Plastic parts manufacturing is on the rise. Globally, there is a massive e demand of plastic machined parts but new technology is also echoing. It is 3D printing (additive manufacturing). Both methods boost unique strength and properties. Let’s have a look on some latest research on both methods and try to figure out which one is the best.
They figured out some amazing facts:
Three factors affecting tensile strength were examined:
- Melt temperature (190°C, 205°C, 220°C)
- Layer thickness (0.06mm, 0.10mm, 0.19mm, 0.35mm)
- Raster pattern orientation (+45°/-45° crisscross, horizontal, vertical)
In this experiment, they found that the raster pattern and tensile strength achieved high accuracy (R² values of 0.999+).
In another research held in February 2024 on 3D Printing and CNC Machining, it states the following findings:
- Traditional manufacturing methods struggle with complex shapes. However, 3D printing can produce them layer-by-layer.
- CNC machining offers a post-processing solution for 3D-printed parts
- Possibilities to combine both methods for higher precision parts
You might be wondering when both methods carry significant advantages, which is the best method to machine plastic parts.
This is the crux of our article today.
Key Takeaways of the Content:
- 3D Printing & CNC Machining Process Breakdown
- Design Features & Surface Finishing
- Applications
O no matter if your focus is on rapid prototyping for complex designs or looking for affordable high-volume production, understanding these factors will help you to take the best decision.
Process Breakdown of 3D Printing & CNC Machining
As mentioned above, both 3D printing and CNC machining boost excellent features. However, they manufacture parts in different ways. Read a brief comparison below:
3D Printing (Additive Manufacturing):
- Process: Builds objects layer-by-layer, incorporating digital files.
- Pros: Creates complex geometries & is suitable for prototypes.
- Cons: Slower than CNC machining.
CNC Machining (Subtractive Manufacturing):
- Process: CNC machines remove material from a solid block.
- Pros: Faster for larger quantities & high precision.
- Cons: Limited tool access for complex designs.
1. 3D Printing
3D printing, also known as “Additive manufacturing,” is a revolutionary concept. To understand that concept easily, let’s take an example. You have a digital model of some object. With 3D printing technology, you develop the shape layer by layer by adding the material. So ultimately, you bring a digital model into real life.
This technology incorporates a digital blueprint. It is called an STL file. This file is sliced into incredibly thin horizontal layers. Just like the above example, a printed builds the layers and convert that digital file into a plastic object. We shall read about the different plastics after reading about more printing technologies.
1) Fused Filament Fabrication (FFF):
This method has another popular name; FDM (Fused Deposition Modeling). This is a complex process; a thin filament of plastic, ranging from 1.75mm to 2.85mm in diameter, works in the following pattern:
- It is unwound from a spool
- Heated to a molten condition
- Finally, extruded through a tiny nozzle
A computer precisely controls this tiny nozzle. The nozzle deposits the molten plastic layer by layer. This process continues until the final part is completed. FDM offers a suitable range of filament options. For example:
- ABS
- PLA
- Nylon
Comparison Table of ABS, PLA, and Nylon
Property | ABS | PLA | Nylon |
Material Type | Thermoplastic (Amorphous) | Thermoplastic (Semi-crystalline) | Thermoplastic (Semi-crystalline) |
Printing Temperature | 210-250°C | 190-220°C | 220-260°C |
Heat Resistance | High (up to 105°C) | Low (deforms around 60°C) | High (up to 150°C) |
Chemical Resistance | Moderate | Low | High |
Warping | More prone to warping | Minimal warping | Less prone to warping than ABS |
Cost | Moderate | Lower cost option | Higher cost |
2) Stereolithography Apparatus (SLA)
SLA adopts a laser-focused approach. What does it mean? A laser beam cures liquid resin. It solidifies the resin layer by layer following the digital model. For your information, SLA possesses significant resolution, which can produce parts with layer thicknesses as low as 0.025mm to 0.1mm. This thickness is ideal for complex designs with in-depth details.
3) Selective Laser Sintering (SLS):
SLS incorporates a bed of powdered plastic material. A high-powered laser is used for this method. The laser selectively fuses the plastic particles together. This process is done layer by layer to build the final part. Compared to SLA, SLS has wide options of materials such as engineering-grade nylons.
Layer thickness in SLS ranges from 0.07mm to 0.1mm.
2. CNC Machining
CNC machining is a highly satisfying process that involves several machines to complete a custom part. How exactly is the machine able to cut such complex geometric patterns? If you want to produce a custom part, you must feed the CNC machine a code called G-code and M-code.
What happens when you feed this code to a CNC machine? The tool’s movement is beautiful, but it’s slightly difficult to understand.
Suppose you want to engrave this logo on a steel plate. The tool motion needed to make this engraving seems simple, requiring only two dimensions. Just by moving the tool in the X and Y directions, we can perfectly achieve this engraving. Such CNC machines are known as two-axis machines.
What are G and M codes? First, G stands for geometry. This means the G-code transfers all the information required to complete a shape. M, on the other hand, stands for machine.
This means all the machine-related information, such as;
- Coolant control
- Tool change
- and M-code controls spindle speeds.
Now, we shall discuss two main CNC machining processes:
CNC Milling
CNC milling is a machining method that removes material from a workpiece by rotating a cutting tool. During machining, the tool moves along multiple axes, such as 3-axis and 5-axis. Each axis configuration has its own unique advantages and areas of application.
Comparison of 3-axis and 5-axis machines
- 3-axis machines: The tool moves along the X, Y and Z axes. This configuration is suitable for most common milling tasks and is capable of efficiently machining 2D and simple 3D shapes. 3-axis machines are ideal for small to medium volume production due to their lower production costs and operational complexity.
- 5-axis machines: The tool can not only be moved along the X, Y and Z axes, but can also be operated in two rotary axes, A and B. This configuration allows the 5-axis machine to machine a wide range of shapes. This configuration allows 5-axis machines to machine more complex and finer geometries, especially for parts that require high precision and multi-angle machining. Compared to 3-axis machines, 5-axis machines offer significant advantages in creating complex features and reducing the need for secondary setups, which can significantly improve machining efficiency and accuracy.
Material Selection in CNC Milling
CNC milling technology is widely used for machining a variety of plastic materials, with common materials including ABS, PC (polycarbonate) and Delrin (homopolymer acetal). Each material has its own unique properties and is suitable for different application scenarios:
- ABS (Acrylonitrile Butadiene Styrene Copolymer): ABS has good rigidity, toughness, and impact resistance, and is commonly used to make housings, mechanical parts, and toys. Its easy machinability makes it one of the common materials for CNC milling.
- PC (Polycarbonate): Known for its high transparency and excellent impact resistance, PC is suitable for applications requiring high transparency and impact resistance, such as protective covers, transparent gears and optical components. CNC milling provides high-precision machining results, making it ideal for working with complex shapes and details.
- Delrin (homopolymer acetal): Delrin offers high hardness, low coefficient of friction and good dimensional stability, making it suitable for precision gears, bearings and sliding parts. CNC milling ensures its high precision and consistency for demanding applications.
Advantages of CNC Milling
CNC milling technology is popular for its excellent accuracy and speed in plastics processing. Key advantages include:
- High Accuracy: CNC milling is capable of achieving extremely high machining accuracy, ensuring consistent size and shape of each part.
- High efficiency: Automated machining processes significantly increase productivity and reduce manual intervention and errors.
- Flexibility: CNC milling is capable of handling a wide range of complex geometries and features to meet different design requirements.
- Material compatibility: Suitable for a wide range of plastic materials, enabling the selection of the most suitable material for a specific application.
CNC Turning
CNC turning primarily focuses on rotating the workpiece. During this process, a stationary cutting tool removes material. This method is used to create custom metal and plastic parts with cylindrical shapes and features. CNC turning in machining can accelerate mass production, ensuring precision and consistency while maintaining efficient production speeds.
Common CNC Turning Parts
CNC turning technology is widely used to manufacture various precision parts that play crucial roles in multiple industries:
- Knobs: Used for control in various mechanical and electronic devices, requiring high precision and durability.
- Gears: Essential in transmission systems, demanding high-precision teeth and dimensional tolerances.
- Bushings: Sleeves used to reduce friction and wear, typically made from wear-resistant materials.
- Shafts: Commonly used in mechanical equipment and the automotive industry, requiring high strength and precise dimensions.
- Nuts and Bolts: Used for mechanical assembly and fastening, requiring high strength and corrosion resistance.
- Pipe Fittings and Connectors: Used in fluid systems, demanding high-precision sealing and connection performance.
Material Selection in CNC Turning
CNC turning parts can be made from various metal and plastic materials, each with unique characteristics suitable for different applications:
Metal Materials:
- Aluminum: Offers good mechanical properties and corrosion resistance, suitable for lightweight and high-strength parts.
- Stainless Steel: Provides excellent corrosion resistance and strength, suitable for medical devices, food processing, and chemical industries.
- Copper: Has good electrical and thermal conductivity, often used in electrical and electronic equipment.
- Brass: Easy to machine with good mechanical properties, suitable for valves, fittings, and connectors.
Plastic Materials:
- Nylon: Exhibits excellent mechanical strength, wear resistance, and self-lubricating properties, commonly used for sliding parts and bearings.
- PEEK (Polyether Ether Ketone): A high-performance engineering plastic with high-temperature resistance, chemical resistance, and good mechanical properties, suitable for demanding applications like aerospace and medical devices.
- POM (Polyoxymethylene): Offers high hardness, low friction coefficient, and good dimensional stability, ideal for precision gears, bearings, and sliding parts.
- ABS (Acrylonitrile Butadiene Styrene): Known for its good rigidity, toughness, and impact resistance, often used for housings and mechanical components.
Key Comparison Between CNC Machining and 3D Printing
Previously, you have read about the basic understanding of CNC machining and 3D printing, including some pros and cons. So it is crucial to understand the technical details of each process. Therefore, in the following section, you will read about factors like design complexity, part strength, production volume, surface finish, and lead time.
1. Design Complexity
3D Printing
3D printing has an advantage over CNC machining in terms of design freedom. Its additive feature can produce parts with complex geometries.
FDM printers, for example, can reach minimum feature sizes of around 0.2 – 0.4 mm. Subsequently, SLA delivers finer resolutions down to 0.025mm. So ultimately, 3D printing is the best process for prototypes with complex geometries. Building such shapes will be nearly impossible for CNC subtractive methods. That is the reason not every company provides CNC machining services for plastic parts; it is difficult.
CNC Machining
CNC machining cannot be underestimated. If your focus is tight tolerances, then CNC machines deliver you the optimum results. For example, CNC milling machines handle moderately complex geometries. Milling machines can effortlessly manufacture features like:
- Pockets
- Slots
- and undercuts
Minimum feature size in CNC milling depends on two factors:
- The tool size
- Material
However, it falls within the range of 0.1mm to 0.5mm. So again, if your focus is on precision, CNC machining has a significant advantage for parts requiring tight tolerances.
2. Part Strength and Function
CNC machining takes the lead in part strength. The subtractive process incorporates solid plastic workpieces, resulting in parts with isotropic properties. This means the strength is consistent throughout the material. CNC-machined parts are ideal for functional applications.
3D-printed parts show some degree of anisotropy. Why does this happen? This is due to the layered nature of the printing process. The strength between layers (often referred to as the “Z-axis”) is weaker compared to the strength within the layer (the “XY-plane”). This feature can make parts vulnerable under significant stress.
3. Production Volume and Cost
For low-volume production or prototypes, 3D printing is an affordable and efficient option. This affordability stems from the minimal initial setup costs associated with 3D printing. Unlike traditional manufacturing methods, 3D printing does not require complex tooling, molds, or jigs, which can be expensive and time-consuming to produce.
Advantages of 3D Printing for Low-Volume Production
- Minimal Initial Setup Cost: One of the primary reasons 3D printing is cost-effective for low-volume production is the lack of need for specialized tooling. This significantly reduces the upfront investment required to start production.
- Lower Cost Per Part: In low-volume production runs, the cost per part in 3D printing is generally lower compared to traditional manufacturing methods. This is because the expenses associated with setup and tooling are spread over fewer units, making 3D printing a more economical choice.
- Flexibility and Speed: 3D printing allows for rapid prototyping and quick iterations. Design changes can be implemented easily without the need to modify or create new tooling, saving both time and money.
- Complex Geometries: 3D printing can produce complex geometries and intricate designs that might be difficult or impossible to achieve with traditional manufacturing methods. This capability is especially beneficial for creating prototypes that require detailed features.
Cost Reduction with CNC Machining for Large-Batch Orders
While 3D printing excels in low-volume production, CNC machining offers significant cost advantages for large-batch orders, particularly with the use of advanced technologies such as 5-axis machining and high-speed tooling.
- 5-Axis Machining: This advanced machining technology allows for the simultaneous movement of the cutting tool along five different axes. This capability reduces the need for multiple setups and fixtures, significantly cutting down on production time and costs. It also enhances precision and allows for the production of more complex parts in a single setup.
- High-Speed Tooling: High-speed CNC machines can operate at faster speeds than traditional machines, reducing cycle times and increasing production efficiency. This leads to lower labor costs and higher throughput, making it more cost-effective for large-batch production.
- Economies of Scale: In large-batch production, the cost per part decreases as the total volume increases. The initial setup and tooling costs are amortized over a larger number of units, reducing the overall cost per part.
- Consistent Quality: CNC machining ensures high precision and consistency across all parts in a production run. This reduces the likelihood of defects and rework, further lowering production costs.
4. Surface Finishing
The appearance of a part is as crucial as its functionality. In this regard, CNC machining and 3D printing offer a range of surface finishing options to achieve the desired aesthetic and functional qualities.
CNC Machining Surface Finishing Options
CNC machining provides numerous surface finishing techniques to enhance the appearance and performance of the final product. Some of the common CNC machining surface finishes include:
- Milling and Polishing: CNC milling and polishing can achieve exceptionally smooth surface finishes with a roughness value (Ra) as low as 0.1 microns. This is ideal for parts that require high precision and a flawless appearance.
- Anodizing: This electrochemical process forms a protective oxide layer on the surface of aluminum parts, enhancing corrosion resistance and providing a decorative finish available in various colors.
- Powder Coating: A dry powder is applied electrostatically and then cured under heat to form a durable, high-quality finish. This is suitable for parts requiring a robust and uniform appearance.
- Bead Blasting: This technique uses fine glass beads or other abrasives to create a smooth, matte finish. It is often used to remove tool marks and improve the surface texture of metal parts.
- Electroplating: A metal coating is deposited onto the part’s surface through an electrochemical process. This can enhance corrosion resistance, increase wear resistance, and provide an attractive finish.
3D Printing Surface Finishing Options
3D printed parts typically require post-processing to achieve a smooth and aesthetically pleasing finish. Common post-processing techniques include:
- Sanding: Manually or mechanically sanding the part to remove layer lines and achieve a smoother surface. This is labor-intensive and adds to the overall production time and cost.
- Vapor Smoothing: Exposing the part to solvent vapors that melt the outer surface slightly, resulting in a glossy, smooth finish. This is particularly effective for ABS and other solvent-reactive materials.
- Infiltration Techniques: Applying infiltrants such as resins or epoxies to fill in gaps and layer lines, enhancing the part’s strength and surface finish. This method is beneficial for porous materials or parts requiring additional structural integrity.
Surface Finishing Considerations for Different 3D Printing Technologies
The targeted surface finish for 3D printed parts also depends on the materials and printing process technology used. For example:
- Fused Deposition Modeling (FDM): FDM parts often have a visible layer texture due to the extrusion process. Sanding, vapor smoothing, and infiltration techniques can significantly improve the surface finish.
- Stereolithography (SLA): SLA parts offer smoother finishes straight out of the printer, thanks to the high resolution of the UV curing process. Minimal post-processing is required, making it a preferred choice for applications demanding fine details and smooth surfaces.
- Selective Laser Sintering (SLS): SLS parts typically have a grainy texture due to the sintering process. Bead blasting, infiltration, and painting can enhance the surface quality and achieve the desired finish.
5. Speed and Lead Time
Turnaround time is a crucial factor in making any business successful. It directly impacts project schedules, customer satisfaction, and overall competitiveness in the market. For any project, the first thing that determines the project duration is part design. Depending on the complexity and volume of the order, different manufacturing methods can be chosen to optimize turnaround time.
Choosing the Right Method Based on Part Design
Simple Designs:
- 3D Printing: For simple designs, 3D printing is an excellent choice. It allows for rapid prototyping and production without the need for complex tooling or setup. This makes it possible to quickly iterate on designs and make necessary adjustments, significantly shortening the overall project duration. Additionally, the ability to produce parts on-demand reduces lead times, making 3D printing ideal for projects with tight deadlines.
Complex Designs and Large Batch Orders:
- CNC Machining: For large batch orders and complex designs, CNC machining can outperform 3D printing in terms of speed and efficiency. CNC machines are capable of handling high volumes with consistent quality and precision. Advanced CNC technologies, such as 5-axis machining and high-speed tooling, enable faster production cycles and reduced turnaround times. This is particularly important for complex parts that require intricate geometries and tight tolerances.
Advantages of CNC Machining for Fast Turnaround
High-Speed Production: Modern CNC machines are equipped with high-speed spindles and advanced control systems, allowing for rapid material removal and efficient machining processes. This reduces the time needed to produce each part, enabling faster completion of large orders.
Simultaneous Multi-Axis Machining: 5-axis CNC machining can perform multiple operations simultaneously, reducing the need for multiple setups and fixtures. This capability not only speeds up the machining process but also improves accuracy and consistency, further enhancing turnaround time.
Automation and Repeatability: CNC machining benefits from automation, which minimizes manual intervention and allows for continuous production runs. Automated tool changers, robotic arms, and integrated quality control systems ensure that parts are produced quickly and with minimal downtime.
Scalability: CNC machining is highly scalable, making it suitable for both small and large batch productions. Once the initial setup and programming are complete, CNC machines can operate continuously to produce large quantities of parts without compromising on quality or speed.
Applications
1. Applications of 3D Printing
3D printing is a versatile technology that finds applications in various industries due to its ability to produce complex geometries, customize designs, and reduce lead times. Here are some key applications of 3D printing:
Prototypes
3D printing is widely used in the prototyping phase of product development. It allows for the rapid creation of multiple iterations, enabling designers and engineers to test and refine their concepts quickly and cost-effectively.
- Example: A drone manufacturer incorporates 3D printing to create multiple iterations of drone components. For instance, they can produce new wing designs and test their aerodynamics in real-world conditions. This iterative process helps in optimizing the design for better performance and efficiency before moving to mass production.
Low-Volume Functional Parts
3D printing is also ideal for producing low-volume functional parts. It allows for on-demand manufacturing, customization, and the creation of parts with complex geometries that would be difficult or impossible to achieve with traditional manufacturing methods.
- Example: A robotics company uses 3D printing to produce customized grippers for their robots. Each gripper is designed to handle specific objects with precision, enhancing the robot’s functionality and adaptability. This customization capability is particularly valuable in applications where the robot must interact with a variety of objects or materials.
Custom Tooling and Fixtures
In addition to final parts, 3D printing is useful for creating custom tooling and fixtures that streamline the manufacturing process and improve efficiency.
- Example: An automotive manufacturer uses 3D printing to produce custom jigs and fixtures for assembly lines. These tools are tailored to the specific needs of the production process, ensuring that components are accurately positioned and assembled, reducing errors and increasing throughput.
Medical and Dental Applications
The healthcare industry benefits significantly from 3D printing due to its ability to produce patient-specific solutions, such as prosthetics, implants, and surgical guides.
- Example: A dental clinic uses 3D printing to create custom dental implants and orthodontic devices. Each device is tailored to the patient’s unique anatomy, improving fit and comfort and enhancing the overall effectiveness of the treatment.
Educational and Research Applications
3D printing is a valuable tool in educational institutions and research laboratories for creating models, conducting experiments, and fostering innovation.
- Example: A university engineering department uses 3D printing to fabricate models and components for student projects and research experiments. This hands-on approach helps students understand complex concepts and develop practical skills in design and manufacturing.
Consumer Goods and Customization
The ability to produce customized products on demand makes 3D printing attractive for the consumer goods market, where personalization is a growing trend.
- Example: A fashion designer leverages 3D printing to create bespoke jewelry and accessories. Customers can choose unique designs, colors, and materials, resulting in personalized items that stand out in the market.
2. Applications of CNC Machining
CNC machining is a highly versatile and precise manufacturing process that is essential for producing high-quality parts in a wide range of industries. Here are some key applications of CNC machining:
High-Volume Production
CNC machining is particularly well-suited for high-volume production runs due to its ability to produce consistent and precise parts with minimal variation.
- Example: Automotive manufacturers rely on CNC machining for the mass production of plastic engine components, such as intake manifolds and valve covers. The high-speed and precision capabilities of CNC machining ensure that each component meets stringent quality standards, contributing to the overall performance and reliability of the vehicle.
Parts with High Strength and Precision
CNC machining excels in producing parts that require high strength, precision, and intricate geometries. This makes it ideal for industries where the performance and reliability of components are critical.
- Example: A medical device company uses CNC machining to manufacture high-precision gears for a surgical robot. These gears must meet exacting standards for accuracy and durability to ensure the robot operates smoothly and reliably during delicate surgical procedures.
Hybrid Approaches Combining 3D Printing and CNC Machining
In some cases, a hybrid approach that combines the strengths of both 3D printing and CNC machining can be employed to optimize manufacturing processes and achieve the best of both worlds.
- Example: A manufacturer might use 3D printing to create complex internal geometries of a part that would be difficult or impossible to machine. The part is then finished with CNC machining to achieve high precision on critical surfaces and features. This approach leverages the design flexibility of 3D printing and the precision and strength of CNC machining, resulting in a high-quality, optimized part.
Conclusion
In summary, both CNC machining and 3D printing are essential for manufacturing plastic parts. 3D printing excels in customization, rapid prototyping, and small-volume production, making it ideal for unique and complex designs. Conversely, CNC machining is perfect for high-precision and large-volume production needs. To determine the best method for your specific project, contact RALLY Machining today. Our experts will help you choose the optimal manufacturing solution to meet your requirements. Reach out now and ensure your parts are produced with the highest quality and efficiency.
FAQs
1. What is 3D printing?
2. What is CNC machining?
3. Which method is better for prototyping?
4. Which method is better suited for high volume production?
5. What is the difference in material selection?
6. Which method is less expensive?
7. Which method is better suited for high precision applications?
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