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What is a Milling Machine
In manufacturing, one of the most important machine tools is the milling machine. Basically, a milling machine is used in shaping solid materials, specifically metals. More than anything else, the milling machine is used in shaping flat and irregular surfaces. Aside from this main function, the milling machine can also perform other tasks such as drilling, routing, planning, cutting gears, boring, and producing slots among others. There are some milling machines that are most effective in performing specific tasks. In order to identify the most appropriate milling machine to use, it is helpful to distinguish each type of milling machine. Generally, there are only two categories of milling machines which are the vertical mills and the horizontal mills. The vertical mills have a vertical orientation of the spindle axis, while the horizontal mills employ a horizontal orientation of the spindle axis.
There are two popular types of the vertical mill. One of these is the bedmill which is set up in such a way that the spindle is allowed to move parallel to its own axis only, while the table is contrastingly allowed to move perpendicular to the axis of the spindle. On the other hand, the set up the turrent mill is such that the spindle stays stationary during cutting operations while the table is allowed to move in both the perpendicular and vertical directions to the axis of the spindle. Although this mill is smaller than the bedmill, this is considered as the more versatile type.
The horizontal mills have the cutters mounted horizontally on an arbor across the table. With this set up, the workpieces can be fed from three axes. Although side milling can be done by these mills, these are most commonly used in end and face cutting. One of the major disadvantages of these mills though is the great number of controls which make the operation of these mills relatively slower.
There are some important factors to consider in choosing milling machines. These include the milling feed direction, cutting speeds, feed rates, and lubrication. The feed direction is important because it affects the performance of the mill and the quality of the workpieces. Cutting speeds have to match accordingly with the type of material and cutter. Moreover, cutting speeds should also match the type of work done by the mill such as finishing. A recommended list of feeding rates is also provided by various manufacturers for the proper operation of milling machines. It is worth noting that the recommended feeding rates vary for every type of milling cutter used. Finally, proper lubrication should be provided when milling metals and alloys.
Today, there are various types of milling machines available in the market. Although there are still a lot of machinists that prefer the traditional manual operated and the mechanical automated milling machines, the computer numerical control (CNC) milling machines are also gaining popularity worldwide.
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Fig.1. Horizontal Milling Machine with Work in Process Courtesy of Cincinnati Milling Machine Company, Cincinnati, Ohio.
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Fig.2. Vertical Milling Machine in Action. Work-Holding Fixture Rotates at Rate of 10 Inches per Minute; Production 195 Yokes per Hour.
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Fig.3. Plain and Helical Milling Cutters Courtesy of americanmachinetools.com