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CNC machining or 3D printing, what is the best way to make your part?

As stronger 3D printing materials have been developed in recent years, more and more manufacturers across various sectors are exploring if additive manufacturing might be a better way to make a part than CNC machining. They also find ways to use CNC machining services to create functional parts that were CNC machined in the past. The 3D printing process gives manufacturers the possibility to save time and money, while it can still generate the needed quality. Below you can read more about CNC machining versus a 3D printing service.

Tolerances

Some of the best composite 3D printers are able to hold dimensional tolerances down to about 0.005”. Typically they also have a compliant surface for press fitting. On top of that, the tight tolerance features on 3D printed parts can be machined after they have been printed. However, it may be easier to CNC machine the whole thing, which mainly depends on the other features of the part at hand. It is highly likely that your results will vary based on the machine, material, and part geometry used. 

Feature size

Both 3D printing and CNC processes are constrained by tool size unfortunately. In the case of Computer Numerical Control, the tool diameter decides what the smallest negative feature is that can be created. When looking at 3D printing, the size of the smallest positive features that can be created is decided by the nozzle diameter. For extrusion-based 3D printers the nozzle diameter is usually between 0.25 millimeters and 0.8 millimeters. The minimum feature size for those machines is four times that, which results in a minimum feature size between 1.0 millimeters and 3.2 millimeters. You should take this into account when deciding which manufacturing process you are going to use.

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Typically, non-structural parts can be created with the help of conventional 3D printing. However, you can produce structural parts with continuous fiber reinforcement, although you could also decide to use CNC machining for this. Continuous fiber reinforcement can offer significant strength improvement over other 3D printed products, but composite parts are even better. They do not exhibit isotropic properties, while they are also stronger in the X and Y axes than in Z. Again, take this into account.

Surface finishes

CNC machines are capable of creating much smoother surfaces than 3D printers, although you will have to use the right tools in order to do this. On the other hand, 3D printers are capable of creating parts for fit and finish. Does your part require exceptional smoothness? In this case, 3D printing is not really a suitable manufacturing technique. CNC machining is in this situation, which is also the case when your part is a precision component.

Both CNC machining and 3D printing are capable of creating parts in metals and polymers. Therefore, the process that is more readily available to form the material that you need is more important. Typically, the service temperature of a specific metal has some linkage to its melting temperature. On the other hand, alloys can often push the useful range even higher, in some cases they are able to do this with about 65 percent of the melting temperature. 3D printed polymers and composites generally have service temperature limits lower than metals. 

Chemicals

Will your part be subjected to chemicals? In this case, it is important to check the chemical compatibility of the material you are planning on using. Many metals are suited to use with several chemicals, but you will still have to check before you actually start doing it. On top of that, nylon-based materials are also chemically resistant.


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