The Process of CNC MILLING
CNC milling is an acronym for computer numerical control milling. It is a machining operation that uses computerized controls and rotating multi-axis cutting tools to actively remove material from a workpiece to produce a custom-designed product. For quality and efficiency, you will often see a moveable tabletop and moveable cutters. The process of CNC milling is ideal for fabricating parts from a variety of materials such as aluminum, steel, glass, plastic, and wood.
There are a variety of different processes that can be done through CNC machining, including mechanical, electrical, thermal, and chemical processes. Mechanical machining refers to any process where the material is removed from the workpiece through mechanical processes, such as turning, drilling, and milling. Milling allows an opportunity to explain the full process of CNC mechanical machining due to its ability to be automated and operated in a single setup.
There are four main processes that occur during the CNC milling process beginning with designing the part in a CAD, then converting the CAD files into code for machining, setting up the machinery and, finally, manufacturing the part. While the CNC milling machine really only entails the fabrication process, an extensive overview of the complete process is helpful.
CAD Files Design and Coding
To begin, a visual representation of the product has to be virtually created through a CAD software program. There are several reliable CAD-CAM programs that allow users to create the required G code for machining.
Machinists can simulate the entire cutting operation using CAD software. This is extremely helpful for checking for mistakes in the design that could create models that are impossible to manufacture.
G codes can be written manually. However, it takes a considerable amount of time and can delay the entire process. We recommend machinists take full advantage of the capabilities modern machine software offers with pre-programmed G codes.
CNC Milling Machine Setup
While CNC machines are automated and do the cutting without human intervention, many other areas of the operation require the touch of a machinist. For instance, fixing the workpiece to the work table, as well as adding the milling tools to the spindle of the machine.
Manual milling relies heavily on machinist intervention while CNC models have advanced automation. Modern milling stations can also have live tooling capabilities to automatically change tools during the manufacturing process. This enables fewer stops in the operation, but a machinist or machine operator still has to set them up beforehand.
Once the initial setup is completed, the machinist checks the program one last time before starting the machining process.
Unlike older milling machines that rely on conventional milling for cutting, CNC milling machines employ a technique known as climb milling. The features are as follows:
- The cutting chip works from thick to thin material removal, heating the chip rather than the actual workpiece.
- The cutting surface is cleaner, allowing for less rubbing for increased tool lifespan.
- The chips land at the back of the cutter, limiting the problem of contaminating the cutting path.
- Horizontal climb milling forms downward forces, limiting the need for extra clamping.
Milling operations usually encompass several different operations however this relies on the shape of the finished product and the state of the raw material. Typically, milling is required for accuracy and precision as well as adding a few features such as slots and threaded holes.
It is also acceptable, however, for manufacturing a finished part from solid material. The first operations use bigger tools to quickly remove the material to speed up the process until getting to an approximate shape of the final product.
A tool change is required to create highly precise parts. The great distinction precision milling is known for is achieved in the last stage of the process, which is taking specified tolerances and surface roughness to levels hard to match with any other fabrication process.