Will 3D Printing Replace Machining?

3D printing has evolved beyond its nascent utility, which was mostly limited to prototyping. As 3D printing technologies improve further, they are becoming a practical alternative to machining. Hence, you might wonder if 3D printing can or will replace machining, such as CNC.

3D printing will probably not replace machining to the extent that it is deemed obsolete. Both 3D printing and CNC machining, such as milling and turning, have their strengths and weaknesses, including accuracy, cost, lead time, materials, and scale of production.

3D printing offers a few advantages that machining can’t deliver. Likewise, CNC machining can outmatch and outperform all desktop and industrial 3D printing technologies available right now. Read on to find out why 3D printing may not replace machining, with the two coexisting instead. 

3D Printing vs. Machining: Which Is Better?

You can theoretically compare additive 3D printing technologies with any subtractive machining process, including 5-axis CNC milling. However, such a comparison may not have sweeping practical implications owing to the limitations of both additive and subtractive manufacturing.

3D printing and machining both offer unique benefits and disadvantages. The better option depends on the product, production size, and materials used. 

Thus, the pragmatic approach is to assess the pros and cons of 3D printing vs. machining so that you can determine which is better for you, subject to your objectives and priorities. Let’s explore the pros and cons of each below: 

3D Printing Technologies Are More Automated Than CNC Machining

3D printing technologies require little to no intervention after a design is finalized, sliced, and fed into the machine. 

This applies to all types of 3D printing technologies, including but not limited to the following:

• Thermoplastics or filaments: FDM/FFF
• Photopolymers or resin: DLP, LCD, SLA
• CDLM: Continuous Digital Light Manufacturing 
• SLM: Selective Laser Melting
• SLS: Selective Laser Sintering
• DMLS: Direct Metal Laser Sintering

CNC machining also has extensive automation, but it requires some manual intervention during the manufacturing process, such as realigning, reorienting, or repositioning the blank. Plus, it is not necessary for anyone to monitor or supervise a 3D print in progress, unlike CNC machining.

Machining Typically Requires a Longer Lead Time Than 3D Printing

Both 3D printing and machining require designers, engineers, and manufacturers to provide operating instructions through software. However, this process is typically longer for machining.

3D printers can configure the required operating paths for the extruders, lasers, and other parts. CNC machining requires the operator to assess these details for the specific tools involved and make necessary changes for a given project before finalizing the whole process.

Thus, machining demands a longer lead time. That said, the turnaround time is only significantly less if you are 3D printing anything simple or small. Complicated designs may warrant a longer lead or prep time for 3D printers, too.

3D Printing Is Better for Prototypes and Smaller Production Sizes

Most 3D printers don’t have the build volume that machining can conveniently manage. This makes 3D printing better for prototypes and manufacturing smaller parts. The production scale is thus a lot smaller than machining.

Consider the standard capacities of machining. You can get a build volume or working space of 78.74 inches x 31.5 inches x 39.37 inches (2,000 mm x 800 mm x 1,000 mm) with CNC milling. CNC lathes can work on parts with a diameter of up to 20 inches (508 mm) and, at times, larger.

Here’s how the capacities and maximum build volumes of most 3D printers’ beds or plates compare:

• Desktop FDM and SLS: 11.81 inches x 11.81 inches x 11.81 inches (300 mm x 300 mm x 300 mm)
• Desktop SLA (large): 13.2 inches x 7.9 inches x 11.8 inches (335 mm x 200 mm x 300 mm)
• Industrial FDM or FFF: 35.43 inches x 23.62 inches x 35.43 inches (900 mm x 600 mm x 900 mm)
• SLM (multi-laser): 11.02 inches x 11.02 inches x 14.37 inches (280 mm x 280 mm x 365 mm)

Machining Delivers Better Accuracy or Tolerance Than 3D Printing

The accuracy or tolerance of 3D printing can range from as low as 100 microns (0.1 mm) to 500 microns (0.5 mm) or more, depending on the material and technology. CNC machining delivers exceptional accuracy or tolerance of as little as 5 microns (0.00508 mm).

Also, 3D printing can have layering issues, including poor finish and visible inaccuracies, which are more evident on curved parts and other finer details or elements of a design. Machining isn’t vulnerable to any such layering problems because it is a subtractive process, not additive.

3D Printing Is Suitable for Complex Geometries; CNC Machining Isn’t

CNC machining isn’t ideal for complex geometries because the tools can’t reach certain parts of a blank. 3D printing builds one layer at a time, irrespective of height or thickness. So, almost all 3D printing technologies are more suitable for complex geometries than CNC machining.

The starkest difference is evident when you consider topology optimization. If you combine any complex geometry with topology optimization for a specific component or product, machining is unlikely to deliver. You might even struggle to begin chalking out the path of the tools with CNC.

CNC Machining Offers Better Mechanical Properties Than 3D Printing

3D printing doesn’t enable any material to attain its full or optimum isotropic properties. Since an additive process is, by default, a directional manufacturing technique, the isotropic properties will not be identical to those of the same type of material if it is machined.

Plus, the mechanical and physical characteristics of parts manufactured through machining are significantly more reliable and stronger than the attributes of 3D-printed components. This issue continues to be the most significant factor for functional components, especially due to safety.

3D Printing Is Financially More Viable Than Machining on a Small Scale

CNC machining requires a greater investment for the setup. Machining also uses more material than 3D printing, leading to wastage. Much of the material wasted in 3D printing is recycled and repurposed, which is not necessarily the case with machining.

Additionally, the manufacturing cost per unit is less with 3D printing due to a shorter lead time and faster process. However, machining becomes more viable financially on a medium to large scale. Besides, machining has more predictable repeatability with the same accuracy than 3D printing. 

CNC Machining Isn’t Ideal or Suitable for Some Materials and Superalloys

Machining wastes more material than 3D printing, so it isn’t ideal if you are working with a costly blank. Also, CNC machining isn’t suitable for superalloys, unlike 3D printing. And some flexible materials may be easier to work with in 3D printers than in CNC machining.

Conclusion

While there are workarounds for machining superalloys, 3D printing is still evolving to work as flawlessly as desired with the ever-growing list of materials. Considering all the pros and cons, 3D printing and machining will coexist and complement one another for the foreseeable future.