CNC (Computer Numerical Control) and 3D printing are two of the leading manufacturing technologies for rapid prototyping and low-volume production but use completely different production techniques to get there. While CNC uses subtraction, removing unwanted parts from a block of material, 3D printing uses addition, building a product layer by layer with material on a blank.

Both methods of fabrication have pros and cons, and it’s hard to say which one you’d use in your own project or when. Please be aware that other manufacturing techniques such as plastic injection molding are more suitable and more efficient in large scale production, eg manufacturing more than 200 parts. In this article, we have prepared an exhaustive comparison of CNC and 3d printing, you can use these details to compare the two methods and decide which one to use.

What is CNC prototype machining?

CNC Prototype machining is a subtractive process, so it creates the final part by removing material from the initial workpiece with a CNC machine.it involves removing portions of material from a block (or workpiece) to create the desired part using cutting tools. Computer Numerical Control (CNC) technology controls the sequence of motion of the cutting tool and workpiece to create the desired part.

What is 3D Printing prototyping?

3D printing prototyping is an additive manufacturing process involves adding materials layer by layer to form the desired product. A 3D prototype is created using 3D modeling software. The process requires no special tooling or fixtures. parts being created layer-by-layer using materials such as plastic filaments (FDM), resins (SLA/DLP), plastic or metal powders (SLS/DMLS/SLM). Using a source of energy such as a laser or heated extruder, layers of these materials are solidified to form the finished part.

CNC Machining VS 3D printing, which is better for making a prototype

Materials

CNC prototyping offers more versatility, ranging from plastics and wood to the strongest metal prototype. Material options that you can use with CNC prototype machining include plastic prototpye materials like ABS, Nylon (PA66), Polycarbonate (PC), Acrylic (PMMA), Polypropylene (PP), POM and PEEK. Metals and metal alloys ideal for CNC metal prototyping include aluminum alloys, steel, stainless steel, magnesium, titanium, zinc, copper, bronze, and brass.

3D printing materials mainly include liquid resin (SLA), nylon powder (SLS), metal powder (SLM), gypsum powder (full-color printing), sandstone powder (full-color printing), wire (DFM), sheet (LOM), etc. Liquid resin, nylon powder and metal powder occupy most of the market for industrial 3D printing.

Geometric Complexity

CNC machining is subtractive manufacturing, through various high-speed cutting tools, cutting out the required parts according to the programmed cutting path. Therefore, CNC precision machining can only process rounded corners with a certain radian, but cannot directly process inner right angles. It must be realized by wire cutting/sparking and other processes. Outside right-angle CNC machining is no problem. Therefore, parts with inner right angles can be considered for 3D printing processing. There is also the curved surface. If the part has a large surface area, it is recommended to choose 3D printing. CNC machining the curved surface is time-consuming, and if the programming and operator experience is not enough, it is easy to leave obvious lines on the part.

3D printing is a kind of additive manufacturing. Its principle is to cut the model into N layers/N multi-points, and then pile them up layer by layer/little by little in order, just like building blocks. Therefore, 3D printing can effectively process and produce parts with complex structures, such as hollow parts, while CNC is difficult to process hollow parts.

Accuracy, Size limitations

CNC machining offers tight tolerance and excellent repeatability. Very large to very small parts can be CNC machined accurately. Thanks to the shape of most cutting tools, internal corners will always have a radius, but external surfaces can have sharp edges and can be machined very thin. 

Each 3D printing system offers a different dimensional accuracy. Industrial machines can produce parts with very good tolerances. If tight clearances are required, the critical dimensions can be 3D printed oversized, and then machined during post-processing.

TechnologyToleranceMinimum wall thicknessMaximum part size
CNC machining± 0.01 – 0.125 mm0.75 mmMilling: 2000 x 800 x 1000 mm Lathe: Ø 500 mm
SLA± 0.2 mm0.7 – 1.0 mm300 x 300 x 300 mm
SLS± 0.3 mm0.7 – 1.0 mm300 x 300 x 300 mm
FDMDesktop: ± 0.500 mmIndustrial: ± 0.200 mm0.8 – 1.0 mmDesktop: 200 x 200 x 200 mmIndustrial: 900 x 600 x 900 mm
SLM/DMLS± 0.100 mm0.40 mm230 x 150 x 150 mm

Surface Quality and post-processing

3D printed plastic part (left) and CNC machined plastic part (right)

In terms of surface quality, CNC is better than 3D printing. This is because of the wide range of tooling CNCs use. With different tools like a ball end mill, face mill, sanding belt, etc., CNC can produce workpieces with a high surface quality. The layer-by-layer printing process of 3D printers leaves behind a rough surface texture on the workpiece.

There are not many post-processing options for 3D printed parts, usually grinding, oil spraying, deburring, dyeing and so on. While There are various post-processing options for CNC machined parts, in addition to grinding, oil injection, deburring, electroplating, silk screen printing, pad printing, Aluminum oxidation, laser engraving, sandblasting and so on.

Cost

In terms of Rapid Prototyping Cost, CNC machines are comparatively more expensive than a 3D printer that provides a similar work area.

Generally, CNC equipment consumables and materials are less expensive than 3D printers. However, CNC requires trained experts to pre-program process parameters and tool paths. This adds additional time and money on top of the cost of making the finished product. This is why, while manufacturing is relatively fast, in some cases 3D printing is preferable.

For small businesses making prototypes, a 3D printer is a cost-effective option as it allows them to create prototypes without needing expensive equipment. The entry cost of 3D printing is lower and faster than other technologies. However, consumables and materials are much cheaper compared to CNC. In summary, additive production is more advantageous for unique items of limited volume, however, for manufacturing more than 20 items, CNC or other technologies are more recommended.

Speed

CNC machining-Depending on the complexity of the design and the materials chosen, the speed of fabrication can be exceptionally fast, in some cases unrivaled. But be aware that the pre-programming process can also be time-consuming, especially for high-precision projects. The total time for CNC processing is 3-4 days (3D printing is about 1-2 days).

3D printing-The additive manufacturing process can be slow, sometimes very slow. It’s not the best option for series production. But why is 3D printing relegated to rapid prototyping? The reason is simple – the 3D printer does not require lengthy pre-programming before it is fully warmed up, just load the material, cut the file a few minutes before sending it to the 3D printer. Plus, additive manufacturing is improving every time, and the latest equipment is several times faster than its predecessors.

Part Quality

Regarding prototype quality, CNC machines offer a distinct advantage in producing products with a polished appearance due to their higher tolerance levels. The manufacturing process of CNC machining ensures minimal deformation of materials, resulting in precise and well-defined parts. Conversely, 3D printing may encounter challenges such as bending, warping, and visible layer lines, particularly around curved surfaces. While certain 3D printers claim high accuracy, occasional failures can still occur. Geometric limitations exist for both manufacturing methods. CNC machining excels at creating thin walls, while 3D printing may face constraints in this aspect due to the size limitations of its end-effector. Understanding these distinctions aids in selecting the most suitable manufacturing method based on specific project requirements and desired outcomes.

In Summary

The above are the respective technical characteristics of CNC machining and 3D printing for rapid prototyping . There is no such thing as better or worse, only choosing the one that suits you is the best.

CNC machines excel in producing parts with smoother surfaces compared to 3D-printed counterparts. If you prioritize precise component fitting, CNC machining is the preferred choice. However, 3D printing can also deliver excellent parts in terms of finish and fit, depending on the specific 3D printer used. The quality of both CNC-machined and 3D-printed parts is influenced by the capabilities and characteristics of the respective manufacturing technologies.

KUSLA Prototype is a leading prototype manufacturer of CNC machining service and 3D printing service in Asia. We have a team of highly experienced engineers and machinists, and Advanced manufacturing technologies to get your product done right.

Related Blog

Similar Posts