Introduction to CNC Milling

From geometric dimensioning and tolerancing to grinders, lathes and mills, there are a lot of different concepts to know when it comes to the world of computer numerical control (CNC) machining.

If you’re new to the industry, this can be intimidating. But once you learn the craft, this knowledge and skill set can become second nature.

For those who work in CNC machining, understanding CNC milling is crucial. This is a mechanical process that uses computerized controls and rotating cutting tools to create custom-designed parts.

So, how exactly is this process used in the CNC industry? Keep reading to learn all about CNC milling—what it is, how a CNC mill works and more.

What is CNC Milling?

Using computerized controls and rotating cutting tools, CNC milling removes material from the workpiece to create a finished product that meets the required specifications. This process can be used with a variety of materials, including plastic, metal, wood and glass. When it comes to CNC machining, there are several different processes that can be used, including:

• Mechanical
• Electrical
• Chemical
• Thermal

CNC milling falls under the category of a mechanical process since cutting and drilling is powered mechanically with no manual operation required.

Read: What is a CNC Maintenance Technician?

How a CNC Mill Works

The CNC milling process follows the same steps many other machining types do, including making a computer-aided design (CAD) model, getting the CNC milling machine set up and operating the machine to create the desired part. Here’s a quick step-by-step breakdown:

• Create a 2D or 3D CAD part design and export it to a CNC file format, which is converted to a CNC machine program utilizing CAM software.
• The CNC program informs the actions of the machine.
• The operator prepares the machine by setting up the worktable and the work-holding device and attaching the milling tools and machine spindle.
• Using the machine interface, the operator will start the program and monitor it throughout the process to ensure everything is going smoothly.

Depending on the type of part that needs to be created, there are horizontal or vertical milling machines that can be used. Once the milling starts, the machine will rotate the cutting tool at incredibly high speeds—up to thousands of revolutions per minute!

This cutting tool can rotate in various directions and along multiple axes. It can create many different shapes, holes and any other impression the part requires. Milling is often used to add finishing details to a workpiece that has already been machined, but it can also be used to shape a piece of raw material from beginning to end.

Whether the material has been previously machined or not, a milling machine will gradually chip away at the material to create the desired shape. As the process goes on, it becomes more accurate and precise, so the finished part is within the right specifications.

Read: Ferrous vs. Non-Ferrous: How They Differ & Identifying Them

CNC Milling Machine Parts

CNC mills are categorized based on the number of axes they can operate on. X and Y axes represent how the mill’s workpiece moves horizontally, and the Z axis refers to vertical movement. The W axis symbolizes diagonal movement. Most CNC milling machines operate on three to five axes.

As one might expect, the makeup of a CNC milling machine is quite complex, just like the parts they create. While different machines can vary, they generally have these parts:

• Frame/Base: The frame is the bottom piece that supports the machine. Essentially, it’s a base that provides stability during the milling process.
• Spindle: The spindle is the top portion of a milling machine where tool holders can be installed. This part rotates as the part is being worked on.
• Table: The table of a milling machine is what holds the workpiece for machining.
• Axes: As mentioned, there are several different axes on a CNC milling machine: W, X, Y and Z. The machine operates on these axes depending on the requirements of the part.
• CNC controller: The CNC controller is what controls the machine. It’s where the CNC operator will input the G-code that dictates the functions of the machine.

Read: CNC vs. Manual Machining: Which is Better?

4 Key CNC Milling Operations

The CNC milling process is versatile, so it’s used to support a variety of industries. There are different types of milling operations, including angular milling, form milling, plain milling and face milling.

1. Angular milling

In this type of milling operation, single-angle milling cutters are used to create angular features, like grooves. The cutting tool is at an angle to the surface of the material being machined, and this angle is determined based on the design of the workpiece.

2. Form milling

Form milling deals with irregular surfaces, like materials with curved surfaces. This process uses cutters that are specifically designed to work with these types of materials, such as corner-rounding cutters.

3. Plain milling

In plain milling, the cutting tool is parallel to the surface of the material being machined. Wide cutters are ideal for large surface areas, whereas narrow cutters can create deeper cuts.

4. Face milling

Last but certainly not least, in face milling the cutting tool is positioned perpendicular to the surface of the material that is being worked on. Face milling cutters are used, which are ideal for creating flat surfaces and contours. This creates detailed, high-quality finishes to the part.

Read: CNC Machining Tolerances: Standard Tolerances Explained

Other Types of Milling Operations

Alongside angular, form, plain and face milling, several other milling operations play critical roles in manufacturing and engineering.

End milling

End milling involves a cutting tool with teeth on the end and the periphery, used for milling pockets, slots and contours. This versatile process can handle a variety of materials and component shapes.

Slab milling

Slab milling, or horizontal milling, features cutting operations performed by a milling cutter that revolves on an axis parallel to the workpiece. It's particularly effective for creating large, flat surfaces.

Thread milling

Thread milling is utilized to produce threads, offering advantages over tapping such as higher speed and flexibility in thread size. It can create a wide range of thread sizes in both standard and custom forms.

Gear milling

Gear milling is a process specifically designed for creating gears. It employs either form milling or involute gear cutters, depending on the gear’s specifications. This process is critical for manufacturing precise and functional gears.

Each of these operations has its distinct advantages and applications, contributing to the versatility and efficiency of the milling process in modern manufacturing.

Read: What Is a CNC Maintenance Technician?

Types of Milling Machines

CNC milling machines are categorized based on their operational capabilities and the orientation of the spindle.

Vertical milling machines

Vertical milling machines feature a vertically oriented spindle. This design allows the spindle to approach the workpiece directly from above, which is mounted on the mill's table. This configuration makes these machines suitable for a variety of tasks such as drilling, bore cutting and thread cutting.

The adaptability of vertical mills makes them a popular choice in many workshops and manufacturing facilities, providing a solid foundation for precise and intricate machining work. One of the key benefits of vertical milling machines is their ability to handle complex parts and operations with ease.

The spindle’s vertical orientation provides greater visibility and access to the workpiece, which can be especially beneficial when dealing with detailed or delicate tasks. Furthermore, the versatility of vertical mills means they can quickly switch between different operations, reducing downtime and improving productivity in a manufacturing or engineering environment.

Horizontal milling machines

Horizontal milling machines are recognized by their horizontally oriented spindle. This setup positions the spindle along the same plane as the machine's table, making it particularly well-suited for heavy cutting operations. The strength of horizontal mills lies in their ability to handle large and heavy workpieces, thanks in part to the support offered by the machine's table and the orientation of the spindle.

Another notable feature of horizontal milling machines is the inclusion of a rotating table. This allows for the milling of complex shapes such as helical gears, expanding the range of possible applications. The capability to perform such complex operations makes horizontal mills invaluable in settings where precision and versatility are very critical, such as in the production of parts for the automotive or aerospace industries.

Universal milling machines

Universal milling machines combine the mechanics of vertical and horizontal milling machines. Equipped with a swiveling head, these machines can pivot to position the spindle for either vertical or horizontal milling. This flexibility allows for a wide range of tasks to be performed, making universal mills a highly adaptable addition to any workshop or manufacturing floor.

The key advantage of a universal milling machine is its ability to easily switch between different milling modes. This adaptability not only improves the machine's utility in performing various operations, but also facilitates complex machining tasks that would otherwise require multiple machines. Whether it's slot cutting, angle cutting or gear cutting, the universal milling machine's versatility makes it a valuable tool for any machining operation.

Turret milling machines

Turret milling machines, often referred to as Bridgeport-type mills, have a design that features a stationary spindle. The table of these machines is capable of moving both perpendicular and parallel to the spindle axis, allowing for precise control over the cutting process. This range of movement can be particularly useful for tasks that require a high degree of accuracy, such as when cutting slots or creating complex shapes.

Turret mills are known for their robustness and reliability. The flexibility of table movement, combined with the stationary spindle, provides a stable and precise milling environment. This setup is extremely conducive to producing high-quality work, making turret milling machines a staple in tool rooms, R&D departments and manufacturing plants looking for precision and efficiency.

CNC bed milling machines

CNC bed milling machines differ from turret mills in that their table moves only in a perpendicular direction relative to the spindle's axis. Meanwhile, the spindle itself is able to move parallel to its axis. This configuration offers a stable and rigid setup for heavy milling operations, making bed mills particularly suitable for large and heavy workpieces.

The CNC aspect of these machines brings added precision and efficiency, allowing for highly accurate milling operations to be carried out at increased speeds. With CNC, bed milling machines can perform complex cutting and shaping tasks with minimal human intervention. This capability makes CNC bed mills indispensable in high-volume production environments where precision and repeatability are key.

Read: What Is CNC Programming? CNC Programmer Description

FAQs

1. What is CNC milling and how does it work?

CNC milling is a process used in manufacturing that involves the use of computer numerical control to automate the operation of milling machines. This process allows for the precise cutting, shaping and drilling of materials by translating a digital design into a physical object through the mill’s controlled movement.

2. What are the main components of a CNC milling machine?

The main components of a CNC milling machine include:

• Controller, which operates the machine based on the programmed instructions
• Spindle, which does the actual cutting of the material
• Bed, on which the material rests during milling
• Tool turret, which holds various cutting tools

3. What are the advantages of using CNC milling machines over traditional milling methods?

Compared with traditional milling methods, CNC milling machines offer higher precision and consistency. They also significantly reduce the time and labor involved in the production process, as they can operate autonomously once programmed.

4. What are the different types of CNC milling machines?

There are several types of CNC milling machines available in the market, including vertical and horizontal milling machines, which differ in the orientation of the spindle. Other variations include 3-axis, 4-axis and 5-axis CNC mills, which refer to the number of directions in which the cutting tool can move.

Train To Pursue a Career as a CNC Machinist at UTI

Are you fascinated by the CNC industry and interested in learning more about processes like CNC milling? Pursuing a career as a CNC machinist may be the right choice.

In UTI’s CNC Machining Technology program, you can get an introduction to CNC machining and be taught the skills to craft performance parts and components from raw materials using processes like CNC milling.¹ You’ll take courses on a variety of topics, including:

• Basic Machine Shop Skills
• Interpreting Blueprints/Job Layout
• CNC Basics
• Manual Machining Basics
• CNC Milling
• CNC Turning
• CAD and CAM

The CNC program is offered at our campus in Mooresville, North Carolina, and can be completed in just 36 weeks. To learn more, visit our program page to request information or call 1-800-834-7308 to get in touch with an Admissions Representative today.