Types of CNC Milling Machine
CNC milling is a machining process suitable for producing high accuracy, high tolerance parts in prototype, one-off, and small to medium production runs. While parts are typically produced with tolerances ranging between +/- 0.001 in. to +/- 0.005 in., some milling machines can achieve tolerances of up to and greater than +/- 0.0005 in. The versatility of the milling process allows it to be used in a wide range of industries and for a variety of part features and designs, including slots, chamfers, threads, and pockets. The most common CNC milling operations include:
- Face milling
- Plain milling
- Angular milling
- Form milling
Face milling refers to milling operations in which the cutting tool’s axis of rotation is perpendicular to the surface of the workpiece. The process employs face milling cutters which have teeth both on the periphery and tool face, with the peripheral teeth primarily being used for cutting and the face teeth being used for finishing applications. Generally, face milling is used to create flat surfaces and contours on the finished piece and is capable of producing higher quality finishes than other milling processes. Both horizontal and vertical milling machines support this process.
Types of face milling include end milling and side milling, which use end milling cutters and side milling cutters, respectively.
Plain milling, also known as surface or slab milling, refers to milling operations in which the cutting tool’s axis of rotation is parallel to the surface of the workpiece. The process employs plain milling cutters which have teeth on the periphery that perform the cutting operation. Depending on the specifications of the milling application, such as the depth of the cut and the size of the workpiece, both narrow and wide cutters are used. Narrow cutters allow for deeper cuts, while wider cutters are used for cutting larger surface areas. If a plain milling application requires the removal of a large amount of material from the workpiece, the operator first employs a coarse-toothed cutter, slow cutting speeds, and fast feed rates to produce the custom-designed part’s approximate geometry. Then, the operator introduces a finer toothed cutter, faster cutting speeds, and slower feed rates to produce the details of the finished part.
Angular milling, also known as angle milling, refers to milling operations in which the cutting tool’s axis of rotation is at an angle relative to the surface of the workpiece. The process employs single-angle milling cutters—angled based on the particular design being machined—to produce angular features, such as chamfers, serrations, and grooves. One common application of angular milling is the production of dovetails, which employs 45°, 50°, 55°, or 60° dovetail cutters based on the design of the dovetail.
Form milling refers to milling operations involving irregular surfaces, contours, and outlines, such as parts with curved and flat surfaces, or completely curved surfaces. The process employs formed milling cutters or fly cutters specialized for the particular application, such as convex, concave, and corner rounding cutters. Some of the common applications of form milling include producing hemispherical and semi-circular cavities, beads, and contours, as well as intricate designs and complex parts with single machine setup.
Other Milling Machine Operations
Besides the aforementioned operations, milling machines can be used to accomplish other specialized milling and machining operations. Examples of the other types of milling machine operations available include:
- Straddle milling: Straddle milling refers to milling operations in which the machine tool machines two or more parallel workpiece surfaces with a single cut. This process employs two cutters on the same machine arbor, arranged such that the cutters are at either side of the workpiece and can mill both sides at the same time.
- Gang milling: Gang milling refers to milling operations which employ two or more cutters—typically of varying size, shape, or width—on the same machine arbor. Each cutter can perform the same cutting operation, or a different one, simultaneously, which produces more intricate designs and complex parts in shorter production times.
- Profile milling: Profile milling refers to milling operations in which the machine tool creates a cut path along a vertical or angled surface on the workpiece. This process employs profile milling equipment and cutting tools which can be either parallel or perpendicular to the workpiece’s surface.
- Gear cutting: Gear cutting is a milling operation which employs involute gear cutters to produce gear teeth. These cutters, a type of formed milling cutters, are available in various shapes and pitch sizes depending on the number of teeth necessary for the particular gear design. A specialized lathe cutter bit can also be employed by this process to produce gear teeth.
- Other machining processes: Since milling machines support the use of other machine tools besides milling tools, they can be used for machining processes other than milling, such as drilling, boring, reaming, and tapping.