The first milling machine came into existence in about 1770 and was of French origin.
The milling cutter was first developed by Jacques de Vaucanson in 1782.
The first successful plain milling machine was designed by Eli Whitney in 1818.
The universal milling machine was invented by Joseph R Brown a member of the Brown and Sharpe company in 1861.
A milling machine is a machine tool that removes metal as the work is fed against a rotating multipoint cutter. The cutter rotates at a high speed and because of the multiple cutting edges
it removes metal at a very fast rate.
it removes metal at a very fast rate.
The machine can also hold one or a number of cutters at a time so the milling machine finds wide application in production work.
Types of Milling Machine :
According to the general design of the milling machine are :
1. Column and knee type
The fixed bed type milling machine is comparatively large, heavy and rigid and it different from column and knee type milling machine by the construction of its table mounting.
The table is directly mounted directly on the ways of a fixed bed.
The cutter mounted on the spindle head may be moved vertically on the column and the spindle may be adjusted horizontally to provide cross adjustment. It can be classified below :
Comparison between Plain and Universal Milling
Principle parts that are used in milling machine are described below :
Cutting Speed :
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Types of Milling Machine :
According to the general design of the milling machine are :
1. Column and knee type
For general shopwork, the most commonly used is the column and knee type where the table is mounted on the knee casting which is turn in mounted on the vertical sides of the main column.
The knee is vertically adjustable on the column so that the table can be moved up and down to accommodate work of various heights. The column and knee type milling machines are classified according to various methods of supplying power to the table, different movements of the table and the different axis of rotation of the main spindle.
- Hand milling machine
The cutter is mounted on a horizontal arbour and is rotated by power.
This machine is particularly suitable for light and simple milling operation such as machining slots, grooves and keyways.
- Plain milling machine
A plain milling machine having a horizontal spindle. In a plain milling machine, the table may be fed in a longitudinal, cross or vertical directions.
The feed is longitudinal when the table is moved at right angles to the spindle.
The feed is cross when the table is moved parallel to the spindle.
The feed is vertical when the table is adjusted in the vertical plane.
- Universal milling machine
It may be also produced spur, spiral, bevel gears, twist drills, reamers, milling cutters including all conventional milling operation. so a universal milling machine essentially a tool room machine designed to produce very accurate work.
- Omniversal milling machine
The additional swivelling arrangement of the table enables it to machine taper spiral grooves in reamers, bevel gears etc.
- Vertical milling machine
The machine is adapted for machining grooves, slots and flat surfaces.
The fixed bed type milling machine is comparatively large, heavy and rigid and it different from column and knee type milling machine by the construction of its table mounting.
The table is directly mounted directly on the ways of a fixed bed.
The cutter mounted on the spindle head may be moved vertically on the column and the spindle may be adjusted horizontally to provide cross adjustment. It can be classified below :
- Simplex milling machine
- Duplex milling machine
- Triplex milling machine
In the duplex machine, the spindle heads are arranged one on each side of the table.
In the triplex machine, the third spindle head is mounted on a cross rail.
The feed cycle of the table includes the following: start, rapid approach, slow feed for cutting, rapid traverse to next work piece, quick return and stop.
The planer type machine is built up for heavy-duty work, having spindle heads adjustable in vertical in transverse directions. It has a cross rail capable of being raised or lowered carrying the cutters their heads, and the saddles, all supported by rigid uprights.
The use of the machine is limited to production work only and is considered ultimate in metal removing capacity.
4. Special type
The planer type machine is built up for heavy-duty work, having spindle heads adjustable in vertical in transverse directions. It has a cross rail capable of being raised or lowered carrying the cutters their heads, and the saddles, all supported by rigid uprights.
The use of the machine is limited to production work only and is considered ultimate in metal removing capacity.
4. Special type
- Rotary table milling machine
The face milling cutters are mounted on two or more vertical spindles and a number of workpieces are clamped on the horizontal surface of a circular table which rotates about a vertical axis.
The cutters may be set at different heights relative to the work so that when one of the cutters is roughing the pieces the other is finishing them.
- Drum milling machine
The face milling cutters mounted on three or four spindle heads rotate in a horizontal axis and removal metal from workpieces supported on both the faces of the drum.
The finished machined parts are removed after one complete turn of the drum, and then the new ones are clamped to it.
- Planetary milling machine
This machine is adapted for milling internal or external threads of different pitches.
- Pantograph, profiling & tracer controlled milling machine
A pantograph is a mechanism that is generally constructed of four-bar which are joined in the form of the pantograph. Pantograph machine is available in two dimensional or three-dimensional models.
Profiling machine duplicates the full size of the template attached to the machine. This is practically a vertical milling machine or bed type in which the spindle can be adjusted vertically and cutter head horizontally across the table.
The movement of cutter regulated by a hardened guide pin.
Tracer controlled milling machine reproduces irregular or complex shapes of dies, moulds etc.
The feeding motion of the machine is controlled by means of a stylus that scans a profiled template or a contoured model which is to be reproduced.
Comparison between Plain and Universal Milling
Principle parts that are used in milling machine are described below :
- Base
- Column
- Knee
- Saddle
- Table
The table rests on guideways in the saddle and provides
support to the work.
The table is made of cast iron, its top surface is
accurately machined and carriers T-slots that accommodate the clamping bolt
for fixing the work.
A lead screw under the table engages a nut on the saddle to move the table horizontally by hand or power.
The worktable and hence the job fitted on it is given
motions in three directions:
Vertical (up and down) the movement provided by raising or lowering the knee.
Cross (in or out) or transverse motion provided by moving the
saddle in relation to the knee.
Longitudinal (back and forth) the motion provided by hand wheel fitted on the side of the feed screw.
For universal milling, the machine table may also swivel 45° to either side of the centre line and thus
fed at an angle to the spindle.
- Overarm
- Front Brace
The front brace is slotted to allow adjustment of the height of
the knee relative to the overarm.
- Spindle
- Arbor support
- Elevating screw
Operating Principle of Milling Machine :
In a milling machine operating principle machine tool used for the shaping of metal and other solid materials. By use of table and different work holding devices, the work piece is affixed and the milling cutter is rotated about the spindle axis. Milling operation involves movement of the rotating cutter sideways as well as in and out. The
cutter and work piece move relative to each other producing a toolpath along
which material is removed. Generally in all case of milling multi-tooth cutter is used so that the material removal rate is high and cutting action of the multi-tooth provides a fast method of machining. The machined surface may be flat, angular or curved but the most usually flat surface is produced by a milling machine. Many types of milling machine are used, ranging from relatively simple and versatile milling machine are used for the general purpose of machining to highly specialized machine for mass production. The milling machine may be operated manually or by CNC or NC machines.
Milling Machine Operations :
- Plain Milling
- Face Milling
- Side Milling
- Straddle Milling
- Angular Milling
- Gang Milling
- Form Milling
- End Milling
- Saw Milling
- Profile Milling
- Keyways, slots and grooves Milling
- Gear Cutting
- Helical Milling
- Cam Milling
- Thread Milling
Cutting Speed :
The speed of the milling cutter is its peripheral linear speed
resulting from rotation.
Cutting speed of milling machine
expressed in meters per minutes.
v = πdn/1000 metres per min
Where v = cutting speed
d = diameter of the cutter
n = cutter speed
Feed :
The feed-in milling machine is defined as the rate with which the work piece advances under the cutter. There are different three methods to expressed feed.
- Feed per tooth Sz
- Feed per cutter revolution Srev
- Feed per minute Sm
Sm = n * Srev = Sz * Z * n
Depth of cut :
The depth of cut in milling machine is the thickness of the material removed in one pass of the work under the cutter.
Number of Cutter Teeth :
The number of cutting teeth should be properly designed on a milling cutter for effective machining operation.
The number of cutter teeth is calculated from equation below :
Z = Sm / Sz
* n
The course teeth cutter having lesser number of teeth on their periphery which are efficient in metal machining.
Advantages of a course teeth cutter :
- Greater chip space may be provided
- Cutter tooth cross-section may be increased
- Increasing strength
- Less power required to drive the cutter
- Less sliding friction
- Longer life of cutter
Safety Measures in Milling Operation :
Milling machine operators must be extremely careful in running this machine tool therefore some of safety points should be required to know milling operators.
Following safety points must be followed by operators :
- Learn to operate controls before operating the machine.
- Work piece must be rigidly held on the worktable.
- Keep hands and body away from the revolving cutter.
- Do not change spindle speed when machining is running.
- Do not remove or tighten the milling machine arbour nut while the power is on.
- Do not measure work while continuous operation.
- Do not remove guards while machining.
- Do not remove chips when the machining is running.
- Wear snugly fitting clothing.
- Do not lean on the machine when it is running.
For the use of lubrication life, any machine increases so we can also know about Milling machine lubrication
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