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.
We decided to compare the advantages and disadvantages for each method to establish where these technologies are most appropriate.
What is 3D Printing?
3D printing is an additive manufacturing process that uses digital CAD models to build physical, often layered, real-life objects. 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.
Early-stage prototypes are typically produced in very small numbers and don’t necessarily have to hold true to all the functional characteristics of production parts. Since material selection and internal structure of the part are not as critical at this stage, prototypes can be produced using a variety of 3D printing technologies that are both fast and affordable.
Common 3D printing applications are:
- Production parts
- Functional models
- Visual aids
- Fit and assembly testing
- Tooling patterns and components
- Jigs and fixtures
- Concept models
- Patterns for casting
What Is CNC Machining
CNC machining is subtractive. This means CNC machining starts with a block of material (called a blank), 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.
You’re probably reading this on a computer. Thank a machinist. Without precision machine tools and the people who operate them, your computer, desk, office chair, the cars in the parking lot, and the building around you wouldn’t exist. In fact, machining makes every aspect of modern life possible, from the food in your refrigerator to the clothes on your back. It has been that way since the discovery and subsequent refinement of metals such as copper and iron.
Granted, machining is a subset of a much broader manufacturing industry, but it’s important to recognize that sheet metal fabricating, injection molding, casting, semiconductor fabrication, and all the rest would never have developed without machined parts.
Even that new kid on the manufacturing block, 3D printing, relies on and indeed owes its very existence to machining, despite the fact that additive manufacturing is changing the way we design and build many products. Long story short, machining is here to stay, and it gets a little bit better, faster, and more accurate every day.
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.In 3D printing, commonly used thermoplastics include ABS, PLA, Nylon, ULTEM, but also photo-polymers such as wax, calcinable or biocompatible resins.
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 are aluminium, stainless steel, magnesium alloy, zinc alloy titanium, and brass.
3D Printing vs CNC Machining: Accuracy
Though there are a number of 3D printing technologies, we have chosen to compare CNC machining with SLS, industrial (not desktop) FDM, and DMLS metal 3D printing. In terms of tolerance, CNC machining is superior to all 3D printing processes, even DMLS. However, with minimum layer thicknesses the superiority is not so profound, and is not as precise as DMLS.Therefore, CNC and 3D printing stand toe-to-toe in this regard.
3D Printing vs CNC Machining: Size
Powder bed fusion 3D printing processes such as SLS and DMLS are limited in their build volume however. Even technologies with larger build volumes such as FDM cannot compete with CNC in terms of maximum size of parts.
3D Printing vs CNC Machining: Geometric Complexity
3D printing is well-known for its advantages in creating parts with high geometric complexity. Though supports are required for some technologies, 3D printing can create parts with geometries that no traditional manufacturing method can replicate. Technologies such as SLS and Multi Jet Fusion by HP can even do this without any support structures.
3D Printing vs CNC Machining: Post-Processing
Generally, CNC machines deliver a part that is 100% ready for the market. 3D printers are a little different. Their common applications are related to prototyping or assisting in mold creation. For both cases, a rough surface finish works just fine. Otherwise, you’ll have to further process the part before it’s ready for any other application.
Apart from that, metal 3D printed components even have another requirement of heat treatment. Because of how 3D printing works, the developed part doesn’t have much fatigue strength and impact properties. Heat treatment allows the internal structure to set better and deliver better performance. However, it still doesn’t work as well as CNC parts.
3D Printing vs CNC Machining:Eco-Friendliness
Both CNC and 3D printing materials can work with a plethora of materials. The CNC process is generally free from harmful materials while 3D printers use more thermos plastics for prototyping. If used correctly, they can be a great way to recycle the plastic that would otherwise remain in circulation for the longest time. Therefore, depending on your application and commitment to the environment, both CNC and 3D printing can potentially be eco-friendly options.
3D Printing vs CNC Machining:Cost
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).
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 tell AMPERR FUTURE you specific need,and we will give you some useful advise.