What is CNC Milling?

Learn more about CNC Milling in our guide to the CNC Milling process. Discover the anatomy of a CNC machine and the different types of CNC milling available.

5
May

What is CNC Milling?



CNC Milling is a specific process of CNC Machining. It employs computerised controls to produce a custom-designed part or product. It is favoured in many industries due to its accuracy, consistency and ability for high production and uniformity.

At Get It Made, CNC Milling is one of the key CNC Machining services we offer. In this article, we will describe the milling process, highlighting the different types of CNC Milling Machines, offering insight into what a milling machine does and the CNC Milling process as a whole. 

cnc machine machining an aluminium aerospace part
The article will also focus on the benefits of CNC milling, so those considering implementing CNC Machining into their business processes can do so with further understanding. This can help to assure businesses that they are effectively utilising the technical ability of CNC Milling machines.


How does a CNC Milling machine work?


CNC Milling can produce high volumes of highly complex and intricate parts using subtractive machining technology. Material is removed from a blank workpiece and the milling machine uses a rotating cylindrical tool called a milling cutter. Depending on the type of milling machine being used, the machine is able to cut in different angles and move along different axes. 

CNC milling machines are engineered to mass-produce many components from various materials. The core function involves mechanically cutting away at a workpiece, with all instructions delivered via a computer-aided program, delivering the specific measurements with little or no human intervention. 

The final part will have first been designed via CAD, or Computer-Aided Design, before being inputted into the milling machine for final production. 

The CNC Milling process works by the machine reading coded instructions and then putting them into operation. It all starts with the development of a 3D CAD file representing the final part. Once completed, the design is converted into a machine-readable format. CAM (Computer-Aided Manufacturing) software then exports this to a CNC machine program, usually in G-code format, which then acts as the instructions, directing every move that the machine makes. This replicates the CAD design with the chosen material with a high level of accuracy and efficiency. 

CNC Machined Grey Anodised

What does a CNC Milling machine do?


A CNC milling machine is used by various industries - including aerospace and medical industries - to manufacture and mass-produce intricate parts. The milling machine does this via the process of subtractive machining technology. The milling machine cuts away at the workpiece, and, via the 3, 4 or 5 axes, crafts the final piece. Depending on the number of axes the CNC milling machine has, the more complicated and intricate the final piece can be. 

For simpler designs, a fewer number of axes is needed to achieve the final design. The cutting tools are attached to a spindle that works on 3 linear axes. In general, simple geometries can utilise a 3-axis milling machine. 3-axis machines are easy to program and operate, achieving excellent accuracy at a low cost. The cutting tools in question have the ability to spin at thousands of RPM, meaning even the sturdiest of materials can be cut through with ease and accuracy. 

3-axis machines are the most common variety of milling machine and can cut vertically (Z-axis) and in an X and Y direction. However, it’s not normally possible to machine undercuts (features that cannot be accessed with a standard end mill) with a 3-axis milling machine. Therefore, more complex designs may require a more complex milling machine. 

The 4-axis milling machine is more sophisticated, with the additional ability to rotate on the X-axis (similar to a lathe). 

5-axis milling machines include rotation in both the X and Y-axis. They are the most complete milling machines available and are implemented for highly complex designs such as medical devices and implants for the medical industry, car models and aerospace structures.

CNC Machined Parts Acid Etched aluminium

Types of CNC Milling


Vertical milling


  • With vertical milling, a 3-axis milling table is the work surface, which sits below the arm, to which a spindle is attached. 
  • The spindle can be stationary if a vertical turret mill is used. In this case, the table moved along both X and Y axes. Meanwhile, if a bed vertical mill is used, the table only moves along the X-axis. The spindle travels along the length of the arm, in the Y-Axis direction. 

Horizontal milling


  • With horizontal milling, the spindle operates horizontally as opposed to vertically and all other components are similar to vertical milling.
  • Generally speaking, horizontal mills are best suited to heavier projects or longer projects. They are also suited to parts that require a large amount of material to be removed.

Face milling


  • The cutting tool’s axis of rotation is perpendicular to the surface of the workpiece.
  • Employs face milling cutters, with teeth both on the periphery and the tool face, the latter of which is used for finishing applications.
  • Used to create flat surfaces and control on a finished piece. 
  • Face milling can produce higher quality finishes than other milling processes and is compatible with both vertical and horizontal milling machines.
cnc face milling aluminium block

Plain milling


  • The cutting tool’s axis of rotation is parallel to the surface of the workpiece.
  • Plain milling cutters have teeth on the periphery that perform the cutting operation.
  • Both narrow and wide cutters are used. This allows for deeper cuts, and for larger surface areas to be worked on. 
  • A course and fine-toothed cutter are both used. Slow cutting speeds & fast feed rates are used for the course cutter, and vice versa for the fine-toothed cutter. This enables a more detailed final part.

Angular milling


  • This is a milling operation where the cutting tools’ axis of rotation is at an angle relative to the surface of the workpiece.
  • Single angled milling cutters can, therefore, produce more angular features, such as grooves, serrations or chamfers

Form milling


  • Form milling is best used for milling operations where there are more irregular surfaces involved. Contours, outlines, edges, for example, or parts with curved, flat surfaces.
  • It employed milling cutters or fly cutters specialised for particular applications – for example, concave cutters or corner rounding cutters
  • Hemispherical or semi-circular designs or other similarly intricate designs with complex parts would benefit from the form milling technique. 

Components of CNC Milling Machine


To fully understand the working of a CNC Milling machine, we have compiled a brief list of the main features that a CNC mill consists of:

Worktable


This is where the material or workpiece is secured, to be worked on. It’s located on top of the saddle. Depending on the type of machine being used, the worktable is adjustable horizontally, vertically, sometimes both, or not at all.

Saddle


The saddle, located at the top of the knee, supports the worktable. It moves parallel to the axis of the spindle. This function enables the worktable to be horizontally adjusted. This fixes the worktable in relation to the spindle axis. 

Knee


Below the saddle, this supports the worktable and saddle and can be moved up and down depending on what height is needed. This is an adjustable part of the machine, affixed to the column. The knee provides support to the saddle and worktable. It is adjustable along the Z-axis, depending on the specific milling operation being carried out.

Column


The column in a CNC Milling machine is the component that provides support to other components – it’s essentially the fixed base of the machine. Additionally, it can also house things like coolant, or oil for the machine. 

Spindle


This component is driven by a motor within the column by which it is supported. This is what controls and spins the machine tool. 

Machine tool


This component is sometimes referred to as a mill cutter. This is the equipment which touches and removes material from the workpiece and will vary in type depending on the job at hand, e.g. cutter, drill, bore etc. The specifications of the machine tool vary, for example, the diameter, length, spacing of teeth, and material etc. CNC Milling is so versatile largely due the huge variety in cutting tools.

Arbour


The arbour essentially connects the machine tool to the spindle. It’s available in various lengths and diameters, again depending on the specifications of the CNC Milling machine in question. 

Ram


The core function of this component is to support the spindle in vertical milling machines, typically. It is adjustable to accommodate different positions during the milling process. 


Benefits of CNC Milling process


Precision


The very nature of CNC Machining as a process leaves very little room for error and high levels of accuracy and precision. This is because it operates from a computer led program, inputting 3D designs that have been developed via CAD (Computer-Aided Design). All operations are launched via a machine interface. 

The machine executes these instructions 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


The level at which CNC Machines operate means they are capable of high levels of production due to the automated processes involved. Should a part need to be produced in high volume, with every part meeting the same level of consistency in terms of quality and finish, CNC Milling is a trusted and popular option. It is particularly easy to program and operate a 3-axis machine, achieving high accuracy at a low cost.

Less labour


Using a CNC Milling Machine significantly reduces the amount of labour involved in the production process. At full capacity, the tools used in a CNC Milling machine can spin at thousands of RPM (revolutions per minute), resulting in high productivity output, while also being a time-saving expense. No manual processes could achieve a similar output.

Uniformity


CNC machining tools are designed and developed to cut away at the workpiece with the highest levels of accuracy. The movement is directed from the computer program, meaning every single part is produced to the same level of accuracy. On a wider scale, parts can be produced in high volume, with the manufacturer safe in the knowledge all completed parts will be of the same standard and finish. 

Get It Made is an established bespoke manufacturing partner for high precision CNC Milling and Machining. Get in touch to discuss your project’s requirements and kick-start your manufacturing. Arrange a CNC Milling quote today and our team will get back to you in 24 hours.