Understanding CNC Milling​

14 December 2023
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In today’s industrial landscape, CNC (Computer Numerical Control) machining stands as a prominent manufacturing method with diverse applications. CNC technology plays a pivotal role in crafting essential components of modern life, including planes, trains, and automobiles.

CNC machining represents a sophisticated manufacturing process where precise computer instructions orchestrate the creation of products. This subtractive manufacturing technique harnesses specialized tools like drills, mills, and lathes to meticulously sculpt workpieces, gradually transforming raw materials into the desired end products.

This article will dive into the CNC Milling process, detail the anatomy of a CNC machine, and the different types of CNC milling available.

What is a CNC milling machine?

CNC milling machines are renowned for their ability to produce precision parts with exceptional detail and a superior finish. These machines employ rotary tools, following instructions derived from CAD (Computer-Aided Design) files, to meticulously craft intricate part designs.

The milling machine’s computer governs the cutter’s actions and coordinates, requiring minimal human intervention for the manufacturing process to reach completion.

Engineered for high-volume production across a spectrum of materials, including plastics, CNC milling machines are proficient in churning out diverse components. At their core, these machines excel in mechanically sculpting workpieces into the desired shapes.

5 axis machining

How does CNC Milling work?

The CNC milling process hinges on the precise execution of coded instructions by the machine. It starts with the creation of a 3D CAD file representing the intended part. Once this design is finalized, it’s converted into a format readable by the CNC machine.

Subsequently, CAM (Computer-Aided Manufacturing) software exports the design into a CNC machine program, often in G-code format, which serves as the directive, governing every move of the machine. This results in a faithful replication of the CAD design in the selected material, marked by remarkable accuracy and efficiency.

CNC milling, rooted in subtractive machining technology, is adept at producing complex and intricate parts in both high and low volumes. The process involves the removal of material from a blank workpiece, with a rotating cylindrical tool known as a milling cutter. Depending on the specific CNC milling machine in use, it can cut at varying angles and traverse different axes.

The initial part design typically originates from CAD, before it’s fed into the milling machine for the final production phase.

What does a CNC Milling Machine do?

A CNC milling machine makes intricate parts for several industries using subtractive machining technology. The milling machine cuts away at the workpiece and crafts the final piece via the 3, 4 or 5 axes

Depending on the number of axes the CNC milling machine has, the more complicated and intricate the final piece can be. A CNC milling machine is used by various industries – including aerospace and medical industries – to manufacture complex parts.

CNC Milling

The CNC Milling Process

Choosing the right milling machine depends on various factors, particularly the complexity of CNC milling operations dictated by the final part’s design. High-end and structurally critical components require intricate designs to achieve the desired finish and aesthetics.

In cases demanding exceptional precision, like the creation of medical or aerospace components, advanced milling machines are essential. These machines ensure the realization of the final design with the utmost precision and quality.

On the other hand, basic parts intended for general use may not necessitate such high precision or a top-tier finish. They can typically be crafted with fewer axes, such as a 3-axis milling machine. These machines are user-friendly, cost-effective, and offer excellent accuracy.

In 3-axis milling machines, cutting tools are attached to a spindle operating on three linear axes. They can achieve precise cuts even in robust materials, moving vertically (Z-axis) and in the X and Y directions. However, 3-axis machines cannot handle undercuts or inaccessible features, necessitating a more advanced milling machine for complex designs.

The 4-axis milling machine adds sophistication, introducing the ability to rotate along the X-axis, similar to a lathe.

For the most intricate and demanding designs, 5-axis milling machines come into play. They provide rotation in both the X and Y axes, making them suitable for highly complex projects in fields like medical device manufacturing, impeller production, and aerospace structures.

The Tempest Fighter Jet

What are the Applications for CNC Milling?

CNC mills, prized for their precision, find widespread application across diverse industries like aerospace, medical, and electronics.

In aerospace, they craft essential components like manifolds, bushings, and landing gear. Medical reliance on CNC milling extends to creating prostheses, FDA-approved devices, and instruments. Similarly, CNC mills contribute to electronic industry essentials, producing heat sinks, amplifier housings, and various parts.

Moreover, these machines are pivotal in supporting other manufacturing technologies. For instance, CNC mills intricately shape copper mold patterns and cavities vital in injection molding processes.

5 axis machining

Features of a Milling Machine

The main features of a milling machine can generally be condensed into seven separate parts. These features include:

 

Knee: The knee, attached to the column, is adjustable, providing support for the saddle and worktable. It facilitates vertical movement on the Z-axis.

Column: The column serves as the primary structural support for the milling machine, enhancing the stability of all other machine components.

Saddle: Positioned between the knee and the worktable, the saddle moves parallel to the spindle axis, allowing horizontal adjustments for workpiece positioning.

Worktable: Atop the saddle, the worktable secures the workpiece and can be adjusted vertically and horizontally to accommodate various machine types.

Spindle: This rotating component, powered by an electric motor, holds either the machine tool or the arbor, enabling cutting operations.

Arbor: Exclusive to horizontal milling machines, the arbor inserts into the spindle and functions as a shaft for mounting different machine tools.

Ram: Commonly found in vertical milling machines, the ram is affixed to the column’s top, providing support for the spindle.

Machine Tool: The machine tool executes the milling operation, held by the spindle. It removes material from the workpiece, offering a diverse array of tooling options

CNC Milling

Types of CNC Milling

Vertical Milling

In vertical milling, a 3-axis milling table serves as the work surface, positioned beneath the arm where a spindle is attached.

When employing a turret vertical mill, the spindle can remain stationary while the table moves along both the X and Y axes. 

Alternatively, with a bed vertical mill, the table moves solely along the X-axis, and the spindle travels along the arm’s length in the Y-axis direction.
 

Horizontal Milling

Horizontal milling involves a horizontally oriented spindle, with the remaining components resembling those of vertical milling machines.

Horizontal mills are typically preferred for heavier or longer projects and are especially effective for workpieces that demand substantial material removal. This is because swarf, or waste material, easily falls away from the part and cutter during the process.

Plain Milling

In plain milling, the cutting tool rotates parallel to the workpiece’s surface. Plain milling cutters feature teeth along the periphery to execute cutting tasks, and both narrow and wide cutters find application.

This versatility accommodates deeper cuts and larger surface areas. The use of coarse and fine-toothed cutters is common, with slow cutting speeds and fast feed rates for the coarse cutter, and the reverse for the fine-toothed cutter. This approach contributes to the creation of more intricate and detailed final parts.

Angular Milling

This is a machining process where the cutting tool’s axis of rotation is set at an angle in relation to the workpiece surface. This unique setup allows single-angled milling cutters to create distinct angular features like grooves, serrations, or chamfers with precision.

Face Milling

Face milling is a machining technique where the cutting tool’s axis is perpendicular to the workpiece surface. It employs specialized face milling cutters equipped with teeth on both the periphery and tool face, the latter being ideal for finishing tasks.

This method is widely used to produce flat surfaces and ensure precise, high-quality finishes. Face milling outshines other milling processes in terms of surface finish. It’s compatible with both vertical and horizontal milling machines, making it a versatile choice in machining.

Form Milling

Form milling is an ideal method for milling operations involving irregular surfaces, such as contours, outlines, edges, or components with curved or flat surfaces.

This technique employs specialized milling cutters, including concave cutters, corner rounding cutters, and more, tailored to specific applications. It’s particularly advantageous for intricate designs like hemispherical or semi-circular shapes, as well as other complex components requiring precise milling.

5 axis machining

Types of Milling Machine

Just as there are various types of CNC milling, there is also a broad array of unique milling machines with distinct characteristics and functions. Some different types of milling machines are

Ram-type

Ram-type milling machines offer the flexibility for the machine tool to move along the XY axes using a spindle affixed to a movable arm on the column. Ram-type configurations are commonly found in horizontal milling machines.

Knee-type

Knee-type milling machines feature vertical adjustments of the worktable rather than the spindle. The knee mechanism enables the up-and-down movement of the worktable along the column to access the machine tool. Knee-type machines are frequently employed for plain milling operations.

Planner-type

Planner-type milling machines have a stationary worktable positioned along the YZ axes, while their spindles are mobile along the XYZ axes. Additionally, they can efficiently accommodate up to four machine tools simultaneously.

Bed-type

Bed-type milling machines feature a setup where the workpiece is securely positioned beneath the cutting tool. These machines offer the flexibility for the machine tool to maneuver along the XYZ axes.

5 axis machining

Benefits of CNC Milling

High Quality and Precision

CNC machining leaves very little room for error and necessitates high levels of accuracy and precision. This precision is a direct result of the process’ computer-guided instructions, which originate from 3D designs crafted using CAD (Computer-Aided Design). The manufacturing journey begins when these operations are set into motion via a machine interface.

The machine executes instructions from the machining program without the need for manual input. These automated processes allow for ultimate precision to ensure even the most finite and complex geometry can be technically managed.

 

High Production Output

CNC machines operate at a remarkable efficiency level, primarily due to their automated processes.

CNC milling is a reliable and favored choice when high-volume part production is essential, ensuring uniform quality and finish across all pieces. Programming and operating a 3-axis machine is straightforward, resulting in outstanding accuracy while maintaining cost-efficiency.

Less Labor-Intensive

CNC milling machines drastically minimize labor requirements in the production process. With tool spindles spinning at thousands of RPM (revolutions per minute), these machines not only deliver enhanced production efficiency but also significant time and cost savings. Manual methods simply cannot match this level of output.

It’s important to recognize that the complexity of the design dictates the level of human involvement. For instance, intricate designs may necessitate manual intervention, particularly if the workpiece needs to be repositioned during the process to ensure safety and precision.

Uniformity

CNC machining tools are meticulously engineered to achieve unparalleled precision when shaping the workpiece. The computer program directs these tools, ensuring that each part is manufactured with unwavering accuracy.

On a broader scale, this technology enables high-volume production, providing manufacturers with the assurance that every finished component will meet the same exacting standards and quality.

 
CNC milling machine

What are the Disadvantages
of CNC Milling?

High Material Waste

CNC milling, a subtractive manufacturing method, commences with a solid material block that’s carved to shape the final part. Consequently, this process tends to generate more waste compared to additive manufacturing techniques like 3D printing.

Scarcity of Skilled Technicians

Despite significant automation, CNC milling demands adept engineers or technicians to program, assess specifications, and oversee operations for consistently delivering top-notch parts.

Finding proficient CNC mill operators remains a challenge for numerous machine shops, leading to instances of subpar machined parts and quality concerns.

CNC machining materials

CNC Milling Costs

The cost of CNC milling is dependent on various factors. The expenses of CNC milling largely stem from how long it takes to machine each piece. Longer milling times could be a result of needing to remove large amounts of material or hard materials.

Depending on the part design, some parts may involve more complex tools or cutting. Other factors that define the cost of CNC milling are material and part complexity.

AMFG DARK

About AMFG

AMFG is a leading provider of MES software for manufacturing. Our software solutions empower manufacturers, allowing them to manage their workflows and achieve streamlined, automated processes.

With over 500 successful implementations in 35 countries and across a range of industries, we specialize in enabling companies to successfully integrate our software for AM and CNC production, into their wider manufacturing processes and scale their manufacturing operations. 

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