CNC Milling is a machining operation that is performed with milling cutters that are fixed to a milling machine. Milling machines are mainly categorised according to their CNC mill orientation. There are two basic configurations of mills, they are vertical and horizontal.
Vertical mill: A vertical mill has a mill cutter, a top slide or an over arm, a spindle, a column, a knee, a base, a table and a Y- axis slide. The spindle axis is oriented vertically and the cutter is held in the spindle and rotates on its own axis. The spindle usually extendable or the table’s height can be adjusted to get the same effect and this enables plunge cuts and drilling. Vertical mill has two subcategories which are described below:
- Bed mill: in this machine the table advances only perpendicular to the spindle’s axis and the spindle by itself advances parallel to its own axis.
- Turret mill: This mill has a stationary spindle and the table will move both perpendicularly and parallel to the spindle axis to make a cutting. Turret mills usually have a quill that allows the milling cutter to be moved higher or lower just like in a drill press. These mills are usually considered to be more versatile out of the two mill designs but they are only practical for relatively small machines.So larger milling machines generally have bed mill.
Horizontal mill: This mill has a similar type of x-y axis table but the cutters are placed up on a horizontal arbor across the table. Most horizontal mills also have built-in rotary table feature that enables milling at different angles. This rotary table is called a universal table. End mills and other kind of tools available in a vertical mill can also be used in a horizontal mill but the main advantage in using a horizontal mill is the arbor-mounted cutters known as side and face mills. They have a cross section similar to a circular saw, but they are usually smaller and wider in diameter. Since these cutters get good support from the arbor and have a bigger cross-sectional area than end mills, very heavy cuts can be done allowing quicker material removal rates. These mills are used mostly to mill grooves and slots.
Apart from vertical and horizontal mills there are various other CNC mills used in industries. A few of them are mentioned below.
- Box mill or column mill: It is a basic hobbyist bench-mounted milling machine that has a head feature that moves up and down on a column or box way.
- C-Frame mill:These mills are large industrial production mills that have a knee and fixed spindle head which can only move vertically.
- Floor mill: This mill has a row of rotary tables with a horizontal pendant spindle placed on a set of tracks which run parallel to the table row.
- Gantry mill: The milling head of this mill moves over two steel shaft rails that lie on either side of the work surface.
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