How can CNC Machining be used on 3D Printed Parts?
3D printing and computer numerical control (CNC) machining are two of the most disruptive manufacturing technologies to emerge in recent decades. Both technologies allow for the creation of highly complex and customizable parts with accuracy and repeatability. However, each technology has its own strengths and limitations. Used together in a complementary fashion, 3D printing, and CNC machining provide unparalleled design flexibility and enable the production of parts that would be impossible or impractical to make using either technology alone.
In this blog post, we will explore how CNC machining can be applied to 3D-printed parts to improve design features, accuracy, strength, and aesthetics. We will also discuss the benefits of combining these technologies and review example applications in various industries. As 3D printing and CNC machining continue advancing, their synergy will shape the future of manufacturing.
Overview of 3D Printing and CNC Machining
First, let’s briefly review how 3D printing and CNC machining work.
3D Printing
3D printing, also known as additive manufacturing, creates objects by depositing materials layer-by-layer based on a digital 3D model. The technology can use various materials including plastics, metals, ceramics, and even living cells. Common 3D printing processes include fused deposition modeling (FDM), stereolithography (SLA), selective laser sintering (SLS), and binder jetting.
3D printing enables complex geometries and customization without the need for retooling. Parts can be optimized for lightweight construction and consolidated assemblies. Rapid prototyping is streamlined and mass customization is achievable. However, 3D printing faces challenges in surface finish, precision, speed, and material options. Parts may require post-processing and have anisotropic properties depending on print orientation.
CNC Machining
CNC machining is a subtractive manufacturing process where computer numerically controlled tools remove material from a stock workpiece based on a programmed design. Common CNC processes include milling, turning, drilling, and grinding. CNC machining is extremely precise with tight tolerances down to microns and excellent surface finishes. It works with metals, plastics, wood, foams, and waxes. Setup is required but rapid production of identical parts is possible. However, CNC machining has more geometrical limitations and extensive tooling/fixturing requirements.
Complementary Strengths and Weaknesses
When we examine the strengths and weaknesses of each technology, we can see how they complement each other. 3D printing offers unmatched geometric freedom but lacks precision and surface finish. CNC machining provides precision and repeatability but requires geometrical compromises. Using both technologies in combination allows designers to gain benefits that would not be possible using either technology alone.
3D Printing to Enable Complex Geometries
One of the greatest strengths of 3D printing is the ability to economically produce complex and customized parts with intricate details and shapes that would be impossible through subtractive methods. 3D printing eliminates the constraints around undercuts, enclosed voids, and organic geometries. Parts can be consolidated into a single component.
Take for example a lattice structure designed to be lightweight yet retain high stiffness. The intricate lattice can only be manufactured as one single piece using 3D printing. CNC machining would require the lattice to be divided into simpler sub-components and assembled, which adds time and mass. 3D printing can create optimized shapes not possible through machining.
Likewise, consider a part with complex internal channels for fluid flow. The channels’ organic shapes and overhanging geometry could not be created through drilling or other subtractive processes but can be 3D printed without issue. 3D printing enables designs unrestricted by CNC machining limitations.
CNC Machining for Precision and Surface Finish
While 3D printing enables complex geometries, CNC machining brings precision and repeatable accuracy. Machining tight tolerances down to 0.001 mm or less. The process can also create smooth surface finishes far superior to the layer lines left by 3D printing.
Post-processing 3D printed parts with CNC machining is an excellent way to enhance precision and finish. Machining can accurately size parts to hit engineering tolerances. Printing a slightly oversized version first provides machining stock to arrive at the final dimensions. The superior finish from machining also improves aesthetics and can reduce friction or corrosion.
Machining extremely precise features into a 3D printed part, like bores, slots, threads, and chamfers, is very challenging for additive processes alone but readily achieved with CNC. Machining delivers reliable accuracy and repeatability part-to-part. This pairing combines 3D printing’s geometric freedom with CNC’s precision.
Improved Material Properties
In some situations, CNC machining can also improve the strength, structure, and material properties of 3D-printed parts. While 3D printing techniques continue advancing, layer-wise construction can still result in anisotropic behavior where mechanical properties vary based on print direction.
Machining can remove the weaker layered exterior to reveal a stronger core material. The process can also relieve internal stresses. Finishing methods like annealing, shot peening, and vibratory tumbling after machining further enhance material properties. The combined approach produces a part with superior and more uniform properties.
Hybrid Manufacturing Systems
To fully realize the combined potential of these two technologies, engineers have developed hybrid manufacturing platforms that integrate 3D printing and CNC machining capabilities into a single system. This provides seamless automated transitions between additive and subtractive processes without part removal.
One example is hybrid CNC systems with print heads mounted directly on the machining center, allowing the deposition of thermoplastics. Parts can be printed, precision machined, and have more material added. This interoperability between 3D printing and machining expands potential geometries and enables consolidated, complex components.
Likewise, some metal 3D printers have also incorporated CNC milling capabilities for finishing processes like surfacing and drilling. The hybrids aim to capitalize on the strengths of each technology in an automated fashion. More turnkey hybrid systems are emerging to bring this synergistic approach to various industries.
Application Examples Across Industries
The complementary use of 3D printing and CNC machining is proving advantageous across diverse industries. Here are some examples.
Aerospace and Defense
Aerospace companies use 3D printing to produce lightweight and optimized components like hydraulic manifolds, brackets, and complex geometries like engine parts. CNC machining then provides precise dimensional accuracy and necessary tolerances. Machining creates smooth finishes to reduce drag. Adding machined threads, holes, and fasteners installs the printed parts.
Medical and Dental
3D printing enables customized prosthetics, implants, and anatomical models tailored to individual patients with control over geometry and materials. CNC machining then provides essential precision on the interfaces and contact surfaces to ensure proper fit and function. Machining also forms higher-tolerance features for assembly and delivers smoother surfaces for aesthetics and comfort.
Automotive
Automakers can 3D print design prototypes, customized components, tooling, and end-use parts. CNC machining then provides dimensional accuracy for fitting assemblies like dashboards and rigorous surface finishing on visible parts. Machining also creates features for fasteners and installation not easily produced through printing alone.
Molds, Tooling, and Fixtures
For mold-making applications, 3D printing can create conformal cooling channels in a mold to improve injection molding cycle times. Machining finishes the mold surface for a smooth end product. For jigs, fixtures, and other tooling, CNC machining provides precision while 3D printing enables consolidation and lightweight construction.
Education and Research
Engineering students benefit from learning both technologies hands-on. 3D printing allows rapid prototyping without extensive machine setup. CNC machining teaches essential skills in subtractive processes, fixturing, and precision techniques. Using both methods also reinforces consideration of how part design and geometry affect manufacturability.
Other Applications
Other diverse applications taking advantage of 3D printing with CNC machining include shoes customized and finished with machines, dental aligners fitted and machined in-office, high-performance racing components, and furniture printed with wood materials and then machined for precision and surface finish. As engineers become more familiar with both technologies’ capabilities, we will continue seeing innovative applications across industries.
The Future of Additive and Subtractive Manufacturing
3D printing and CNC machining each have limitations that are overcome by the other technology. Using the two processes together provides complementary benefits in accuracy, surface finish, feature details, part consolidation, customization, and material properties. Automated hybrid systems will further streamline this integrated approach.
Additive and subtractive methods still face individual challenges for resolution, process speed, material options, part size limits, and cost that drive continued development. However, their synergistic use is already shaping the future of manufacturing. 3D printing combined with CNC machining will open new possibilities in design optimization, mass customization, and performance across production applications. Engineers trained in both additive and subtractive techniques will have a great influence on manufacturing innovations in the years ahead.
Conclusion
In summary, 3D printing excels at producing highly complex and customized components, while CNC machining provides unmatched precision, tolerances, and surface finish. Using CNC machining to finish and enhance features on 3D printed parts combines the strengths of both technologies for designs not practical with either alone. Integrated additive/subtractive systems will further increase adoption across industries where custom, lightweight, and high-performance parts are valued. The synergistic future of these technologies will drive advances across automotive, aerospace, medical, dental, education, molds and tooling, and more. As engineers leverage the complementary benefits of 3D printing and CNC machining, they will create breakthrough products and reshape manufacturing possibilities moving forward.