CNC machining or 3D printing: Which is the better manufacturing process? The answer is simple: “It depends!”
Many workshops rely on CNC machining as the backbone of their production processes. However, with the rise of additive manufacturing, more and more companies are considering integrating 3D printing into their workflows, or even replacing their CNC machines. Let’s outline what 3D printing can do for you and how to best integrate these two processes.
Overview of CNC Machining or Subtractive Manufacturing:
CNC machining uses computerized tools to produce the desired objects by removing excess material from a blank. It remains the most cost-effective process for manufacturing large to medium-sized parts. As a well-established method, CNC machines are used in workshops worldwide and have a comprehensive understanding of the entire process chain. It is versatile in terms of the materials that can be machined, the geometries that can be produced, and the surface quality and tolerances that can be achieved. Therefore, in many cases, CNC machining is still the preferred method.
However, CNC machining is still a highly specialized process, especially when geometries are more complex or involve challenging materials. CNC machining also requires highly skilled designers and programmers, leading to high labor costs. Specialized clamping tools are often required, which must also be designed and manufactured. This increases part costs, especially for lower quantities. Additionally, since CNC machining starts with a block of material, material costs are always higher, and there is more waste.
Overview of 3D Printing or Additive Manufacturing:
While various 3D printing methods have proven to be viable manufacturing processes, it is still not as widespread as traditional machining.
However, FFF (Fused Filament Fabrication) is gaining popularity across various industrial sectors for producing small to medium batches of final-use parts or prototypes. Plastic is melted and then extruded through a nozzle, layer by layer, to build up the part.
Only the amount of material needed to constitute the final component is used, so there is virtually no waste. Objects are printed directly onto the flat plane of the print bed, eliminating the need for fixtures. Setting up a BigRep printer and starting a print job requires only minimal specific knowledge. The printing process itself does not impose any limitations on part design; almost any geometry can be printed. This helps to overcome established ways of thinking in design and development.
Riley Gillman, Technical Operations Manager at Nikola Motor Company, says, “You can really challenge engineering and manufacturing processes!”
Due to the layer-based process, surface quality cannot match that of milled parts, and post-processing may be necessary to some extent. Although increasingly tighter tolerances can be achieved with 3D printing, they typically cannot match the common values of milled parts. The choice of materials is also limited; FFF only allows the use of melt-able plastics.
How to Best Utilize Large-Scale 3D Printing?
Manual Fixtures and Production Tools:
A handheld tool used in the automotive assembly process demonstrates a typical application. A part over 120 centimeters long was initially planned to be milled from a block of aluminum. However, the total cost, including machine, personnel, and material costs, was around 10,000 euros, with an estimated completion time of two weeks. A manufacturer in China quoted $5,800 with a similar delivery time. Ultimately, the decision was made to 3D print the part on the BigRep PRO using BigRep HI-TEMP CF, taking 32 hours. The cost was approximately $790, saving 86%! A popular side effect for users handling the part is a weight reduction of about 50% compared to the aluminum version. Overall, this is a highly successful use case.
End-Use Parts with 3D Printing:
Boyce Technologies utilizes 3D printing to produce end-use parts in their 5G information kiosks manufactured for Verizon. Due to the unique shapes of these ducts, milling would take a long time and require extensive setup and post-processing. By 3D printing the parts, not only is time and material cost saved, but also the number of staff needed for support preparation and post-processing. Another benefit of using large-format additive manufacturing is the ability to print many parts simultaneously, optimizing the build volume of the printer.
How to Combine 3D Printing and CNC Machining?
By integrating additive manufacturing with other manufacturing processes, the advantages of additive manufacturing can be further enhanced. 3D printed objects can be reinforced with metal parts in high-stress areas; brass inserts can be inserted into plastic parts. Printed parts can also be machined to achieve dimensions with critical tolerances or desired surface quality, and threads can even be milled. Fixtures, clamping devices, and positioning tools made through 3D printing assist in working alongside CNC machines. By intelligently combining 3D printing and CNC machining, users can benefit from the advantages of both processes.
A perfect example illustrating how 3D printers can assist in designing and manufacturing simple fixtures (such as positioning or assembly tools) is shown below. In this application, Nikola’s Gillman’s task was to find a way to securely fix an aluminum part in place for CMM inspection. Due to highly specific geometric requirements, the aluminum part itself could not be produced through 3D printing and had to be milled on a CNC machine.
However, manufacturing a fixture with aluminum required open space on CNC machines and a large amount of raw material. Therefore, Gillman decided to use his BigRep PRO to make it. From conception to part, it took only a few hours, with material costs of less than $20!
In recent years, Nikola Motor Company has experienced exacerbated material shortages due to decreasing availability from external suppliers. Here, 3D printers offer flexibility and independence.
Riley Gillman sums up the reasons for using his 3D printer: “We often produce large parts under very challenging time constraints. The geometry of the parts plays a big role; some parts are too complex to be manufactured using traditional methods. Sometimes we simply don’t have the budget for any other process outside of 3D printing!”
How Can You Benefit from Additive Manufacturing?
3D printing is most commonly used when large parts are needed in a short amount of time or when multiple iterations of a single part are required. 3D printing allows you to make changes to 3D models quickly and easily and then manufacture them internally, greatly reducing delivery times. The availability of functional prototypes is much faster, and you have a better understanding of the appearance of the final product.
Is 3D Printing Beneficial for You?
Understanding the costs behind 3D printing and the return on investment is essential for a company. Here’s a simple example: if you pay about $5,000 per part using a 3D printing service, and you need four similar-sized parts every month, you’ll spend about $20,000 per month! When you start comparing this to the cost of purchasing a printer, it becomes clear that buying a printer is a worthwhile investment.
Which Process is Best for You?
After considering all these factors, the answer is “it depends!” is easier to understand. The first step should always be to determine which technology is best suited for your part and its intended use. Both technologies have their advantages and applications, so 3D printing will not completely replace CNC machining.
If your goal is to combine these two processes to complement each other, then purchasing a 3D printer will bring you many benefits, including:
Increased flexibility and independence
Time and cost savings
Expanding the manufacturing portfolio
Improving internal processes
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