2009

Sobuj

SUST

11/16/2009

Milling operation

Milling machine and operation

Name of the Experiment: “Study of different components function of a milling

machine (including gear teeth cutting operation).”

Objectives:

1. To study about milling machine with its different components.

2. To study different operations performed by a milling machine.

3. To learn about indexing system of milling machine.

4. Performing gear cutting operation by using milling machine.

Introduction: Milling machine is one of the most important machine tools in a tool room as nearly all the operations can be performed on it with high accuracy. The operation performed

in a milling machine is called milling. Milling is the process of machining flat, curved, or irregular surfaces by feeding the work piece against a rotating cutter containing a number of

cutting edges. The usual Mill consists basically of a motor driven spindle, which mounts and revolves the milling cutter, and a reciprocating adjustable worktable, which mounts and feeds the work piece.

Gear teeth are cut on the milling machine using formed milling cutters called involutes gear

cutters. These cutters are manufactured in many pitch sizes and shapes for different numbers of teeth per gear.

Classification of milling machine:

According to design, the distinctive classification of milling machine is as follows:

1. Column and knee milling machine

a. Horizontal milling machine.

b. Vertical milling machine. c. Universal milling machine.

d. Ram type universal milling machine.

2. Bed type milling machine.

A. Simplex milling machine. B. Duplex milling machine.

C. Triplex milling machine.

3. Plano type milling machine.

5. Special purposes milling machine.

a. Rotary table milling machine b. Drum milling machine.

c. Profile milling machine. d. Duplicating milling machine. e. Placatory milling machine.

In our workshop we’ve performed with “Universal horizontal milling machine.”

Now I’m going to describe about the machine with its main components.

D. Table.

E. Saddle.

F. Cross feed handle.

G. Vertical feed crank.

H. Knee.

I. Vertical positioning screw.

J. Base.

K. Column.

L. Table hand wheel.

M. Table transmission

N. Ram type over arm.

O. Arbor support.

P. Spindle.

Figure 1: Milling machine

Principal part of milling machine:

The principal parts of universal horizontal milling machine are as follows.

1. Base: it is the foundation of the machine and is the part upon which all other parts are

mounted. It gives the machine rigidity and strength.

2. Column: It is the main supporting frame. The motor and other driving mechanisms

are contained within.

3. Knee: The knee projects from the columns and slides up and down on its face. It

supported by the elevating screw, which adjust its height.

4. Saddle: It supports and carries the table and guided by the accurately machined

surfaces of the knee.

5. Over arm: It is mounted on and guided by the top of spindle. It obtains its power from

the motor through belts, gears and a clutch and transmits it to an arbor. Cutters are

directly mounted in the spindle nose.

6. Arbor: It is an accurately machined shaft for holding and driving the arbor type cutter.

TOOLS AND EQUIPMENT

1. Milling cutters:

Milling cutters are usually made of high-speed steel and are available in a great variety of shapes and sizes for various purposes

Figure 2: Arbor installation

Figure 3: Different types of milling cutter

Blab mill Helical mill

Course tooth Mill

Helical Mill (Arbor type)

Side Mill Metal slitting saw Interlocking Milling Staggered Yooth Mill

Arbor Arbor Support Intermediate

Arbor support

Spindle

Draw in Bolt Milling cutter Journal Bearing Arbor Nut

Milling Cutter Nomenclature

The given figure shows two views of a common milling cutter with its parts and angles identified. These parts and angles in some form are common to all cutter types.

The pitch refers to the angular distance between like or adjacent teeth.

The pitch is determined by the number of teeth. The tooth face is the forward

facing surface of the tooth that forms the cutting edge.

The cutting edge is the angle on each tooth that performs the cutting.

The land is the narrow surface behind the cutting edge on each tooth.

The rake angle is the angle formed between the face of the tooth and the

centerline of the cutter. The rake angle defines the cutting edge and provides a path for chips that are cut from the workpiece.

The primary clearance angle is the angle of the land of each tooth measured from

a line tangent to the centerline of the cutter at the cutting edge. This angle prevents each tooth from rubbing against the workpiece after it makes its cut.

This angle defines the land of each tooth and provides additional clearance for passage of cutting oil and chips.

Arbor: The standard milling machine arbor has a tapered, cylindrical shaft with a

standard milling taper on the driving end and a threaded portion on the opposite end

to receive the arbor nut. One or more milling cutters may be placed on the straight

cylindrical portion of the arbor and held in position by sleeves and the arbor nut. The

standard milling machine arbor is usually splinted and keys are used to lock each

cutter to the arbor shaft.

Figure 4: Milling Cutter Nomenclature

Figure 5: Standard milling machine arbor

Land

Outside diameter Heel

Pitch of Teeth

Hole diameter

Depth of tooth

Face of tooth

Key way

Cutting Edge

Rake angle

Primary clearance angle Secondary clearance angle Wide

End or slide of cutter

Spiral or

Helix angle

Taper Cutter Bearing bushing Spindle Lock nut

Draw in Bar Arbor

Nut

2. Collects, Spindle, Adapters, and Quick-change tooling:

Milling cutters that contain their own straight or tapered threaded portion to provide

alignment and support for tools shanks are mounted to the milling machine spindle with

collets, spindle adapters, and quick-change tooling which adapts the cutter shank to the

spindle.

Collets: A collect is a form of a sleeve bushing for reducing the size of the hole in

the milling machine spindle so that small shank tools can be fitted into large spindle

recesses (Figure 6). They are made in several forms, similar to drilling machine sockets and sleeves, except that their tapers are not alike.

Spindle Adapters: A spindle adapter is a form of a collect having a standardized

spindle end. They are available in a wide variety of sizes to accept cutters that cannot be mounted on arbors. They are made with either the Morse taper shank or the

Brown and Sharpe taper with tang having a standard spindle end (Figure 7).

Figure 6: Collect

Figure 7: Spindle adapters

Chuck Adapter: Chuck adapter (Figure 8) is used to attach chucks to milling

machines having a standard spindle end. The collect holder is sometimes referred to

as a collect chuck. Various forms of chucks can be fitted to milling machines

spindles for holding drills, reamers, and small cutters for special operations.

Quick-Change Tooling: The quick-change adapter mounted on the spindle nose is used to speed up tool changing. Tool changing with this system allows you to set up

a number of milling operations such as drilling, end milling, and boring without changing the setup of the part being machined. The tool holders are mounted and

removed from a master holder mounted to the machine spindle by means of a clamping ring.

3. Adjustable angle plate: The adjustable angle plate is a workpiece holding device,

similar to the universal vise in operation. Workpiece are mounted to the angle plate with T-bolts and clamps in the same manner used to fasten workpiece to the worktable of the milling machine. The angle plate can be adjusted to any angle so that

bevels and tapers can be cut without using a special milling cutter or an adjustable cutter head.

4. Indexing fixture: The index fixture (Figure 9) consists of an index head, also called a

dividing head, and footstock which is similar to the tailstock of a lathe. The index head and footstock attach to the worktable of the milling machine by T-slot bolts. An index plate containing graduations is used to control the rotation of the index head

spindle.

Figure 8: Chuck adapter

Figure 9: Indexing fixture

Tail Stock

Driving plate

Index Head

Spindle

Index Head

Index Crank

Index Plate

Indexing work:

Indexing: Indexing is the process of evenly dividing the circumference of a circular

workpiece into equally spaced divisions, such as in cutting gear teeth, cutting splints, milling grooves in reamers and taps, and spacing holes on a circle. The index head of

the indexing fixture is used for this purpose.

Index Head: The index head of the indexing fixture (Figure 10) contains an indexing mechanism which is used to control the rotation of the index head spindle to space or

divide a workpiece accurately. A simple indexing mechanism consists of a 40-tooth worm wheel fastened to the index head spindle, a single-cut worm, a crank for turning

the wormshaft, and an index plate and sector. Since there are 40 teeth in the worm wheel, one turn of the index crank causes the worm, and consequently, the index head spindle to make 1/40 of a turn; so 40 turns of the index crank revolve the spindle one

full turn.

Index Plate: The indexing plate (Figure 10) is a round plate with a series of six or

more circles of equally spaced holes; the index pin on the crank can be inserted in any hole in any circle. With the interchangeable plates regularly furnished with most index heads, the spacing necessary for most gears, bolt heads, milling cutters, splints,

and so forth can be obtained.

The following sets of plates are standard equipment:

Brown and Sharpe type consists of 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

Figure 10: Indexing head

Index Plate

Driving Plate Index Head

Index Head

Spindle Index Crank

Cincinnati type consists of 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

Sector: The sector (Figure 10) indicates the next hole in which the pin is to be

inserted and makes it unnecessary to count holes when moving the index crank after each cut. It consists of two radial, beveled arms which can be set at any angle to each

other and then moved together around the center of the index plate.

Work performed in milling machine:

1. All kinds of grooves. 2. Splints and key-ways on shaft.

3. Concave and convex surfaces. 4. Sawing, slotting, gear cutting, and so forth. 5. Gear teeth cutting.

6. Plate and barrel cams. 7. Facing operation of all kinds etc.

Among them we’ve performed “Gear teeth cutting” operation in our IPE workshop.

Now I’m going to describe the operation in briefly.

Figure 11: Sector

6 Holes 5

spaces

Operation of Sector

Index plate with crank and sector

Sector

Radial crank adjustment screw

Sector

binding screw

Sector

Gear cutting: Gear teeth are cut on the milling machine using formed milling

cutters called involutes gear cutters. These cutters are manufactured in many pitch

sizes and shapes for different numbers of teeth per gear.

Working procedure:

1. At first we’ve fixed a milling cutter on the arbor. 2. Then we’ve fixed a workpiece on the vice.

3. Then we start the milling machine and give proper feed to complete the gear cutting operation.

4. We use cutting fluid to avoid excess heating and laggards. 5. We’ve performed only one tooth cutting in the gear.

6. After completing the operation we’ve stopped the milling machine and remove the workpiece from the vice.

Data for gear cutting operation:

1. Work diameter was 6.3 cm.

2. Milling cutter diameter 6.8 cm. 3. Number of tooth in the cutter was 10

4. Pitch of tooth was 0.8 cm.

5. Depth of tooth was 1.3 cm. 6. Revolution per minute was 280 during operation.

7. Depth of cut was 0.5 cm. 8. Feed rate was approximately 0.01 (mm/rev)

9. Minimum RPM of the milling machine is 35.

10. Maximum RPM of the milling machine is 1600.

Figure 11: Gear cutting operation

Workpiece

Milling cutter

Finishing to Minor Diameter

Cutting condition of milling:

1. Cutting speed v, (m/min): The tangential velocity of the periphery of the periphery of the cutter.

The cutting speed is expressed by, “v.”

v= m/min.

Here, Dn= diameter of the cutter.

n=Spindle revolution number in per min.

During our operation the cutting speed was,

v= Diameter of cutter= 68 mm. RPM was=280;

So, v =59.8

2. Depth of cut “t”: Depth of cut is the distance between the

stock and the machined surface.

During our operation the depth of cut was 0.5 cm

Discussion: Performing gear cutting operation in milling machine is not a new concept for us. But in this time we become familiar with the indexing system of

milling machine. But the limitation is it was not shown but only gives a virtual concept to us. I think it will be much efficient if the indexing system shown us practically. Although we can

perform a much wider range of operation in milling machine but we are just limited in gear cutting operation for 2 semesters. Insist of them gear cutting operation is very common operation for milling machine. It uses most the criteria of milling machine. So to learn about

milling machine the gear cutting operation is very efficient for us.

Conclusion: Milling machine is a complex machine and widely used and versatile for many jobs. It is a common machine in workshop and production sector. We can perform a wide

range of operation in milling machine among them the gear cutting is one of the most simple and important operation. Gear teeth are cut on the milling machine using formed milling cutters called involutes gear cutters. As the milling machine is very useful both industrial and

non industrial purpose, so to be update with the world we should know about the milling machine and its applications.

Feed

D

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t Feed

Edited by Sobuj

SUST

Dept of Industrial & Production

Engineering

Registration No. 2008334053

k.sobuz@gmail.com