A common challenge for CNC machinists is achieving precise, sharp-edged part designs. This difficulty stems from the cylindrical shape of most CNC tools, which inherently limits their ability to machine sharp internal edges. Despite advancements in machining technology and the increasing performance of modern CNC machines, machining these delicate features remains a complex task. But what exactly do we mean when we discuss sharp internal corners in CNC machining? And what strategies can be implemented to effectively address or circumvent these challenges? This article aims to summarize how the Xtproto team of engineers addresses these issues, providing insights and guidance for efficiently and accurately machining complex geometries in CNC machining.
Why Avoid Sharp Corners in CNC Parts?
- Internal vs. External Sharp Corners: In CNC machined parts, sharp corners can occur either inside or outside the part. Internal corners are formed on the inside of the part, while external corners are located on the outside surface. These distinctions are crucial because they affect the machining process differently.
- Manufacturing Challenges: One of the primary challenges associated with sharp corners, especially internal ones, is the complexity they introduce into the manufacturing process. The reduced tool contact area makes it difficult to create precise internal features. Furthermore, using larger cutting tools can cause the design to deviate from expectations.
- Tool Geometry: Tool geometry plays a crucial role in resolving challenges associated with corners. Designers can encounter difficulties when working with these features. Therefore, reliable CNC machining services often provide guidance on optimizing part designs to avoid issues associated with sharp internal corners.
- Reduced Efficiency: One common challenge with machining sharp corners is the need for smaller CNC tooling. Reduced tool size results in slower material removal rates, which reduces productivity. Striking a balance between achieving the desired part geometry and maintaining efficiency is crucial.
- Chip Re-cutting and Tool Engagement: When machining internal corners, changing the direction of the cutting tool can lead to chip re-cutting, excessive tool engagement, and difficulty in chip evacuation. These issues can negatively impact the surface finish and overall quality of the machined part.
- Positioning and Workholding: Part geometries with sharp internal corners can pose challenges for secure and stable positioning. This can impact the efficiency and effectiveness of workholding solutions like fixtures and clamps. To mitigate these issues, careful consideration of part design is crucial.
- Increased Cost: Complex internal features increase CNC machining costs. Overcoming these complexities may require specialized tooling or specialized techniques, increasing production costs. Implementing design adjustments to simplify part geometry is a cost-effective strategy for controlling CNC machining costs.
Sharp-Cornered CNC Parts Are Not Completely Unmachinable
While sharp internal corners are challenging to machine in CNC part machining, they can still be processed. Common situations where sharp corners are necessary include:
- Precision: Cutting sharp corners is crucial in machining operations requiring absolute precision, particularly in the automotive, aerospace, and medical industries. While the feasibility of the machining operation depends on the machining method, material, and CNC design, employing internal corner radii can ensure the functionality of the final product.
- Design Intent: In certain products, design intent can determine whether a manufacturer chooses sharp or rounded corners to achieve a specific look or feel. This intent, driven by innovation or market demand, can guide the machining process.
- Functional Benefit: The functional requirements of a part can determine whether a manufacturer allows sharp corners in such products. Parts requiring sharp internal corners are common in assembly parts and those used in tool and mold manufacturing.
How to Optimize Sharp Corner Design for CNC Parts
Optimizing sharp corners in CNC machining can be achieved through early design considerations, the proper use of non-CNC and CNC processes, and an understanding of how both affect machining cost and practicality.
Incorporating CNC machining considerations into the early design phase
Integrating CNC machining considerations into the early design phase will enhance angle management, improve accuracy, reduce expenses, and streamline the machining workflow, allowing you to achieve sharp internal features without compromising machinability. Cutting tool geometry, such as nose radius and length, can determine the feasibility of machining operations. To achieve precise results on internal and external corners, especially when machining deep internal corners, tools with smaller radii and longer tool lengths are generally preferred. The material properties used, such as hardness, ductility, and machinability, significantly impact the ability to machine sharp corners and the selection of appropriate tools. Soft and thermally unstable materials can easily deform due to the heat generated during machining. Developing a thorough toolpath strategy and optimizing feeds and speeds based on the material and cutting tool are crucial steps. This helps prevent issues such as material deformation, tool deflection, and tool wear during machining. The required machining tolerances determine the selection of materials, CNC machines (such as lathes and milling machines), and cutting tools. Selecting a high-rigidity CNC machine helps reduce vibration and improve accuracy, making it easier to produce sharp internal features.
How to Design Parts with Sharp Corners for CNC Machining
When designing parts with sharp corners, it is important to consider the type of corner and the inherent limitations of CNC machining, particularly the cylindrical geometry of the cutting tool. When working with external sharp corners, it is recommended to avoid using fillets, as fillets are easily processed by the cutting tool. A fillet radius of at least 0.1 mm is recommended. This prevents tool breakage and ensures a smoother tool path, improving tool continuity. To further improve machining efficiency, adjust the tool tip radius to match the diameter of the CNC tool being used. This optimization minimizes tool stress during machining. To ensure accuracy, it is recommended to maintain a tolerance of ±0.1 mm for overall dimensions. Additionally, reduce the fillet radius to match the CNC tool diameter. For very sharp corners, a small internal radius of 0.2 mm can be used to reduce stress during machining. Overall dimensional tolerances are generally ±0.1 mm. If a part design with sharp corners is not suitable for CNC machining, it is worth exploring alternative manufacturing methods. Technologies such as CNC milling, EDM (Electrical Discharge Machining), end milling, or machining with undercuts are all viable solutions.
Trade-offs between CNC Part Design, Machining Cost, and Practicality
Complex CNC part designs requiring sharp internal corners typically incur higher CNC machining costs because they require specialized CNC tooling, technology, and specialized operators. These drawbacks manifest themselves in several ways. For example, sharp corners with a small internal radius require cutting tools with smaller radii. However, these tools increase machining costs and processing time. Another example is a part with a deep internal corner, which requires a longer CNC tool. This increases machining costs because manufacturers must use compatible rapid machining processes to manufacture the tool. Furthermore, this can lead to tool deformation or breakage, as well as chip evacuation issues. The feasibility of CNC part manufacturing also depends on the complexity of the design and the resulting cost factors. Experts can use design for manufacturability to evaluate complex designs with sharp corners. This approach assesses the importance of sharp corners to part functionality. If the presence of a sharp corner does not affect part functionality, it can be avoided. Practicality also impacts machining costs. If adding a sharp corner increases machining costs, a machine expert can recommend avoiding sharp internal features, using alternative methods, or using alternatives such as T-bone fillets or dogbone fillets.
Material Considerations When Machining CNC Parts with Sharp Corners
This section discusses how material type and properties such as hardness and ductility affect the part’s internal corner radius and the overall machining process.
Common Types of Materials in CNC Machining
Three common CNC machining material categories are metals, plastics, and composites.
- Metals: Metals such as aluminum, steel, and brass are common CNC machining materials due to their hardness (<50 HRC) and inherent properties such as strength and durability. Some materials also possess special properties, such as aluminum’s lightweight and corrosion resistance.
- Plastics: Plastics such as ABS, Delrin, and nylon are versatile CNC machining materials, popular for their ease and cost-effectiveness. They are also affordable, lightweight, and some offer high stiffness and excellent dimensional stability.
- Composites: Composites consist of two materials with distinct properties. Common composites used in CNC machining include carbon fiber reinforced polymer (CFRP), known for its high strength-to-weight ratio, and fiberglass, known for its strength, flexibility, and corrosion resistance.
How Different Materials Affect Custom Machining of Sharp-Angled CNC Parts
The choice of material will affect the quality of the CNC machined part or the ability to use the process effectively.
- Hardness: To achieve precise internal sharp corners when machining hard metals such as stainless steel and titanium, specialized, durable tools must be used and cutting speeds adjusted to match the specific material.
- Ductility: Selecting a metal with sufficient ductility is crucial to avoid deformation and stress when machining sharp corners. The correct material selection ensures a smoother and more precise machining process.
- Melting Point: This is particularly common with parts made from plastics, especially those with lower melting points. By controlling cutting speeds, feed rates, and other machining parameters, overheating and deformation can be prevented, allowing for the successful manufacture of such plastic parts with sharp corners.
- Material Stability: Some plastics exhibit dimensional changes at different temperatures, which can affect the machining process. Understanding these material stability characteristics is crucial for ensuring consistent and accurate CNC machining operations.
- Wear: When machining abrasive composites like carbon fiber, predicting tool wear is crucial, especially when machining sharp corners. Therefore, specialized tools are often required to maintain machining efficiency and accuracy.
- Layer Orientation: When machining composites with layered structures, the orientation of the layers requires careful consideration, as it can significantly affect the accuracy of cutting sharp corners. Operators should pay close attention to this aspect for optimal results.
How to Machining CNC Parts with Sharp Internal Corners
When necessary, the following methods can be used to create sharp internal corners in CNC machining:
- Using a Ball End Mill: A ball end mill has a small, spherical tip, making it suitable for machining smaller internal corner radii. For external parts, the rounded geometry of the cutting tool also ensures that CNC-machined parts are free of sharp edges. Ball nose end mills are commonly used in the aerospace and medical device manufacturing industries. They require extreme flexibility and may not be suitable for handling very sharp corners. Therefore, their use must be determined based on the specific requirements of the project.
- Using Angle Chamfer End Mills: Chamfer end mills are designed for achieving precise internal features and are often used in mold and die manufacturing. Their finely crafted cutting edges facilitate the creation of sharp internal details while reducing the risk of chipping. This makes them ideal for CNC machining of materials prone to chipping or for creating intricate details. However, machinists need to weigh the complexity of the design, the material properties, and the specific details of the corner features before selecting.
- Using Grinding Wheels: Using grinding wheels requires a skilled operator, especially on parts with very tight tolerances. This method involves using a grinding wheel (coated with abrasive particles) to remove material and create precise contours. This method is versatile, suitable for different materials, and compatible with parts with tight tolerances. However, challenges with this process include over-grinding, which can reduce accuracy, and compatibility with extremely sharp corners.
- Using EDM: Electrodischarge machining (EDM) uses electrical sparks to remove material from a workpiece. Two types of machining methods are suitable for machining sharp corners: wire EDM and wire EDM.
- Sinker EDM: In sinker EDM, the process involves inserting a custom die into the workpiece, creating a cutting action. The die, a negative mirror image of the feature geometry, acts as an external component, making it ideal for achieving precise, sharp corners during machining.
- Wire EDM: Wire EDM uses a thin wire cutting technique that follows the contours of the feature while cutting the material. Due to its slender profile (less than 0.1 mm in diameter), it excels at machining sharp internal corners with radii as small as 0.05 mm. Despite its corner machining capabilities, wire EDM has limitations. Manufacturers may avoid it due to its slow processing speeds, complex process, compatibility with conductive materials only, and potentially unsatisfactory surface finishes.
- CNC Routing: CNC milling is a versatile and highly accurate machining process suitable for two-dimensional workpieces made from materials such as plastics, wood, and composites. It uses a CNC milling cutter with a small diameter and a programmed cutting path to achieve consistent and repeatable results. While CNC milling is effective in many applications, achieving extremely sharp corners may be limited. While the cutting tool is precise, it may not be as sharp as some specialized methods. Machinists should evaluate the specific requirements of the project, considering factors such as material type, design complexity, and corner sharpness.
- Using Laser Cutting: Laser cutting uses a laser beam to cut a workpiece. It is a non-contact process that is better suited for cutting two-dimensional designs made from thin sheet metal. The availability of numerous laser cutting facilities makes this process very economical. Laser cutting cannot achieve perfectly square corners because the diameter of the laser creates a kerf. However, the resulting kerf radius is small and negligible. The disadvantage of this process lies in surface finish and accuracy. While tight tolerances up to +/- 0.005 inches can be achieved, the resulting surface is rougher than a machined surface that requires additional finishing.
Additional Technical Tips for Custom Fabricating Sharp-Angled CNC Parts
Choosing the ideal machining method to achieve sharp internal corners is a breeze when you work with a trusted CNC machining service like Xtproto. Our experienced specialists have extensive experience and can recommend the most suitable machining method based on factors such as material properties, design complexity, precision requirements, and cost considerations. To improve the quality of machining sharp corners using the above methods, CNC machinists should employ the following tips:
- Use sharp cutting tools: Regardless of the method used, CNC cutting tools should be very sharp to achieve cleaner cuts and precise corners.
- Use cutting fluid: Using cutting fluid will increase machining efficiency and prevent heat buildup during cutting, thereby extending tool life.
- Make multiple passes: Multiple passes improve accuracy and surface finish, making it easier to create precise, sharp internal corners.
Experience the precision of Xtproto’s CNC machining services for your custom sharp-angled CNC part needs
CNC machining parts with sharp corners can be challenging, requiring an experienced CNC machinist or CNC machining service provider. This article explores how to avoid and address these issues. However, to maximize the benefits of this process, it’s important to outsource the machining to a reputable CNC machining service provider. Xtproto can provide you with precise, high-quality, and fast CNC machining services. We offer unparalleled expertise across a wide range of industries. We utilize advanced equipment to deliver high-quality, high-precision custom components at competitive prices. Our Engineering Our team of engineers is experienced in all aspects of CNC machining and can advise you on how to create the perfect product. Let’s get started on your project today!