there is no perfect, one-size-fits-all technique. Though both methods are very competent and useful technologies, the most appropriate one will depend on the material, geometric complexity, manufacturing volume, and budget. To find out which is best for your particular job, we advise you approach a local or international service, and ask for their advice. If attempting to manufacture in-house, reflect on the machinery available to you and decide whether it is appropriate for the job at hand.