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CNC machining vs. 3D printing

Which works best for medical device manufacturing?

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October 19, 2021

CNC machining and 3D printing technologies are in significant demand for medical device manufacturing. These solutions have made it possible to produce even smaller, more complex medical components with great accuracy. Owing to the extensive perks of both technologies, many manufacturers wonder which of the two might be the better option.

3D printing and CNC machining - The fundamental difference
The primary difference between these two techniques is that 3D printing is an additive manufacturing technique, while CNC machining is a subtractive manufacturing type. 3D printers produce products by fusing layer after layer of material over each other, while CNC machinery cuts out desired parts from a bigger whole of material, such as a horizontal milling machine

Physical considerations
Geometry

  • Feature size: For CNC, the tool diameter determines the smallest negative feature that can be manufactured. For 3D printing, the nozzle diameter determines the smallest positive feature feasible in terms of production. 
  • Surface finish: CNC machines can produce more smooth surfaces than 3D printers. 3D printers are suitable for creating parts for fit and finish.
  • Tolerances: High-quality composite 3D printers can keep dimensional tolerances down to +/- 0.005”. Besides, they also feature a compliant surface for press-fitting over CNC machines.
  • Loading: Non-structural components are easier targets for conventional 3D printing, but structural parts that must withstand enormous physical loads can be produced by CNC machining. 

Environment

  • Temperature: Both 3D printing and CNC machining can produce parts in metals and polymers, so the final decision revolves around which approach is more readily feasible for shaping the material you require. 
  • Moisture: Some polymer filaments absorb moisture, leading them to lose strength through submersion or prolonged exposure. Moisture rarely affects aluminum but might cause rusting on steel.
  • Chemicals: If your component is subjected to chemicals, check your material's chemical compatibility against different chemicals. While most metals are suited for usage with several chemicals, you must check for compatibility before subjecting them to a new environment.

Pros and cons
3D printing
The technology of 3D printing is witnessing rapid evolution. It uses a digital 3D model to produce objects by infusing several layers of materials together.

It is a type of additive manufacturing, implying that this technology creates 3D objects one layer at a time, with successive layers bonding to the molten material of the preceding layers.

The high precision levels are made possible via computer-aided-design (CAD) software which helps deconstruct objects into thin layers. CAD software creates detailed .stl files that drive a high-precision laser to melt materials under those layers, which combine to create a 3D object. 

Pros:

  1. 3D printing is exceptionally flexible, which allows manufacturers to make alterations conveniently without setting up extra equipment.
  2. 3D printing offers high accuracy levels that enable manufacturers to produce customized medical equipment with complex internal structures. 
  3. Offers extensive customization options for the intricate details when manufacturing sensitive medical equipment. 

Cons:

  1. 3D printing has a slower pace of manufacturing compared to CNC machining, as the material layers take time to melt and solidify. This situation makes it non-ideal for extensive-scale production.
  2. Inferior mechanical strength of the component compared to the CNC manufactured part because their layers cannot maintain a firm bond.
  3. 3D printing is limited in terms of material choice compared to CNC machining. The most common materials used are plastics over metals and specialty materials. 

CNC machining
CNC machining is a subtractive manufacturing technique that cuts out desired parts from a gigantic mass of material. Several CNC solutions are available for different components, such as Swiss machining, wire EDM, and CNC laser welding.

CNC machining produced parts exhibit extreme strength and toughness alongside accuracy in dimensions. This perk makes them an ideal choice for medical devices and several other commodities. 

Using 2D or 3D models in CAD software lets manufacturers feed precise cutting instructions to CNC machines, which further employ blades, lasers, or rotating tools to deliver the desired shape to the material blocks.

CNC machines offer customizations in terms of several axes. They use servo motors to render accurate movement throughout the cutting operation

Pros:

  1. CNC machining can produce entire medical device parts with no further processing.
  2. It delivers fast cycle times, flexibility, efficient workflows, and exceptional precision levels.
  3. CNC machining is compatible with an extensive range of metals, plastics, and other specialized materials. This perk makes it ideal for manufacturing different forms of medical equipment. 

Cons:

  1. CNC machining is more labor-intensive relative to 3D printing.
  2. It requires skilled operators to pick the correct cutting tools, cutting paths, and rotation speeds, which helps build an accurate end product.
  3. Since CNC machining cuts objects from bigger chunks of material, it produces more waste than 3D printing or any other alternative. 

Scope of 3D printers replacing CNC machining
The modern 3D printing solutions are incompatible with hard steel and other materials and thus cannot deliver the desired efficiency and mechanical strength required for large-scale production. This critical factor renders 3D printers incompetent at replacing CNC machining in the future. 

Final words
Settling the debate between 3D printing and CNC machining is not straightforward, with each offering different perks and cons. Depending on the use case, manufacturers can pick a suitable approach. 

CNC machining is a cost-effective mass production approach, while 3D printing offers high accuracy levels and seamless customizations. 3D printing has a slower manufacturing pace, while CNC machining produces significantly more waste.