gear report

7/29/2019 Gear Report

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Machining Report 3

Milling3

rdProduction

For:

Dr. Wael Akl

By:

1- Mohammed Farag Farag

2- Mohammed Taha Anwer

3- Mohammed Hassan Mohammed4- Mohammed Abdelraoof Mohammed

5- Mahmoud Mohammed Abdelaziz


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Contents

Cutting gears :

Introduction

1- form cutting method

2-Indexing mechanism:

1.Direct2.Simple3.Differential

3-Gear finishing process

1.Gear shaving2.Roll Finishing of Gear Tooth3.Gear Grinding4.Lapping of a Gear5.Gear honning


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-Introduction:

GGeeaarrccuuttttiinngg is the process of creating a gear.

The most common processes

include hobbing, broaching, and machining; other

processes

include shaping, forging, extruding, casting, andpowder metallurgy.It else transmitte power between two shafts inmore condition.

Involute tooth profile is the smooth motion

source but it is also the reason of hardmanufacturing


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- Indexing operations :

Indexing may be defined as the process of causing the work to

be moved any desired amount on its axis.Each tooth of a gear is the same size and shape as its neighbor

and they are spaced exactly the same distance apart.This exact spacing is accomplished by means of a machine

operation called indexing.

- Methods of indexing :

1- Direct2- Simple3- Differential


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Direct Indexing :

Direct indexing plate: Most dividing heads have an

indexing plate permanently attached to the spindle. This plate

is located at the end of the spindle, very close to where the

work would be mounted.

It is fixed to the spindle and rotates with it. This plate is

usually equipped with a series of holes that enables rapidindexing to common angles, such as 30, 45, or 90 degrees.

A pin in the base of the dividing head can be extended

into the direct indexing plate to lock the head quickly into one

of these angles.

The advantage of the direct indexing plate is that it is fastand simple and no calculations are required to use it. The

disadvantage is that it can only be used for a limited number

of angles
http://upload.wikimedia.org/wikipedia/commons/1/1a/IndexingHead-SimplePlate.jpg


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Direct Indexing Divisions:

Direct indexing plate usually contains three sets of

holes circles or slots: 24, 30, and 36.

Number of divisions possible to index limited to

numbers that are factors of 24, 30, 36.

Direct indexing divisionsslots2 3 4 _ 6 8 _ __ 12 __ __ 24 __ __242 3 _ 5 6 _ _ 10 __ 15 __ __ 30 __302 3 4 _ 6 _ 9 __ 12 __ 18 __ __ 3636


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Simple indexing :

Simple indexing, also called plain indexing, is

accomplished by means of a mechanism as in the figure

shown below

Which consists essentially of a 40-tooth worm wheel

fastened to the index-head spindle , a single-threaded worm ,a crank for turning the worm shaft and an index plate . since

there are 40 teeth in the worm wheel , one complete turn of

the index crank will cause the worm wheel to make 1/40 of a

turn or in the other words , 40 turns of the index crank

revolves the spindle one full turn .


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- Rule for calculating the number of turns of the

index crank :

To obtain the number of turns ( whole or fractional ) of

the index crank for division of any desired number of equal

divisions on the work , divide the number of turns for one

revolution of the spindle ( usually 40 ) by the number of equal

divisions desired .

The formula to find the number of turns is :

T = 40/N

Where :

T = number of turns or parts of a turn

N = number of divisions required


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Index plate and Sector :

The fractional parts of a turn involve the use of an

index plate and a sector , it will be observed that the

index pin at the end of the index handle enters a hole inthe index plate . if only full turns were used in indexing

, one hole only would be necessary , if only turns and

half turns were required , two holes in opposite sides of

the plate would answer , but a great number of different

fractional parts of a turn are required for different

spacings , and in order to measure them accurately andeasily , the index plates and the sector are provided .

For divisions which cannot be obtained using index

plate and sector , the differential indexing is used.


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Differential indexing :

There are many divisions of the circle that are not

possible to obtain with simple indexing .

It then becomes necessary to use the method known as

differential indexing .

The term differential is used because the needed

division is obtained by a combination of two

movements : (1) the simple indexing movement of the

index crank , and (2) the movement of the index plate

itself . these two movements happen at the same timewith a differential in their movement relationship .

With the change gears and the three index plates

that are standard equipment with the (B) and (S) index

head , it is possible all numbers not obtained by simple

indexing from 1 to 382 . in addition , many other

divisions beyond 382 can be indexed .


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The index-head spindle and the index plate are

connected by a train of gears so that the index plate will

turn either in the same direction as the movement of the

crank or in the opposite direction , depending upon the

requirements of the job .


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GEAR FINISHING OPERATIONS:

Surface of gear teeth produced by any of the generating

process is not accurate and of good quality (smooth).

Dimensional inaccuracies and rough surface generated so

become the source of lot of noise, excessive wear, play and

backlash between the pair of gears in mesh. These all result in

loss of power to be transmitted and incorrect velocity ratios.

This can be summarized as inefficient power transmission. In

order to over come these problems some finishing operations

are recommended for the produced gears.

1- GEAR SHAVING:

Gear shaving is a process of finishing of gear tooth by

running it at very high rpm in mesh with a gear shaving tool.

A gear shaving tool is of a type of rack or pinion having

hardened teeth provided with serrations. These serrations

serve as cutting edges which do a scrapping operation on themating faces of gear to be finished. Both are gears in mesh are

pressed to make proper mating contact.


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2- ROLL FINISHING OF GEAR TOOTH :

This process involves use of two hardened rolling dies

containing very accurate tooth profile of the gear to befinished. The gear to be finished is et in between the two dies

and all three are revalued about their axis. Pressure is exerted

by both the rolling dies over the gear to be finished. The

material of the die is very hard as compare to the material of

gear so there is a plastic deformation of high points and burrs

on the profile of gear tooth resulting to smooth surface.

3- Gear Grinding :


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In this operation abrasive grinding wheel of a particular shape

and geometry are used for finishing of gear teeth. Gear to be

finished is mounted and reciprocated under the grinding

wheel. Each of the gear teeth is subjected to grinding

operations this way.

4- Lapping of a Gear :

The process of lapping is used to improve surface finish of

already made teeth. In this process the gear to be lapped is run

under load in mesh with cast iron toothed laps. Abrasive paste

is introduced between the teeth. It is mixed with oil and made

to flow through the teeth. One of the mating members (either

gear or lapping tool) is reciprocated axially along with the

revaluations.

5- GEAR HONNING :

It is used for super finishing of the generated gear teeth.

Honing machines are generally used for this operation. The

hones are rubbed against the profile generated on the gear

tooth. Gear lapping and gear honing are the lost finishingoperations of a gear generation process.


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In the above gear finishing operations some operations are

based on metal cutting by removing very small size of chips

like gear shaving, gear grinding, lapping and honing and some

other operations like gear burnishing, roll finishing and based

on finishing by plastic deformation of metal

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