The computer numerical control (CNC) milling machines are the most widely used type of CNC machine tools. They are usually grouped by the number of axes on which they operate. Each axis is labeled with a letter. X and Y designate horizontal movements of the work-piece (forward-and-back and side-to-side on a flat plane). Z represents vertical (or up-and-down) motion, while W represents diagonal movement across a vertical plane. Most machines can operate from 3 to 5 axes, offering performance along at least the X, Y and Z axes. Advanced machines, such as 5-axis milling centers, require CAM programming for optimal performance because of the incredibly complex geometries involved in the machining process. These devices are very useful because they can produce shapes that would be almost impossible using manual tooling methods.
Tooling
The basic cutting tool is a rotating cylindrical cutting instrument. This tool looks like a drill bit, but it moves along multiple axes and can create a variety of shapes, slots, and holes. In addition, the work-piece is often moved across the milling tool in different directions, unlike the single axis motion of a drill.
Other tools may not be cylindrical. For example, they may be tapered at one end, or shaped like a ball or shaped like a barrel. These tools serve different machining requirements. Some machines have automatic tool changers to improve the production and tool carrying capacity.
The different tooling used in CNC milling machines is based on the material and desired shape of the part. If a tool piece is not strong enough, the tooling, as well as the machine itself, may be damaged. Tooling that is too strong for softer materials may damage the workpiece.
Usage
Although the cost of tooling CNC milling machines is becoming more affordable, large production runs requiring relatively simple designs are better served by other methods such as punching. Nevertheless, CNC machining is flexible enough to accommodate various manufacturing needs, producing everything from prototyping to small quantity manufacturing of complex parts.
