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What's the Best for Injection Molding Prototyping 3D Printing or CNC Machining?

Rapid prototyping is an important aspect of any design project. When you need to make a quick, cheap and easy prototype production for a new product or invention.

Through rapid prototyping can quickly make the function or appearance of the product similar to real injection molded parts, and test all aspects of demand before produce molds, so that you can effectively avoid some potential problems, to avoid injection mold done because of the potential problems not considered in the early injection mold change, reduce tooling costs and the development time.

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There are two manufacturing methods to do it

3D printing and CNC machining are both used heavily in the manufacturing industry today, and for good reason. While the two have different rapid prototyping processes. 3D printing and CNC (Computer Numerical Control) machining. Both have their pros and cons, It’s decision time: which manufacturing methods is best for your project? The choice really depends on what you’re making, how much it will cost, and how fast you need it. For that reason it’s good to be familiar with the differences between these two processes so you know which one would work best for your project.

In this article we will discuss everything you need to know about these two methods so that you can choose the right one for your next project before production mold!

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CNC (Computer Numerical Control) machining

CNC machining is a common subtractive manufacturing technology. CNC machining(subtractive manufacturing) begins with a solid block of material (blank) and removes material to achieve the required final shape.

The most common CNC machines processes are cnc milling and turning. CNC offers excellent repeatability, high accuracy and a wide range of materials and surface finish.

3D Printing

Additive Manufacturing (AM) or 3D Printing processes build parts by adding material one layer at a time.

3D Printing can produce parts that are not as durable or accurate as parts made with CNC machining, due to the lack of surface finish and low tolerances.

CNC Machining vs 3D Printing: Subtractive vs Additive

The key difference between 3D printing and CNC machining is that 3D printing is a form of additive manufacturing processes, whilst CNC machining is subtractive process. 

Additive manufacturing process means that material is added together to create a product, 3D printing, or additive manufacturing process, involves 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 cutting or heated extruder, layers of these materials are solidified to form the finished part.

Advantages of 3D printing include its freedom of shape, applications in many sectors, accuracy, speed, and ability to cut costs and weight in parts.


whereas subtractive manufacturing process means that material is removed to create a product.This means CNC machining starts with a block of material (called a blank), and cuts away material to create the finished part. To do this, cutting tool and spinning tool are used to shape the piece.

Some advantages of CNC machining include great dimensional accuracy as well as many compatible materials, including wood, metals and, plastics.

Figure 2

CNC Machining vs 3D Printing: Mass Production vs Rapid Prototyping

For large scale production CNC is likely to be more appropriate. For low volumes, 3D printing is more appropriate and cost effective.

CNC offers excellent repeatability, high accuracy and a wide range of materials and surface finishes. It can also be used for high volume production manufacture of metal castings, intricate plastic injection molding, and other small- to medium-sized manufactured parts. CNC mills can produce complicated profiles that are hard to create with other methods.

3D printing is also more appropriate if you need your prototypes or parts very quickly. 3D printing can produce parts for small volumes that are not as durable or accurate as parts made with CNC machining, due to the lack of surface finishes and low tolerances.

The Price CNC Machining Vs 3D Printing

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CNC Machining vs 3D Printing: Expensive vs Inexpensive

When it comes to cost 3D printers are generally the better option. This is due to the 3D printer material being cheaper than the material used for CNC machines.

3D printer material is usually sold on a spindle whereas the material used in a CNC machine is a large slab of the material. Also, the additive manufacturing process 3D printers use is more conservative than the subtractive process used in CNC machines. Subtractive manufacturing often has material left over afterwards, and sometimes that material can’t be reused. Additive manufacturing on the other hand only uses the exact amount of material needed.

CNC Machining is expensive because it requires a machine tool that can be costly for a hobbyist. It also takes up a lot of space because the milling machine need to be fairly large to accommodate your project. Also CNC machines require a skilled operator to watch over. While a lot of machining can be done on its own, CNC machines have different properties such as choosing the cutting path and rotation speeds of tools that only a trained operator would know how to setup. .

Another con is that CNC machining produces acoustic noise. This will make it difficult to work in an office setting with other people around. Finally, this method may take longer because you would have to wait for the machine to produce each layer of the object sequentially. while 3D printing is cost effective,not only the cheap materials but also it’s easy to use and doesn’t take up a lot of space.

CNC Machining vs 3D Printing: Heavy Material vs Light Material

CNC Machining is typically better for greater material needs. 3D printing is often the more affordable option when there are lighter material needs.

The CNC router is relied upon by the aerospace, automotive, and other industrial segments because CNC machining has the ability to manufacture heavy material with high precision.

The 3D printer has substantial limitations in creating multi-material parts and cannot layer denser materials. For the 3D printer, the additive layering process is fickle and underdeveloped making it complex for a single material product.

It is nearly impossible to produce an item that requires more than one material type with 3D printing construction. While 3D printing has moderate prototyping functionality with plastic, it has yet to show any capacity for denser metals or heavier materials.

The CNC router has heat management systems and a powerful servo mechanism equipped to deal with heavy, dense materials that the 3D printer cannot handle.

Figure 4

CNC Machining vs 3D Printing: Quality vs Hand Finishing

Though there are a number of 3D printing technologies, we have chosen to compare CNC machining with SLS, industrial (not desktop) FDM, and DMLS metal 3D printing. In terms of tight tolerances, CNC machining is superior to all 3D printing manufacturing processes.

However, if you need something that’s reliable and fully functional, CNC machining is the better option. This process will allow you to produce quality prototypes with consistent finishing perfect for mass production. For the industries that the CNC router serves, one of the most important differences between these two machine types is their quality and tolerance sensitivities.

While 3D printers are breaking into smaller markets with custom items, the products still require post processing some form of hand finishing the support structures after production. This makes 3D printers less efficient than CNC machines. The refinement element is missing in 3D print production along with the tolerance for creating very specific and accurate products.

Highly-detailed products that require a very high tolerance for accuracy is the expertise of a specialized CNC router. While there are some similarities between the 3D printer and CNC router, they will serve different purposes in their processes, production capacities, material loads, product sizes, post processing and refinement abilities.

CNC Machining vs 3D Printing: Large Products vs Small Products

The size and shape of the prototype or part determines a lot of times whether a 3D printer or CNC machine is used. Larger parts are generally made with a CNC machine while smaller prototype are 3D printed. 

There are a few exceptions. One major advantage of 3D printers is the freedom to make just about any shape. Therefore, parts with high geometric complexity are usually 3D printed, as CNC machine have trouble with these, due to the subtractive manufacturing

CNC machining is better for larger plastic parts, whereas 3D printing is more appropriate for smaller products. Larger products require more material, and CNC machining is better suited for this because it can cut away material to create the finished part. 3D printing is not as accurate or durable as CNC machining, so it is not suitable for larger plastic parts.

The 3D printer, at this time, cannot create any product bigger than a mini fridge and something of that size can take the 3D printer a few days to complete. The layering process is not meant for the creation of large products. This is a huge advantage for CNC routers.

The 3D printer primarily succeeds on the layering of smaller simpler designs. The CNC router is a powerhouse industrial tool that has the capacity to produce the largest of parts such as those needed for aviation, nautical, construction, and automotive.

Figure 5

Figure 6

CNC Machining vs 3D Printing: Plate Material vs Reform Material

CNC machines don’t heat material and reform it. The material remains stronger and with better structural integrity than most 3D printers.

CNC machines’ simple prototype creation process also provides the a better surface finish than some 3D printers because materials don’t deform during the process. Their rigid material and cutting action keeps the form together, allowing for fewer chances for mistakes and deformations to occur. Aging 3D printers models may have a poorer surface finish because of their layered heated plastic and need some post processing techniques.

But professional 3D printers manufacturing workflow eliminate the issue of warping, bending and distortion from the prototype process.

Both 3D printing and CNC machining are compatible with materials varying, including both plastics and metals. 3D printing however is more focused on plastics overall, though this is changing rapidly as better and more affordable ways of 3D printing metal are being developed by manufacturers such as 3D Systems, Arcam, Desktop Metal and Markforged.

The most commonly used plastics used in CNC include ABS, Nylon (PA66), Polycarbonate (PC), Acrylic (PMMA), Polypropylene (PP), POM and PEEK. A very commonly used metal alloys in CNC machining is aluminium, used by prototyping companies to create high-quality prototypes in a variety of industries. Aluminium is recyclable, has good protective qualities, and can create effective prototypes for machining. Other commonly used metal parts include stainless steel, magnesium alloy, zinc alloy titanium, and brass.

In 3D printing, commonly used thermoplastics include ABS, PLA, Nylon, ULTEM, but also photo-polymers such as wax, calcinable or biocompatible resins. Some niche 3D printers also allow for the printing of parts in sand, ceramics, and even living materials. The most common metal alloys used in 3D printing include aluminium, stainless steel, titanium, and inconel. It is also worth noting that to 3D print metal, expensive industrial machines are required. Some materials such as superalloys or TPU (flexible material) cannot be created with CNC, so must be used with 3D printing or rapid tooling technology.

CNC Machining Vs 3D Printing

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What's the Best for Prototyping?

When choosing between CNC Manufacturing and Additive Manufacturing (AM), there are a few simple guidelines that can be applied to the decision about cnc vs 3d printing for prototyping.

3D Printing Advantages:

  1. Highly complex, topology-optimized geometries.
  2. Easy to use: easy to prepare for an operation.

  3. Part complexity does not affect the price of the part.

  4. Flexibility to quickly change production jobs.
  5. Lower cost and for small volumes
  6. Materials are required that cannot be easily machined, like metal superalloys or flexible TPU.
  7. CNC machining produces less noise than 3D printing, making it better for use in an office setting

CNC Machining Advantages:

  1. A broad selection of materials to use for production process.
  2. Freedom to choose the resolution of production parts in exchange for speed or production costs benefits.
  3. Superior quality surfaces and high precision.
  4. CNC machining is better for larger plastic parts.
  5. For larger quantities CNC is likely to be more appropriate.
  6. CNC machining can create parts with better structural integrity than many 3D printers

In many areas, CNC technologies/subtractive manufacturing and 3D Printing/additive manufacturing overlap in capability, but their individual strengths make them suitable for specialized applications. CNC Machining is the best method for large-scale, sophisticated, high-precision plastic parts made from readily available materials. 3D printing is the go-to method for custom-designed, small scale projects requiring multiple prototypes to ensure plastic part integrity and don‘t need skilled operator.

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