CNC milling is a versatile CNC machining process known for producing precise and complex parts. It involves a variety of techniques and operations and can accommodate a wide range of tooling; end milling is one of them. In fact, it is the second most popular machining process after CNC turning. A wide range of tooling options, high material removal rates, precise surface finishes, and other factors have made this process widely used across various industries. This article will detail what end milling is, compatible tooling, applications, advantages, potential challenges, and machining considerations.
Definition of CNC End Milling
Like all other subtractive manufacturing processes, end milling uses a multi-edge rotating tool to remove material until the desired shape and features are formed. It is capable of producing intricate and detailed features in metals, alloys, plastics, composites, and other engineered materials.
What distinguishes end mills from other tools is the helical design of their cutting edges. The cylindrical shank features teeth on both ends and sides, allowing them to cut the workpiece in multiple directions. Furthermore, a variety of CNC end mills (square nose, ball nose, radius nose, etc.) allow you to produce multi-feature 3D shapes. With the right tool, you can machine complex contours, deep holes, pockets, slots, flat profiles, grooves, and more.
How a CNC end mill works
A dedicated end mill or conventional CNC machine tool mounts a suitable end mill in its spindle (or other rotating component). It then precisely controls the motion on the workpiece according to a predetermined tool path. The size, depth, speed, cycle time, and all other variables depend on the CNC input, the geometry, and the size of the end mill.
Part Design and Programming: The part to be milled begins with a detailed design outlining all features, dimensions, and machining directions. During the design process, the capabilities of the end mills must be considered; what shapes can they machine?
Machine Setup: The end mill is secured to the spindle chuck or toolholder, while a vise, clamp, or fixture holds the workpiece. This position ensures the workpiece is parallel to the worktable or spindle axis. The values of the input parameters depend on the workpiece material and tool coating. After setting up the tool and workpiece, the operator sets the reference point (work offset).
Milling Process: After the program runs, the spindle rotates the end mill, where the cutting edges interact with the material, shearing and forming chips. The end cutting edge cuts axially, while the side cutting edges cut radially. The spiral flute design facilitates chip evacuation. The entering angle and cutting path are determined by the CNC program. The same program code controls the spindle movement of the tool in the X, Y, and Z axes.
Advantages of End Milling
Precision and Accuracy: End milling achieves precise and accurate cuts. This process removes material from the workpiece while ensuring that the workpiece conforms to the desired dimensions. End milling focuses on precisely creating certain contours, features, and surfaces. Therefore, it is best suited for applications requiring high tolerances.
Capable of Complex Geometries: End milling is ideal for creating complex geometries because it can cut in multiple directions simultaneously. It can also create complex shapes, grooves, slots, and holes of varying sizes. Common use cases for this process include contour cutting, complex 3D machining tasks, and profiling.
Internal Feature Machining: This is another key advantage of end milling over other machining operations. It can create internal features that would be complex with other machining processes.
Operational Flexibility: Because end milling can perform a variety of machining operations, many industries rely heavily on it. For example, end milling is used to produce surgical instruments, dental prostheses, and other medical devices. This machining method can create complex designs in molds, various types of tools, and furniture. It can also cut plastic, aluminum, wood, and even composite materials.
Cost-Effective for Low-Volume Production: It is a cost-effective solution for small-batch production. The end milling process is automated, which speeds up production. With end mills, manufacturers can produce parts in a matter of hours. Furthermore, end milling is ideal for prototyping and production because it allows manufacturers to scale up to moderate production through a trial process.
Types of End Mills and Their Applications
There are various types of milling cutters used for end milling, depending on the geometry of the cutting edge and application preference. Their tip shape and flute characteristics distinguish them from one another. Let’s briefly discuss the common types of CNC end mills.
Roughing End Mills: These end mills remove large amounts of material while leaving a relatively rough surface. Their rough or wavy cutting edges and larger core diameter enable heavy-duty cutting with minimal vibration. These tools are primarily used for heavy-duty machining of steel, aluminum, iron, and other metals. Applications include molds, shipbuilding, and pre-finishing of automotive parts.
Ball-nose milling cutters: Ball-nose milling cutters are characterized by a hemispherical tip and two or four-edged cutting edges. These cutters can continuously cut the workpiece to create complex 3D contours, curves, and concave profiles. They are used for facing, cavity machining, profiling, and corner radiusing. These CNC tools are commonly used for 3D contouring of molds, engraving of automotive and aerospace parts, and adding fillets to complex designs.
Radius end mills: Radius end mills have rounded edges that remove material from the workpiece to create rounded corners or specific radii. The radius size of these cutters can be selected based on your needs. These CNC tools are primarily used for deburring, corner fillets (or radii on sharp edges), aesthetic finishing, and transition curves between complex part contours. Square-nose milling cutters: As the name implies, these cutters feature a flat, square tip perpendicular to the tool’s axis of rotation. This geometry produces perfectly 90-degree edges, corners, and flat bottoms on the workpiece. As a result, square-nose milling cutters are very popular for general-purpose machining tasks, often used for keyways, slots, external contours, vertical cuts, flat-bottomed holes, and smoothing surfaces.
Dovetail end mills: Dovetail or fishtail end mills are characterized by an angled cutting edge (matching the desired dovetail profile) and are available in standard angles such as 45°, 60°, and 90°. Choose from these tools for machining dovetail slots or profiles, slot and slide arrangements, dovetail joints, grooves, notches, undercut features, and more.
Finishing end mills: These are carefully ground and precision-machined end mills designed to achieve tighter dimensional tolerances and smoother surface finishes. Their head designs incorporate a higher number of flutes (2 to 6) and feature a higher helix angle, resulting in lower roughness, with Ra values as low as 0.4 µm. Various industrial products requiring smooth surface finishes, such as medical device parts, radiators, measuring instruments, and vehicle engine parts, are also suitable.
V-shaped end mills: These milling cutters feature V-shaped tooth tips with angles of 30, 60, or 90 degrees. The tapered tip of a V-shaped milling cutter is suitable for chamfering, engraving, and 3D engraving. V-shaped drills can be used to engrave logos, emblems, symbols, numbers, and letters onto work surfaces. Therefore, they are also suitable for chamfering and narrow cuts.
Materials that CNC end mills can process
You can choose from a variety of plastics, metals, alloys, and composites to process using the end milling process. Material selection is directly related to the tool and machining conditions; suitable tool coatings and milling variables vary depending on the material type. We have outlined common materials and the end mills suitable for them.
- Aluminum Alloys: 6061, 7075, 2024
- Steel and Stainless Steel: High-Speed Steel (HSS) or Carbide, TiCN-Coated AISI 304, AISI 316, AISI 1018, AISI 1045
- Titanium Alloys: Grade 5 (Ti-6Al-4V), Grade 2
- Plastics: Acrylic, Polycarbonate, Nylon, Polyoxymethylene, Polyethylene, Polypropylene
- Composites: CFRP, GFRP, Kevlar, Epoxy, Thermoplastics
End mill applications across various industries
CNC end mills can be used to create a variety of precision features, including flat surfaces, complex contours, channels, holes, and more. Consequently, their applications are diverse, ranging from general consumer goods to industries with stringent precision requirements. Here are some key application areas:
Aerospace Industry: End milling is very useful in producing complex components, such as engine mounts and bracket housings in the aerospace sector. These components are often made of aluminum and require very high precision and quality. Other examples include rough surface machining of aircraft wings, turbine barrels, and many other components.
Automotive Parts: CNC end mills can produce both rough and smooth automotive parts; their precision, fine detail, and surface quality make them popular in automotive manufacturing. You can create engine components, valve seats, transmission housings, oil passages, wheel hubs, and more.Furthermore, this milling method meets the growing demands of electric vehicles, such as motor components, battery housing features, and powertrain components.
Electronic Precision Parts: Miniaturization and high precision are key requirements for electronic parts; carbide tools are used in the manufacture of printed circuit boards (PCBs). For example, smooth holes and keyways facilitate smooth connections. Other applications include electronic device housings, mounting components, thermal management components, and more.
For Medical Devices: Precise dimensions and finish are crucial in medical device manufacturing, directly impacting treatment effectiveness and safety. End milling can process medical-grade titanium alloys, stainless steel alloys, and some plastics for the manufacture of diagnostic devices, implants, and surgical tools. End milling also allows for customized implants tailored to patient needs.
Prototyping and Custom Part Manufacturing: Engineers and manufacturers use multi-axis CNC end mills to test and refine designs. They can produce complex designs in metals, plastics, and composites. Examples include molding tools, jigs, fixtures, and custom parts.
Differences between End Milling and Face Milling
Face milling is a more specialized machining process focused on machining flat workpieces, removing large amounts of material to achieve surface flatness. Face mills are often used as preparatory steps for complex machining tasks. Unlike end mills, face mills have large, flat machining faces with cutting edges around the perimeter. The following table of face mills and end mills summarizes their key differences.
Cutting Direction and Tool Application: Face milling requires the cutting edges to be perpendicular to the workpiece surface. In contrast, end milling typically involves cutting edges on the sides and face of the tool. Face mills typically have more cutting edges and wider flutes, allowing them to machine larger materials. End mills, due to their smaller diameter, process less material.
Surface Finishing: Face milling is a more efficient and faster process for large workpieces. Its design allows for more frequent contact with the workpiece surface, resulting in a smoother surface. You can also use both traditional inserts and scrapers for a better surface finish on parts. Furthermore, end mills can handle complex shapes and contours. Their flexibility allows for excellent surface quality even in challenging areas.
Use and Applicability for Various Materials: Face milling is an efficient machining method for flat, large surfaces and vertical features, ensuring that the workpiece meets milling requirements. It can be used for machining a variety of metals, including aluminum, titanium, steel, and brass. Face milling can also be used to create grooves and parallel and horizontal surfaces. End mills allow you to precisely create holes, contours, grooves, and shapes. They can be used for both roughing and finishing, as well as for fine cuts requiring precise features. End mills can also be used to mill a variety of materials, including composites, metals, and non-metals.
Tool Type and Shape: Face milling requires a face milling cutter, which creates a smooth workpiece surface. End milling, on the other hand, primarily uses end mills, which come in a variety of shapes and sizes, such as radius end mills, ball end mills, and square end mills. Face mills have a large number of cutting edges and a larger diameter, allowing them to machine large surface areas in a single operation. End mills, on the other hand, are smaller and are used for precision profiling, slotting, and grooving.
Depth of Cut: End milling and face milling require different depths of cut depending on the machining process. You can adjust the depth of cut based on parameters such as material type, machine tool capabilities, and surface finish requirements.
When to Use Face Milling vs. End Milling
The differences between face milling and end milling also make them suitable for different machining scenarios. Face milling is a perfect choice when you need to smooth a surface and create different features on that surface. This machining process is often used in industries that require machining large components and prioritize precision and a fine surface finish. Face milling is also suitable for machining aluminum, steel, and other metals that require a smooth surface finish. Face milling can also be used when you need to prepare parts for assembly. This milling method achieves excellent flatness on large components, such as engine blocks and frames, before they are assembled with other parts.
When time is of the essence, face milling is preferred because it can quickly remove large amounts of material in a short period of time. It’s a better choice for larger projects because it’s faster and more efficient.
End mills have a smaller diameter, which helps achieve more precise cuts. Due to their smaller diameter, they can fit into tighter spaces. This makes them the best choice for applications where precision is a primary concern. You can use end mills to produce complex parts, molds, and dies. They are widely used in applications requiring intricate designs, such as aerospace and medical devices.
Another common application for end mills, demonstrating their efficiency, is the machining of slots and grooves. End mills can remove material in a more controlled manner, creating features such as cavities and keyways in the workpiece.
Additionally, you can use end milling for materials such as plastics, metals, and composites. This machining method can create complex cuts and is ideal for machining intricate features and shapes.
How can Xtproto support your milling needs?
For any end milling project, considering the final requirements and arranging the right end mill type is crucial, and Xtproto understands this. Our engineers will work closely with you until your part is delivered, including assistance with design optimization, material selection, and finishing recommendations. Furthermore, our in-house facility features milling machines equipped with the latest CNC integration, enabling high-precision processing of custom and complex designs. Whether you’re a small startup or an established brand, our CNC machining services provide high-quality parts to your exacting designs for a wide range of industries.
Conclusion
Overall, end milling is a process capable of creating complex features and contours on a wide variety of workpiece types. Using the correct tool type, milling variables, and settings is crucial for manufacturing parts with high geometric complexity. Furthermore, understanding the potential challenges a machine tool will encounter before it’s put into operation can help prevent defects and the risk of failure. This process is driving innovation in complex mechanical structures across various industries, continuously improving manufacturing precision and efficiency.