MILLING MACHINE

INTRODUCTION

A milling machine is a machine tool that removes metalas the work is fed against a rotating multipoint cutter.

The milling cutter rotates at high speed and it removesmetal at a very fast rate with the help of multiple cuttingedges.

Milling machine is used for machining flat surfaces,contoured surfaces, surfaces of revolution, external andinternal threads, and helical surfaces of various cross-sections.

Job surfaces generated by milling machine

MILLING METHODS

There are two distinct methods of milling classifiedas follows:

a) Up-milling or conventional milling

b) Down milling or climb milling.

a) UP-Milling or Conventional Milling Procedure

The metal is removed in form of small chips by acutter rotating against the direction of travel of theworkpiece.

In this type of milling, the chip thickness isminimum at the start of the cut and maximum at theend of cut. As a result the cutting force also variesfrom zero to the maximum value per toothmovement of the milling cutter.

The major disadvantages of up-milling process arethe tendency of cutting force to lift the work from thefixtures and poor surface finish obtained. But being asafer process, it is commonly used method of milling.

UP-Milling or Conventional Milling Procedure

b) Down milling or climb milling.

It is also known as climb milling. In this method, the metal isremoved by a cutter rotating in the same direction of feed ofthe workpiece.

The effect of this is that the teeth cut downward instead ofupwards. Chip thickness is maximum at the start of the cutand minimum in the end. In this method, it is claimed thatthere is less friction involved and consequently less heat isgenerated on the contact surface of the cutter and workpiece.

Climb milling can be used advantageously on many kinds ofwork to increase the number of pieces per sharpening and toproduce a better finish. With climb milling, saws cut long thinslots more satisfactorily than with standard milling. Anotheradvantage is that slightly lower power consumption isobtainable by climb milling, since there is no need to drive thetable against the cutter.

Down milling or climb milling.

TYPES OF MILLING CUTTERS

Milling Machine

Universal Horizontal Milling Machine

12

Milling Machine Parts

Base Gives support and rigidity to

machine Acts as reservoir for cutting

fluids

Column face Precision-machined and

scraped section used tosupport and guide knee whenmoved vertically

Knee Houses feed mechanism Attached to column face and

moved vertically

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Milling Machine Parts

Saddle

On top of knee

Moved in or out by

means of crossfeed

handwheel (manually

or automatically)

Swivel table housing

Fastened to saddle on

universal milling

machine

Enables table to beswiveled

45º either side of centerline

14Milling Machine Parts Table

Rests on guidewaysin saddle and travelsleft and right

Supports vise andwork

Crossfeed handwheel

Used to move table inand out

Table handwheel

Used to move tableleft and right

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Milling Machine Parts

Feed dial Used to regulate table

feeds

Spindle Provides drive for

attachments, arbors,cutters

Overarm Provides for correct

alignment and support ofarbor and variousattachments

Can be adjusted andlocked in variouspositions

16Milling Machine Parts Arbor support Fitted to overarm and can

be clamped Aligns and supports various

attachments

Elevating screw Gives upward or downward

movement to knee andtable (manually orautomatically)

Spindle speed dial Set by crank used to

regulate spindle speed

17Arbors

Arbors Used for mounting milling cutter

Inserted and held in mainspindle by draw bolt

Shell-end mill arbors Permit face milling horizontally

or vertically

Fit into main spindle

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Collets and Adapters

Collet adapters used for mounting drills or other

tapered-shank tools in main spindleof machine or vertical millingattachment

Quick-change adapter Mounted in spindle

Permits such operations as drilling,boring, and milling without changein setup of workpiece

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Arbors, Collets, and Adapters

20Milling Machine Vises

Plain vise Jaws parallel or 90º to axis of spindle

21Milling Machine Vises

Swivel base vise Can swivel through 360º in horizontal plane

22Milling Machine Vises

Universal vise Can swivel through 360º in horizontal plane and tilted

from 0º to 90 in vertical plane

DEPTH OF CUT

The depth of cut in milling is defined as the thicknessof the material removed in one pass of the workunder the cutter. Thus it is the perpendiculardistance measured between the original and finalsurface of the workpiece, and is expressed in mm.

Cutting Speed(CS) of a material is the idealnumber of Feet-per-Minute that the tool-bit shouldpass over the work-piece. Different materials(High-Carbon/Low-Carbon Steels, Aluminums,Different kinds of Plastics) have different CuttingSpeeds and can be worked/cut at different rates. Inaddition, some tools or processes (like threading,knurling, or cutting-off) will need to be worked atslower speeds than the Cutting Speed wouldindicate.

Feed Rate(Milling Machine) refers to how fasta milling-tool moves through the material beingcut. This is calculated using the Feed PerTooth(FPT) to come up with the Inches PerMinute that a milling bit can move through aparticular type of material. Thus, a Four-FluteEnd-Mill will cut through material at twice thespeed of a Two-Flute End Mill. Feed Rates willdecrease with dull tools, a lack of coolant, or deepcuts.

RPM(Revolutions Per-Minute) is the turningspeed of whatever is spinning: On a Lathe this isthe work-piece. On a Mill or a Drill it is the cutting-tool. *Using Cutting Speed and Diameter you cancalculate RPM as shown further down on thispage.

Milling Machine Safety

Be sure that the work and the cutter are mountedsecurely before taking a cut.

Always wear safety glasses.

When mounting or removing milling cutter,alwayshold them with a cloth to avoid being cut.

Be sure that the cutter and machine parts clear thework.

Never attempt to mount ,measure parts clear thework.