Milling Machine: Types of Milling Machine, Hand milling machine, Planer type milling machines, Production milling machines, Special purpose milling machines, Vertical milling machine, Plain or horizontal milling machine, Universal milling machine

Milling Machine

Introduction to milling machine:-

·        Milling is the machining process in which the metal removal takes place due to the cutting action of a revolving cutter when work piece is fed past it.

·        The revolving cutter is held on a spindle or arbor and the work piece clamped on the machine table.

·        During the process, to produce the desired shape, the cutter removes the metal in the form of chips from the work piece surface'

·        The machine tool on which the milling operation is performed is called as milling machine.

·        Also, the work piece can be fed in a vertical, longitudinal or cross direction shows the working principle of a milling machine.

Fig: Working principle of milling machine

    Types of Milling Machines:

A large variety of different types of milling machines are available. Aclassification of these machines according to the general design can be done as follows:

1.     Column and knee type milling machines :

a.      Hand milling machine

b.     Plain or horizontal milling machine

c.      Vertical milling machine

d.     Universal milling machine

e.      Omniversal milling machine

2.     Fixed bed or manufacturing type milling machines :

a.      plain type milling machine (having single horizontal spindle)

b.     Duplex head milling machine (having double horizontal spindles)

c.      Triplex head milling machine (having two horizontal and one vertical spindle)

d.     Rise and fall type milling machine (for profile milling)

3.     Planer type milling machines

4.     Production milling machines:

a.      Rotary table or continuous type milling machine

b.     Drum type milling machine

c.      Tracer controlled milling machine

5.     Special purpose milling machines :

a.      Thread milling machine

b.     Profile milling machine

c.      Cam milling machine

d.     Gear milling or gear hobbing machine

e.      Planetary milling machine

    Column and Knee Type Milling Machines

·        Column and knee type milling machines are most commonly used in machine shops and tool rooms. These machines are general purpose machines and have a single spindle only.The worktable is supported on a knee-like casting. Which can slide in vertical direction along a vertical column? Depending upon the spindle position and table movements, they are further classified as follows:

a.      Hand milling machine

b.     plain or horizontal milling machine

c.      Vertical milling machine

d.     Universal milling machine

e.      Omniversal milling machine

f.       Column and Knee type milling machines

                        Hand Milling Machine:

·        It is the simplest of all the milling machines and smaller in size.

·        All the operations are performed by hand except the rotation of an arbor.

·        The table carrying the work piece over it is moved by hand to feed the work piece.

·        This machine is mostly useful in producing small components such as hexagonal or

square headed bolts, cutting key ways and slots on screw heads.

                        Plain or Horizontal Milling Machine:

·        Fig. shows block diagram of a plain milling machine, in which the vertical column serves as housing for electrical, main drive, bearings, etc.

Fig: Horizontal Milling Machine

                                         

·        For supporting the saddle, worktable and other accessories such as indexing head, knee is provided.

·        Overarm provides support for the yoke which supports the free end of the arbor

·        The arbor carrying the cutter rotates about a horizontal axis.

·        Except swiveling, the table can be given motion in three different directions i.e.

Ø  Longitudinal direction

Ø  Vertical direction

Ø  Cross direction

·        For vertical movement of the table, the knee along with whole unit over it slides up and down in the guide ways provided on the column.

For cross movement of the table, the saddle is moved towards or away from the column along with the whole unit over it.

· To provide additional support and rigidity to the arbor, a brace is employed.

                        vertical milling machine

·        In this type of machine spindle position is vertical hence, called as vertical milling machine.

   ·        This machine is available in two types i.e. fixed bed type and column and knee  type.

  ·        Fig.  shows the block diagram of vertical milling machine with fixed head.

  ·        It consists of a vertical column on a heavy base and overarm is made integral with the column and carrying housing at its front. 

·        This housing is called as head which can be of fixed type or swivelling type. In fixed head type, the spindle always remains vertical and can be adjusted up and down. 

·        Whereas, in swivelling head type, the spindle can be swivelled to any required angle for machining inclined surfaces. Refer Fig.

·                      

Fig: Vertical milling machine with fixed head

·        The knee carries a screw jack with the help of which it is moved up and down along the guide ways provided on the column.

·        The saddle is mounted on the knee which can be moved towards or away from the column, along the horizontal guide ways provided on the knee.

    ·        This enables the table to move in cross direction.

·        Similar to horizontal milling machine, in vertical milling machine also there are three motions for the table i.e. longitudinal, vertical and cross.

·        Hence, with the help of knee the work piece gets vertical movement, by using cross movement; and longitudinal movement by the table.

                        Universal Milling Machine:-

·        Universal milling machines are most versatile of all the milling machines and most useful because, they are capable of performing most of the machining operations.

   ·        By using this machine, large number of other machine tools can be avoided.

   ·        Universal milling shine is similar to horizontal milling machine, except that the table can be given one more additional movement. Refer Fig.  Its table can be swivelled in a horizontal plane and for this purpose circular guide way are provided on the saddle.

·        To read the angle of swivelling, a graduated circular base is provided under the table with datum mark on the saddle. Hence, Work piece can be set at an angle with the cutter for milling helical and spiral flutes and grooves.

·        By using some attachments, this machine can be worked as a vertical milling machine.

                        Omniversal Milling Machine:- 

·        Omniversal milling machine is a modified form of a plain milling machine.

·        It is provided with two spindles, out of which one is horizontal and other is carried by a universal swivelling head.  The latter can be fixed in vertical position or can be set at any required angle up to 90⁰ on both the sides of vertical.

·        One more special feature of this machine is that, it carries two more adjustments in addition to all the adjustments provided in a universal machine.  Its knee can be swivelled about a horizontal axis to tilt the table and can be moved horizontally also.

·        Hence, this machine is very useful for tool room work.

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