Milling Machine: Parts, Types, Operations, Milling Cutter-Mazurek Gravity

Milling Machine: Parts, Types, Operations, Milling Cutter

Milling is the machining process in which the removal of metal takes place due to the cutting action of a rotating milling cutter. In a milling machine, the cutter is rotating due to workpiece is fed against it. This machine can hold more than one tool at a time. The cutter rotates at high speed, and because of the many cutting edges, it removes metal at a very fast rate.

The machine can also hold one or a number of cutters at a time. Thus, the milling machine is one of the most important machines in the workshop. In this machine, all the operations can perform with high accuracy.

The machine can also hold one or a number of cutters at a time. Thus, the milling machine is one of the most important machines in the workshop. In this machine, all the operations can perform with high accuracy.

The metal removal rate is high as compared to a lathe machine, planner machine, and shaper machine. It has good accuracy and a better surface finish. This is why a milling machine finds wide application in production work.

Parts of Milling Machine

Following are the different parts of milling machine:

  1. Base
  2. Column
  3. Saddle
  4. Table
  5. Overhanging arm
  6. Front brace
  7. Spindle
  8. ArborMilling machine parts diagram

Base

  • The base of the machine is grey iron casting and serves as a foundation member for all other parts which rests on it.
  • The base carries the column at its one end. In some other machines, the base is hollow and works as a reservoir for cutting fluid.

Column

  • The column is the main supporting frame mounted on the base.
  • It is box-shaped and houses all the driving mechanism for the spindle and feed table.
  • The front vertical face of the column is precisely machined and is equipped with dovetail guideways for supporting the knee.
  • The top of the column is finished to hold an overarm that extends beyond the front of the machine.

Knee

  • The knee is a fixed grey iron casting that slides up and down on the vertical ways of the column face.
  • The adjustment of height is affected by an elevating screw mounted on the base that also supports the knee.
  • The knee houses the feed mechanism of the table and controls to operate it.
  • The top face of the knee forms a slideway for the saddle that gives cross travel to the table.

Saddle

  • On the top of the knee is placed the saddle, which slides on guideways set exactly at 90 degrees to the column face.
  • A crossfeed screw near the top of the knee engages a nut on the bottom of the saddle to move it horizontally, by hand or power, to apply cross-feed.
  • The top of the saddle is precisely machined to provide guideways for the table.

Table

  • It rests on guideways on the saddle and travels longitudinally.
  • The top of the table is finished accurately and T-slots are provided for clamping the work and other fixtures.
  • A lead-screw is provided under the table that engages with a nut on the saddle, it helps to move the table horizontally by hand or power.
  • The longitudinal travel of the table possibly limited by fixing trip dogs on the side of the table.
  • In universal machines, the table may also be swivelled horizontally. For this purpose, the table is mounted on a circular base, which in its turn is mounted on the saddle.
  • The circular base is graduated in degrees.

Overhanging arm

  • Overhanging arm act as a support for the arbor.
  • It is mounted on the top of the column extends outwards the column face and works as bearing support for the other end of the arbor.
  • The Overhanging arm is adjustable so that the bearing support may be provided nearest to the cutter.
  • More than one bearing support can be provided for the arbor.

Front brace

  • It is extra support, which provides rigidly to the arbor and the knee.
  • The front base is fitted between the knee and overarm.
  • The front brace is slotted to allow for the adjustment of the height of the knee relative to the overarm.

Spindle

  • The spindle of the machine is located in the upper part of the column and receives power from the motor through belts, gears, and clutches and transmit it to the arbor.
  • The front end of the spindle just projects from the column face and is provided with a tapered hole into which various cutting tools and arbor may be inserted.
  • The accuracy in metal machining by the cutter depends on the strength, accuracy and rigidity of the spindle.

Arbor

  • Arbor is an extension of the machine spindle on which milling cutters are securely mounted and rotated.
  • These are made with taper shanks for proper alignment with the machine spindles having taper holes at their nose.
  • The taper shank of the arbor match to the Morse taper or self-release taper whose value is 7:24.
  • The arbor may be supported at the farthest end from the overhanging arm or maybe of cantilever type which is called stub arbor.

Working Principle of Milling Machine

The working principle of the milling machine, applied in the metal removing operation on a milling machine. The work is rigidly clamped on the table of the machine and revolving multi teeth cutter mounted either on a spindle.

Capture

The cutter revolves at a normal speed and the work fed slowly past the cutter. The work can be fed in a longitudinal, vertical or cross direction. As the work progress further, the cutter teeth remove the metal from the work surface to produce the desired shape.

Size of Milling Machine

The size of the milling machine is determined by the dimensions of its maximum length of the longitudinal, cross, and vertical travel of the table and also by the working surface of the machine. The below image shows the typical size of a horizontal knee type milling machine.

Milling machine
size of milling

In addition to the above dimensions, number of spindle speeds, number of feeds, power available, spindle nose taper, net weight and the floor space required, etc. Should also be considered in order to specify the machine fully.

Milling Machine Operations

Following are the different types of operations performed on milling machine:

  1. Plain Milling Operation
  2. Face Milling Operation
  3. Side Milling Operation
  4. Straddle Milling Operation
  5. Angular Milling Operation
  6. Gang Milling Operation
  7. Form Milling Operation
  8. Profile Milling Operation
  9. End Milling Operation
  10. Saw Milling Operation
  11. Milling Keyways, Grooves, and Slot
  12. Gear Milling
  13. Helical Milling
  14. Cam Milling
  15. Thread Milling

1. Plain Milling

Plain-milling

  • The plain milling is the most common types of milling machine operations.
  • Plain milling is performed to produce a plain, flat, horizontal surface parallel to the axis of rotation of a plain milling cutter.
  • The operation is also known as slab milling.
  • To perform the operation, the work and the cutter are secured properly on the machine.
  • The depth of cut is set by rotating the vertical feed screw of the table. And the machine is started after selecting the right speed and feed.

2. Face Milling

Face milling machine operation

  • The face milling is the simplest milling machine operations.
  • This operation is performed by a face milling cutter rotated about an axis perpendicular to the work surface.
  • The operation is carried in plain milling, and the cutter is mounted on a stub arbor to design a flat surface.
  • The depth of cut is adjusted by rotating the crossfeed screw of the table.

3. Side Milling

  • The side milling is the operation of producing a flat vertical surface on the side of a workpiece by using a side milling cutter.
  • The depth of cut is set by rotating the vertical feed screw of the table.

4. Straddle Milling

straddle milling machine operation

  • The straddle milling is the operation of producing a flat vertical surface on both sides of a workpiece by using two side milling cutters mounted on the same arbor.
  • Distance between the two cutters is adjusted by using suitable spacing collars.
  • The straddle milling is commonly used to design a square or hexagonal surfaces.

5. Angular Milling

angular milling machine operation

  • The angular milling is the operation of producing an angular surface on a workpiece other than at right angles of the axis of the milling machine spindle.
  • The angular groove may be single or double angle and may be of varying included angle according to the type and contour of the angular cutter used.
  • One simple example of angular milling is the production of V-blocks.

6. Gang Milling

Gang milling machine operation

  • The gang milling is the operation of machining several surfaces of a workpiece simultaneously by feeding the table against a number of cutters having the same or different diameters mounted on the arbor of the machine.
  • The method saves much of machining time and is widely used in repetitive work.
  • Cutting speed of a gang of cutters is calculated from the cutter of the largest diameter.

7. Form Milling

form-milling machine operation

  • The form milling is the operation of producing the irregular contour by using form cutters.
  • The irregular shape may be convex, concave, or of any other shape. After machining, the formed surface is inspected by a template gauge.
  • Cutting rate for form milling is 20% to 30% less than that of the plain milling.

8. Profile Milling

profile-milling

  • The profile milling is the operation of reproduction an outline of a template or complex shape of a master dies on a workpiece.
  • Different cutters are used for profile milling. An end mill is one of the widely used milling cutters in profile milling work.

9. End Milling

end-milling machine operation

  • The end milling is the operation of producing a flat surface which may be vertical, horizontal or at an angle in reference to the table surface.
  • The cutter used is an end mill. The end milling cutters are also used for the production of slots, grooves or keyways.
  • A vertical milling machine is more suitable for end milling operation.

10. Saw Milling

saw milling machine operation

  • Saw-milling is the operation of producing narrow slots or grooves on a workpiece by using a saw-milling cutter.
  • The saw-milling also performed for complete parting-off operation.
  • The cutter and the workpiece are set in a manner so that the cutter is directly placed over one of the T-slots of the table.

11. Milling Keyways, Grooves and Slots

Keyways milling operation

  • The operation of producing of keyways, grooves and slots of varying shapes and sizes can be performed in a milling machine.
  • It is done by using a plain milling cutter, a metal slitting saw, an end mill or by a side milling cutter.
  • The open slots can be cut by a plain milling cutter, a metal slitting saw, or by a side milling cutter. The closed slots are produced by using endmills.

T-slot-operation

  • A dovetail slot or T-slot is manufactured by using special types of cutters designed to give the required shape on the workpiece.
  • The second slot is cut at right angles to the first slot by feeding the work past the cutter.
  • A woodruff key is designed by using a woodruff key slot cutter.
  • Standard keyways are cut on the shaft by using side milling cutters or end mills.
  • The cutter is set exactly at the centre line of the workpiece and then the cut is taken.

12. Gear Cutting

Gear-cutting-operation

  • The gear cutting operation is performed in a milling machine by using a form-relieved cutter. The cutter may be a cylindrical type or end mill type.
  • The cutter profile fits exactly with the tooth space of the gear.
  • Equally spaced gear teeth are cut on a gear blank by holding the work on a universal diving head and then indexing it.

13. Helical Milling

helical milling operation

  • The helical milling is the operation of producing helical flutes or grooves around the periphery of a cylindrical or conical workpiece.
  • The operation is performed by rotating the table to the required helix angle. And then by rotating and feeding the workpiece against rotary cutting edges of a milling cutter.
  • Production of the helical milling cutter, helical gears, cutting helical grooves or flutes on a drill blank or a reamer.

14. Cam Milling

The cam milling is the operation of producing cams in a milling machine by the use of universal dividing head and a vertical milling attachment. The cam blank is mounted at the end of the dividing head spindle and an end mill is held in the vertical milling attachment.

The axis of the cam blank and the end mill spindle should always remain parallel to each other when setting for cam milling. The dividing head is geared to the table feed screw so that the cam is rotated about its axis while it is fed against the end mill. The axis of the cam can be set from 0 to 90° in reference to the surface of the table for obtaining a different rise of the cam.

15. Thread Milling

The thread milling machine operations are used to produce threads by using a single or multiple thread milling cutter. Thread milling operation is performed in special thread milling machines to produce accurate threads in small or large quantities.

The operation requires three driving motions in the machine. One for the cutter, one for the work and the third for the longitudinal movement of the cutter.

When the operation is performed by a single thread milling cutter, the cutter head is swivelled to the exact helix angle of the thread. The cutter is rotated on the spindle and the workpiece is revolved slowly about its axis. The thread is completed in one cut by setting the cutter to the full depth of the thread and then feeding it along the entire length of the workpiece.

When the thread is cut by multiple thread milling cutter, the cutter axis and the work spindle are set parallel to each other after adjusting the depth of cut equal to the full depth of the thread. The thread is completed by simply feeding the revolving cutter longitudinal through a distance equal to the pitch length of the thread while the work is rotated through one complete revolution.

Fundamentals of Milling Machine

The milling process performed may be grouped under two separate headings

  1. Peripheral milling
  2. Face milling
  3. End milling

Peripheral Milling

It is the operation performed by milling cutter to produce a machined surface parallel to the axis of rotation of the cutter.

Peripheral milling is classified under 2 types.

  1. Up milling
  2. Down milling

Face Milling

It is the operation performed by a milling cutter to produce a flat-machined surface perpendicular to the axis of rotation of the cutter.

The peripheral cutting edges of the cutter do the actual cutting, whereas the face cutting edges finish up the work surface by removing a very small amount of the metal.

End Milling

End milling is the combination of peripheral and face milling.

Up Milling V/S Down Milling

In up milling the cutter is rotate clockwise when cutting the work piece from right to left. In this type of milling the tool spins against the direction of feed. In this milling process, the cutting chips are carried upward by the tool.

Difference Between Up Milling and Down Milling

In down milling, the cutter rotates clockwise while cutting the work piece from left to right. In this milling operation, the tool spins with the direction of feed. The cutting chips are carried downward by the tool.

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Difference between Up milling and Down milling:



Up Milling



Down Milling

1. In up milling the cutter rotates against direction of feed. In Down milling, the cutter rotates with direction of feed.
2. It is also known as conventional milling. It is also known as climb milling.
3. In this, chip width size is zero at initial cut and increase
with feed. It is maximum at the end of feed.
In this cutting process, chip size is maximum at start of cut
and decrease with the feed. It is zero at the end of feed.
4. In this process, heat is diffuse to the work piece which
causes the change in metal properties.
In down milling most of heat diffuse to the chip does not
change the work piece properties.
5. In up milling, tool wear is more because the tool runs
against the feed.
In this, tool wear is less compare to the up milling, due
to the cutter rotate with the feed.
6. Tool life is low. Tool life is high.
7. The cutting chips are carried upward by the tool so known
as up milling.
The chips are carried downward by the tool so known as
down milling.
8. The cutting chips fall down in front of the cutting tool
which again cut the chips cause less surface finish.
The cutting chips fall down behind the tool. This gives
better surface finish.
9. Due to upward force by tool, high strength zig and fixture
required to hold the work piece.
In down milling, downward force act on work piece normal
zig and fixture required.
10. It is the traditional way of cutting the work piece. It is non-traditional way, but now days, down milling used
more than up milling.
11. High quality cutting fluid is required because heat
diffuse in the work piece.
In this process heat does not diffuse in the work piece,
so simple cutting fluid is required.
12. It required high cutting force compare to down milling. It required low cutting force.