Is CNC machining or 3D printing the better manufacturing process? The answer is simple: “It depends!”
Many cnc machining brand shops rely on CNC machining as the backbone of their production process. However, with the rise of additive manufacturing, more and more companies are considering incorporating 3D printing into their workflow, or even replacing their CNC machines. Let’s give an overview of what 3D printing can do for you, and how to best combine the two processes.
Overview of CNC Machining or Subtractive Manufacturing
CNC machining uses computerized machine tools to produce the desired object by removing excess material from a blank. It remains the most cost-effective process for manufacturing large and medium-sized parts. As a tried and tested method, CNC machines are used in workshops all over the world and have extensive knowledge of the entire process chain. It is versatile in terms of machinable materials, producible geometries, and achievable surface qualities and tolerances. Therefore, CNC machining is still the preferred method in many cases.
However, CNC machining remains a highly specialized process, especially when geometries have greater complexity or involve challenging materials. CNC machining also requires highly skilled designers and programmers, resulting in high personnel costs. Often special clamping tools are required, which also have to be designed and manufactured. This increases part cost, especially if the part count is low. Also, since you start with a single piece of material when CNC machining a part, there will always be more material cost and more waste.
3D Printing or Additive Manufacturing Overview
Although various 3D printing methods have proven to be a viable manufacturing process, it is still not as common as traditional machining. But FFF (Fused Filament Fabrication) is gaining popularity in various branches of industry for the production of small to medium batches of end-use parts or prototypes. The plastic is melted and extruded through a nozzle, and the parts are built up layer by layer. Apart from the supporting structure, only the amount of material that makes up the final part is used, so hardly any waste is generated. Objects are printed directly on the flat surface of the print bed, so no fixtures are required. All it takes is a little specific knowledge to set up a BigRep printer and start printing. The printing process itself does not limit the part design in any way; virtually any geometry can be printed. This helps to overcome established ways of thinking in design and development. “You can really challenge the engineering process and the manufacturing process!” says Riley Gillman, Technical Operations Manager, Nikola Motor Company.
Due to the layer-based process, the surface quality cannot match that of milled parts and may require some degree of post-processing. Although it is possible to print more and more parts with very narrow tolerances, it is often not possible to match the common values of milled parts. The choice of materials is also limited; FFF only allows the use of meltable plastics.
How to best use large 3D printers?
This handheld tool used in the automotive assembly process demonstrates a typical application. Parts longer than 120 cm were initially planned to be milled from a single block of aluminum. However, the total cost including machinery, personnel and material costs was approximately 10.000 Euros and the estimated completion time was approximately two weeks. A Chinese manufacturer quoted $5.800 with a similar delivery time. In the end, it was decided to print the part with BigRep HI-TEMP CF on the BigRep PRO, which took 32 hours. Cost about $790, an 86% savings! A welcome side effect for users dealing with the part is a weight reduction of around 50% compared to the aluminum version. All things considered, this is a very successful use case.
3D printed end-use parts
Boyce Technologies used 3D printing to produce end-use parts in a 5G kiosk they built for Verizon. Due to the special shape of these ducts, milling would have taken a long time and required a lot of preparation time and post-processing. By 3D printing parts, you save not only time and material costs, but also the number of staff required to support preparation and post-processing. Another benefit of using large-format additive manufacturing is that many parts can be printed simultaneously, making optimal use of the printer’s build volume.
How to combine 3D printing and CNC machining?
The advantages of additive manufacturing can be further increased by combining additive manufacturing with other manufacturing processes. 3D printed objects can be reinforced with metal parts where the load is high; insert nuts made of brass can be inserted into plastic parts. Printed parts can also be machined to obtain dimensions with critical tolerances or desired surface quality, even milling threads. 3D printed jigs and fixtures as well as clamping and positioning tools help work with CNC machines. By intelligently combining 3D printing and CNC machining, users can benefit from the advantages of both processes.
A perfect example of how 3D printers can also be helpful when designing and manufacturing simple fixtures such as positioning or assembly tools is shown below. In this application, Nikola’s Gillman was tasked with finding a way to securely hold aluminum parts in place for CMM inspection. Due to very specific geometrical requirements, the aluminum part itself cannot be produced by 3D printing and must therefore be milled on a CNC machine. But making a jig out of aluminum requires open space on a CNC machine and a lot of raw material. So Gilman decided to use his BigRep PRO to make it. From idea to parts in just a few hours and less than $20 in materials!
Over the past few years, Nikola Motor Company has experienced exacerbated material shortages due to declining availability from outside suppliers. Here, 3D printers provide flexibility and independence.
Riley Gillman sums up the reasons for using his 3D printers: “We often produce large parts under very challenging time constraints. Part geometry plays a big role; some parts are too complex to be manufactured using traditional methods. Sometimes we simply don’t have the budget to use anything other than 3D printing!”
How to Profit from Additive Manufacturing?
3D printing is most commonly used when large parts are required in a short period of time or when multiple iterations of a single part are required. 3D printing enables you to quickly and easily alter 3D models and then manufacture them in-house, drastically reducing lead times. Functional prototypes are available much faster and you have a better idea of what the final product will look like.
Is 3D printing good for you?
It is important for companies to understand the costs behind 3D printers and the return on investment. Here’s a simple example: if you pay about $5.000 per part with a 3D printing service, and you need 4 similarly sized parts per month, you’ll be spending about $20.000 per month! When you start comparing this to the cost of buying a printer, it becomes clear that buying a printer is a worthwhile investment.
Which process is best for you?
After all these considerations, the answer “it depends!” is easier to understand. The first step should always be to determine which technology is best for your part and its intended use. Both processes have their own advantages and applications, so 3D printing will not completely replace CNC machining.
If your goal is to combine these two processes so that they complement each other, purchasing a 3D printer will bring you many benefits, including:
- Increase flexibility and independence
- save time and cost
- Expand Manufacturing Portfolio
- Improve internal processes