Which One Has More Speed: CNC or Additive Manufacturing?

When comparing CNC machining and additive manufacturing, businesses often face the challenge of choosing the faster production method to meet tight deadlines. Making the wrong choice could lead to delays, inefficiencies, or compromised quality. By understanding the speed differences between these two processes, you can ensure optimal results for your production needs.

Quick Answer:

CNC machining is typically faster than additive manufacturing (AM) for producing simple parts in large volumes, thanks to its high material removal rates and optimized workflows. It excels in high-speed production, especially for straightforward geometries and larger components. On the other hand, AM can be faster for complex, low-volume prototypes or customized parts, as it requires minimal setup and eliminates the need for tooling. Advanced AM technologies like Multi Jet Fusion (MJF) are narrowing the speed gap, particularly for intricate designs. The choice depends on factors such as part complexity, volume, and material requirements.

Understanding CNC Machining Speed

CNC (Computer Numerical Control) machining is a subtractive manufacturing process that removes material from a solid block (blank or workpiece) using cutting tools controlled by computer programs. It is a cornerstone of modern manufacturing, offering precision and repeatability. However, the speed of CNC machining depends on several interrelated factors.

Factors Affecting CNC Speed

• Material Type (Hardness, Machinability):
  The material being machined plays a critical role in determining cutting speed and feed rates.

  • Harder materials like titanium alloys or hardened steel require lower cutting speeds and feed rates to prevent excessive tool wear or breakage.
  • Softer materials such as aluminum or brass allow for higher speeds, making machining faster.
  • Machinability, a measure of how easily a material can be cut, is influenced by hardness, ductility, and microstructure. Materials with higher machinability ratings, such as free-machining steel, enable faster machining.

• Part Complexity (Number of Axes, Intricate Features):
  Part geometry has a direct impact on machining time.

  • Simple parts with basic shapes are quicker to machine.
  • Complex parts may require:
  • Multiple setups: Each repositioning of the workpiece adds setup time.
  • Multi-axis machining: Using 4-axis or 5-axis machines reduces setups but involves intricate programming and slower feed rates in specific directions.
  • Frequent tool changes: Each tool change for operations like drilling, tapping, or finishing adds non-cutting time.

• Cutting Tools and Parameters (Feed Rate, Cutting Speed, Depth of Cut):
  Proper selection of cutting tools and parameters directly affects material removal rate and machining efficiency.

  • Cutting speed: Faster speeds increase productivity but may cause faster tool wear.
  • Feed rate: Determines the amount of material removed per revolution; higher rates speed up machining but increase cutting forces.
  • Depth of cut: Deeper passes remove more material but demand more power and generate heat, affecting tool life.
  • Optimization involves balancing these factors with material and tooling considerations to achieve desired speeds without compromising tool longevity or surface finish.

• Number of Parts (Setup Time and Economies of Scale):
  CNC setup time, which includes loading the workpiece, tool setup, and program loading, is fixed.

  • For small production runs, setup time is a significant portion of the total process.
  • For large batches, the fixed setup time is distributed across more parts, reducing per-part time and increasing efficiency.

• Machine Setup and Programming Time:
  Preparing the CNC machine involves:

  • Workholding and fixture preparation.
  • Tool loading and calibration.
  • CNC program development and verification, which can be time-intensive for intricate parts.
  • Advanced CAM software can streamline programming, optimize toolpaths, and reduce setup time, improving overall efficiency.

CNC Strengths in Speed

• High Material Removal Rates for Simpler Parts:
  CNC excels in quickly removing material, particularly for straightforward geometries, leading to short production cycles. For materials with high machinability, this capability is even more pronounced.

• Excellent for Large Batch Production Due to Economies of Scale:
  Once the initial setup is complete, CNC machines can operate continuously with minimal intervention, making them highly efficient for mass production. Larger batch sizes further reduce the impact of setup time per part.

• Fast Cycle Times for Well-Optimized Processes:
  With optimal tooling and machining strategies, CNC machines achieve high-speed performance. For example, high-speed spindles and advanced toolpath algorithms minimize unnecessary movements, maximizing throughput.

CNC Limitations in Speed

• Slower for Highly Complex Parts Requiring Multiple Setups and Tool Changes:
  Intricate parts demand multiple setups or specialized multi-axis machines. Each setup introduces downtime, and frequent tool changes add non-cutting time, slowing overall production.

• Material Waste Can Increase Processing Time, Especially for Intricate Geometries:
  As a subtractive process, CNC generates waste material. For complex geometries, excessive material removal extends machining time and increases costs, particularly for expensive raw materials.

• Longer Lead Times for Tooling and Setup Compared to Some AM Processes:
  CNC machining often requires dedicated tooling and fixtures, which take time to procure and prepare. In contrast, additive manufacturing (AM) processes often require minimal setup and no specialized tooling, offering quicker turnaround for certain applications.

Understanding Additive Manufacturing Speed

Additive Manufacturing (AM), also known as 3D printing, builds parts layer by layer directly from digital designs. Unlike subtractive methods like CNC machining, AM adds material, offering distinct advantages and limitations in terms of speed. The speed of AM depends on several factors, from the technology used to post-processing requirements.

Factors Affecting AM Speed

• Technology Used (e.g., FDM, SLA, SLS, MJF, DMLS/SLM):
  Different AM technologies exhibit varying speeds depending on their underlying mechanisms:

  • Fused Deposition Modeling (FDM): Uses thermoplastic filaments extruded layer by layer. Best for simple parts but slower for detailed, high-resolution components.
  • Stereolithography (SLA): Employs a UV laser to cure liquid resin layer by layer. Offers high resolution but can be slower due to the curing process.
  • Selective Laser Sintering (SLS): Fuses powdered material (usually polymers) with a laser. Faster than SLA for larger parts, with no need for support structures.
  • Multi Jet Fusion (MJF): Deposits fusing and detailing agents onto a powder bed, followed by infrared energy to fuse layers. Faster than SLS, particularly for high-volume production.
  • Direct Metal Laser Sintering/Selective Laser Melting (DMLS/SLM): Sinter or melt metal powders layer by layer. Slower than polymer-based processes due to the higher energy input required.

• Part Size and Volume:
  Larger parts take longer to build, as the process involves depositing or curing more material. The build volume of the printer also constrains the maximum part size that can be created in a single run.

• Layer Height/Resolution:
  The layer height directly impacts printing time:

  • Finer layers: Result in smoother surfaces and better detail but require more layers and longer build times.
  • Thicker layers: Reduce build time but may produce a more noticeable "stair-step" effect on surfaces.

• Part Orientation:
  How the part is oriented on the build platform influences the need for support structures and build time:

  • Vertical orientation: Increases build height and the number of layers, slowing the process.
  • Horizontal orientation: Can reduce height but may require more supports, increasing post-processing time.

• Material Type:
  The properties of the material used influence build speed:

  • Polymers: Often process faster due to lower melting and curing requirements.
  • Metals: Require higher energy input, slowing the process in DMLS/SLM systems.
  • Material characteristics such as thermal conductivity and melting point also affect layer solidification times.

• Post-Processing Requirements:
  Post-processing adds significant time to the overall production process and includes:

  • Support removal: Complex geometries with extensive supports require manual or automated removal.
  • Curing: Parts from resin-based technologies like SLA often need UV curing to achieve final properties.
  • Powder removal: Powder-based processes like SLS or DMLS involve removing excess powder.
  • Surface finishing: Steps like sanding, polishing, or coating improve aesthetics or functionality but increase overall production time.

AM Strengths in Speed

• Fast for Prototyping and One-Off Production of Complex Geometries:
  AM excels in scenarios requiring rapid design iteration and customization. Complex geometries or low-volume production can be achieved quickly without additional tooling.

• Little to No Tooling Required, Reducing Setup Time:
  AM bypasses the need for dedicated tooling such as molds or fixtures. This agility is particularly advantageous for short production runs or iterative designs.

• Can Produce Complex Internal Geometries Without Significantly Increasing Manufacturing Time:
  Intricate designs, such as lattice structures or internal channels, are feasible with AM without a proportional increase in build time. Traditional methods would struggle or fail to create such features.

AM Limitations in Speed

• Generally Slower Than CNC for High-Volume Production of Simple Parts:
  For straightforward, high-volume parts, CNC machining is faster due to higher material removal rates and economies of scale.

• Build Speed is Limited by Material Deposition Rate or Layer Curing Time:
  The fundamental layer-by-layer approach of AM restricts speed. Technologies like SLA and DMLS are particularly affected by curing or melting rates.

• Post-Processing Can Add Significant Time to the Overall Process:
  Extensive post-processing, such as support removal and surface finishing, can significantly delay time-to-market, especially for parts with complex geometries or stringent surface quality requirements.

Comparative Analysis: CNC vs. Additive Manufacturing

This section provides a direct comparison of CNC machining and additive manufacturing (AM) in terms of speed, focusing on different production scenarios.

Prototyping and Low-Volume Production

• AM Often Faster for Complex Prototypes Due to Minimal Setup:
  Additive manufacturing is ideal for producing prototypes, especially those with intricate geometries. The absence of tooling and minimal setup requirements enable rapid design iterations and quick turnaround times. Complex internal features, organic shapes, and undercuts are produced seamlessly with AM, making it particularly advantageous for industries like aerospace and medical devices. For example, a heat exchanger with intricate internal channels can be printed in a single AM process, which would require multiple setups or be infeasible with CNC.

• CNC Can Be Faster for Simple Prototypes, Especially with Minimal Material Removal:
  CNC machining excels at producing simple prototypes when the design involves basic geometries and minimal material removal. With standard tooling and straightforward operations, CNC offers shorter production times. However, as complexity increases—requiring multiple setups or custom fixtures—AM often becomes the more efficient option. For instance, a flat aluminum bracket can be machined in minutes using CNC, whereas AM might take hours.

High-Volume Production

• CNC is Significantly Faster and More Cost-Effective for Larger Production Runs of Simple Parts:
  In high-volume manufacturing, CNC machining dominates due to its high material removal rates and economies of scale. Once setup is complete, CNC machines operate continuously with minimal intervention, delivering consistent quality and rapid cycle times. For example, producing 10,000 identical aluminum components is far more cost-effective and faster with CNC compared to AM.

• AM is Gaining Traction in High-Volume Applications with Advanced Technologies like MJF:
  While CNC is preferred for simple, high-volume parts, AM is increasingly competitive in specific high-volume applications. Advanced technologies like Multi Jet Fusion (MJF) have significantly improved AM build speeds, particularly for customized products or parts with intricate geometries. For instance, MJF can efficiently produce hundreds of unique dental aligners simultaneously. However, for very high volumes of simple parts, CNC retains a substantial advantage.

Part Complexity

• AM Excels at Producing Complex Geometries with Minimal Impact on Production Time:
  Additive manufacturing's layer-by-layer approach makes it inherently suitable for complex designs. Features like internal channels, lattice structures, and intricate surface details can be created without adding significant production time. Complexity in AM primarily influences material usage and build height, not the manufacturing process itself. For example, an orthopedic implant with a porous surface for bone integration can be printed directly using AM, which would be impossible to achieve with CNC.

• CNC Can Be Slower for Complex Parts Requiring Multiple Setups and Specialized Tooling:
  CNC machining often requires multiple setups, advanced programming, and specialized tooling for complex parts. These factors increase production time and costs. Additionally, internal features or undercuts that are straightforward in AM might be unachievable or require assembly in CNC. For instance, machining a turbine blade with internal cooling channels would demand multiple setups and custom tools, making CNC slower and less efficient.

Part Size

• CNC is Faster for Very Large Parts Due to Higher Material Removal Rates:
  CNC machining is well-suited for large parts that require significant material removal. Large-format CNC machines with high spindle speeds and robust cutting tools can quickly process substantial workpieces, making them ideal for structural components or heavy industrial parts. For example, machining a large steel mold for automotive panels is far faster with CNC than AM.

• AM Build Volume Limitations Restrict Part Size or Require Joining Multiple Printed Components:
  Most AM machines have limited build volumes, which constrain the maximum size of parts they can produce. Larger parts may need to be divided into sections, printed separately, and joined using adhesives, welding, or mechanical fasteners. This adds complexity, potential weak points, and additional time to the process. While emerging large-format AM machines are addressing this limitation, CNC still holds a clear advantage for very large parts. For instance, producing a single, monolithic airplane wing spar is achievable with CNC but not with most AM technologies.

In summary, the choice between CNC machining and additive manufacturing depends heavily on specific application requirements:

• CNC offers speed and cost-efficiency for high-volume, simple parts and large components, benefiting from its material removal rates and scalability.
• AM provides flexibility and speed for prototypes, complex geometries, and customized designs, especially in low-volume or specialized production scenarios.

Future Trends in Manufacturing Speed

The drive to achieve faster and more efficient manufacturing processes is shaping innovations in both CNC machining and additive manufacturing (AM). Below is a comprehensive analysis of the key trends that are revolutionizing the manufacturing landscape.

Innovations in CNC Machining

• Multi-Axis Machines:

  • Advancement: The increasing adoption of 5-axis and multi-axis CNC machines allows for the machining of complex parts in a single setup, reducing setup time and improving precision. Simultaneous 5-axis machining enables the efficient creation of intricate geometries, particularly for aerospace and automotive components.
  • Impact: By eliminating multiple setups, these machines streamline production, reduce errors, and significantly increase machining speed.

• High-Speed Machining (HSM):

  • Advancement: HSM employs higher cutting speeds, feed rates, and reduced depths of cut to achieve rapid material removal. Innovations in cutting tool materials, such as carbide and ceramic tools, paired with enhanced machine rigidity, are driving improvements in HSM.
  • Impact: HSM is particularly beneficial for lightweight materials like aluminum and composites, allowing manufacturers to produce parts faster without compromising accuracy.

• Advanced CAM Software and Automation:

  • Advancement: Modern CAM software optimizes toolpaths, automates machining operations, and reduces programming time. Features like collision detection, automatic tool selection, and real-time simulation enhance operational efficiency. Integration with robotic automation systems further minimizes non-cutting time by automating tasks like loading and unloading.
  • Impact: These innovations reduce manual intervention and accelerate the transition from design to production, enhancing speed and reliability.

• Adaptive Machining:

  • Advancement: Adaptive machining uses sensor feedback to dynamically adjust cutting parameters in real time based on material conditions and tool wear. This prevents errors, optimizes cutting performance, and reduces downtime.
  • Impact: Real-time adjustments ensure consistent machining quality and faster cycle times, particularly in high-precision industries like medical devices and aerospace.

Advances in Additive Manufacturing (AM) Technologies

• High-Speed Sintering (HSS):

  • Advancement: Technologies such as Multi Jet Fusion (MJF) and binder jetting significantly accelerate the production of polymer parts by processing entire layers simultaneously, rather than point-by-point laser scanning.
  • Impact: HSS enables the rapid production of large batches of functional parts, making AM competitive with CNC for certain applications.

• Multi-Laser Systems:

  • Advancement: Powder bed fusion technologies like Direct Metal Laser Sintering (DMLS) and Selective Laser Melting (SLM) now employ multiple lasers working in parallel, dividing the build area to increase material deposition rates.
  • Impact: Multi-laser systems drastically reduce build times for large and intricate metal parts, making AM viable for industrial-scale production.

• Continuous AM Processes:

  • Advancement: Research into continuous AM aims to break away from the layer-by-layer paradigm by developing technologies that allow for uninterrupted material deposition or solidification.
  • Impact: These processes could revolutionize AM by significantly increasing production speeds while maintaining high quality.

• Advanced Materials and Process Optimization:

  • Advancement: The development of faster-curing resins, optimized sintering powders, and improved laser scanning strategies enhances AM efficiency. New materials with superior thermal and mechanical properties are also expanding AM applications.
  • Impact: Faster material processing reduces build times and broadens the applicability of AM in high-performance industries like aerospace and healthcare.

Hybrid Manufacturing Approaches Combining CNC and AM

• Combining Subtractive and Additive Processes:

  • Advancement: Hybrid manufacturing integrates CNC machining and AM within a single workflow. AM builds complex internal features, while CNC machining finishes external surfaces to achieve tight tolerances and superior surface quality.
  • Impact: This approach reduces production steps and enhances the capabilities of both technologies, offering a balanced solution for speed and precision.

• Near-Net-Shape AM Followed by Precision Machining:

  • Advancement: AM is used to produce near-net-shape components, minimizing the material that needs to be removed during CNC finishing operations. This approach reduces machining time while maintaining high dimensional accuracy.
  • Impact: Near-net-shape manufacturing is particularly effective for expensive materials like titanium, as it reduces waste and shortens production cycles.

• Integration of AM into CNC Machines:

  • Advancement: Manufacturers are developing multi-functional platforms that combine AM and CNC capabilities in a single machine. This eliminates the need to transfer parts between separate systems, reducing handling time and potential errors.
  • Impact: These integrated systems streamline production, enabling faster turnaround for complex parts.

Conclusion

When comparing the speed of CNC machining and additive manufacturing (AM), the answer is not straightforward. Both technologies have unique strengths and limitations that make them suitable for specific applications:

• CNC machining excels in high-volume production, simple geometries, and large parts due to its fast material removal rates, scalability, and precision. It remains the go-to choice for industries requiring consistent quality and efficiency in mass production.

• Additive manufacturing, on the other hand, shines in prototyping, low-volume production, and highly complex geometries. Its ability to create intricate designs with minimal setup makes it indispensable for customization and innovation-driven fields like aerospace and healthcare.

Looking ahead, innovations in both technologies and the rise of hybrid manufacturing solutions promise to redefine speed and efficiency in production. By leveraging the strengths of CNC, AM, or a combination of both, manufacturers can achieve unparalleled flexibility, precision, and speed tailored to their specific needs.

Ultimately, the choice between CNC and AM depends on factors such as part complexity, production volume, material type, and size. The future lies in the integration of these technologies, where businesses can optimize production by adopting the right process—or combination of processes—for their unique requirements.

We’d love to hear from you! Have you used CNC machining or additive manufacturing before? What challenges have you faced in choosing the right method for your project?

Visit PROMACHINED for expert advice tailored to your needs. Let’s work together to create the perfect solution!

FAQ:

Is CNC faster than 3D printing?

Yes, CNC machining is generally faster than 3D printing for producing simple parts in high volumes. Its high material removal rates and optimized workflows make it ideal for mass production. However, for complex prototypes or customized designs, 3D printing can be faster due to minimal setup time and no need for tooling.

What is the speed of additive manufacturing?

The speed of additive manufacturing depends on the technology and part complexity. For example:

• FDM (Fused Deposition Modeling): Slow for high-detail parts but faster for simpler designs.
• MJF (Multi Jet Fusion): Significantly faster than many other AM technologies for medium to large batches.
• DMLS/SLM (Metal Printing): Generally slower due to high-energy requirements but suitable for intricate metal parts.
  Build times can range from a few hours to several days, depending on the part size and layer resolution.

Is additive manufacturing slow?

Additive manufacturing can be slower than CNC machining for simple, high-volume parts because it builds layer by layer. However, it is not inherently slow—advanced technologies like Multi Jet Fusion (MJF) and high-speed sintering are bridging the gap, especially for complex geometries and low-volume production.

Is CNC machining fast?

Yes, CNC machining is considered fast, especially for straightforward designs and large production runs. With high spindle speeds, efficient material removal rates, and optimized setups, CNC machines can produce parts in minutes to hours. Its efficiency increases further in high-volume manufacturing due to economies of scale.