3D printing vs CNC machining, which is the better manufacturing solution for you?

With the continuous development of market demand and 3D printing technology, the application fields of 3D printing technology is very wide, ranging from aerospace to automobile, medical treatment, education. The development of 3D printing technology has subverted our understanding of traditional manufacturing. Now, more and more people realize the great potential and advantages of 3D printing. For example, the quality and strength of 3D printed products are pretty good, 3D printing parts can be assembled on end products, and it enable mass production of goods on a large scale.

CNC machining is a matured prototyping and manufacturing way for decade years. CNC machining is liked by engineers all over the world. Because it’s one of the most accurate manufacturing technologies out there. In addition, CNC machining is very price-competitive for one-off custom parts and medium-volume production.

Compared with CNC machining, 3D printing is relatively new and potential manufacturing way. CNC manufacturing and 3D printing are basically opposites. CNC machining is a subtractive manufacturing process, while 3D printing is an additive manufacturing method. For a better understanding, we can metaphor 3D printing as making a statue out of clay, and CNC as making a statue out of marble.

Many engineers and product designers care about those questions.

 

3D printing vs CNC machining, which is more expensive?

What is the difference between 3D printing and CNC machining?

3D printing parts and CNC machining parts, which is stronger?

3D printing vs CNC machining, Which is the best solution?

3D printing parts vs CNC machining parts, which is more accurate?

Which is better CNC machining or 3D printing?

Is 3D printing cheaper than CNC machining?

Can 3D printing replace CNC machining?

 

In the debating regarding CNC machining and 3d printing, the key question is about, 3D printing vs CNC machining which manufacturing option is better. Here we discuss the comparison of CNC machining and 3D printing, mainly in prototyping and machining industry. 

  1. CNC machining Materials vs 3D printing materials

Both 3D printing and CNC machining are compatible with a wide variety of plastics and metal materials. CNC can also machine the acrylics, glass, modeling foams, hardwoods, and machining waxes. A key advantage of CNC machining is that it can be used for almost all solid engineering materials.

The plastic and metal materials used in CNC machining are mass-produced by big and well-known factories, so these materials have stable performance, guaranteed quality, and can be traced back to their origins. CNC machined plastic parts almost have the same quality and material properties as injection molded parts.Due to the perfect material performance, CNC machined parts has excellent mechanical and thermal properties. CNC machined metal parts is strong enough for high strength applications.

 

Common used CNC machining metal materials

Aluminum alloy series: AL2012, AL5052, AL5058, AL6061, AL6063, AL7075 etc

Stainless steel series: SS303, SS304, SS316, SS316L, SS420, SS430, SS-17-4OH, SS301, SS321 etc

Alloy steel series: Q235, (A3 steel), #40 steel, #45 steel, Cr12, 3Cr13, Gcr15, 40Cr, Spring steel-65Mn, Mold steel-SKD11.

Copper alloy series: Brass-H59, Brass-H62, Copper-T2, Oxygen-free copper TU2, Tin bronze-Qsn-6-6-3, Beryllium copper-C17200

Other metal alloy: Electrical pure iron-DT4C, electrician pure iron-DT4E, Titanium alloy, Magnesium alloy-AZ91D.

 

Common used CNC plastic materials

ABS, POM, PC, PMMA, PP, PPS, PU, PVC, HDPE, LDPE, PA6, PA66, PEEK, etc

 

Other common CNC materials

Carbon sheet, graphite, epoxy tooling board

The 3D printing materials

3D printing is mostly used on plastic materials and some metal materials. 3D printing technology is more common to used for plastic parts building. Some leading manufacturers are developing a better and more cost-effective metal printers to produce 3D printing metal parts. 3D printing technique can also produce parts from materials like ceramic, wax, sand, and composite materials.

3D printing materials are generally formed by powder or wire printing. As the molding conditions directly affect the mechanical properties, pressure resistance and material stability of the  products, the quality of 3D printed parts is inferior to CNC machined parts in all aspects. This is the reason why 3D printing parts with the worse material properties.

 

Common 3D printing materials

Common 3D printing materials
Plastic mateirals White resin, clear resin, light green resin, soft resin, heat-resistant gray resin, black resin

Black PA, white PA, 30GF gray PA, PA/ABS, ASA, ABS, PA+40% GF
Metal materials Aluminum alloy, stainless steel, titanium alloy, steel alloy

 

 

  1. Product Accuracy, Dimensional Constraints, and machine finish surface

CNC machining process can be applied to both small and extremely large parts. The inside corners of CNC machined parts is with inevitable fillet or radius, while the outside surface is sharp and smooth.

CNC machining provides superior surface quality and precise tolerance when compared with 3D printers. The tolerances, strength, and repeatability of CNC machining parts are excellent.  CNC milling machine can reach mechanical accuracy of one micrometer on every axis. This is a level of precision that a 3D printing equipment impossible to achieve.

3D printing can create parts with complex geometries that most traditional manufacturing method can not realize. Different 3D printing technique offers different dimensional accuracy. With the rapid development, more and more Industrial-grade 3D printer can produce parts with high precise demand. When a 3D printed part needs to with high accuracy that it can not reach, we can realize from secondary processing or post-processing.

The minimum wall thickness dimension of a 3D printed part is limited by the size of the end machine, for example the nozzle diameter of FDM machine, or laser spot size of SLS machine.

The surface of CNC parts is turned over and milled by high-speed tools and cutters at high temperature, so CNC machined parts is always produced with smooth surfaces. 3D printing parts is made one layer by one layer, the layer lines may be seen on surfaces of the parts. Compared to CNC, the clarity and surface quality of 3D printers are not so nice. In this term, 3D printing is more suitable to produce verification-purpose prototype or mechanical assembly parts without demands on outward appearance.

 

Tolerance Minimum wall thickness Maximum size
CNC Machning +/-0.01mm to +-/0.125mm 0.75mm CNC milling：2000*800*1000mm

CNC turning: 500mm
SLS +/-0.3mm 0.7-1.0mm 450*300*300mm
FDM +/-0.2mm 0.8-1.0mm industrial grade: 900*600*900mm

desktop: 200*200*200mm
SLM/DMLS +/-0.1mm 0.4mm 230*150*150mm
SLA +/-0.1mm 0.05-0.25mm 450*450*350mm

 

3.product structure

There are many constraints that must be considered when designing a CNC machining part. For example the CNC tool entry and clearance, the holding or mounting points, and the parts inner corners. Some geometries cannot be CNC machined even with a 5-axis CNC system, because the CNC tool cannot access all surfaces of the parts.

In order to machining and accessing the different sides of the geometries with complex structure, we need to rotating the whole part. Repositioning increases machining time, and may need some customized jigs and fixtures, so the final cost will be increased.

3D printing is to cut the model into N layers/N multi-points, and then pile them up layer by layer/bit by bit in sequence, just like building blocks. Therefore, 3D printing can effectively process parts with complex structures, such as hollow parts, while CNC machine is difficult to achieve the processing of hollow parts.

3D printing has few geometric limitations compared to CNC. Most 3D printing techniques (like FDM or SLM/DMLS), the support structure is required during production and will be removed during post-processing. Plastic free-form, organic geometries can be easily fabricated using polymer-based powder bed fusion processes such as SLS or MJF, as they do not require supports. Being able to generate highly complex geometries is one of the key advantages of 3D printing.

 

4.The manufacturing process of 3D printing and CNC machining

 

The workflow of 3D printing is very simple and easy. Firstlym the machine operator prepares the digital file (chooses orientation and adds supports), then sends it to the machine system. Then the 3D printer starts its work. The parts can be printed with little human intervention. After printing, the parts need to be cleaned and post-processed. However, it takes longer times to do the the post-processing after the part coming out from a 3D printer. The deburring, sharpening, and grinding work is required for a 3D printed parts

When a factory receive a CNC machining order, the production process is quite complicated.

CNC machining order is handled by Professionally trained engineers with rich production experience. Firstly, CNC machine programming according to the customer’s design, to pre-designing the working path of CNC tools and cutters. In CNC machining, an expert operator or engineer should consider the tool selection, spindle speed, cutting path and part repositioning at first. These factors can greatly affect the machining time and quality of the final part. Once the machining work is complete, the part is ready for use or post-processing.

 

From the production process point of view, the production process of 3D printing is more simple than CNC machining. 3D printer is easy to operate. Here listed the advantages of 3D printing in the manufacturing process.

  • l3D printing is able to process parts with complex structure and curved surfaces. 3D printing can also print special-shaped structures easily.
  • lThe printing process is a one-time forming process, the complete parts is coming out after removing the support.
  • lEven for complicated structured parts, fixture is not needed
  • l3D printing machine is smart. The built-in software can quickly calculate the printing time and required materials.
  • l3D printing machine is easy to use. Employees who operating 3D printing machines do not need to be trained.
  • lAs long as the size of the XYZ forming area is sufficient, multiple parts can be processed at one time.
  • lThe 3D printing machine automatically makes the parts without human intervention, and the parts are printed with almost no error rate.
  • lComplicated maintenance is not required, and the worktable can be easily cleaned after printing

 

5.The production time of 3D printing and CNC machining

 

The production time of a parts is depended by the complexity of the design and the selected material. The CNC machining fabrication speeds can be exceptionally fast. However the pre-programming process can also be time-consuming, especially for high-precision projects. The total time for CNC machining is at least 3-4 days for 1pcs or low quantity works.

3D printing has excellent production speed. This is the why 3D printing can be defined as a rapid prototyping method.3D printing works can be completed within few hours.

However, 3D printing is not the best choice for mass production. The total production time will be long for mass quantities. For simple structure parts, CNC machining process is also very fast. However, as we CNC machining can require an operator manually reposition fixture or parts during the build, so the machining time is longer.

 

6.Post Processing

The post-processing treatments are applied to CNC machined and 3D printed parts to enhance the functionality or aesthetics of the as-built part.

The most common post-processing techniques are listed below:

CNC machining Sandblasting, anodizing, spraying, electroplating, vacuum coating, blackening, carbonization, heat treatment
3D printing Sandblasting, grinding and polishing, micro-polishing, metal plating

 

7.Product Cost 

CNC machining

CNC machining needs to cut the whole piece of material to get the final product, so the utilization rate of CNC machining material is not high. CNC machining process is able to provides parts with higher dimensional accuracy and better mechanical properties. This often comes with higher costs, especially when the number of parts is low.

CNC machining requires professional programmers and operators. This adds extra time and money to the total cost of the finished product. 3D printing is preferable because the production cost is lower for making prototype and low volume quantity production.

 

3D printing

3D printing has a lower and faster entry cost than other technologies. The 3D printing machine comes with its own driver software to automatically calculate the printing time and consumables. 3D printing has extremely high material utilization due to its unique additive manufacturing.

Additive manufacturing is more advantageous for unique items of limited volume. The price of the 3D printed part is mainly determined by the weight of the part.

 

3DP vs CNC: Which is a manufacturing technology for your parts?

Both 3D printing and CNC have its own advantages and disadvantages. In most cases, there are both 3D printed and CNC machined parts in a project.

For most plastic parts, 3D printing is a better solution, especially for prototype or low volume sample quantity. When manufacturing for more than 20 items or 50 items, vacuum casting is a better solution. For mass production of plastic parts, injection molding will be a good choice.

For manufacturing metal parts, CNC has its undeniable superiority. CNC machining can produce much better dimensional accuracy. CNC can make large size, high precision metal parts. 3D printed metal parts is worse than CNC machined metal parts in product performance and surface finish.

When considering whether to choose 3D printing or CNC, you need to assess your project situation and specific requirements for the part.