MILLING MACHINE
The milling machine is a machine tool in which metal is removed by means of a revolving cutter with many teeth, each tooth having a cutting edge which removes metal from a workpiece.
The work is supported by various methods on the work table, and may be fed to the cutter, longitudinally, transversely or vertically.
A great variety of work may be done on a milling machine.
The machine is perhaps next to the late in importance.
Generally there are two type of milling machine
1. Upmilling process - In upmilling process the workpiece is fed opposite to the cutter's tangential velocity.
2. Downmilling process - In downmilling process the workpiece is fed in the same direction as that of the cutter's tangential velocity.
Specification of milling machine
The following are the specification of a column and knee type milling machine:
1. Width and length of the table.
2. Maximum distance the knee can travel.
3. Maximum longitudinal movement and cross feed of the table.
4. Number of spindle speeds.
5. Power of the main drive motor.
Type of milling machines
According to the general design of the milling machine, the usual classification of the milling machine are:
1. Column and knee type:
(a) Hand milling machine (b) Plain milling machine (c) Universal milling machine
(d) Omniversal milling machien (e) Vertical machine
2. Manufacturing of fixed bed type:
(a) Simplex milling (b) Duplex milling machine (c) Triplex milling machine
3. Planer type:
4. Special type:
(a) Rotary table milling machine (b) Drum milling machine (c) Planetary milling machine
(d) Pantograph, Profiling and tracer controlled milling machine
Types of milling cutter
Common types of milling cutters are enumerated below:
1. Plain milling cutter 2. Side milling cuttter
3. End milling cutter 4. Face milling cutter
5. Metal slitting cutter 6. Angle milling cutter
7. Formed milling cutter 8. Woodruff-key milling cutter
9. T-slot milling cutter 10. Fly cutter
Milling Operation
The milling operation are classified as follows:
1. Plain or slab milling 2. Face milling 3. Angular milling 4. Form millijng
5. Straddle milling 6. Gang milling 7. End milling 8. T-slot milling
9. Dove-tail milling 10. Saw milling 11. Involute gear cutting
1. Plain or slab milling - Plain milling is used to machine flat and horizontal surfaces .Here plain milling cutter is used, which is held in the arbor and rotated. The table is moved upwards to give the required depth of cut.
2. Face milling -This milling process is used for machining a flat surface which is at right angles to the axis of the rotating cutter. The cutter used in this operation in the face milling cutter.
3. Angular milling - In angular milling an angle milling cutter is used. The cutter used may be a single or double angle cutter, depending upon whether a single surface is to be machined or two mutually inclined surface simultaneously.
4. Form milling - This milling process is used for machining those surface which are of irregular shapes. The form milling cutter used has the shape of its cutting teeth conforming to the profile of the surface to be proved.
5. Straddle milling - Straddle milling is an operation is an which a pair of side milling cutters is used for machining two parallel vertical surfaces of a workpiece simultaneously. The distance between the cutters is adjusted by the spacers. This process is used to mill square and hexagonal surfaces.
6. Gang milling - Gang milling is the name given to a milling operation which involves the use of a combination of more then two cutters, mounted on a common arbor, for milling a number of flat horizontal and vertical surfaces of a workpiece simultaneously. This method saves much of machining time and is widely used in repetitive work. The cutting speed of a gang of cutters is calculated from the cutter of the largest diameter.
7. End milling - It is an operation of producing narrow slots, grooves and key ways using an end mill cutter. The mill tool may be attached to the vertical spindle for milling the slot. Depth of cut is given by raising the machine table.
8. T-slot milling - In the milling machine operation, first a plain slot is cut on the workpiece by a side and face milling cutter. Then the T-slot cutter is fed from the end of the workpiece.
9. Dove-tail milling - In this milling operation, the end of the cutter is shaped to the required dove-tail angle. The cutter is passed from one end of the workpiece to the other end.
10. Saw milling - It is an operation of production narrow grooves and slots on the workpiece. A slitting saw is used for saw milling.
11. Involute gear cutting - Gear milling operation, often referred as gear cutting, in-volves cutting of different types of gear on a milling machine. For this, either an end mill cutter or a form relieved cutter is used, which carries the profiles on its cutting teeth corresponding to the required profile of the gap between gear teeth.
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