Machining Report 3

Milling
3rd Production For: Dr. Wael Akl

By:
1- Mohammed Farag Farag 2- Mohammed Taha Anwer 3- Mohammed Hassan Mohammed 4- Mohammed Abdelraoof Mohammed 5- Mahmoud Mohammed Abdelaziz

Contents

Cutting gears :

Introduction
1- form cutting method

2-Indexing mechanism:
1. Direct 2. Simple 3. Differential

3-Gear finishing process

1. Gear shaving 2. Roll Finishing of Gear Tooth 3. Gear Grinding 4. Lapping of a Gear 5. Gear honning

-Introduction: Gear cutting is the process of creating a gear. The most common processes include hobbing, broaching, and machining; other processes include shaping, forging, extruding, casting, and powder metallurgy. It else transmitte power between two shafts in more condition. Involute tooth profile is the smooth motion source but it is also the reason of hard manufacturing

- 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- Direct 2- Simple 3- Differential

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 rapid indexing 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 fast and simple and no calculations are required to use it. The disadvantage is that it can only be used for a limited number of angles

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.

slots 24 30 36

Direct indexing divisions 2 3 4 _ 6 8 _ __ 12 __ __ 24 __ __ 2 3 _ 5 6 _ _ 10 __ 15 __ __ 30 __ 2 3 4 _ 6 _ 9 __ 12 __ 18 __ __ 36

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 .

- 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

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 in the 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 and easily , the index plates and the sector are provided . For divisions which cannot be obtained using index plate and sector , the differential indexing is used.

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 time with 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 .

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 .

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 the mating faces of gear to be finished. Both are gears in mesh are pressed to make proper mating contact.

2- ROLL FINISHING OF GEAR TOOTH :

This process involves use of two hardened rolling dies containing very accurate tooth profile of the gear to be finished. 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 :

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 finishing operations of a gear generation process.

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