3D Printing vs CNC Machining: A Straightforward Comparison

CNC machining vs 3D printing

These days, a wide array of manufacturing methods are available, offering product designers and engineers numerous choices. While this variety is advantageous for companies, it can sometimes lead to decision-making challenges. Selecting the best process for custom part designs and applications poses many challenges.

CNC machining and industrial-grade 3D printing stand out among the many methods available. These techniques are well-suited for prototyping and low- to mid-volume part production. However, several key factors come into play when choosing between 3D printing vs CNC machining. Let’s compare these two processes and help you decide which is ideal for your project.

What is 3D Printing?

the 3d printing process

3D printing, or additive manufacturing, involves constructing three-dimensional objects layer by layer based on a digital design. In this process, a digital file guides the creation of a three-dimensional solid object by laying down sequential layers of material until the object is complete. 

Unlike subtractive manufacturing, where the material is cut or hollowed out, 3D printing builds objects layer by layer without molds or material blocks. This approach offers fast production, low initial infrastructure costs, and the ability to create intricate geometries using various materials.

What is CNC Machining?

cnc machining process

CNC (computer numerical control) machining is a subtractive manufacturing method that uses computerized controls and machine tools to carve custom-designed parts from a stock piece. It merges traditional machining with CNC technology, computer-aided design (CAD), and other secondary processes.

Designers use CAD software to craft a digital 3D model of the desired part. Then, a skilled programmer converts the CAD model into a series of instructions (G-code) that the CNC machine can follow. Once the program is loaded, the CNC machine securely clamps a block of raw material (workpiece) and employs computer-controlled motors to guide the cutting tools along precise paths. These tools gradually remove material from the workpiece, shaping it into the final form specified by the CNC machining program. This results in high-quality parts with accurate dimensions and intricate features.

3D Printing vs CNC Machining: What Are the Differences?

Although these two technologies are among the most valuable in the manufacturing industry, they are unsuitable for all applications. They have significant differences that make them distinct. Let’s examine them.

Accuracy and Geometric Complexity 

Renowned for its ability to produce intricately shaped parts, 3D printing surpasses traditional manufacturing methods in geometric complexity. Due to the advanced printers used, it achieves exceptional accuracy unmatched by other methods.

cnc machining for complex geometries

While highly precise, CNC machining requires significant time. The technology is also constrained by tool access, square corner geometry, and mounting points. These factors often limit design possibilities.

Cost-Effectiveness 

Cost-effectiveness in 3D printing varies depending on part specifications and urgency. It is relatively inexpensive per part because costs are primarily based on material usage rather than setup. This makes it an attractive choice for prototyping and small production runs. However, its cost benefits may reduce as the batch volume increases.

On the other hand, CNC machining may be more cost-effective for larger quantities and bigger parts. However, it incurs higher labor costs from tool path programming, setup time, and managing machines. The subtractive process also generates substantial waste, particularly for large, lightweight parts. This may result in up to 90% material wastage.

Materials

CNC machines handle various materials like metals, plastics, and wood, producing durable parts vital for applications requiring robustness. However, due to their subtractive manufacturing process, they generate considerable waste.

Materials for 3d printing

In contrast, 3D printing’s additive approach enables precise material control, minimizing waste compared to CNC machining. Though it can also work with multiple materials, its range is narrower than that of CNC machines. It is typically limited to plastics, resins, and a few metals.

Lead Time

CNC machines outpace 3D printers in speed for part production. It only takes a few hours to complete a CNC machining run, whereas 3D printers might take days or weeks. Yet additive manufacturing holds a lead in prototyping time. CNC machining involves costly setups for product changes. In contrast, 3D printing requires minimal setup, enabling swift transitions between products. With quick and cost-effective printing, designers can iterate designs rapidly, slashing development time.

Convenience 

Compared to CNC machining, 3D printing is simpler and doesn’t need highly skilled labor. Once the CAD file is prepared, printing can start after selecting part orientation, fill, and support structures. Operating a 3D printer doesn’t require specialized skills; anyone can be trained for it. Once printing begins, supervision isn’t necessary, and post-processing is minimal. Batch designs can be created remotely and sent directly to the printer.

Conversely, CNC Machining is labor-intensive and demands skilled labor for quality output. It requires a skilled operator to choose tooling, rotation speeds, cutting paths, and repositioning. CNC machines need programming by an engineer for safe and accurate operation. Additionally, more extensive post-processing steps are involved.

Applications

CNC machines find applications across diverse sectors like aerospace, automotive, and medical manufacturing. They excel in crafting intricate, high-precision final products featuring complex geometries that may be challenging for conventional printing methods.

In contrast, additive manufacturing excels at crafting intricate, one-of-a-kind shapes that are challenging for traditional manufacturing methods. 3D Printing suits prototyping and small-scale production. It enables quality end-product creation in architecture, product design, etc.

Here’s a brief comparative overview of both processes:

Table of 3D printing vs cnc machining comparison

Limitations of 3D Printing vs CNC Machining

While these technologies offer several benefits and applications, they also have some downsides that must be noted. Let’s check them out:

Limitations of 3D Printing

Here are some of the drawbacks of 3D printing:

• Production Volume: 3D printing operates within a low-to-medium-volume production range, primarily due to its layer-by-layer manufacturing approach. This limitation becomes more pronounced when aiming for high-quality parts, necessitating thinner layers and consequently extending the production time.
• Limited Materials: This technology consistently introduces new materials. However, its range remains constrained compared to established manufacturing methods. While printing in various plastics and metals is feasible, it only encompasses a limited array of alloys and compounds due to their incompatible forms for 3D printing.
• Build-Size Restrictions: 3D printers typically feature smaller build volumes than large-scale manufacturing technologies such as horizontal mills, metal casting, etc. Consequently, 3D printing is primarily employed for small-scale manufacturing of intricate components.
• Design Limitations: 3D printed objects often lack precision and dimensional stability, potentially warping during printing. Even the most precise 3D printers fall short of the accuracy attainable with top-tier CNC machines. CNC machines can consistently produce parts with an accuracy of 0.025 mm compared to 0.4 mm with DMLS 3D printing machines.
• Post-Processing: Most 3D-printed parts need post-processing. This usually involves removing supports, furnace sintering, UV-light curing, polishing, and sometimes machining for precise features such as bearing housings.

Limitations of CNC Machining

Here are CNC machining cons to consider:

• High Initial Investment: CNC machines have multiple components, including a CNC controller, advanced software, gantry, cutting tools, stepper motors, and more. These components collectively contribute to their initial high cost, which can be a barrier for small-scale businesses.
• Requires Expert Programmers and Operators: Operating a CNC machine requires a specialist skilled in programmable codes and machine operations. Unlike traditional machining, which depends on manual labor, CNC machining relies on individuals with technical expertise. This increases the operational expenses per part.
• More Costly for Smaller Batches: CNC machining might not be the most efficient option for small-scale production because of the substantial setup investment. These machines entail significant upfront costs for machines, tooling, and programming skills. Moreover, each workpiece necessitates a tailored CNC machining program, increasing the time and cost of setting up the process. This setup time can pose a significant challenge for small-scale production runs requiring frequent changes or handling small batches.
• Limited Scalability: CNC machining centers have scalability limitations. Despite their ability to craft high-quality parts with consistent precision, they are constrained by bed size and axis capacity. These limitations restrict the size and complexity of producible parts.

Conclusion

Understanding the differences between 3D printing and CNC machining allows companies of all sizes to explore alternative product development processes. Embracing different technologies enables product development teams to learn more about designs faster and earlier in the cycle. There’s no one-size-fits-all solution; 3D printing offers an alternative to CNC, expanding options and capabilities. 

CNC mills and 3D printers coexist in well-equipped shops, offering a workflow where the best solution is always accessible. Therefore, it’s always best to consider the different aspects of each technology to know which one is best for your project. 

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