There’s certainly no shortage of manufacturing processes available these days, both on the additive manufacturing side and the traditional. But with so many choices, how are you to know which one is the best for your project?
The questions to ask yourself when exploring what manufacturing process to choose include; what materials you want to use, how many parts you are looking to have produced, the part geometry capabilities of both processes, how you plan to use the parts, and how parts produced in the various processes perform, and finally the costs.
Subtractive vs Additive Manufacturing
CNC machining is a subtractive process that begins with programming a combination of CNC tools to build a part directly from a CAD file. The machines etch out the design from a solid block of metal, plastic or other material to reveal the part shape.
If it’s a larger part, it is created in sections and then each section is bonded together to form the completed part geometry at which point it is ready to finish using plating, painting, or polishing.
3D printing, or additive manufacturing, builds parts by adding the material layer-by-layer. There are a few processes under the additive manufacturing umbrella;
- Fused Deposition Modeling (FDM) creates more durable parts for tough industrial environments by building each part in successive layers of materials directly from the CAD file using melted plastic from a spool that is extruded through a heated tip. The parts are printed in production-grade thermoplastics with support structures that are printed simultaneously from different materials so they can be separated from the final part.
- HP Multi Jet Fusion (MJF) is a powder bed process where the powdered material is rolled onto the print bed in a thin layer. Thermal inkjet arrays deposit fusing and detailing agents in the cross-sectional shape of the part. A high-intensity heat source is passed over the print bed and wherever the agents are deposited, the material fuses. Then the process repeats with the next layer until the complete part is formed. The un-fused powder is then removed from the part revealing the final net shape part.
- Selective Laser Sintering (SLS) creates 3D parts out of a wide range of polymers including rigid nylons, filled nylons, and elastomers. High-powered lasers heat and fuse the material, layer by layer, forming the final product with intricate details and internal channels. SLS is a powder bed technology that yields parts that are supported by the surrounding unfused powder.
- Direct Metal Laser Sintering (DMLS) creates metal parts by melting fine-metal powder, layer-by-layer, with a laser beam to create a final part comparable to traditionally manufactured metal parts. DMLS parts are printed in the same metal material as its supports. They must be removed mechanically by cutting, snipping, or grinding.
- Stereolithography (SLA) uses a laser-based system that builds parts, layer-by-layer, using a photosensitive epoxy-based polymer. Once the model has been printed, it’s finish-cured with UV light to solidify the resin material and strengthen its structure. SLA parts have support material printed simultaneously with the part that is the same material that are removed with mechanical means.
Physical Considerations for CNC Machining and 3D Printing
Part Size
Part size is an important consideration when weighing whether to use CNC or additive.
Both processes are good for producing parts that are medium-sized, from half an inch cubed to a couple of feet cubed. CNC is a better solution for very small, high-precision parts, or very large parts that can be machined in sections and bonded together.
Additive can also be used for large parts, however printing in sections and fabricating together is not as precise.
Size consideration is not a major contributing factor, because both processes can create parts of all sizes, however, CNC machining can be a better solution for larger parts from a cost savings perspective.
Materials
CNC machining is capable of producing parts in both plastics and metals and it offers a wider range of materials to select from. Essentially all materials are available for use with the CNC machining process, and the finished part with the material is largely undisturbed, keeping the native properties of the material.
3D printed parts are restricted to the materials that are supported by the process.
Surface Finishes
CNC machining can produce much smoother surfaces than 3D printing. Because of the layer-by-layer process of 3D printing, you can often see the layers in the finished product.
| The finishes we offer for CNC machining include: | The finishes we offer for 3D printing include: |
| Polishing Painting Electroplating Anodizing Powder coating Cerakote | Vapor Smoothing Dyeing Painting Tumbling Hydro dipping Cerakote Inserts Sanding/polishing Bead blasting Anodizing (metal) Heat treating (metal) |
Costs
We understand that cost is a very important consideration when comparing CNC machining and additive manufacturing. The results of costs vary widely with material, part complexity, part size, part materials, and quantity.
Generally, CNC machining is more cost-effective for large, simple parts such as plates for jigs and fixturing and threaded bars, and other linear parts. Additive can be more cost-effective for small-to-medium-sized parts with high geometric complexity such as electronics enclosures, mechanical housings, and parts that interface with humans such as grips.
Selecting the appropriate manufacturing method is critical for success in today’s competitive market. The decision affects product quality, production efficiency, and overall cost.