CNC milling is one of the most prevalent machining methods in the manufacturing industry. It utilizes a variety of materials and shapes them into desired parts or products. CNC milling machines can perform a variety of milling operations to handle complex designs. Essentially, each operation involves removing material from the workpiece using a milling cutter mounted on a movable spindle. However, different types of milling cutters and spindles vary in their movement. This article will discuss the different milling operations in detail, explaining their advantages and applications. Ultimately, you will be able to select the appropriate milling process for your project.
How CNC Milling Works
Each milling operation in machining involves designing a printed part, translating that design into G and M codes (commands understood by the CNC machine), tooling and setup, and process execution. Let’s examine how a CNC milling machine uses its components and milling tools to perform milling operations. The CNC milling process involves a series of steps to transform a digital design into a physical component:
- Design Creation: The part is first created with the help of CAD software such as Autodesk Fusion 360. This design is the actual design used to manufacture the product.
- Generate Instructions: Use CAM software to convert the CAD model into a form understandable by the CNC machine. This generates G-code, a set of codes that describes the machine’s positions and functions.
- Machine Setup: Secure the harder material to the milling machine’s bed and control it with the aid of the aforementioned tools. Position the spindle and adjust the machine to the requirements of the work to be completed.
- Milling Operation: The first operation in CNC milling is to input the G-code into the CNC milling machine. The machine’s cutting tool then rotates and trims the block to the desired shape and thickness.
Additionally, selecting the appropriate CNC milling operation type based on the 3D design ensures optimal results. For example, face milling creates smooth surfaces, while thread milling precisely cuts threads. This ensures the most appropriate technology is used for each specific task.
12 Different CNC Milling Operation Techniques Explained
This classification is based on the type of geometry that can be created by milling. This can include flat surfaces, angular features, threads, irregular shapes, or specialized geometries such as gears or mechanical CAM. The versatility of CNC milling technology stems from its ability to perform a variety of milling operations, meeting a wide range of machining needs, from slots to complex undercuts. We’ll discuss 12 of these operations later. Before that, let’s provide an overview of the 12 different CNC milling types.
Face milling: This operation creates a flat surface on a workpiece. As part of the vertical milling process, the tool used in this method has an axis of rotation perpendicular to the surface, with the tool face parallel to the workpiece. Consequently, the sharp teeth of the tool remove material, while the face smoothes the surface. One of the main advantages of this method is its tool geometry, which enables high material removal rates. This enables rapid part production with smooth surfaces. Facing is particularly effective for creating flat surfaces in applications such as automotive cylinder heads and radiators.
General milling: This operation specializes in machining flat surfaces and contours on workpieces. Using a cylindrical milling cutter with straight or helical teeth, the material is milled to create flat or stepped surfaces, slots, and grooves. The cutter axis is parallel to the workpiece surface. General milling is known for its consistent material removal capabilities across a wide range of machining operations. It’s ideal for light or finishing operations. For example, it can be used to remove material from the outer layers of a larger workpiece, preparing it for subsequent machining steps.
Side Milling: As the name suggests, side milling involves machining the side of a workpiece using a side milling cutter or end mill. Both vertical and horizontal milling machines can perform this task. During machining, the side edges (teeth) of the rotating milling cutter remove material, creating flat vertical surfaces, edges, grooves, slots, complex contours, flash, and more. Side milling cutters have specially designed spiral flutes that target the side of the material, unlike other machining methods (such as flat machining) that focus on the top surface. This technique is particularly useful in a variety of applications, including creating automotive suspensions, machining channels or slots in aircraft parts, producing injection molding or casting molds, manufacturing medical implants, and constructing heat sinks for electrical and electronic equipment.
Straddle Milling: This method stands out for its ability to simultaneously machine two parallel surfaces on a workpiece while maintaining a uniform distance between them. How does straddle milling achieve the goal of machining two surfaces in a single setup? This process uses two or more side milling cutters mounted on a single spindle, removing chips from the material surface during feed. This makes it ideal for creating parallel slots, grooves, and various contours in workpieces. This technique is primarily used in the manufacture of automotive jigs, fixtures, brackets, levers, gears, sprockets, transmissions, and axle housings.
Gang milling: Why is it called gang milling? Because it involves mounting multiple tools (such as end mills, form mills, and slab mills) on a single spindle to create complex features and fine details. This setup allows for simultaneous operations on a single workpiece, reducing machining time and increasing efficiency. First and foremost, any milling application requires multiple features, such as slots, channels, grooves, and flat surfaces. This technique is primarily used in automotive engine blocks and transmission housings, but it is also applicable to frames, brackets, gears, sprockets, and housings for a wide range of machinery and tools, as well as in mold prototyping and manufacturing.
Angle milling: Angular features in CNC machined parts are often created using angle milling. In this operation, the tool axis is angled relative to the workpiece, while angle plates or fixtures are used to maintain the workpiece in the desired orientation. The tool precisely machines the workpiece at a specific angle, which can be fixed at 45°, 60°, or 75°. This method is used to create features such as small chamfers, bevels, T-slots, dovetails, and other complex geometric contours.
Profile Milling: Do you know how CNC machines can create irregular contours? This is achieved through profile milling, which uses a tool with a shape that is the inverse of the desired contour. For example, to machine a turbine blade, a tool is first fabricated with the geometry that matches the blade. This method allows for precise and customized machining of complex designs. As the tool rotates, it moves across the workpiece, or the workpiece moves beneath it. The tool’s cutting edge then removes material, creating the desired geometry. This technique is primarily used to manufacture domed pistons, orthopedic implants, turbine blades, moldmaking, guitar bodies, custom prototypes, and more.
End Milling: This is one of the most popular milling operations. End mills perform this operation by feeding the workpiece into the cutter at a vertical or angled angle. Simultaneously, multiple cutting edges on the face and periphery of the end mill remove material as it feeds into the workpiece.End milling is particularly advantageous when you need complex contours, precise edges, slots and grooves of varying depths, and a smooth surface finish on the workpiece.
Sawing: Sawing uses a large milling cutter with a tooth profile that rotates around it. This method is particularly suitable for milling narrow slots and dividing a workpiece into two parts. The cutter moves downward, cutting the material with a continuous feed. However, due to the large cutter size, sawing operations are generally slower than other methods, and the rapid material removal generates significant heat, potentially causing thermal damage to both the workpiece and the cutter. Furthermore, CNC sawing machines are not limited to the common grooving and parting tasks of conventional machine tools; they can also process other geometries, such as slight curves or contours.
Gear Milling: Gear milling is a specialized operation used to finish manufactured gears to precise dimensions and surface finishes, or to create fine tooth profiles. For example, it can finish extruded bevel gears to a surface finish of Ra 1.2 µm. In some cases, it can also create complete gears from scratch. Tools used in gear milling include gear milling cutters, hobbing machines, and form milling cutters. These tools enable high-precision gear shaping, far exceeding other gear machining techniques. Furthermore, the operation can process nearly all types of gears, regardless of shape and complexity, such as spur gears, bevel gears, helical gears, and rack and pinion arrangements.
Thread Milling: As the name suggests, thread milling is used to cut both internal and external threads on a workpiece. For internal threads, an insert tool removes material from the surface of an existing hole to form the thread. In contrast, external threads can be easily produced using a thread mill or thread cutter of the appropriate type and size. However, thread milling is more suitable for internal threads in larger holes.Thread-milled parts are used in a wide range of industries, from automotive engines to consumer products, for assembly and other purposes.
CAM Milling: Cam systems (CAMS) are essential components in various mechanical systems and mechanisms, used to convert linear motion into rotary motion, or vice versa. CAM milling operations use a down-the-hole milling cutter to machine these components. This cutter rotates the workpiece and positions it so that it can remove surface material according to the designed CAM profile.
Different Types of CNC Milling Operations Based on the Milling Mechanism
There are three main types of milling machine operations: manual, CNC, conventional, and ramp.
- Manual Milling: In manual operation, the operator manually sets the workpiece and tool in the machine. Milling parameters such as depth of cut, speed, and feed also require manual adjustment. Tool motion control is manual, allowing the operator to cut the workpiece in the desired direction and orientation to achieve the desired shape. The milling machine can also be adjusted using handwheels. While manual operation is more time-consuming and less accurate, it offers flexibility in terms of cost and customization.
- CNC Milling: CNC milling is the most precise and fastest machining operation because it automates the process. Tool motion and workpiece positioning are computer-controlled, eliminating the possibility of error and significantly reducing time. Almost all operations can be performed with a CNC milling machine, but any specific operation requires the appropriate tool or cutter. The latest multi-axis machines (typically 3-6 axes) are capable of machining complex shapes and details on workpieces with greater precision. As a result, their applications are more extensive than any other milling process, encompassing diverse sectors such as automotive, aerospace, and medical components.
- Up-cut milling and down-cut milling: Fundamentally, these two machining methods involve different feed mechanisms. In up-cut milling, the tool (or cutter) rotates in the opposite direction of the feed. Down-cut milling, on the other hand, involves tool rotation in the direction of the feed. Two other common techniques or operations are vertical milling and horizontal milling, which are based on the spindle’s orientation.
Different Types of CNC Milling Machines
Before delving into CNC milling technology, let’s first familiarize ourselves with the various types of machines. CNC milling machines have evolved significantly, diversifying their capabilities and uses. Different milling machines meet different production needs, each with unique characteristics and capabilities.
Vertical Milling Machines: Vertical milling machines, generally considered the most common type, feature a vertically oriented spindle. This orientation means the cutting tool moves up and down, aligned with the machine’s vertical axis. Vertical milling machines are primarily characterized by turret milling machines and bed milling machines. Turret milling machines contain a fixed spindle and a bidirectionally movable table; the table moves only perpendicular to the spindle axis. Vertical machines are often favored for their versatility. They are useful for processing individual pieces and small batch sizes, whereas the table moves only perpendicular to the spindle axis.
Horizontal milling machines: As the name suggests, these machines have a horizontally oriented spindle, forcing the mounted cutting tool to move left and right. Horizontal milling machines excel at heavy-duty cutting and processing heavier materials. These machines are often equipped with multiple cutting tools, enabling them to perform multiple tasks simultaneously.
Knee milling machines: These machines get their name from the adjustable knee-shaped structure that supports the table. This design facilitates vertical movement and adjustment of the table. Notable features include a sturdy design, making them ideal for heavy-duty milling. They can handle a wide range of operations, from simple tasks to complex procedures. Knee milling machines are extremely versatile and form the backbone of many manufacturing facilities.
C-frame milling machines: These are more robust than knee milling machines and are often used in industrial settings. Their heavy-duty nature is defined by their single-column design, which provides greater rigidity and a larger work area for handling critical operations.
Gantry Milling Machines: These machines feature dual-motion capabilities, with a linearly moving table while the cutting operation remains stationary. Highlights of this type include processing multiple workpieces simultaneously and the ability to handle larger tasks with ease and precision.
Specialty Milling Machines: Specific tasks require unique approaches. Enter the world of specialty milling machines. These are designed for specific tasks, such as:
- Turntable Machines: Designed for circular cutting operations.
- Drum Milling Machines: Designed for camshaft and mold production.
- Tracker-controlled Machines: Suitable for complex designs and replica models.
How to Choose the Right Milling Operation?
Do you know how many operations are required to manufacture a car transmission? The answer is many, including face milling, end milling, and gear milling. This is just one example of how different operations accumulate to form the final part. This applies to nearly every project.
Therefore, project success depends on selecting the right operation based on the 3D model. To do this, consider the factors that influence the milling machine. Factors that influence the results of various operations on the workpiece.
Material Type: First, the workpiece material type significantly influences the type of CNC milling operation selected, as variations in performance directly impact material removal rates and tool wear. Therefore, the operation you choose should be compatible with properties such as hardness, thermal conductivity, and toughness. For example, conventional milling is challenging for forming hard materials like tool steel.
Surface Roughness: Surface finish requirements are another consideration when selecting a milling operation for your design. This is because each operation produces a different surface roughness. Therefore, select an operation that achieves the Ra value required for the final product’s functionality and aesthetics.
- Face Milling: 0.8–3.2
- End Milling: 0.8–6.3
- Slot Milling: 1.6–6.3
- Thread Milling: 1.6–3.2
- Gear Milling: 1.6– 3.2
Geometric Complexity: Not all milling techniques are capable of creating intricate and fine details on a workpiece. Some milling processes, such as plane milling, face milling, and slot milling, are only suitable for simple contours and shapes. On the other hand, processes such as end milling, thread milling, and gear milling are known for their ability to produce complex parts and assemblies. Another factor in design complexity considerations is whether you can optimize the toolpaths for the selected operations as needed.
Consider Machine Parameters and Setup: Machine parameters such as spindle speed, feed rate, and depth of cut are crucial for selecting the appropriate milling operation. These parameters affect machining quality, accuracy, and production speed. Furthermore, the machine setup, such as axis motion capabilities, workholding, and rigidity, should also be compatible with the intended milling operation.
Select the Right Tool for Different Milling Operations: Not all tools are suitable for all milling operations. Each type of operation requires its own tool combination, and using the wrong tool type can result in poor machining results or even damage to the tool and workpiece. Furthermore, even after selecting an operation, the specific circumstances are crucial. For example, when selecting a tool for end machining,You can choose between flat nose, ball nose, or radiused nose tools, each suited to different applications.
What are the basic types of milling machines?
The basic types of milling machines include horizontal milling machines and vertical milling machines. These classifications are based on the machine’s axis motion and orientation.
Which milling operation achieves the highest precision?
Form milling is generally considered the most accurate milling operation because it involves a single-pass mechanism, significantly reducing tool deflection and inaccuracy.
Which milling operation has the highest cost?
Gear milling operations tend to incur the highest costs because they require specialized tools, long cycle times, and precise setups.
What is the most cost-effective type of milling operation?
Face milling, or slab milling, is the most economical. It involves simple tools and a mechanism for removing material directly from a flat surface. However, this operation alone cannot create complex shapes.
Conclusion
CNC milling is a powerful manufacturing process that offers unparalleled precision, efficiency, and versatility. Using the right CNC milling technology, you can create precise and complex geometries. Furthermore, efficient CNC milling operations, toolpath strategies, and the use of the correct software and cutting tools all need to be considered. Complex shapes and features achieved through CNC milling can only be achieved by selecting the right process for your project. Each process offers unique advantages and capabilities for creating specific geometries. Furthermore, advanced machine tools and the right cutting tools are essential for effectively executing these various processes. Only then can the desired precise results be achieved.
Xtproto’s Precision CNC Milling Technology
Xtproto has been dedicated to on-demand manufacturing for over a decade, continuously pushing the boundaries of what is achievable. With a commitment to excellence, Prolean’s CNC milling services go beyond simply removing material from a workpiece; they involve precisely carving it, ensuring that every cut, groove, and contour embodies quality and craftsmanship. Whether it’s the intricate threads of thread milling or the flawless surfaces of face milling, Xtproto’s expertise is evident in every micron. What makes Xtproto’s CNC milling services unique is not only its advanced machinery, but also the combination of cutting-edge technology and experienced expertise. Our engineers and technicians ensure that each milling technique is optimally applied to achieve impeccable results, both functional and aesthetically pleasing.
At Xtproto, you’ll have full access to the latest CNC milling machines and extensive experience handling milling projects. Our CNC machining and CNC milling services encompass design optimization, all milling operations, and even surface finishing of milled components. Furthermore, our dedicated quality control team ensures that you receive parts that meet your desired specifications. Request a quote today to start your CNC milling project with xtproto.