Creating successful CNC-milled parts for low-volume production goes beyond generating a CAD model. It demands a practical understanding of machining limitations and best practices that you have to use to get the best results.
In this discussion, we present a collection of actionable design tips to equip engineers and designers with the knowledge to optimize their designs for the CNC milling process. Once you start following these, you can improve your manufacturability and reduce production hurdles. So, let’s go ahead and learn how you can elevate the design of your CNC-milled low-volume parts.
Why is Design Important for CNC Milled Low-Volume Parts?
Design is critically important for CNC-milled low-volume parts due to several key factors impacting cost, efficiency, and the final product’s quality. Here’s a breakdown:
Cost Optimization
A well-thought-out design considers CNC machining’s limitations and capabilities. This helps minimize machining time, reduce material waste, and avoid the need for complex and expensive tooling.
Simple designs with standard features significantly reduce production costs. Optimized designs minimize material waste, especially when working with expensive materials.
Enhanced Precision and Quality
CNC machining is known for its precision, but achieving tight tolerances requires careful design. Design considerations impact how well these tolerances can be met.
Design influences the achievable surface finish. Considerations such as tool paths and material selection play a role.
Increased Flexibility and Speed
Low-volume CNC machining is ideal for prototyping and testing designs. A good design allows for quick iterations and modifications. Efficient designs streamline the manufacturing process, reducing lead times and getting products to market faster.
Minimizing Risks
Low-volume production allows for the testing and validation of designs before committing to large-scale production. This helps to identify and correct potential problems early on.
Low-volume production allows for quick design changes to adapt to market changes or to correct design flaws found in early production runs.
Practical Design Tips for CNC Milled Low-volume Parts
Now, let’s get down to the practical design tips you can use for CNC-milled low-volume parts. These DFM for machining tips help you achieve the best results for producing CNC milled parts.
Avoiding sharp internal corners
When designing parts for CNC milling, a critical consideration is handling internal corners. The nature of CNC milling tools, which are typically cylindrical, makes the creation of perfectly sharp internal corners practically impossible. Here’s a deeper dive into why avoiding sharp internal corners is so important:
The Limitation of Tool Geometry
CNC milling relies on rotating cutting tools. By their very design, these tools remove material in a circular path. Consequently, any internal corner created will inherently have a radius.
This means that even when a design calls for a “sharp” corner, the finished part will have a small radius determined by the cutting tool’s size.
Challenges and Consequences of Sharp Corners
Attempting to create sharp internal corners often requires very small cutting tools. These tools are more fragile, prone to breakage, and result in slower material removal rates, increasing machining time and cost.
The need for specialized tooling, additional machining passes, and potentially manual finishing to achieve near-sharp corners significantly drives production costs.
In engineering terms, sharp corners act as stress concentrators. This means that when the part is subjected to force, the stress is concentrated at those sharp corners, increasing the risk of failure.
When machining internal corners, changes in the direction of the cutting tool can result in chip recutting, excessive tool engagement, and difficulties in chip evacuation. These issues can negatively impact the machined part’s surface finish and overall quality.
Best Practice
The most effective solution is to design internal corners with radii from the outset. This not only simplifies machining but also improves the part’s structural integrity. Maintaining consistent radii throughout the part minimizes the need for tool changes, further streamlining the manufacturing process.
Of course, there are times when a sharp corner is needed. Consider options such as EDM, which can produce sharper internal corners in these cases. Also, consider whether design changes can be made or the mating part can be adjusted.
When a mating part with a sharp corner must fit into an internal corner, “dogbone” or “T-bone” fillets can provide the necessary clearance.
Optimal wall thickness recommendations
Optimal wall thickness is a crucial design consideration for CNC-milled low-volume parts, directly impacting structural integrity, manufacturability, and cost. Here’s a detailed look at why wall thickness matters and how to determine the right dimensions:
The Importance of Adequate Wall Thickness
- Structural Integrity
Thin walls are inherently weaker and more susceptible to deformation under stress. This is particularly critical for parts subjected to loads or vibrations.
Insufficient wall thickness can lead to premature failure, compromising the functionality and reliability of the part.
- Machining Stability
During CNC milling, cutting forces can cause thin walls to vibrate or deflect. This can result in inaccurate dimensions, poor surface finishes, and even tool breakage.
Adequate wall thickness provides the rigidity to withstand these forces, ensuring precise and consistent machining.
- Material Properties
The optimal wall thickness varies depending on the material being used. Softer materials like aluminum or plastics may require thicker walls than harder materials like steel or titanium.
Understanding the material’s strength, stiffness, and machinability is essential for determining the appropriate wall thickness.
General Guidelines and Recommendations
Here are some general CNC milling design guidelines and recommendations for CNC milling various materials –
- Metals
A minimum wall thickness of 0.8mm is generally recommended for most metals. This provides a good balance between strength and machinability. However, thicker walls may be necessary for larger parts or those subjected to high loads.
- Plastics
Plastics are more flexible than metals, so thicker walls are typically required. A minimum wall thickness of 1.5mm is a good starting point. The specific type of plastic also influences the optimal wall thickness. Some plastics are more brittle than others and may require even thicker walls.
Factors to Consider
- Part Size and Geometry: Larger parts and those with complex geometries may require thicker walls to maintain structural integrity.
- Load and Stress: Parts subjected to high loads or stresses require thicker walls to prevent deformation or failure.
- Material Properties: The material’s strength, stiffness, and machinability will influence the optimal wall thickness.
- Machining Process: The specific CNC milling process and tooling can also affect the minimum achievable wall thickness.
- Vibration: Thin walls will vibrate during machining, causing poor surface finishes.
Practical Considerations
- To avoid costly modifications later, incorporate adequate wall thickness into the design from the outset.
- Choose a material with the necessary strength and stiffness for the application, considering the required wall thickness.
- For critical applications, consider prototyping and testing to validate the design and ensure sufficient wall thickness.
Minimizing undercuts and complex features
Minimizing undercuts and complex features is a fundamental principle in designing for efficient and cost-effective CNC milling. While sometimes necessary, these features can significantly increase manufacturing complexity and expense.
Here’s a breakdown of why and how to minimize them in precision machining services:
Understanding the Challenges
- Increased Machining Time
Undercuts and complex geometries often require specialized tooling, multiple machining setups, and slower cutting speeds. This translates directly to increased machining time and, consequently, higher costs.
- Specialized Tooling
Creating undercuts often necessitates the use of specialized tools like T-slot cutters or lollipop cutters. These tools can be more expensive and may not be readily available.
- Multi-Axis Machining
Complex features frequently require multi-axis CNC machines (4-axis or 5-axis) to access and machine all surfaces. These machines are more expensive to operate and program.
- Fixturing Complexity
Complex parts often require intricate fixturing to hold them securely during machining. This can add to setup time and cost.
Strategies for Minimization
- Design Simplification
The most effective approach is to simplify designs whenever possible. Eliminate unnecessary undercuts and complex features. Consider breaking down complex parts into simpler components that can be machined separately and assembled.
- Feature Reorientation
Sometimes, simply reorienting a feature can eliminate the need for an undercut. Analyze the design to see if features can be modified or repositioned to facilitate easier machining.
- Alternative Manufacturing Methods
If an undercut is essential, consider alternative manufacturing methods such as:
- EDM (Electrical Discharge Machining): EDM can create complex shapes and undercuts that are difficult or impossible to achieve with conventional CNC milling.
- 3D Printing: In some cases, 3D printing may be a more cost-effective option for producing parts with complex geometries.
- Modular Design
Designing in a modular way can allow for undercuts to be placed on a smaller, more easily machined part that is then assembled into the main body of the part.
- Design for Assembly
Consider how the part will be assembled into the final product. Sometimes, design changes can be made to the assembly to eliminate the need for complex features.
- Early Collaboration
Collaborate with the CNC machinist early in the design process. They can provide valuable feedback on manufacturability and suggest design modifications to minimize complexity.
File preparation best practices (STEP, IGES)
Proper file preparation is crucial for successful CNC milling. The accuracy and integrity of your digital model directly impact the final product. Here’s a breakdown of best practices, focusing on STEP and IGES files:
Understanding STEP and IGES
- STEP (.step, .stp)
STEP (Standard for the Exchange of Product Model Data) is generally the preferred format. It is an ISO standard for representing 3D CAD data.
STEP files are known for their accuracy and ability to preserve geometric information, including solid models, surfaces, and topology. Compared to IGES, they are less prone to data loss during translation.
- IGES (.iges, .igs)
IGES (Initial Graphics Exchange Specification) is an older standard. While still used, it’s less robust than STEP. IGES files can sometimes lose data during translation, particularly with complex geometries or surface models.
It primarily represents surfaces and curves, and solid model information may not always be accurately preserved.
Proper Hole Design
Effective hole design is crucial for successful CNC milling, influencing functionality and manufacturing efficiency. Here’s a breakdown of the best practices for designing holes in your parts:
Understanding Hole Design Considerations
- Functionality
The primary function of the hole dictates its design. Consider whether it’s for fasteners, alignment pins, fluid flow, or other purposes.
- Manufacturing Costs
Hole size, depth, and tolerance directly affect machining time and cost.
- Tooling Availability
Using standard hole sizes minimizes the need for custom tooling, reducing costs and lead times.
- Tolerance Requirements
Specifying appropriate tolerances ensures proper fit and function without unnecessary expense.
Best Practices for Hole Design
- Standard Hole Sizes
Utilize standard drill and reamer sizes whenever possible. This reduces the need for custom tooling, which is more expensive and time-consuming. Consult standard drill size charts to determine available sizes.
- Hole Depth
Limit the depth of holes to minimize machining time and tool wear. Deep holes require specialized tooling and can be challenging to machine accurately.
A general rule of thumb is to limit hole depth to no more than 4-5 times the hole diameter.
- Threaded Holes
For threaded holes, ensure sufficient clearance at the bottom of the blind holes for the tap. Limit the thread depth to 1.5 times the hole diameter, as deeper threads generally do not significantly increase strength.
Use standard thread sizes and pitches. Consider using thread milling for difficult materials or very precise threads.
- Tolerance Specifications
Only specify tolerances where they are necessary. Overly tight tolerances increase machining time and cost. Understand the capabilities of your CNC machine and design within its tolerance range.
For clearance holes, allow for adequate clearance and avoid unnecessary tight tolerances.
Conclusion
In summary, these design tips aim to empower you to create high-quality, cost-effective CNC-milled parts that meet your exact specifications. Adhering to these best practices can minimize manufacturing challenges, reduce lead times, and bring your designs to life with precision and efficiency.
Whether prototyping a new product or producing end-use parts, these design considerations will help you achieve your manufacturing objectives. And if you want to achieve such results, then Zintilon can be a great solution for you. They provide exceptional CNC milling services for low-volume production.
Great, Together
