MANUFACTURING PROCESSES

Milling Machines & Operations1

Introduction2

Addition to producing various external or internal round profiles, Cutting operations can produce many other parts with more complex shapes

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Highly versatile machining operationMultitooth tool that produces a number of chips in one revolution

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MILLING Milling is another basic machining process by which surface is generated progressively by the removal of chips from a work piece as it is fed against a rotating cutter.

Milling operations can be classified into two broad categories1. Peripheral Milling2. Face Milling

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Peripheral Milling 6

Peripheral MillingOperation performed by milling cutter to produce a machined surface parallel to axis of rotation of cutter

Cutting force is not uniform throughout the length of the cut by each tooth

Quality of surface generated and shape of the chip formed depends upon the rotation of cutter relative to direction of feed movement

It can be either UP milling or DOWN milling

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Up millingAlso called conventional milling,- Cutter rotation opposite of the feed- The chip formed by each cutter tooth starts out very thin and increases its thickness- The length of the chip is relatively longer- Tool life is relatively shorter- Need more clamping force to hold the work part still.

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Down milling:

Also called climb milling,- Cutter rotation is parallel to the feed- The chip formed by each cutter tooth starts out thick and leaves out thin- The length of the chip is relatively short- Tool life is relatively longer- Need less clamping force to hold the work part still.9

Face Milling

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Face MillingThe generated surface is at right angles to the cutter axis

It is the combined result of actions of the portions of the teeth located on both periphery and the face of the cutter

Most of the cutting is done by the peripheral portions of the teeth, with the face portions provides the surface finish.

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MILLING MACHINES12

Milling MachinesThe milling machine supplies an accurate rotating spindle for the cutter and a table (vise) to fix and position the work part.

Types of Milling Machines are -:

Column & Knee Type Fixed Bed Type Planer Type Special Type

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Column & Knee Milling Machine14

General purpose

Column, spindle, cutter, table, knee, base are the common parts of the vertical and horizontal milling machines

The milling machines having only the three mutually perpendicular table motions (x-y-z axes) are called plain column and knee type

Vertical type is especially well suited for face and end milling operations

Horizontal Milling Machine15

In horizontal, arbor supports the cutter and an over arm supports arbor

The vertical column houses the electrical, main drive, spindles etc mounted on a heavy base

Vertical Milling Machine16

In vertical, milling cutters can be mounted directly in the spindle

Housing (Head) can be fixed or Swiveling type

Fixed Type - Head is always vertical and can be adjusted up and down

Swiveling Type Head can be swiveled to any desired angle

17Universal Milling Machine Has a table that can be rotated in a horizontal plane to any specified angle

Bed Type Milling Machine18

Continue...Bed Type Milling Machines:

Designed for mass production

Achieves heavier feed rates and depth of cuts, high MRR

Work table is directly fixed on the bed of the machine tool

The cutter mounted in a spindle head that can be adjusted vertically along the machine column

Three types are available w.r.t. the count of spindles available

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Simplex 20

Fixed bed replaces saddle and knee. The table has longitudinal travel only

Spindle head carries spindle to which arbor is fitted to carry cutter that moves up and down along column ways

Continue...

Duplex: Has two spindles, permitting simultaneous milling of two surfaces at a single pass

Triplex: Has three spindles, permitting simultaneous milling of three surfaces at a single pass21

22Planer type milling machines

23Consists of a fixed bed carrying a table having longitudinal movements

Consists of 2 vertical columns on each side of the bed

Cross rail fitter across columns can be raised or lowered

Each column carries a milling head(side/horizontal) moving upwards or downwards

All cutters can be operated simultaneously to machine 4 surfaces at a time

Continue...24

CNC Milling Machines

Cutter path controlled by numerical data Suited to profile, pocket, surface contouring.

Milling Operations

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26Type of work materialCutter materialDiameter of cutterSurface finish requiredDepth of cut takenRigidity of machine and work setupImportant Factors in Determining Cutting Speed

27High-Speed Steel Cutter Carbide CutterMaterialft/min m/minft/minm/minAlloy steel4070 1220150250 4575Aluminum5001000 15030010002000300600Bronze65120 2035 20040060120Cast iron5080 1525 1252004060Free m steel100150 3045 400600120180Machine steel 70100 2130 1502504575Stainless steel 3080 1025 1003003090Tool steel 6070 1820 125200 4060

Milling Machine Feed28Defined as distance in inches (or mm) per minute that work moves into cutterIndependent of spindle speedFeed: rate work moves into revolving cutterMeasured in in/min or mm/minMilling feed: determined by multiplying chip size (chip per tooth) desired, number of teeth in cutter, and r/min of cutterChip, or feed, per tooth (CPT or (FPT): amount of material that should be removed by each tooth of the cutter

Factors in Feed Rate29Depth and width of cutDesign or type of cutterSharpness of cutterWorkpiece materialStrength and uniformity of workpieceType of finish and accuracy requiredPower and rigidity of machine, holding device and tooling setup

1. Plain Milling(Slab Milling)

Operation of production of plane flat surface parallel to axis of rotation of plain milling cutter

Cutter width extends beyond the work piece on both sides

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2. Face Milling

The face milling cutter is rotated about an axis perpendicular to the work surface

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32More Examples on Face Milling

3. End Milling

Combination of peripheral and face millingCutter has teeth both on end face and peripheryVertical milling machine is most suitable for end milling operation

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4. Side Milling

Operation of production of flat vertical surface on side of work piece by using side milling cutter

Depth of cut adjusted by rotating vertical feed screw of the table34

5. Straddle Milling

Operation of production of flat vertical surfaces on both side of the workpiece by using two side milling cutters mounted on the same arbor35

6. Angular MillingOperation of production of angular surface on a workpiece other than at right angles to the axis of milling machine spindle

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7. Gang Milling

Operation of milling several surfaces of the workpiece simultaneously by feeding the table against a number of cutters having same or different diameters

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8. Form Milling

It is the operation of production of irregular contours using form cuttersThe contours maybe convex, concave or any other shape

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9. Profile Milling

It is the operation of reproduction of an outline of a template or complex shape of a master die on a workpiece

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10.Milling Keyways, Grooves & Slots

Operation of production of keys, grooves and slots of varying shapes and size by using a plane milling cutter, a metal slitting saw, an end mill or by side milling cutter40

11. Thread Milling

Operation of production of threads by using a single or multiple thread milling cutter.It is performed in special thread milling machine to produce accurate threads

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Bibliography

42Reading Material Wikipedia www.howstuffworks.com www.custompart.netWorkshop Tech - Hajra Choudhury Vol 2