1、 Passage Three Milling Milling introduction Milling is a machining processing that is carried out by means of a multi edge rotating tool known as a milling cutter. In this process, metal removal is achieved through combining the rotary tool motion of the milling cutter and linear motion of the work
2、piece simultaneous. Milling operations are employed in producing flat, contoured and helical surfaces as well as for thread and gear cutting operations. Each of the cutting edges of a milling cutter acts as an individual single point cutter when it engages with the work piece metal. Therefore, each
3、of those cutting edges has appropriate rake and relief angles. Since only a few of the cutting edges are engaged with the work piece at a time, heavy cuts can be taken without adversely affecting the tool life. In fact, the permissible cutting speeds and feeds for milling are three to four times hig
4、her than those for turning or drilling. Moreover, the quality of the surfaces machined by milling is generally superior to the quality of surfaces machined by turning, shaping, or drilling. A wide variety of milling cutters is available in industry. This, together with the face that a milling machin
5、e is a very versatile machine tool, makes the milling machine the backbone of a machining workshop. As far as the direction of cutter rotation and work piece fed are concerned, milling is performed by either of the following two methods. Up milling (conventional milling).In up milling the work piece
6、 is fed against the direction of cutter rotation. The depth of cut gradually increases on the successively engaged cutting edges. Therefore, the machining process involves no impact loading, thus ensuring smoother operation of the machine tool and the longer tool life. The quality of the machined su
7、rface obtained by up milling is not very high. Nevertheless, up milling is commonly used in industry, especially for rough cuts. Down milling (climb milling). In down milling the cutter rotation coincides with the direction of feed at the contact point between the tool and the work piece. The maximu
8、m depth of cut is achieved directly as the cutter engages with the work piece. This results in a kind of impact, or sudden loading. Therefore, this method cannot be used unless the milling machine is equipped with a backlash eliminator on the feed screw. The advantages of this method include higher
9、quality of the machined surface and easier clamping of work piece, since the cutting forces act downward. Milling machine There are several types of milling machines employed in industry. They are generally classified based on their construction and design feature. They vary from the common general
10、purpose types to duplicators and machining centers that involve a tool magazine and are capable of carrying out many machining operations with a single work piece setup. Following is a survey of the milling machine types commonly used in industry. Plain horizontal milling machine. The construction o
11、f the plain horizontal milling machine is very similar to that of the universal milling machine except that the machine table cannot be swiveled. Plain milling machines usually have column and knee type construction and also have three table motions, i.e., longitudinal, transverse, and vertical. The
12、 milling cutter is mounted on a short arbor, which is, in turn, rigidly supported by the over arm of the milling machine. Universal milling machine. The construction of a universal milling machine is similar to that of the plain milling machine, except that it is more accurate and has sturdier frame
13、, and its table can be swiveled with an angle up to 50. Universal milling machine are usually equipped with an index or dividing hear, allows cutting of gear and cams. Vertical milling machine. As the name vertical milling machine suggests, the axis of the spindle that holds the milling cutter is ve
14、rtical. Table movements are generally similar to those of plain horizontal milling machines； however, an additional rotary motion is sometimes provided for the table to enable machining helical and circular grooves. The cutter used with vertical milling machines are almost always of the end mill type. Duplicators. A duplicators is sometimes referred to as a copy milling machine because of reproducing an exact replica of a model. The
