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The Difference Between CNC Machining and 3D Printing

CNC machining vs 3D printing

When you want to create a new part, there are two manufacturing methods you can turn to: CNC machining and 3D printing . Although both processes are standard today, each has evolved to meet different demands — so it's important to know which method will best suit your needs.

Overview of CNC Machining

Computer numerical control (CNC) is a common type of subtractive manufacturing, meaning it carves out needed components from large blocks of material. MIT introduced this technology in the 1950s , and it has since become a staple of the manufacturing industry. For this reason, you will also hear people call it traditional manufacturing.

CNC machining vs 3D printing

CNC machining can produce parts that are strong and have precise dimensions. It tends to be best for engines, airplane machinery and other fields where robust parts are needed. It is common in industries such as woodworking, lettering and engraving .

How It Works

First, an engineer makes a 2D or 3D model using CAD, or computer-aided software . The CAD file then gets translated into instructions using a computer-aided manufacturing (CAM) program. Once the instructions are created, a post-processing program converts them to specific commands and transfers them to the CNC machine for execution.

This process typically begins with a block of material, which an array of rotating tools and sharp blades cut away. Some of the more basic machines move along three axes, while more advanced machines have four or five axis. Stepper or servo motors ensure the movements will be precise.

Some common types of CNC machines are:

  • Mills , which use rotary cutting tools to sculpt components
  • Lathes , which rotate the material on a spindle
  • Grinders , which cut using an abrasive wheel
  • Drills , which use a spinning drill to carve stationary material
  • Routers , which cut large-scale components from wood, plastic and sheet metal
  • Plasma cutters , which use a plasma torch to cut two-dimensional shapes into sheet metal.
  • Laser cutters , which are powerful cutting tools good for cutting metal, plastic and wood

CNC machines often involve the use of multiple tools, such as drills and saws, to make the needed cuts. CNC machines may combine various tools into single "cells" to maximize efficiency. Most new CNC machines are completely electronic.

Overview of 3D Printing

3D printing is the popular name for additive manufacturing, which refers to building products from the bottom up, adding one layer at a time. Invented at MIT in the late 1980s , it found its first uses in prototyping, but its applications have since expanded into a variety of fields.

3D printing in medical field

3D printing is of great use in the medical field, where it can create organs, prosthetics and implants . The food industry has also made use of this technology, producing foods by squeezing them out layer by layer . Artists regularly use it to produce artwork, and fashion designers use it to create their apparel and jewelry.

3D printing has some exotic applications, as well. People can use it to make 3D selfies , and create coral-shaped structures to help repair damaged reefs . NASA has even developed a zero-gravity 3D printer to manufacture parts on their spacecraft .

How It Works

First, an engineer makes a 3D model using CAD. Another option is to use a 3D scanner, which is a device that analyzes the shape and appearance of a real 3D object and creates a digital model from it. A third choice is using photogrammetry software, which helps construct 3D objects by just analyzing photographs.

The completed model then gets analyzed for errors, which commonly include holes and intersecting faces .

Then, a program called a slicer prepares the model for the 3D printer by turning it into a series of thin, 2D layers, producing a G-code file. This file includes a set of instructions for the printer to carry out.

Next, a 3D printer reads the G-code file and lays down the material, one layer at a time, to product a three-dimensional object. The way the printer deposits these layers varies, but here are some common methods:

  • Fused deposition modeling , which uses a plastic filament to produce the product
  • Selective laser sintering , which fuses metallic powders by heating them
  • Selective laser melting , which fuses metallic powders by fully melting the materials
  • Stereolithography , which uses light to cause chains of molecules to link and form polymers

Depending on the size and complexity of the model and the method used, the printing process can last from a few hours to a few days.

Sometimes post-processing is necessary as a final step. The component may need to get washed, polished or sealed before anyone can use it.

Key Similarities of 3D Printing vs. CNC Machining

CNC machining and 3D printing have a few basic things in common:

  • They make 3D products based on 3D models.
  • They do so by following instructions from a computer.
  • They are compatible with STL and OBJ file types .
  • They are at the forefront of technology.
  • They are common today.

Beyond these basic similarities, however, CNC machining and 3D printing satisfy largely different demands and offer different benefits.

Key Differences Between 3D Printing and CNC Milling

There are also several major factors that differentiate the two processes.

  • Wastefulness: One of the main differences in additive vs. subtractive manufacturing is the amount of waste they produce. Because CNC machining takes away material, it ends up producing a lot of waste that is impossible to recycle. As you can imagine, the cleanup tends to be messy. 3D printers, however, only use the precise amount of material necessary to produce the part, so no cleanup is necessary afterward. 3D printers also produce less noise, as they don't vibrate during production.
  • File types: Except for the two file formats mentioned above, CNC machining and 3D printing use file types that aren't compatible with each other.

  • cnc milling size capabilities
  • Size of parts: With CNC milling, you can make broad range of sizes — from tiny, delicate parts to refrigerators. In 3D printing, on the other hand, the parts you make cannot be any larger than the printing bed. You can produce large components with a 3D printer, but it would involve breaking the component into smaller parts, printing those parts separately and then assembling them. Needless to say, this adds a large amount of time to the production process.
  • Material availability: CNC manufacturing can work with a wide range of materials , such as metal alloys, wood, acrylics, modeling foam, thermoplastics and wax. 3D printers, in contrast, work with a more limited number of materials, using primarily plastics, metals and polymers. They cannot work with metals with high melting points. In addition to accommodating many materials, CNC machines are also easy to adapt to use new materials. A 3D printer, on the other hand, can only work with one material.
  • Speed: Another key difference between CNC and additive manufacturing is the speed. When it comes to mass-producing a product, CNC machining is faster because it involves an assembly line of machines producing each part. A single 3D printer makes the entire product from start to finish, which makes it less suitable for large-scale production.
  • Production: CNC machining is more precise, providing accuracy to the nearest micrometer. That is because CNC machines have a higher tolerance for heat. 3D printing is still far from achieving this level of precision.
  • Repeatability: CNC machines can consistently produce a product the same way each time.
  • Quality: Because of its higher heat tolerance, CNC machines produce products with a more polished look. The materials don't get deformed during manufacturing. Parts made by 3D printers, however, tend to bend and warp, and layer lines can be visible, especially around curves. Although some 3D printers do promise a high degree of accuracy, they still manage to fail at times . Both manufacturing methods have geometric limitations. CNC, for instance, can produce very thin walls, but 3D printing has limitations in this regard, and the size of its end effector often determines its ability.

Key Decision Factors When Choosing a Manufacturing Type

As you are considering the pros and cons of CNC machining vs. 3D printing, you must weigh other factors, as well.

  • Complexity of component: 3D printing, because of its additive method of manufacturing, is often better for parts with complex geometries. It can only make components out of a single material, though, so making a part out of multiple materials would require using one 3D printer for each material.
  • Customization: 3D printers are also better at creating more customized, unique products. Artists will often use them to make a piece of art, and medical industries like dentistry take advantage of this technology to create a unique item that suits a particular patient .
  • Turnaround time: CNC is much faster than 3D printing, especially in larger-scale production. This is because it generally takes less time to create something by carving a away from a larger material than it does to create something from nothing. Other factors make 3D printers slower: When working, they often have to slow down to get it right. And once 3D printers are finished making a product, the job's still not done — you may have to wash or polish the component. The shape of the component can affect the speed of both manufacturing methods. The surface area of the component determines the speed at which CNC mills finish a product, whereas the total volume of the component is the key to how long 3D printing takes.
  • Accuracy: For CNC, you can increase the speed of production by sacrificing accuracy — which is good to take advantage of where time is short and you do not need a high level of precision, such as when testing prototypes. 3D printers, on the other hand, cannot increase their speed of production. The only way to do so is to buy a faster printer.
  • Flexibility: Although generally slower at producing a component, 3D printers are flexible and can quickly switch between jobs. So if you are making a small amount of several different items, 3D printing may be the better option.
  • Cost: The CNC vs. 3D printing cost often depends on the number of items you want. If you would like to make a large quantity of something, CNC is the better option because the per-unit cost decreases. For 3D printing, the per-unit cost is the same no matter how many you make, so it is usually more economical for small quantities. Even then, however, CNC machining can be more cost-effective with products involving metals. The price of CNC products increases as the product becomes more complex and requires a higher degree of precision. The price of 3D printed products remains the same, regardless of the complexity of the project.
  • cnc machining for mass production

  • Product volume: CNC fits with mass production, so it can produce a much higher output at a time. A CNC machine can produce hundreds of parts in the time it takes a 3D printer to make just one.
  • Material of component: CNC and 3D printers work with mostly different materials, so the materials you need will sometimes determine which technology you must use. CNC can work with a wider range of materials, including high-density metals, wood, wax and plastic. Because it can work with heavy metals, it is better suited for building components for engines, airplanes and other demanding environments that require parts to be particularly strong and heat-resistant. 3D printers work with fewer types of materials, such as specific plastics and resins, and these materials are usually not strong enough to serve as parts for engines or other machinery. 3D printers are better-suited for creating products for personal use at home.

Benefits of CNC Machining Over 3D Printing

3D printing is a younger technology, and although advancements will undoubtedly occur in the future, it is still relatively limited in the materials and benefits it offers. Here are some of the advantages of CNC machining.

  • Cost: CNC machining is more cost-effective at most quantities. While the per-unit cost stays the same with 3D printers, it becomes cheaper with CNC machining.
  • Speed: If you need your product faster and a high level of quality isn't necessary, CNC machines can work at faster speeds.
  • Variety: CNC can make a product with almost any material you desire — and in practically any size you'd like.
  • Strength: CNC machines can make parts strong enough for engines and airplanes.
  • Quality: They can make products of high quality and precision today's 3D printers cannot match.
  • Consistency: Due to their high degree of precision, they will make your part the same way every time.

Request a Quote for Your Part

Although CNC and 3D printing do meet different demands, American Micro Industries believes, in the vast majority of cases, CNC is the cheaper, faster and higher-quality method for manufacturing your parts. Check out the wide variety of materials we have available, and request a CNC machining quote for your part today.