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milling machine is a machine tool that removes
metal as the work is fed against a rotating multi point cutter.
The cutter rotates at a high speed and because of the multiple cutting edges it
removes metal at a very fast rate. The machine can hold one or more number of
cutters at a time. This is why milling machine finds wide application in
production work. This is superior to other machines as regards accuracy and
better surface finish, and is designed for machining a variety of tool work.
TYPES OF MILLING MACHINE: The milling machine may be
classified in several from covering a wide range of work and capacities, but
the choice of any particular machine is determined primarily by the nature of
the work to be undertaken both in relation to the size and operation to be
performed.
1.COLUMN AND KNEE
TYPE: 3. PLANNER TYPE
a)
Hand milling
Machine
b)
Plain Milling
Machine
c)
Universal Milling
Machine
d)
Omniversal Milling
Machine
e)
vertical Milling
Machine
2.FIXED BED TYPE: 4. SPECIAL TYPE:
a) Simplex Milling
Machine a) Rotary
table Milling Machine
b) Duplex Milling Machine b) Drum Milling Machine
c)Triplex Milling Machine
c) Planetary Milling Machine
d)Pantograph, profiling &
tracer controlled milling machine
1.Column and knee type:
For general shop work the most commonly used is the column and knee type
where the table is mounted on the knee casting which in turn is mounted on the
vertical sliders 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 the various method of supplying arbor to the table, different
movements of the table and different axis of rotation of the main spindle.
1. a) Hand Milling Machine:
The simplest of all types of milling machine is the Hand Miller in which the feeding movement of the table is supplied by hand control. The cutter is mounted on a horizontal arbor and is rotated by arbor. The machine is relatively smaller in size than that of other types and is particularly suitable for light and simple milling operations such as machining slots grooves and keyways.
1. b) Plain milling
machine:
The plain milling machines are much more rigid and sturdy than hand millers for accommodating heavy workpieces. The milling machine table may be fed by hand or arbor against a rotating cutter mounted on a horizontal arbor. A plain milling machine having horizontal spindle, is also called horizontal milling machine. In a plain milling machine, the table may be fed in a longitudinal, cross or vertical direction. The feed is longitudinal when the table is moved at right angle to the spindle, it is cross when the table is moved parallel to the spindle, and the feed is vertical when the table is adjusted in a vertical plane.
1.c) Universal milling machine:
Universal milling machine is so named because it may be adapted to a very
wide range of milling operation. A universal milling machine can be
distinguished from a plain milling machine in that the table of a universal
milling machine is mounted on a circular swiveling base which has degree
graduations, and the tail can be swiveled to any angle up to 45 degree on
either side of the normal position. The table can be swiveled about a vertical
axis and set an angle other than right angle to the spindle. Thus, in a universal
milling machine, in addition to three movements as incorporated in a plain
milling machine, the table may be having a fourth movement when it is fed at an
angle to the milling cutter. This additional feature enables it to perform a
helical milling operation which cannot be done on a plain milling machine unless
a spiral milling attachment is used. The capacity of universal milling machine
is considerably increased by the use of special attachments such as dividing
head or index head, vertical milling attachment, rotary attachment, slotting
attachment, etc. The machine can produce spur, bevel gears twist drills,
reamers, milling cutters, etc. besides doing all conventional milling operations.
1.d) Omniversal milling
machine:
In this machine, the table besides having all the movements of a universal
milling machine, can be tilted in a vertical plane by providing a swivel
arrangement at the knee. Also, the entire knee assembly is mounted in a such a
way that it may be fed in a longitudinal direction horizontally. The additional
swiveling arrangement of the table enables it to machine taper spiral groups
in reamers, bevel gears, etc. It is essentially a tool room and experimental
shop machine.
1.e) Vertical milling machine:
A vertical milling machine can be distinguished from a horizontal milling by the position of its spindle which is vertically or perpendicular to the work table. The machine maybe of plane or universal type and has all the movements of the table for proper sitting and feeding the work. The spindle head which is clamped to the vertical column may be swiveled at an angle, permitting the milling cutter mounted on the spindle to work on angular surfaces. In some machines, the spindle can also be adjusted up or down relative to the work. The machine is adapted for machining grooves, slots and flat surface. The end Mills and face milling cutters are the usual tools mounted on the spindle.
2.Fixed bed type milling machine:
The fixed bed type milling machines are comparatively large, heavy and rigid and offer radically from column and knee type milling machine by the construction of its table mounting. The table is mounted directly on the ways of fixed bed. The table movement is restricted to reciprocation at right angles to the spindle axis with no provision for cross or vertical adjustment. The cutter mounted on the spindle head may be moved vertically on the column, and the spindle may be adjusted horizontally to provide a cross adjustment. The name simplex, duplex and triplex indicate that the machine is provided with single, double and triple spindle heads respectively. In a duplex machine, the spindle heads are arranged one on each side of the table.
3. Planer type milling Machine:
The Plano-miller, as it is called, is a massive machine built up for heavy duty work, having spindle heads adjustable in vertical in transverse directions. It resembles a planner and like a planing machine, it has a cross rail capable of being raised or lowered carrying the cutters their heads and the saddles carrying cutters on the rail as well as two heads on the uprights. This arrangement of independently driving multiple cutter swindles enables number of work surfaces to be machine simultaneously, thereby obtaining great reduction in production time. The essential difference between a planner and a Plano Miller lies in the table movement. In a planner, the table moves to give the cutting speed, but in a plano milling machine the table movement gives the feed. Hence the table movement in a plano milling is much slower than that of a planing machine. Modern plano miller are provided with high power-driven spindles powered to the extent of 100 h.p and the rate of metal removal is tremendous. The use of the machine is limited to production work only and is considered ultimate in metal removing capacity.
3. Special type milling Machine:
Milling machines of non-conventional design have been developed to suit
special purpose. The features that they have in common are the spindle for
rotating the cutter and provision for moving the tool or the work in different
direction. The following special types of machines of interest and described
below
3.a) Rotary table milling machine:
The construction of the machine is a modification to a vertical milling machine and is adapted for machining flat surfaces at high production rate. The face milling cutters are mounted on two or more vertical spindles and number of pieces are claimed on a horizontal surface of a circular table which rotates about a vertical axis. The cutter may be set at different heights relative to the work so that when one of the cutter is roughing the pieces, the other can finish them. A continuous loading and unloading of work pieces may be carried out by the operator while the milling is in progress.
3.b) Drum milling machine:
The Drum milling is similar to a rotary table milling machine in that it's work supporting table, which is called a drum, rotates in a horizontal axis. The face milling cutters is mounted on the three or four spindles heads rotate in a horizontal axis and remove metal from the work pieces supported on both the faces of the drum. The finished machine parts are removed after one complete turn of the drum and then the new ones are clamped on it.
3.c) Planetary milling machine:
In a planetary milling machine, the work is held stationary while the
revolving cutter or cutters moved in a planetary path to finish a cylindrical
surface on the work either internally or externally or simultaneously. The
machine is particularly adapted for milling internal or external threads of
different pitches.
3.d) Pantograph milling machine:
A pantograph machine can duplicate a job by using a pantograph mechanism which permits the size of the work piece reproduce to be smaller than equal to or greater than the size of a template or model used for the purpose. A pantograph is a mechanism that is generally constructed of four bars or kinks which are joined in the form of a parallelogram. Pantograph machines are visible in two-dimensional and three-dimensional models. Two-dimensional pantograph is used for engraving letters or other designs, whereas three-dimensional models are employed for copying any shape and contour of the workpiece. The tracing stylus is move manually on the contour of the model to be duplicated and the milling cutter mounted on the spindle moves in a similar path on the workpiece reproducing the shape of the model.
3.e) Profiling milling machine:
A profiling machine duplicates the full size of the template attached to
the machine. This is particularly a vertical milling machine of bed type in
which the spindle can be adjusted vertically and the cutter head horizontally
across the table. The movement of the cutter is regulated by a hardened guide
pin. The pin is held against and follow the outline or profile of a template
mounted on the table at the side of the job. The longitudinal movement of the
table and crosswise movement of the cutter head follow the movements of the
guide pin on the template.
3.f) Tracer control milling machine:
The tracer controlled milling machine reproduce irregular or complex shapes
of dies, moulds, etc by synchronized movement of the cutter and tracing element.
The feeding motion of the machine is controlled automatically by means of a
stylus that scans a profiled template or a contoured model which is to be produced. The movement of
the stylus energizes an oil relay system which in turn operates the main
hydraulic system of the table. This arrangement is termed as servomechanism.
