What Is CNC Milling | Overview of The Milling Process

CNC milling is an incredibly versatile method for creating prototypes or manufacturing large quantities of final-use components. With a wide range of milling materials to choose from, it’s suitable for most types of projects. Our CNC experts know how to quickly cut parts to reduce costs and how to mill complex geometries with tight tolerances in different materials.

This article focuses on the CNC milling process, outlining the fundamental knowledge of the process, as well as the components and tools of CNC milling machines. Additionally, it explores various milling operations and provides alternative methods to the CNC milling process.

What is CNC Milling?

CNC milling is a specialized form of precision machining where a tool removes material by moving at certain angles into the workpiece. The tool’s movements are controlled by computer instructions, resulting in extremely high precision and repeatability.

Milling differs from CNC turning, which is another popular CNC service where a single-point cutting tool is used to cut pieces from block or bar-shaped materials as they rotate rapidly in a chuck. Unlike milling, CNC turning is typically used to create cylindrical or tubular shapes. CNC milling can be employed for rapid prototyping or manufacturing final-use parts.

How does CNC Milling Work？

Like other machining processes, CNC milling starts with a design engineer creating a digital part using CAD (Computer-Aided Design) software. The file is then converted into ‘G-code,’ which is recognized by the CNC milling machine.

A CNC milling machine features a ‘worktable’ and a workpiece fixture to secure a large block of material (referred to as the ‘workpiece’) in the appropriate position. The worktable may or may not move, depending on the machine’s design.

During the CNC milling process, a rapidly rotating cutting tool comes into contact with the workpiece, removing material. The tool moves according to the G-code instructions to make cuts in the correct locations until the part is complete. Some CNC milling machines use a moving worktable to create more cutting angles.

Advantages of CNC Milling

Cost-Effective

By optimizing tool paths and using specialized cutting tools, CNC milling can be performed on 80% of appearance and mechanical parts in a matter of minutes or even seconds. With automated setups, CNC milling is highly cost-effective for batch production in most cases compared to additive manufacturing.

Material and Surface Treatment Options

In addition to short turnaround times, CNC milling allows for the use of various types and specifications of plastics and metal blocks, and it offers the flexibility to apply different types of surface treatments to CNC-milled parts, such as painting, anodizing, and chrome plating. It’s a perfect blend of functionality and aesthetics.

Complexity Unleashed

Due to the ability of milling machine cutting tools to approach the workpiece from several different angles, complex-shaped CNC parts can be created, featuring more axes, which allows for the production of higher complexity parts. If a CNC project requires irregular shapes, milling is often the preferred choice.”

Types of CNC Milling Machines

One important reason why CNC milling machines are valued in today’s manufacturing era is their ability to move on different axes. This feature allows workshops to achieve more complex designs with faster processing speeds and fewer operations. CNC milling machines are primarily divided into three types: vertical CNC milling machines, horizontal CNC milling machines, and multi-axis CNC milling machines.

Vertical CNC Milling Machines

Vertical CNC milling machines are cost-effective and widely used. These machines allow the tool to move up and down. In this case, the equipment moves on three axes—X, Y, and Z. Typically, it’s the worktable that moves, not necessarily the head. This type of CNC milling machine is generally easier to program while still offering various functionalities.

Horizontal CNC Milling Machines

In horizontal CNC milling machines, the milling head is oriented horizontally, not up and down. Similar to vertical CNC milling machines, horizontal CNC milling machines move on at least three main axes. However, horizontal CNC milling machines can also rotate for more complex designs. They can move on up to five axes, making them more expensive.

However, they are better suited for production workshops that need to produce large quantities of identical parts. Programming these machines requires more effort because they require more complex software. Typically, horizontal CNC milling machines are used for cutting grooves and slots in products. However, specialized tools can also be used for cutting slopes and radii, although these specialized tools are often more expensive. Horizontal CNC milling machines are excellent for cutting gear components.”

Multi-Axis CNC Milling Machines

CNC milling machines are typically defined by their number of axes. More axes mean they can move their tools and/or workpieces in more ways, providing greater cutting flexibility and the ability to manufacture more complex parts in shorter timeframes.

3-Axis: Standard CNC milling machines have 3 axes, allowing the spindle (and connected cutting tools) to travel along the X, Y, and Z axes. If the cutting tool can’t reach certain areas of the part, the part must be removed and rotated manually.
4-Axis: Some CNC milling machines add extra versatility by incorporating rotation along a vertical axis. This enhances flexibility and enables the creation of more complex parts.
5-Axis: The most advanced and widely used type of CNC milling machine is the 5-axis milling machine, which adds two additional degrees of movement by introducing rotation of both the worktable and the spindle. Parts typically don’t require multiple setups as the mill can manipulate them into various positions.”

CNC Milling Process

CNC milling is a machining process suitable for the production of high-precision, high-tolerance parts in prototypes, one-offs, and small to medium production runs. While the manufacturing tolerances for parts typically range from +/- 2 microns to +/- 10 microns, certain milling machines can achieve tolerances as tight as +/- 1 micron or even tighter. The versatility of the milling process makes it applicable across a wide range of industries and for various part features and designs, including slots, chamfers, threads, and cavities. Some of the most common CNC milling operations include:

Face Milling

Face milling is perhaps the most common type of milling operation used to create flat surfaces. During this machining operation, the rotational axis of the cutting tool is perpendicular to the surface being machined. As the name suggests, face milling operations involve the use of face mills.

These milling cutters have multiple interchangeable milling inserts, allowing you to efficiently produce the desired surface in a single pass. Compared to peripheral milling, face milling can also help you achieve higher surface finish quality because the design of face mills allows for precise control of the machining operation, resulting in the removal of less material.

Plain Milling

Plain milling, also known as slab milling, is a milling operation used to produce flat, horizontal surfaces. During the machining operation, the axis of rotation of the cutting tool is parallel to the surface being machined. This process employs a specific type of tool called plain milling cutters, which have teeth arranged around the periphery, enabling machinists to perform cutting operations.

Angular Milling

Similar to plain milling, angular milling also helps you create flat surfaces. The difference lies in how the cutting tool is set up. In angular milling, the axis of rotation of the cutting tool is at an angle to the workpiece surface. This allows you to create features such as grooves, serrations, and chamfers.”

Applications of CNC Milling

Automotive Industry

CNC milling machines play a crucial role in the automotive manufacturing industry. They can be used to machine various components such as automobile engines, transmissions, and braking systems. Additionally, they are employed in the fabrication of automotive bodies, chassis structures, and interior components.

Aerospace Industry

CNC milling machines also find significant applications in the aerospace manufacturing industry. They are utilized for machining various components of aircraft, including the fuselage, engines, and propellers. Furthermore, they are employed in the manufacturing of satellites, rockets, missiles, and other aerospace vehicles.

Electronics Industry

CNC milling machines have extensive applications in the electronics manufacturing industry. They are used for machining various electronic components and housing structures. Additionally, they are employed in the production of electronic products such as computer motherboards, displays, and smartphone casings.

Mechanical Industry

CNC milling machines are widely used in the mechanical manufacturing industry. They are employed for machining various mechanical components and housing structures. Furthermore, they are utilized in the manufacturing of various mechanical equipment, tools, and instruments.”

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