One detailed guide for a beginner to understanding the CNC Milling process here.
What is CNC Milling?
CNC, or Computer Numerical Control, places tools under the direct guidance of a computerized operating system.
Successful, high-quality milling is a combination of three elements:
1. A cutter with many teeth and ideal sharpness for a material
2. Spinning a tool at high enough speed to process a material correctly
3. An appropriate feed rate for advancing the chosen material through the process
CNC allows for extremely close control of these elements. The computerized systems read design information directly from an engineer’s drawings or models, eliminating possibilities for error between design and production.
The CNC milling process takes directions in customized software codes such as NC code, G-code, and ISO code, all converted straight from a project’s CAM or CAD designs. The codes are then translated into the machine’s controls, which run along at least two axes (X and Y), in addition to the tool spindle running in the depth, or Z, axis. Some machining centers allow for controls on up to five unique axes.
CNC Milling Machine Function
The CNC machining process works by the machine reading its instructions from a design that was inputted on a CAD programme. These part designs can be 2D or 3D. Once completed the designs are converted into a machine-readable format. CAM (Computer-Aided Manufacturing) software then exports this to a CNC machine programme which then acts as the instructions to direct each and every move that the machine will have to make in order to replicate the CAD design with the chosen material.
CNC Milling Machine Setup
Before the milling manufacturing process can commence, the machine needs to be set up with the right CNC machine tools for the job. The operator will also place the workpiece on the work table and fix it in place with a vice or custom jigs and fixtures. These steps are important to ensure the machine can carry out its job without the material moving out of place. When the necessary preparations are complete, the operator can launch a programme using the machine interface, and the manufacturing process can begin.
CNC Milling Manufacturing Process
When the milling manufacturing process begins, the tools can spin at thousands of RPM and, as such, can cut into even the strongest materials with ease. During the manufacturing process, the tool and workpiece will be moved in relation to each other in order to access different parts of the design. The angles and direction depend on the specific design requirements of the piece but the principle of feeding the workpiece to the rotary tool remains the same.
Types of Milling
The various types of milling can be generally categorized into the following:
You can read more about the types of CNC milling in the next article.
As a rule, superficial surface cuts will be carried out by larger cutters, whereas a more narrow cutter can be used for finer details. Initially, larger amounts of material will be removed with a coarse-toothed tool, then a faster, more fine-toothed cutter is used for more detailed parts of the design and for finishing.
Features of a CNC Milling Machine
A CNC Milling machine is comprised of the following features:
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.
This is just below the worktable to support it and is adjustable in order to fix the worktable in relation to the spindle axis. 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.
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. It is adjustable along the Z-axis, depending on the specific milling operation being carried out.
This is the fixed base of the machine which can also house things like coolant or oil for the machine. 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.
This component is driven by a motor within the column by which it is supported. This is what controls the machine tool.
The machine tool is sometimes referred to as a mill cutter. This is the part 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 to the huge variety in cutting tools.
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.
The core function of this component is to support the spindle in vertical milling machines. It is adjustable to accommodate different positions during the milling process.
CNC Milling Machine Cutting Tools
Types of milling cutter
Face milling tool
Slab mill side and face cutter
Involute gear cutter
Roughing end mill
Depending on the exact finish you are looking for, the type of cutting tool will be important. For example, some mills, such as end mills, can cut axially. Face mills, however, cannot cut axially; the cutting edges are located on the side, which has the benefit of keeping a good cutting quality and extending the lifetime of the tool. Particular types of each mill can be used for more complicated designs. For example, a rough end mill is similar to an end mill, but with a more jagged edge, making the cutting process faster.