MILLING MACHINEPROCESSES & OPERATIONS

INTRODUCTION

•Milling is a basic machining process by which a surface is generated by progressive chip removal.

•The w/p is fed into a rotating cutting tool. Sometimes the w/p remains stationary, and the cutter is fed into the work.

•A multi-point cutting tool is used in milling operation, which is known as milling cutter.

THE PROCESS•The milling process:

▫Typically uses a multi-tooth cutter

▫Work is fed into the rotating cutter

▫Capable of high MRR▫Well suited for mass

production applications▫Cutting tools for this

process are called milling cutters

CLASSIFICATIONS•Milling operations are classified into two major

categories:▫Peripheral (side)

Generally in a plane parallel to the axis of the cutter Cross section of the milled surface corresponds to the

contour of the cutter▫Face

Generally at right angles to the axis of rotation of the cutter

Milled surface is flat and has no relationship to the contour of the cutter

Combined cutting action of the side and face of the milling cutter

MILLING PROCESS

Some basic types of milling cutters and milling operations. (a) Peripheral milling. (b) Face milling. (c) End milling. (d) Ball-end mill with indexable coated-carbide inserts machining a cavity in a die block. (e) Milling a sculptured surface with an end mill, using a five-axis numerical control machine.

RELATED OPERATIONS▫Side milling - machining a plane surface

perpendicular to the milling machine arbor with an arbor mounted tool. This tool is called a side mill.

▫Straddle milling - milling two parallel surfaces using two cutters spaced apart on an arbor.

▫Gang milling - milling multiple surface simultaneously using multiple cutters mounted on an arbor.

Milling Operations

OPERATING PARAMETERS•Conventional vs. Climb Milling

MILLING MACHINES• Two Major Classifications - Knee & Column and Bed

▫ Knee & Column (Bridgeport type) Basic job shop type mill Column mounted to the base which is the major support frame. Construction provides controlled motion of the worktable in three mutual

perpendicular directions. Knee moves vertically on the ways in the front of the machine Table moves longitudinally on the ways on the saddle Saddle moves transversely on the ways on the knee Quill moves parallel in Z axis or, if head is rotated, X axis Versatile general purpose machine

Column-and-Knee Type Milling Machines

Schematic illustration of (a) a horizontal-spindle column-and-knee type milling machine and (b) vertical-spindle column-and-knee type milling machine.

MILLING MACHINES▫Bed

Used extensively in production milling operations Rigid construction capable of heavy cuts Table is mounted directly to the bed Spindle head moves vertically to set depth of cut Head locks into position for cut Base of machine functions as a coolant reservoir

BED TYPE MILLING MACHINE

Fig : Schematic illustration of a bed-type milling machine. Note the single vertical-spindle cutter and two horizontal-spindle cutters.

Horizontal bed

Vertical bed

Mainshaft

TraversSupport

Shaft with milling tool

Milling tool

Part

X slide

Z slide

Y slide

Engine1

Speedbox

Volant

1

2X screw

Z screw

Y screw

Feed box

Engine2

Handle weels

HORIZONTAL MILLING MACHINE

VERTICAL MILLING MACHININING CENTER

Five-Axis Profile Milling Machine

Schematic illustration of a five-axis profile milling machine. Note that there are three principal linear and two angular movements of machine components.

MILLING MACHINES

MILLING MACHINES

MILLING CUTTERS•Milling cutters can be classified according

to the way the cutter is mounted in the machine tool:▫Arbor cutters▫Shank cutters

•Another method of classification applies only to face and end mill cutters and relates to the direction of rotation:▫Right hand cutter▫Left hand cutter

CUTTERS

ARBOR

Face-Milling Cutter

Face-Milling Cutter with Indexable Inserts

TYPES OF MILLING CUTTERS

Milling Operations

(a) Schematic illustration of conventional milling and climb milling. (b) slab-milling operation showing depth-of-cut, d; feed per tooth, f; chip depth-of-cut, tc; and workpiece speed, v. (c) Schematic illustration of cutter travel distance, lc, to reach full depth-of-cut.

Face-Milling Operation

Face-milling operation showing (a) action of an insert in face milling; (b) climb milling; (c) conventional milling; (d) dimensions in face milling. The width of cut, w, is not necessarily the same as the cutter radius.

WORKHOLDING DEVICES•Vise•Chucks•Rotating tables•Angle plates•Special fixtures•Universal dividing head•Modular fixturing systems•Clamp work to table

WORKHOLDING DEVICES

DIVIDING HEAD & INDEXING

STANDARD DIVIDING HEAD•A dividing head is a tool that is used to

divide a circle into equal divisions.

STANDARD DIVIDING HEAD• In a nut shell, a dividing head is simply a spindle mounted with a precision worm

wheel and provided with a crank attached to the worm shaft.

• The crank's handle is equipped with a spring loaded plunger that will drop an indexing pin into equally spaced holes in a disk mounted behind the crank.

• The spindle is provided with the means to mount a chuck or collet attachment for holding a workpiece.

• It is also provided with a lock for clamping the spindle in position for increased rigidity.

• These units are usually mounted such that the spindle's axis can be tilted through 90 degrees, to provide an additional axis of adjustment.

• Most units are made with a 40:1 reduction in the worm, such that 40 turns of the crank will rotate the spindle through one full turn.

• The indexing plate is a disk with concentric circles of equally spaced holes situated behind the crank.

• It provides a handy positive index for positioning the crank at 1/n turns of the crank, where n equals the number of holes in the disk.

• The plunger can be positioned along the arm of the crank to select which circle of holes you wish the indexing pin to engage.

• These indexing plates are usually interchangeable to provide a wide variety of choices for n, so that one turn of the spindle can be divided into a great variety of equal parts.

• The crank is outfitted with a pair of sector arms which can be adjusted to indicate the correct number of holes for any partial turn of the crank you must make.

• This eliminates the need to count holes on every subsequent advance of the spindle.

INDEXING PLATE

Simple Indexing Mechanism

PROCEDURE• Dividing a circle into 40 equal parts is pretty straight forward since the worm

wheel has 40 teeth - one full turn of the crank equals one fortieth of a circle at the spindle.

• To divide a circle into 20 parts: two turns of the crank would equal two 40ths, or one 20th of a circle.

• One fourth of a crank turn (or 6 holes in a 24 hole index circle) would equal one 160th of a circle at the spindle.

• Here is the formula:crank turns = 40 / N

where N = the desired number of equal divisions at the spindle

• Reduce this fraction to its simplest form. Use any whole number to represent complete turns, and use the denominator to determine the index plate to use.

Generally two types of Index Plates are supplied:

1. Brown and Sharpe type, 3 plates of 6 circles, each drilled as follows:

Plate 1- 15, 16, 17, 18, 19, 20 holes.

Plate 2- 21, 23, 27, 29, 31, 33 holes.

Plate 3- 37, 39, 41, 43, 47, 49 holes.

2. Cincinnati type, one plate drilled on both sides with circles divided as follows:

First side- 24, 25, 28, 30, 34, 37, 38, 39, 41, 42, 43 holes.

Second side- 46, 47, 49, 51,53, 54, 57, 58, 59, 62, 66 holes.

PROCEDURE

PROCEDUREExample 1: T0 divide a circle in 6 equal parts:• Using the rule given above, divide 40 by 6, which equals 6 2/3

turns, or six full turns plus 2/3 of a turn on any circle whose number of holes is divisible by 3.

• Therefore, six full turns of the crank plus 12 spaces on an 18-hole circle, or six full turns plus 26 spaces on a 39-hole circle will produce the desired rotation of the workpiece.

Example 2: To Cut a Gear of 42 Teeth:• Using the rule again, divide 40 by 42 which equals 40/42 or 20/21

turns, 40 spaces on a 42-hole circle or 20 spaces on a 21-hole circle. • To use the rule given, select a circle having a number of holes

divisible by the required fraction of a turn reduced to its lowest terms. The number of spaces between the holes gives the desired fractional part of the whole

•Indexing

END