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3D Printing vs CNC Machining

3D printing vs cnc machining

You’ve probably watched a YouTube video of a 3D printer moving back and forth, slowly creating a small plastic object. 3D printers have grown in popularity in the past 5 years. Today they’re reasonably affordable and easy to set up and use in your garage. 

Most 3D printers are used by hobbyists, or people making plastic prototypes. We haven’t seen 3D printers widely used in large scale manufacturing operations yet. Especially for precision metal parts, CNC machining is still the preferred manufacturing method.

CNC machining has been widely used since the 1940s and is one of the traditional manufacturing methods used to produce millions of precision parts around the world.

In this article, we’ll compare the pros and cons of 3D printing and CNC machining, along with how each process works and their capabilities.

Process overview

3D printing and CNC machining are used for similar tasks, such as creating a custom part or component. How each process accomplishes the task is almost the opposite.

3D printing process: The most common 3D printing process is a technique called fused deposition modeling, or FDM. During this process, a 3D printer uses raw material and an additive manufacturing process. A Polylactic Acid or polycarbonate is heated and deposited onto the printing service. The machine adds the material layer by layer to form the desired shape. The raw materials are typically sold in spools of various colors and materials.

CNC machining process: There are a few different types of CNC (computer numerical control) machines. The machines have varying capabilities for machining varying complexities of parts. The basic process involves taking a raw material and using a subtractive manufacturing process. CNC machines use a cutting tool to drill and cut the desired part shape. The raw materials can include most plastics, wood, and metals.

Both manufacturing processes use computer programs that require minimal human involvement after setup. Specific measurements or a CAD program is used to input the part design and specifications. 

CNC machines typically require a more extensive setup process because the machines are more complex and have more moving parts. CNC machining is also used for higher quantities of parts so part accuracy is double and triple checked. There are multiple cutting tools that are used simultaneously to form the part features.

Most 3D printers only have a single nozzle that moves around to deposit the material. It’s also less expensive to make small adjustments because the raw material is much less expensive. 

Making a mistake during 3D printing might cost you $10 or $15. A mistake that’s not caught during a CNC machining operation can cost thousands of dollars. 

3D printing process

The most common 3D printing process is a technique called fused deposition modeling, or FDM. During this process, a 3D printer uses raw material and an additive manufacturing process. A Polylactic Acid or polycarbonate is heated and deposited onto the printing service. The machine adds the material layer by layer to form the desired shape. The raw materials are typically sold in spools of various colors and materials.

CNC machining process

There are a few different types of CNC (computer numerical control) machines. The machines have varying capabilities for machining varying complexities of parts. The basic process involves taking a raw material and using a subtractive manufacturing process. CNC machines use a cutting tool to drill and cut the desired part shape. The raw materials can include metals, and most hard plastics and wood.

3D Printing vs CNC Machining (2)

Both manufacturing processes use computer programs that require minimal human involvement after setup. Specific measurements or a CAD program is used to input the part design and specifications. 

CNC machines typically require a more extensive setup process because the machines are more complex and have more moving parts. CNC machining is also used for higher quantities of parts so part accuracy is double and triple checked. There are multiple cutting tools that are used simultaneously to form the part features.

Most 3D printers only have a single nozzle that moves around to deposit the material. It’s also less expensive to make small adjustments because the raw material is much less expensive. 

Making a mistake with a 3D printed prototype part might cost you $10 or $15. A mistake that’s not caught during a short run CNC machining operation can cost thousands of dollars. 

Materials used

Both 3D printers and CNC machines can use a variety of materials. 

3D printers mostly use hard plastics and polymers. These materials are easy to melt and form into the desired shape, and they’re fairly durable once they harden. Some industrial-style 3D printers can use metal, but these machines are significantly more expensive compared to printers that use the normal plastic filament. 

Metal 3D printed parts may become more popular in the future, but they’ll be more similar to injection molding rather than CNC parts. Melting metal and printing a part with specific dimensions isn’t very practical. Casting parts, where melted metal is poured into a mold is more common.

CNC machines can be used to machine any material, but the majority of machine shops deal primarily with a few metal alloys like aluminum, steel, and copper. CNC is also the primary process used for wood since it can’t be melted. Being able to machine any solid material is a big advantage for CNC machines.

3D printers vs CNC machines

3D printers are much simpler machines compared to CNC machines. Of course, there are different machines with more capabilities. You can buy a small desktop 3D printer for a few hundred dollars. These are suitable for hobbyists and smaller projects. A more complex 3D printer will be more expensive, but still cheaper than a CNC machine.

3D printers are also easier to use and maintain. Running a CNC machine requires more training and is more difficult to repair if something breaks.

Larger industrial 3D printers and CNC machines offer a wide range of part capabilities and can take a few years to pay for themselves.

Part integrity and capabilities

Both 3D printing and CNC machining are capable of producing complex custom designs. 

Most 3D printed parts don’t require the same tight tolerances that CNC machined parts do. And increasing the accuracy of 3D printing also increases production time, so it’s not always worth the extra time and effort for higher precision.

Some 3D printed parts require some additional shaping or sanding to remove the rough edges. The surface quality isn’t as good compared to CNC. The approximate layer thickness for 3D printing is between 0.1mm–0.5mm.

Some parts made with CNC also require post-processing grinding or sanding, but the standard surface roughness is usually good enough for immediate use. Parts can also be sanded or finished on the same machine. CNC machines have significantly tighter tolerances—usually around 0.01mm.

Costs and efficiency

Keeping costs low and efficiency high is a top priority for manufacturers.

3D printing costs have decreased significantly in the past ten years. While CNC machining has continued to be one of the most cost-efficient production methods for decades. 

The raw material for 3D printing is less expensive and easier to get than raw metals for CNC machining parts. The setup process for 3D printing is also much faster. If you need to create a rapid prototype of a part, or a handful of custom parts, 3D printing is faster and cheaper. Some prototype parts need to be metal because they require higher strength or greater precision than plastic parts can achieve. 

3D printing is more difficult to scale and use for mass production. 

The process is slower when the part is bigger or more complex, and the printer can only create one part at a time which can take a few hours. If you want to scale the process, you’ll need to use more printers. 

Since 3D printing is an additive process rather than a subtractive process, there is less scrap material and waste. The plastic and metal scraps from CNC machines are recycled, but there’s generally less waste with 3D printing.

CNC machining involves a more expensive setup process. Setting up a new part design on a CNC machine can take an entire week, compared to a few hours for a 3D printer. However, once the machine is properly set up, it can run 24/7 and produce parts very quickly. This makes CNC machining more efficient for high quantities of parts.

When you need 100 or more identical parts, a CNC machine is a more efficient process, but if you just need one or two, 3D printing is better.

Can 3D printing replace CNC machining?

For now, 3D printing can’t fully replace CNC machining. 

There are certain applications, such as rapid prototyping, where 3D printers have taken over tasks that were previously done using CNC machines. 3D printers can be very cost effective, but it’s a less scalable production process. 

CNC machines are continuing to improve and expand their capabilities along with 3D printers, and they will continue to be used for the majority of manufacturing processes. CNC machines can produce parts on a much larger scale, use a wider range of materials, and reach tighter tolerances.

At Spex, we can provide a rapid prototype of any custom plastic part using our 3D printer. 

We also have a fully capable CNC machine machine shop and screw machine shop for fast production of high quantities of precision machined parts.

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