CNC machining and 3D printing are two of the most common methods for manufacturing end-use parts and prototypes. While both powerful, they have different strengths and weaknesses. Choosing the right manufacturing process can not only help you create the best quality product but save you time and money. Read on to explore the key differences between CNC machining and 3D printing.
What are CNC printing and 3D printing?
CNC machining is subtractive manufacturing.
In CNC machining, a solid block of material called a blank is carved into the shape of the final product using rotating cutting tools such as drill bits. CNC machining tends to generate a greater amount of waste in the form of shavings and the like.
3D printing is additive manufacturing.
In 3D printing, material is added by an end effector such as a nozzle one layer at a time until the final product is formed. 3D printing generally generates very little waste. Any waste is in the form of supports that need to be removed or surfaces that need to be sanded.
What can CNC machining and 3D printing be used for?
CNC machining is great for manufacturing industrial-grade products and machinery and is often used in metal fabrication. For example...
• Mechanical parts for machines and commercial/industrial equipment
• Parts that require a lot of precision, such as engine parts
• Parts that need to be very durable, such as airplane and vehicle components
3D printing is great for manufacturing consumer-grade products or home use products. For example…
• One of a kind pieces such as artwork or prototypes
• Customized parts, such as for medical or dental use
What materials can be CNC machined or 3D printed?
Metal is the most common material used in CNC machining, and it’s particularly effective with high-density metal.
Other compatible materials include…• Wood • Foam • Thermoplastics • Acrylics • Machining wax
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Plastic is the most common material used in 3D printing. It’s also good for metal superalloys or flexible materials that are hard to machine.
3D printing materials include...• Plastic powder and filament • Nylon • Resin • Composites • Food materials • Bio-materials • Metal |
What method is best for the geometry of my part?
CNC machining is great for simple, repeatable geometries.
CNC machined parts need to be designed so that the cutting tool can reach every surface. There are some geometries that are impossible to machine because the tools aren’t physically able to reach all parts of the design. CNC machined parts also need to be able to be mounted in place while the tools do their work. Many parts need to be rotated or repositioned, so having multiple hold or mount points is a necessity. Rotating a part can also add to the processing and labor time of a project and drive the price up.
3D printing is great for complex, organic geometries.
3D printing, on the other hand, has very few restrictions on what geometries can be made. It’s capable of creating complex designs such as mesh or organic, free-flowing structures. However, it does require support structures to be constructed in order to successfully create the desired shape.
What is the dimensional accuracy of each method?
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CNC machining can achieve high accuracy with the help of tool sensors and precise cutting tools |
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3D printing requires the use of supports that later need to be removed |
CNC Machining is highly accurate and can achieve very tight tolerances. It’s ideal for manufacturing parts that require a lot of precision. 3D printing is less accurate. Because 3D printing requires the addition of supports in order to create complex structures, it is generally less precise than CNC machining.
CNC Machining |
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3D printing |
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Surfaces |
CNC machining can produce very smooth surfaces without any post-processing.
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3D printing can sometimes produce layer lines on surfaces, especially curved ones. |
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Walls and Edges |
CNC machining can create very thin, sharp external edges and precise, square external corners. However, on internal edges (such as depressions, sockets, etc.) there will always be a radius due to the shape of the tool. The radius may be larger or smaller depending on the angle of the tool.
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The width of walls created by 3D printers are limited by the width of the end effector, so they can’t get as thin and sharp as CNC machined parts. |
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Post-processing |
CNC machined parts require very minimal post-processing. In many cases, they can be sent directly to their next destination. |
Once 3D parts are finished printing, they typically require supports to be cut off, surfaces to be sanded or polished, and sometimes need to be cured before they can be delivered.
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What method is better for the quantity of product I need?
CNC machining is best for medium to high quantities of parts with a lot of repeatability. Due to the amount of labor and set up required, machining one-off or low quantities of parts may not be cost-effective.
3D printing is cost-effective for one-off or small quantities of parts. Because the cost of a single 3D printed part remains the same no matter how many parts are manufactured, printing high quantities of parts can become cost-prohibitive.
In Conclusion
Selecting the right manufacturing process for your project is key to efficient manufacturing. While both powerful, CNC machining and 3D printing serve different purposes. CNC machining is optimal for producing repeatable, durable metal mechanical parts with high tolerances at a high quantity. 3D printing, on the other hand, is excellent for one-of-a-kind, organic pieces with high complexity but less need for geometric accuracy and durability. By doing a little research and determining which process is the best for your product based on the material you're printing, the geometry of your part, the number of parts you need and more, you can save time, money, and achieve the highest quality part possible.
Sources
Varotsis, Alkaios Bournias, “3D Printing vs. CNC machining.” Hubs, https://www.hubs.com/knowledge-base/3d-printing-vs-cnc-machining.
“CNC Machining of Metal Parts vs 3D Printing.” BuntyLLC, GoodLayers, https://buntyllc.com/settling-the-debate-cnc-machining-vs-3d-printing/.
Grieser, Franz. “T3D Printing vs CNC: Explained and Compared.” All3DP, https://all3dp.com/3d-printing-vs-cnc-milling/.
D., Jamie. “3D Printing vs CNC Machining: Which is best for prototyping?.” 3D Natives, 16 March 2018, https://www.3dnatives.com/en/3d-printing-vs-cnc-160320184/.
Feldman, Robert. “3D Printer Materials Guide.” 3D Beginners, 16 January 2019, https://www.3dbeginners.com/3d-printer-materials-guide/.
ProtoFab, director. "SLA 3D Printing vs. CNC Machining in the Automotive Industry | Great Wall Motors." YouTube, YouTube, 10 Nov. 2018, www.youtube.com/watch?v=w9wakaEN2jw.
