CHAPTER 1

INTRODUCTION

1.0 INTRODUCTION

Hindustan Aeronautics Limited (HAL) was founded way back 1940 by a

visionary Seth Shri Walchand Hirachand Aircraft Limited at Bangalore in

association with the erstwhile princely state of Mysore. Govt. of India became one

of its shareholders in March 1941 and took over the management in 1942.

The present day Hindustan Aeronautics Limited, a Public Sector

Undertaking (PSU), under Ministry of Defence and fully owned by Govt. of India

was formally formed on Manufacturing Dept. with Hindustan Aeronautics Limited.

Today, HAL is the largest PSU under Dept. of Defence Production, GOI and

is declared as “Navratna” (Category-1) company. HAL has emerged as a premier

defence production industry of the country and is fully owned by the Govt. of

India, Ministry of Defence.

HAL, with its wide spectrum of expertise in design, development and

manufacture of aircraft, helicopters, engines, accessories and avionics, has

emerged as a major aeronautical complex in Asia. HAL has nineteen production/

overhaul/ service Divisions well supported nine co-located R & D centers.

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HAL’s mission is “To become a globally competitive aerospace industry

while working as instrument for achieving self-reliance in design, manufacture and

maintenance of aerospace equipment, civil transport aircraft, helicopters and

missiles and diversifying to related areas, managing the business on commercial

line in a climate of growing professional competence”.

The core business of HAL includes:

Design and development of fixed and rotary wing aircraft, Avionics and

Accessories.

Manufacture, maintenance, repair and overhaul of:

Fighter, Transport and Trainer aircraft

Helicopters

Aero-Engines

Avionics

Ground support equipment

Manufacture of structural components for satellites and launch vehicles.

Development of aeronautical software

HAL, over the last six decades, has grown progressively into an integrated

Aerospace organisation with its indigenous design & development of Advanced

Light Helicopter (ALH- Dhruv), Intermediate Jet Trainer (IFT), Light Combat

Aircraft (LCA-Tejas).

The on-going major projects & programmes include ALH (both in military

& civil roles). IJT, LCA, Pilotless Target Aircraft (PTA), S30MK, Hawk-

Advanced Jet Trainer.

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Aligning with the emerging future requirements, HAL has conceptualised

the indigenous development of Light Combat Helicopter (LCH), Combat Air

Trainer (CAT) as well as naval & trainer versions of LCA.

HAL has three joint venture companies:

BAE-HAL Software Limited for development of aeronautical software

Indo-Russian Aviation Limited (IRAL) for spares & Services of Russian origin

aircraft/engines/accessories

Snecma- HAL Aerospace Private Limited for production of aero-engine

components. Further, several co-production and Joint Ventures with international

participation are under consideration, aiming to enhance business and to upgrade

technology.

HAL continues to maintain highest credit rating for long term and shirt term

debt programmes, which is a testimony of the financial soundness of HAL.

HAL as an organization, has won several awards for its achievements in the

field of aeronautics like world Quality Commitment International Star” in Platinum

category by Business Initiative Directions, Golden Peacock Award for Innovation

etc. in recognition of HAL’s contribution in Quality, Leadership, Technology and

Innovation.

1.1 HAL MANAGEMENT ACADEMY (HMA)

HMA is a premier training institute equipped with state-of-art training

facilities & highly qualified faculty. HMA undertakes various training programs

for the executives on regular basis for continued enhancement of managerial

knowledge and leadership.

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1.2 BANGALORE COMPLEX

1.2.1 AIRCRAFT DIVISION

The product profile of the division presently include Jaguar Strike aircraft,

PTA (Lakshya), Composite/ Metal Drop tanks Dornier 228 Landing Gears.

Facilities for manufacture of HAWK-Advance Jet trainer are under establishment.

The division exports high precision aircraft components and sub-assemblies like

Airbus A320/A321 forward Pax Doors, Boeing 757 OWX Doors and other

structure work packages.

1.2.2 ENGINE DIVISION

Engine Division is presently engaged in manufacture of Adour Mk 871 &

811, Garrett TPE 331-5 Artouste IIIB & Shakti, GTSU, PTAE. The divisions also

undertake repair and overhaul of Adour Mk 811, Adour MK 804E, Garrett, Dart,

Gnome, Orpheous, Artouste IIIB and Avon MK 1/ MK 109 engines.

1.2.3 OVERHAUL DIVISION

The present activities of Overhaul division includes Major servicing of Kiran MK

I/IA, Kiran MK II, Jaguar Strike & Trainer and Major inspection of Mirage 2000

Fighter & Trainer, Overhaul & repair of Lycoming (HPT-32 & Islander) engines,

Overhaul and repair/ servicing of accessories.

1.2.4 AEROSPACE DIVISION

The Division undertakes production of light alloy structures for the Polar Satellite

Launch Vehicle (PSLV), Geo Stationary Launch Vehicle (GSLV), Indian Remote

sensing Satellite (IRS), Indian National Satellite (INSAT) and CRYO structures.

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1.2.5 FOUNDARY & FORGE DIVISION

The activities of the division includes development and manufacture of

Aluminum and Magnesium base alloys and indigenous development of castings

and forgings in ferrous and Non- ferrous alloys, rolled rings, brake pads and rubber

products for critical applications for the Aeronautics, Space, Defence, Locomotive,

Earthmover and other industries.

1.2.6 AIRPORT SERVICES CENTER

Presently Airport Services Center is providing the technical services of Air

Traffic Control, maintenance of Runway and navigation/ landing aids and various

other allied services of HAL Airport, which is the third busiest airport in the

country.

1.2.7 INDUSTRIAL & MARINE GAS TURBINE (IMGT) DIVISION

The major activities of IMGT Division presently are manufacture of LM

2500 (Marine) engines and repair/overhaul of Industrial Avon, Allison & LM 2500

(Industrial) engines. A dedicated LCA-LSP unit has been set up to handle LCA-

Tejas production. Limited series production of LCA has commenced.

1.3 DESIGN COMPLEX

1.3.1 AIRCRAFT R & D CENTER (ARDC)

ARDC has full spectrum of expertise in all facets of aircraft design,

prototype manufacturing and extensive testing facilities backed by rich in-service

experience of more than five decades. On-going projects include indigenous design

& development of Intermediate Jet Trainer (IJT) & Light Combat Aircraft (LCA).

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1.3.2 ROTARY WING R & D CENTER (RWRDC)

RWRDC undertakes full range of design tasks for civil & military

helicopters. It has extensive facilities for design & development, testing & analysis

of structure/transmission system/integration of engine/avionics as well as

accessories.

RWRDC is the nodal agency for successful design & development of Dhruv

ALH for wide range of military & civil applications. On-going projects include

development of Light Combat Helicopter (LCH).

1.3.3 HELICOPTER DIVISION

The present activities of the division include series production of Advanced

Light Helicopter (Dhruv), manufacture & overhaul of Cheetah (SA-315 Lama),

Chetak (Alouette III), Lancer, Cheetal and Chetan helicopters. Its service to

customer includes logistic and technical support including training. Barrackpore

Branch Factory, attached to Helicopter Division, primarily undertakes Major

Servicing of Cheetah and Chetak Helicopters.

1.3.4 AIRCRAFT DIVISION, NASIK

The Division is currently engaged in manufacture of SU-30 MKI aircraft,

spares of MiG21 series, MIG 27M, MIG 23 & MIG 29 aircraft.

The Division is also involved in manufacture /repair/overhaul of Undercarriages of

ALH, LCA and Mirage-2000.

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1.3.5 AIRCRAFT OVERHAUL DIVISION, NASIK

The Division is currently engaged in repair/overhaul of MiG-21 aircraft

variants/ MIG-27M aircraft and their aggregates & retables. The Division has

undertaken series up gradation of MiG-21 BIS and MiG-27.

1.3.6 ENGINE DIVISION, KORAPUT

Present activities of the division include manufacture of R-25 series engines

of MiG-21BIS and overhaul of R-11 series engines of MiG-21 FL/MiG-21M, R-

29B engines for/ MIG- 27M aircraft and RD-33 engines of MiG-29 aircraft. The

division also undertakes development & manufacture of forgings & castings for

aeronautical & industrial applications.

1.3.7 SUKHOI ENGINE DIVISION, KORAPUT

A separate Division has been set up for manufacture an AL 31FP engine for

SU-30MKI aircraft. Production programme for AL 31FP commenced in 2004-05

1.4 ACCESSORIES COMPLEX

1.4.1 ACCESSORIES DIVISION, LUCKNOW

The manufacturing range of the division can be grouped under 3 categories.

Mechanical & Hydro Mechanical Accessories

Engine Accessories

Instrument Accessories

The division is also manufacturing a wide range of Ground Support equipment

like Ground Power Unit, Hydraulic Trolley, Weapon loading Trolley,

Transportation Trolley, Alert Trolley, Test Equipment etc

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1.4.2 AVIONICS DIVISION, HYDERABAD

Presently, the product profit of the division includes Precision Apporach

Radar, INCOM, Airborne Rader, Identification of Friend or Foe (IFF), Automatic

Direction Finder (ADF), HFSSB, VHF/ UHF, Aircraft Battery and Ceramic Brake

Pads.

1.4.3 ACIONICS DIVISION, KORWA

Avionics Division Korwa is presently involved in a advanced avionics

systems like Inertial Navigation System (INS), s Combined Map and Electronic

Display (COMED), Head Up Display & Weapon Aiming Computer (HUDWAC),

Laser Ranger and Marked Target Seeker (LRMTS), Auto stabilizer and Flight Data

Recorder (FDR).

The Division has also established the facilities for Depot Level Maintenance

facilities for Digital Map Generator (DMG), Head UP Display (HUD) for Jaguar

and SU-30 aircraft & production Facilities for manufacture of Multi-Function

Display (MFD) for SU-30 MKI aircraft.

1.4.4 TRANSPORT AIRCRAFT DIVISION (TAD), KANPUR

Currently, the activities of TAD-Kanpur Division include manufacturing and

overhaul of DO-228 aircraft in addition to overhaul of HS-748 and HPT-32 aircraft

and their rotables. HAL Detachment Agra, attached to TAD-Kanpur is involved in

servicing of AN-32 aircraft and overhaul of Canberra aircraft

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1.4.4 HAL CUSTOMERS

Defence Customers: Indian air force, Indian navy, Indian army

Civil Customers: Coast Guard, Border Security Force, Corporate Section,

State Governments

Exports: Honeywell, Rolls Royce, Turbomeca etc.

1.5 INTRODUCTION ON GEARS

Gears are machine elements that transmit motion by means of successively

engaging teeth. The gear teeth act like small levers. A gear is a rotating machine

part having teeth which mesh with another toothed part in order to transmit power,

torque, and motion or to change speed or direction.

1.5.1 THE LAW OF GEARING

A primary requirement of gears is the constancy of angular velocities or

proportionality of position transmission, Precision instruments require positioning

fidelity. High speed and/or high power gear trains also require transmission at

constant angular velocities in order to avoid severe dynamic problems. Constant

velocity (i.e. constant ratio) motion transmission is defined as “conjugate action”

of the gear tooth profiles. A geometric relationship can be derived for the form of

the tooth profiles to provide conjugate action, which is summarized as the Law of

Gearing as follows:

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“A common normal to the tooth profiles at their point of contact must, in all

positions of the contacting teeth, pass through a fixed point on the line-of-centers

called the pitch point.” Any two curves or profiles engaging each other and

satisfying the law of gearing are conjugate Curves.

Fig 1.0 Law of gearing

1.5.2 INVOLUTE AND CYCLOIDAL PROFILES

Gear profiles that do not satisfy this law will not have a constant angular

velocity ratio. In other words the driving pinion could travel at a constant rpm but

the driven wheel would speed up and slow down instead of rotating smoothly. This

would cause all kinds of problems.

1.5.3 GEAR TEETH PROFILE

A profile is one side of a tooth in a cross section between the outside circle

and the root circle. Usually a profile is the curve of intersection of a tooth surface

and a plane or surface normal to the pitch surface, such as the transverse, normal, 10

or axial plane. The fillet curve (root fillet) is the concave portion of the tooth

profile where it joins the bottom of the tooth space. A non- fluctuating velocity

ratio is dependent on the profile of the teeth. Friction and wear between two gears

is also dependent on the tooth profile.

There are a great many tooth profiles that will give a constant velocity ratio,

and in many cases, given an arbitrary tooth shape, it is possible to develop a tooth

profile for the mating gear that will give a constant velocity ratio. However, two

constant velocity tooth profiles have been by far the most commonly used in

modern times.

Fig 1.1 Spur gear profile

1.5.4 INVOLTE TOOTH FORM

Imagine unwinding a spool of thread. The arc at the end of the thread forms

an involute curve. Involute gears are economical to make because the cutters used

to make the gears are straight. Another advantage is that the center distance

between the gears can be changed and the gears will still transmit a constant

velocity

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Fig 1.2 Involute tooth form

.

1.5.5 INVOLUTE GEARS IN ACTION

Fig 1.3 Involute gears in action

This shows a pair of full fitting involute gears. Gears found in machines or

purchased from a catalogue would have tooth form like this.

o Very little backlash.

o Three teeth engaged at all times.

o Lots of friction.

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1.5.6 CYCLOIDAL TOOTH FORM

Cycloidal tooth forms are used primarily in clocks for a number of reasons.

o Less sliding friction.

o Less wear.

o Easier to achieve higher gear ratios without tooth interference.

Two generating circles roll on the pitch circle to trace the cycloidal tooth

profile. The outside circle traces the "face" of the gear tooth. The inside circle

traces the "flank" of the gear tooth. Clock gears have a further refinement. Radial

lines are drawn from the center of the gear tangent to the flank. The flank area is

then removed along these lines to reduce friction.

1.5.7 CYCLOIDAL GEARS- MODIFIED FLANK

This cycloidal gear set has the flanks removed. See how the gears do not

engage until the pitch circles nearly come in contact. The length of time the gears

are touching is reduced too. Also see that the only one pair of teeth is engaged at a

time. As one tooth starts to drive, the previous driver loses contact. The teeth are

narrower and easier to make. Backlash is not a problem for clocks because the

gears always turn in one direction.

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Fig 1.4 Cycloidal Gears- Modified Flank

Fig 1.5 Three teeth engaged at all times in cycloidal system

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1.6 TERMINOLOGY IN GEAR MANUFACTURING PROCESS

Pitch Surface: The surface of the imaginary rolling cylinder (cone etc.) that

the toothed gear may be considered to replace.

Pitch circle: Right section of the pitch surface.

Addendum circle: The circle bounding the ends of the teeth, in a right

section of the gear.

Dedendum circle (root circle): The circle bounding the spaces between the

teeth, in a right section of the gear.

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Addendum: The radial distance between the pitch circle and the addendum

circle.

Dedendum: The radial distance between the pitch circle and the root circle.

Clearance: The difference between the dedendum of one gear and the

addendum of the mating gear.

Face of a tooth: The part of the tooth surface lying outside the pitch surface.

Flank of a tooth: Part of the tooth surface lying inside the pitch surface.

Circular thickness (tooth thickness): The thickness of the tooth measured

on the pitch circle. It is the length of an arc and not a length of a straight

line.

Tooth space: The distance between the adjacent teeth measured on the pitch

circle.

Circular pitch (p): The width of a tooth and a space, measured on the pitch

circle.

Diametral pitch (P): The number of teeth of a gear per inch of its pitch

diameter. A toothed gear must have an integral number of teeth. Circular

pitch therefore equals the pitch circumference divided by the number of

teeth. The diametral pitch is the number of teeth divided by the pitch

diameter.

Module (m): Pitch diameter divided by number of teeth. The pitch diameter

is usually specified in inches or millimeters, in the former case the module is

inverse of diametral pitch.

Fillet: The small radius that connects the profile of a tooth to the root circle.

Pinion: The smallest of any pair of mating gears. The largest of the pair is

called simply the gear.

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Velocity ratio: The ratio of number of revolutions of the driving (or input)

gear to the number of revolutions of the driven (or output) gear, in a unit of

time.

Pitch point: The point of tangency of the pitch circles of a pair of mating

gears.

Common tangent: The line tangent to the pitch circle at the pitch point.

Pressure angle: The angle between the common normal at the point of tooth

contact and the common tangent to the pitch circles. It is also the angle

between the line of action and the common tangent.

Base circle: An imaginary circle used in involute gearing to generate the

involutes that forms the tooth profiles

Working depth (hk): Working depth is the depth of engagement of two

gears; that is, the sum of their addenda.

Fig 1.6 Definition of pressure angle

1.7 TOOTH CONTACT NOMENCLATURE

1.7.1 POINT OF CONTACT

A point of contact is any point at which two tooth profiles touch each other.

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1.7.2 LINE OF CONTACT

A line of contact is a line or curve along which two tooth surfaces are

tangent to each other.

Fig 1.7 Line of contact (spur and helical gear)

1.7.3 PATH OF ACTION

The path of action is the locus of successive contact points between a pair of

gear teeth, during the phase of engagement. For conjugate gear teeth, the path of

action passes through the pitch point. It is the trace of the surface of action in the

plane of rotation.

Fig 1.8 Path of Action

1.7.4 LINE OF ACTION

The line of action is the path of action for involute gears. It is the straight

line passing through the pitch point and tangent to both base circles.

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Fig 1.9 Line of Action

1.7.5 SURFACE OF ACTION

The surface of action is the imaginary surface in which contact occurs

between two engaging tooth surfaces. It is the summation of the paths of action in

all sections of the engaging teeth.

Fig 1.10 Surface of action

1.7.6 PLANE OF ACTION

The plane of action is the surface of action for involute, parallel axis gears

with either spur or helical teeth. It is tangent to the base cylinders.

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1.7.7 CONE OF ACTION (CONTACT ZONE)

Zone of action (contact zone) for involute, parallel-axis gears with either

spur or helical teeth, is the rectangular area in the plane of action bounded by the

length of action and the effective face width.

1.7.8 PATH OF CONTACT

The path of contact is the curve on either tooth surface along which

theoretical single point contact occurs during the engagement of gears with

crowned tooth surfaces or gears that normally engage with only single point

contact.

1.7.9 LENGTH OF ACTION

Length of action is the distance on the line of action through which the point

of contact moves during the action of the tooth profile.

1.7.10 ARC OF ACTION

Arc of action is the arc of the pitch circle through which a tooth profile

moves from the beginning to the end of contact with a mating profile.

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1.7.11 ARC OF APPROACH, QA

Arc of approach is the arc of the pitch circle through which a tooth profile

moves from its beginning of contact until the point of contact arrives at the pitch

point.

1.7.12 ARC OF RECESS, QR

Arc of recess is the arc of the pitch circle through which a tooth profile

moves from contact at the pitch point until contact ends.

1.7.13 CONTACT RATIO, MC, Ε

Contact ratio in general is the number of angular pitches through which a

tooth surface rotates from the beginning to the end of contact.

1.7.14 Transverse contact ratio, mp, εα

Transverse contact ratio is the contact ratio in a transverse plane. It is the

ratio of the angle of action to the angular pitch. For involute gears it is most

directly obtained as the ratio of the length of action to the base pitch.

1.7.15 FACE CONTACT RATIO, MF, ΕΒ

Face contact ratio is the contact ratio in an axial plane, or the ratio of the

face width to the axial pitch. For bevel and hypoid gears it is the ratio of face

advance to circular pitch.

1.7.16 TOTAL CONTACT RATIO, MT, ΕΓ

Total contact ratio is the sum of the transverse contact ratio and the face

contact ratio.

εγ = εα + εβ

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1.7.17 MODIFIED CONTACT RATIO, MO

Modified contact ratio for bevel gears is the square root of the sum of the

squares of the transverse and face contact ratios.

1.7.18 LIMIT DIAMETER

Limit diameter is the diameter on a gear at which the line of action intersects

the maximum (or minimum for internal pinion) addendum circle of the mating

gear. This is also referred to as the start of active profile, the start of contact, the

end of contact, or the end of active profile.

Fig. 1.11 limit diameter

1.7.19 START OF ACTIVE PROFILE (SAP)

The start of active profile is the intersection of the limit diameter and the

involute profile.

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1.7.20 FACE ADVANCE

Face advance is the distance on a pitch circle through which a helical or

spiral tooth moves from the position at which contact begins at one end of the tooth

trace on the pitch surface to the position where contact ceases at the other end.

Fig. 1.12 face advance

1.7.21 BACKLASH

Backlash is the error in motion that occurs when gears change direction. It

exists because there is always some gap between the tailing face of the driving

tooth and the leading face of the tooth behind it on the driven gear, and that gap

must be closed before force can be transferred in the new direction. The term

"backlash" can also be used to refer to the size of the gap, not just the phenomenon

it causes; thus, one could speak of a pair of gears as having, for example, "0.1 mm

of backlash."

A pair of gears could be designed to have zero backlash, but this would

presuppose perfection in manufacturing, uniform thermal expansion characteristics

throughout the system, and no lubricant. Therefore, gear pairs are designed to have

some backlash. It is usually provided by reducing the tooth thickness of each gear

by half the desired gap distance.

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In the case of a large gear and a small pinion, however, the backlash is

usually taken entirely off the gear and the pinion is given full sized teeth. Backlash

can also be provided by moving the gears farther apart. For situations, such as

instrumentation and control, where precision is important, backlash can be

minimized through one of several techniques. For instance, the gear can be split

along a plane perpendicular to the axis, one half fixed to the shaft in the usual

manner, the other half placed alongside it, free to rotate about the shaft, but with

springs between the two halves providing relative torque between them, so that one

achieves, in effect, a single gear with expanding teeth. Another method involves

tapering the teeth in the axial direction and providing for the gear to be slid in the

axial direction to take up slack.

1.7.22 UNDERCUT

Undercut is a condition in generated gear teeth when any part of the fillet

curve lies inside of a line drawn tangent to the working profile at its point of

juncture with the fillet. Undercut may be deliberately introduced to facilitate

finishing operations. With undercut the fillet curve intersects the working profile.

Without undercut the fillet curve and the working profile have a common tangent.

Fig. 1.13 Undercut

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1.7.23 MODIFIED ADDENDUM TEETH

Teeth of engaging gears, one or both of which have non-standard addendum.

1.7.24 FULL-DEPTH TEETH

Full-depth teeth are those in which the working depth equals 2.000 divided

by the normal diametral pitch.

1.7.25 STUB TEETH

Stub teeth are those in which the working depth is less than 2.000 divided by

the normal diametral pitch.

1.7.26 EQUAL ADDENDUM TEETH

Equal addendum teeth are those in which two engaging gears have equal

addendums.

1.7.27 LONG AND SHORT-ADDENDUM TEETH

Long and short addendum teeth are those in which the addendums of two

engaging gears are unequal.

Fig. 1.14 long and short-addendum teeth25

1.8 AGMA- AMERICAN GEAR MANUFACTURERS ASSOCIATION

AGMA is a full service trade association representing 400 manufacturers

and users of gears and gearing products, suppliers of equipment and services to the

industry, individual consultants and academicians. AGMA has members in 30

countries and, in fact, is quickly becoming the Association for global

manufacturers in the gear industry.

1.8.1 AGMA QUALITY CLASS NUMBERS

The AGMA gear quality numbers range from 3 through to 15 and identify

the accuracy level of the tooth element tolerances that are permissible in the

manufacture of each particular gear in terms of its specialised use. The permissible

tolerances for the different quality numbers may be obtained from the AGMA

standards, which show the type of gear and the permissible tolerances and

inspection dimensions.

Application for AEROSPACE Quality Number

Actuators 7 - 11

Control Gearing 10 - 12

Engine Accessories 10 - 13

Engine Power 10 - 13

Engine Starting 10 - 13

Loading Hoist 7 - 11

Propellor Feathering 10 - 13

Small Engines 12 - 13

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Once a suitable quality number has been decided, the relevant tolerances for

the tooth elements can be selected from the AGMA quality standards.

1.8.2 GEAR MATERIALS

The gear materials are classified as follows:

Heat resisting steels

Heat resisting alloys

Nickel based alloys

Special alloys:

1. Alacrite (cobalt based alloys)

2. Adnick (Nickel based alloys)

The various materials used for aero- engine gear manufacture are chromic

steel, carburized steel SAE1018, 1054, 4026, 4118,

4340, 4320, 4820 and 9310), Nitriding steel and Carburizing steel.

1.8.3 CHARACTERISTICS OF GEAR MATERIALS

It should resist inter crystalline corrosion.

It should work above 7500C.

It should have high temperature characteristics.

Resistance to hot turbine gases.

Saline corrosion resistance.

It should withstand oxidation upto 11000 C.

Good mechanical properties at elevated temperature.

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1.9 GEAR CELL OF MACHINE SHOP MACHINES

1. Reishauer Gear Grinder: Used for grinding external profile of gear tooth.

2. Voumard Internal Grinder: Used for internal grinding of the gear.

3. Barber Colman Gear Hobber: Used for formation of gears teeth by hobbing

process.

4. Maxicut Gear Shaper: Used for formation of gear teeth by reciprocating

shaping process.

5. Gratomat: Used to provide contour break on the gear teeth by grinding

wheel.

6. Rotomat: Used for final finishing of gear by spindle deburring using

abrasives.

7. Lap Master: Used for lapping, this gives more accuracy than grinding.

8. Herbert 7: Is a lathe which is used for turning, facing etc.

9. Bevel Gear Cutting: Used for cutting bevel gears by shaping.

10.Samputensili Gear Hobber CNC: It’s a CNC used for hobbing process.

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11.Fellows Gear Shaper CNC: It’s a CNC used for shaping process.

12.Okuma and Howa CNC lathe: It’s a CNC lathe used for operations like

turning, facing etc.

13.Hofler Gear Tester: Used to inspect the profile of the gear teeth.

1.9.1FACILITY MATRIX- MANUFACTURE GEARS AT GEARS CELL

Sl.No Machine Type Make Qty Country Remarks

01 Gear Hobbing Barber & Coleman 01 U.S.A Ext Spur/Helical

Gears & Splines

Dowding & Doll 01 U.K Ext Small

Spur/Helical

Gears & Splines

Samputensilli 01 German

y

Ext Spur/Helical

Gears & Splines

Sykes 01 U.K Crown Hobbing

02 Gear Shaping Fellows-conventional 01 U.K Spur/Helical

Gears & Splines

Int & Ext

Fellows-cnc 01 U.K Spur/Helical

Gears & Splines

Int & Ext

Maxicutt 01 U.K Spur/Helical

30

Gears & Splines

Int & Ext

Sykes 01 U.K Spur/Helical

Gears & Splines

Int,Ext&Tapered

03 Gear Grinding Reishauer NZA 01 Swiss Spur & Helical

crowned Gears

CNC Reishauer RZS 01 Swiss Spur & Helical

crowned Gears

04 Gear Honing Red Ring 01 U.S.A Honing External

Gears

05 Jig Grinding Hauser 01 Swiss Max Spindle

RPM 225,000

06 Internal Grinding Studer S145 01 Swiss

Voumard 01 Swiss

07 Unvl Grinding Studer S30 01 Swiss

08 Centre Correction Techinica 01 Swiss

09 Capstan Lathe Ward No 7 02 India

Herbert No 4 02 India

10 Centre Lathe HMT 02 India

11 Gear Deburring Gratomat 01 West

German

y

Gear End

Rounding-Off

Rotomat 01 France Gear Tip

Rounding-Off

12 Gear Shaving Komnhtepha 01 USSR

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1.9.2 GENERAL FLOW CHART- MANUFACTURE GEARS AT GEAR

CELL

RAW MATERIALS(Forging/casting/bar)

↓

BASIC HEAT TREATMENT TOBRING MACHINABILITY(Normalizing & tempering)

↓

GEAR BLANK PREPARATION(Lathe section)

↓

DATUM ESTABLISHMENT(Skim grinding)

↓

GEAR CUTTING(shaping, hobbing, broaching)

↓

BURR REMOVAL↓

CASE HARDENING(carburising, cynaiding, nitriding)

↓

SUPPORTING GRINDING OPERATIONS↓

PROFILE GRINDING↓

TEMPER ETCHING↓

FINAL GRINDING OPERATION (if any)↓

FINAL FINISHED COMPONENT

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1.9.3 BASIC MACHINING OPERATIONS

Facing: An operation performed on lathe that feeds a single point tool

perpendicular to the axis of rotation of work to create a flat surface.

Turning: A machining operation used to make cylindrical or cone shaped

parts. A single point cutting tool passes along the outer surface of a

cylindrical work piece as it rotates and gradually removes a layer of

material.

Drilling: The process of using a multi- point tool to penetrate the surface of

the work piece and make a round hole

Boring: A process of enlarging and truing a pre- existing hole.

Reaming: The process of finishing and sizing the hole which has been

previously drilled or bored

Lapping: It is an operation of sizing and finishing of holes or turned

surfaces.

Chamfering: An operation performed on lathe that feeds tool to create a

beveled edge on the work piece.

Grooving: The process of reducing the diameter of a work piece over a very

narrow surface.

Milling: It is an operation of removing metal by feeding the work against

the rotating cutter having multiple cutting edges

Grinding: It is the operation of removing metal in the form of minute chips

by feeding the work against a rotating abrasive wheel.

Broaching: It is a method of removing metal by pushing or pulling a cutting

tool called broach which cuts in a fixed path.

33

CHAPTER 2

LITERATURE REVIEW

2.0 TURBO JET ENGINE

The turbojet is the oldest kind of general-purpose air breathing jet engine.

Two engineers, Hans von Ohain in Germany and Frank Whittlein the United

Kingdom, developed the concept independently into practical engines during the

late 1930s.

Turbojets consist of an air inlet, an air compressor, a combustion chamber, a

gas turbine (that drives the air compressor) and a nozzle. The air is compressed

into the chamber, heated and expanded by the fuel combustion and then allowed to

expand out through the turbine into the nozzle where it is accelerated to high speed

to provide propulsion.

Turbojets are quite inefficient if flown below about Mach 2 and very noisy.

Most modern aircraft use turbofans instead for economic reasons. Turbojets are

still very common in medium range cruise missiles, due to their high exhaust

speed, low frontal area and relative simplicity.

2.1 HISTORY

The first patent for using a gas turbine to power an aircraft was filed in 1921

by Frenchman Maxime Guillaume. His engine was to be an axial-flow turbojet, but

was never constructed, as it would have required considerable advances over the

state of the art in compressors.

Practical axial compressors were made possible by ideas from A.A.Griffith

in a seminal paper in 1926 ("An Aerodynamic Theory of Turbine Design").

On 27 August 1939 the Heinkel He 178 became the world's first aircraft to fly

under turbojet power with test-pilot Erich Warsitz at the controls, thus becoming

the first practical jet plane. The first two operational turbojet aircraft, the

34

Messerschmitt Me 262 and then the Gloster Meteor entered service towards the

end of World War II in 1944. A turbojet engine is used primarily to propel aircraft,

but has been used for other vehicles, such as cars. Air is drawn into the rotating

compressor via the intake and is compressed to a higher pressure before entering

the combustion chamber. Fuel is mixed with the compressed air and ignited by a

flame in the eddy of a flame holder. This combustion process significantly raises

the temperature of the gas.

Hot combustion products leaving the combustor expand through the turbine

where power is extracted to drive the compressor. Although this expansion process

reduces the turbine exit gas temperature and pressure, both parameters are usually

still well above ambient conditions. The gas stream exiting the turbine expands to

ambient pressure via the propelling nozzle, producing a high velocity jet in the

exhaust plume. If the momentum of the exhaust stream exceeds the momentum of

the intake stream, the impulse is positive, thus, there is a net forward thrust upon

the airframe.

Early generation jet engines were pure turbojets, designed initially to use a

centrifugal compressor (as in the Heinkel HeS 3), and very shortly afterwards

began to use Axial compressors (as in the Junkers Jumo 004) for a smaller

diameter to the overall engine housing. They were used because they were able to

achieve very high altitudes and speeds, much higher than propeller engines,

because of a better compression ratio and because of their high exhaust speed.

However, they were not very fuel efficient. Modern jet engines are mainly

turbofans, where a proportion of the air entering the intake bypasses the

combustor; this proportion depends on the engine's bypass ratio. This makes

turbofans much more efficient than turbojets at high subsonic/transonic and low

supersonic speeds.

35

One of the most recent uses of turbojet engines was the Olympus 593 on

Concorde. Concorde used turbojet engines because it turns out that the small cross-

section and high exhaust speed is ideal for operation at Mach 2. Concorde's engine

burnt less fuel to produce a given thrust for a mile at Mach 2.0 than a modern high-

bypass turbofan such as General Electric CF6 at its Mach 0.86 optimum speed.

Concorde's airframe, however, was far less efficient than that of any subsonic

airliner.

Turbojet engines had a significant impact on commercial aviation. Aside

from being faster than piston engines, turbojets had greater reliability, with some

models demonstrating dispatch reliability rating in excess of 99.9%. Pre-jet

commercial aircraft were designed with as many as 4 engines in part because of

concerns over in- flight failures. Overseas flight paths were plotted to keep planes

within an hour of a landing field, lengthening flights. Turbojets' reliability allowed

for three and two-engine designs, and more direct long-distance flights. Although

ramjet engines are simpler in design as they have virtually no moving parts, they

are incapable of operating at low flight speeds.

2.2 EARLY DESIGNS

Early German engines had serious problems controlling the turbine inlet

temperature. A lack of suitable alloys due to war shortages meant the turbine rotor

and stator blades would sometimes disintegrate on first operation and never lasted

long. Their early engines averaged 10–25 hours of operation before failing, often

with chunks of metal flying out the back of the engine when the turbine

overheated. British engines such as the Rolls-Royce Welland tended to fare better,

being type certificated for initially 80 hours, later extended to 150 hours between

overhauls, as a result of an extended 500 hour run being achieved in tests.

36

Fig 2.1 J85-GE-17A turbojet engine from General Electric (1970)

The United States had the best materials because of their reliance on

turbo/supercharging in high altitude bombers of World War II. For a time some US

jet engines included the ability to inject water into the engine to cool the

compressed flow before combustion, usually during takeoff. The water would tend

to prevent complete combustion and as a result the engine ran cooler again, but the

planes would take off leaving a huge plume of smoke.

Today these problems are much better handled, but temperature still limits

turbojet airspeeds in supersonic flight. At the very highest speeds, the compression

of the intake air raises the temperatures throughout the engine to the point that the

turbine blades would melt, forcing a reduction in fuel flow to lower temperatures,

but giving a reduced thrust and thus limiting the top speed. Ramjets and scramjets

do not have turbine blades; therefore they are able to fly faster, and rocket engines

run even hotter still.

37

At lower speeds, better materials have increased the critical temperature, and

automatic fuel management controls have made it nearly impossible to overheat

the engine.

2.3 EXOSKELETAL ENGINE

The exoskeletal engine (ESE) is a concept in turbomachinery design.

Current gas turbine engines have central rotating shafts and discs and are

constructed mostly from heavy metals. They require lubricated bearings and need

extensive cooling for hot components. They are also subject to severe imbalance

(or vibrations) that could wipe out the whole rotor stage, are prone to high- and

low-cycle fatigue, and subject to catastrophic failure due to disc bursts from high

tensile loads, consequently requiring heavy containment devices. To address these

limitations, the ESE concept turns the conventional configuration inside-out and

utilizes a drum-type rotor design for the turbo machinery in which the rotor blades

are attached to the inside of a rotating drum instead of radially outwards from a

shaft and discs. Multiple drum rotors could be used in a multi-spool design.

Fundamentally, the ESE drum-rotor configuration typically consists of four

concentric open-ended drums or shells:

an outer shell (engine casing) that both supports the bearings for the drum-

rotor shell and constrains it,

the drum-rotor shell that rotates within the bearings and carries the

compressor- and turbine blades,

a static stator shell that supports the guide vanes,

a hollow static inner shell that provides a flow path through the centre of the

engine.

38

In the ESE design, the rotating blades are primarily in radial compression as

opposed to radial tension, which means that materials that do not possess high-

tensile strength, such as ceramic materials, can be used for their construction.

Ceramics behave well in compressive loading situations where brittle fracture is

minimized, and would provide greater operating efficiency through higher

operating temperatures and lighter engine weight when compared to the metal

alloys that typically are used in turbomachinery components. The ESE design and

the use of composite materials could also reduce the part count, reduce or eliminate

cooling, and result in increased component life. The use of ceramics would also be

a beneficial feature for hypersonic propulsion systems, where high stagnation

temperatures can exceed the limits of traditional turbomachinery materials.

The cavity within the inner shell could be exploited in several different

ways. In subsonic applications, venting the centre cavity with a free-stream flow

could potentially contribute to a large noise reduction; while in supersonic-

hypersonic applications it might be used to house a ramjet or scramjet (or other

devices such as a pulse-detonation engine) as part of a turbine-based combined-

cycle engine. Such an arrangement could reduce the overall length of the

propulsion system and thereby reduce weight and drag significantly

39

CHAPTER 3

MECHANICAL OPERATIONS

3.0 GEAR CUTTING

3.1 PRE- CUTTING OPERATIONS

3.1.1 GEAR BLANK MANUFACTURE:

Aero engine blanks are prepared by Drop Forging process. Internal stresses

created are relieved by heat treatment. Basic heat treatment is done to increase the

hardness value to RC 28-38 so that the gear blank is machinable.

3.1.2 LATHE OPERATIONS:

Subsequent operations like step turning, grooving, boring etc. are done on

lathe. Tolerance range is within 5 mm.

3.1.3 OD AND ID GRINDING:

Outer diameters are ground in an external grinding machine. Ex. Studer

Universal Grinder. Internal Diameters or bore grinding is done on an internal

grinding machine. Ex. Voumard Internal Grinder.

3.1.4 SELF-CENTERING:

As the manufacturing is done, the centre line of the gear blank is the same as

the centre line of a gear. Reference surface on the gear blank ends is marked by the

self-centering machine, facilitating easy location of the job on the gear cutting

machines.

40

3.2 GEAR HOBBING

Fig. 3.1 gear hobbing

This is a gear generating process and not gear cutting process. Gear hobbing

is a continuous indexing process in which the hob and the gear rotate in a timed

relationship with one another while the hob is fed into the work. The teeth are cut

at one pass of the hob. This method is employed to manufacture aero engine gears

extensively because of the high profile accuracy that can be achieved by it. Gears

can also be manufactured on a large scale by this method.

3.3 GEAR SHAPING

This is a gear generating process where a pinion type tool is used. The tool

called shaper cutter is made of a material of higher strength than the material to be

cut. The tool rotates and reciprocates in a timed fashion with a gear blank which is

stationary. The cutting action takes place when the tool moves down. During the 41

return stroke, to prevent the dragging of the tool with the work, the work table is

slightly reciprocated in horizontal direction away from the tool. Then it comes

back to the initial position at the beginning of the next cut.

3.4 GEAR MILLING

Gear milling is a gear cutting operation where the gear tooth space is cut by

a form milling cutter. After each tooth space is milled the gear blank is indexed to

the next position for milling. This process is repeated and the entire gear is made.

3.5 GEAR BROACHING

Broaching can be defined as a machining process that removes metal from a

part by pulling or pushing a multiple tooth tool called a broach through or along

the surface of the work. Broaching is actually used in mass production since it

involves less machining time and labour.

3.6 SHEAR SPEED CUTTING

Used for cutting large size gears. A separate tool is used to cut each tooth

space. Non symmetrical gears can be cut by assembling different tools around the

gear blank in the cutting tool holder. The tools can be fed radially to achieve the

full depth of cut and retracted at the return stroke to prevent dragging of tool with

the work. The tool is stationary while the work is reciprocated past the tool in a

straight line.

42

3.7 BEVEL GEAR CUTTING

In bevel gear straight tooth generating machine the tools take the place of the

mating gear and their paths are lines converging on the pitch cone apex. The action

of the machine causes the work piece mounted on the spindle to roll as if it were in

contact with its mating gear.

3.8 GEAR FINISHING

Gear finishing operations are used for improving accuracy and/ or

uniformity of various gear tooth elements. It is necessary to control errors

(eccentricity, pitch, and profile and helix angle) for quietness and maximum

service life. In aero engine gear manufacture the finishing operations is the most

expensive operation.

3.9GEAR SHAVING

Gear shaving is a gear finishing operation which removes small amounts of

metal from the working surfaces of the gear teeth. Its purpose is to correct errors in

index, helix angle, tooth profile and eccentricity. The process can also improve

tooth surface finish, and eliminate by crowned tooth forms, the danger of tooth and

load concentrations in service.

Shaving provides form modifications that reduce gear noise, increase load

carrying capacity, and its service life. The rotary gear shaving process uses a

gashed rotary cutter in the form of a helical gear having helix angle different from

the gear that have to be shaved. The wheel is then passed through the space while

grinding occurs on the two adjacent teeth flanks and the root.

43

3.10 GEAR HONING

Gear honing is a gear finishing process that was developed to improve the

sound characteristics of hardened gears by removing nicks and burrs, improving

surface finish, making minor correction in tooth irregularities caused by heat treat

distortion. This can add significant wear life and sound qualities of both shaved

and ground hardened gears.

3.11GEAR GRINDING

Grinding is a technique of finish-machining, using an abrasive wheel. The two

most common techniques in gear grinding are

Generating Grinding: Here the threaded grinding wheel replaces the gear

hobber in gear hobbing technique. The ratio of work speed and wheel speed

when grinding spur gears is a simple ratio of teeth on the gear and number of

starts on the wheel.

Saucer Wheel Method: In this technique, two saucer shaped wheels are used.

The grinding surfaces of the two wheels represent the rack, and the involute

profile is generated by gear rolling relative to and in contact with the two

grinding wheels.

Form Grinding: In this technique the abrasive grinding wheel is profiled to

represent the space between two adjacent teeth on a gear. The wheel is then

passed through the space while grinding occurs on the two adjacent teeth

flanks and the root.

44

3.12 GEAR LAPPING

Lapping is a method of refining gear elements by removing small errors of

distortion resulting from heat treatment operations. Lapping tool is usually made of

a soft material that will readily carry the abrasive used to do the cutting while the

work gear and lapping gear are running together.

3.13 GEAR DEBURRING

A burr is a plastically deformed material at an edge generated by a chip

producing process. The process of removing burrs is called deburring operation

which is achieved by chamfering the edges of the gear. Deburring reduces gear

noise and stress concentration effects. Gratomat is one of the machines used for

deburring.

3.14 FORM GRINDING

In this technique the abrasive grinding wheel is profiled to represent the

space between two adjacent teeth on a gear. The wheel is then passed through the

space while grinding occurs on the two adjacent teeth flanks and the root.

The reason for heating and holding the steel in the Austenite is to dissolve

Carbide cementites into a matrix. Because of the rapid cooling, there is no time for

Austenite decomposition. At this stage, the trapped carbon causes a shift in the

atom which creates a stressed lattice structure. This stressed lattice structure, called

Martensite, is hard and brittle. The tool rotates and reciprocates in a timed fashion

with a gear blank which is stationary. The cutting action takes place when the tool

moves down. During the return stroke, to prevent the dragging of the tool with the

work, the work table is slightly reciprocated in horizontal direction away from the

tool. Then it comes back to the initial position at the beginning of the next cut.

45

3.15 HEAT TREATMENT

Heat treatment is the controlled heating and cooling of materials in order to

deliberately alter their mechanical properties. All heat treatment processes involve

3 main parts:

Heating the metal to the pre-determined heat treating temperature.

The soaking of the metal at that temperature until the structure becomes

uniform throughout the section.

The cooling of the metal at some pre-determined rate such will cause the

formation of, or will maintain desirable structures within the metal.

The hardness and depth of the case obtained is low in the annealed and

normalized steels with a Ferrite-Pearlite structure than for hardened and tempered

steels with a Sorbite structure. Hence basic hardening and tempering is adopted for

basic heat treatment of gears.

3.15.1 BASIC HEAT TREATMENT

3.15.1.1 NORMALIZING

Objectives:

i. To refine grain size.

ii. To improve machinability of low carbon steel.

iii. To increase strength of medium carbon steel.

iv. To achieve certain mechanical and electrical properties.

v. To relieve internal stresses.

vi. To refine the crystalline structure after steel has been coursed by previous

hot working. Eg: Welding, bending etc.

vii. To obtain more uniform structure for easy machining.

46

This process quite similar to annealing, but this is carried out by slow heating

the steel to above the critical temperature ( 850ºc -950ºc ) and then allowing to cool

freely in still air i.e; slow cooling. All forgings and castings undergo this treatment

before initial machining.

3.15.1.2 HARDENING

This treatment consists of heating the steel to a selected hardening

temperature, and holding it at this temperature for sufficient period to complete

transformation to Austenite (generally 1 hour per 25 mm of section thickness),

followed by cooling or quenching at a rate fast enough to develop the desired

hardness. The reason for heating and holding the steel in the Austenite is to

dissolve Carbide cementites into a matrix. Because of the rapid cooling, there is no

time for Austenite decomposition. At this stage, the trapped carbon causes a shift

in the atom which creates a stressed lattice structure. This stressed lattice structure,

called Martensite, is hard and brittle.

3.15.1.3 TEMPERING

The rapid cooling during hardening induces internal stresses in steels leading

to cracking and warping. This difficulty can be overcome by relieving the stress by

process called tempering. Thus hardening is always followed by tempering. The

process consists of:

Re-heating the quenched steel to a temperature below 7230C

Holding it for a fixed time period.

Slow cooling in air to room temperature.

47

3.15.1.4CASE HARDENING

Aero- engine gears are subjected to both wear and repeated shocks. Hence,

steel must be hard enough to withstand wear, tough enough not to be readily

fractured by shock, and low enough in first cost to be economical. Hence these

parts are subjected to case hardening processes such as Nitriding, Carburizing and

Cyaniding.

3.15.1.5 NITRIDING

Nitriding is a process of case-hardening in which steel is heated in an

atmosphere of NH3 gas at a temperature of 490-5500C, for a prolonged period

depending upon the case depth required. At this temperature range, ammonia gas

dissociates to produce atomic(nascent) nitrogen.

The atomic nitrogen diffuses into the steel forming nitrides, thus producing a

hard wear resisting surface free from scale containing, the minimum of distortion.

Only low alloy steels containing chromium, aluminum, molybdenum, vanadium,

tungsten etc. can be nitrided. Plane carbon steels are not suitable for nitriding.

3.15.1.6 CARBURISING

Carburising is a heat treatment process which increases the surface carbon

content of low carbon steel by 0.7- 1.0% in carbon medium. In practice,

carburizing is done at temperatures between 900- 9500C. During carburizing, three

important changes take place.

First, the atomic carbon liberated from the carbonaceous medium. Secondly,

the carbon atom from the carburizing is transferred to the surface of the steel.

Thirdly, the carbon so absorbed by the surface of the steel is diffused deep into it.

48

The components after carburizing, are usually directly quenched or cooled,

re-heated, and quenched in oil or in warm bath, depending on the alloy content to

get the Martensitic structure.

3.15.1.7 CYANIDING

Cyaniding also called liquid carbo- nitriding, is used to impart carbon and

nitrogen to the surface of the components especially on small parts. The

component is pre-heated to 200- 5000C to remove the moisture and then immersed

in the bath by using some suitable fixture. The charge is then heated until the

required temperature of 850- 9000C is got.

The charge is then allowed to soak for about 10- 60 minutes, depending on

the required case depth. Then the components are quenched in oil or water. This

process is generally applicable to low carbon and low alloy steels, nickel,

nickel/chromium steels.

3.15.1.8 STRESS RELIEVING

Stress relieving is a heat treatment designed to relieve the stress induced in

the component, minimize the distortion during subsequent heat treatment

(nitriding, carburizing etc.) and to avoid the formation of cracks in extreme cases.

Stress relieving is done by heating the steel to a temperature of 550-7000C, and

soaking it for at least 2-4 hours thoroughly to achieve uniformity throughout the

component. Then it is cooled to ambient temperature in a furnace.

49

At temperatures above 500-6000C, steel almost entirely ceases to be elastic,

and becomes ductile. For this reason, the internal stresses developed in the steel at

such temperatures are gradually relieved as a result of local plastic deformations

caused by them.

3.15.1.9 DEEP FREEZING

The deep freeze is another process that can improve hardness and wear and

achieve the proper microstructure. Through the use of the liquid nitrogen system,

sub- zero temperatures as low as -320oF are accurately controlled to completely

transform austenite into martensite.

50

CHAPTER 4

DESIGN

4.1 TURBO- JET ENGINE

Gas turbine engine in which a nozzle is used to obtain thrust by expanding

exhaust gases coming out of Turbine to ambient pressure is known as turbo-jet

engine. It has revolutionized air travel, reducing expense, increasing aircraft safety,

increasing cruise velocities, lengthening ranges, increasing payloads and lowering

maintenance. It has, however, a large fuel consumption rate, more so with after-

burning capability.

The greatest thrust would be obtained if the nozzle expands the gases to the

atmospheric pressure. The thrust delivered by a turbojet decreases as the

surrounding air temperature increases because the decreased density of the hot air

reduces the mass flow through the engine.

fig 4.1 turbo- jet engine

51

• The requirement of this engine to meet a Specific Aircraft Application has

been “Light Weight, Low Cost, Short Life” Turbojet Engine of 380 kg

Thrust with a Maximum Envelope Diameter of 330 mm and Dry Engine

Weight of 72 kg.

• The Engine shall be suitable for operation from a Remote Ground Station

through Tele command. The Engine should have life of approximately 6

hours or 30 Starts or 5 Sea Recoveries whichever occurs early.

4.2 GENERAL DESCRIPTION

4.2.1 ENGINE

This description considers the main functional components of the engine.

The single shaft straight flow turbojet engine consists of:

o A four stage axial flow compressor, rotors and stators with integral blades.

o A straight flow annular combustion chamber.

o A single stage axial turbine with integral blades and an un-cooled nozzle

guide vane.

o A fuel manifold.

o Exhaust cone with integral fixed area propelling nozzle.

o High speed direct driven permanent magnet alternator and fuel pump.

o Use of high capacity fuel cooled switch mode power supply for regulated

28V.

o DC power up to 1.1 kW.

o Elimination of gear drives by using total loss mist lubrication.

52

4.2.2 CONSTRUCTION AND PRINCIPLE OF OPERATION

The direct engine driven brushless alternator of the PGU has stator with

three phase star winding and a rotor with 8 numbers of sintered Samarium Cobalt

permanent magnets. The remanence of the magnets shall be 980 mT (minimum)

and the energy density shall be 180 kJ/m3 (minimum).

The stator is housed in aluminium casing. The rotor is supported on a pair of

grease packed bearings. The alternator generates 3 phase, sinusoidal voltage whose

amplitude and frequency varies with the speed of rotation of the alternator. The

alternator is placed in the nose bullet and mounted directly to the engine. The rotor

is connected to the engine shaft by means of the quill shaft.

The rectifier assembly consists of MIL qualified three phase bridge rectifiers

with electrically insulated heat sink case (JANTX 483- 03 or JANTX 483- 02).The

bridges are mounted on both sides of an aluminium pipe, through which aircraft

fuel can be passed to the engine's fuel pump inlet. A three phase diode bridge

assembly rectifies the three phase AC voltage generated by the alternator to

provide an unregulated DC voltage of 0– 60 Volts.

This ATF-Jet A1 fuel facilitates the necessary cooling for the bridge

rectifier. The rectifier assembly is fixed in the annular space around the alternator

in the nose bullet. The alternator wiring harness is routed to the outside of the

engine and interfaced to the main vehicle through connector.

4.2.3 AIR INTAKE SECTION

This section consists of an Air Intake Casing (AIC) which carries the front

rotor bearing. The alternator and the fuel pump are mounted on the front of the

AIC in that order.

53

A quill shaft connects the alternator rotor to the front of the compressor-

turbine shaft (CT shaft) tie rod and another quill shaft connects fuel pump drive

gear to the alternator rotor. The fuel cooled bridge rectifier is mounted on the

alternator housing. The DECU is mounted in the front of the fuel pump.

fig. 4.2 air intake section

4.2.4 COMPRESSOR SECTION

The Compressor section comprises four stages of axial compressor, each

stage having a rotor and a stator. All the rotors and stators are made of aluminium

alloy and are having integral blades. Labyrinth seals between successive rotors

minimise inter-stage air leakage.

A thrust balancing disc is present at the rear of the fourth stage compressor

which uses the difference in the compressor outlet pressure and the ambient

pressure to minimise end thrust on the engine ball bearing. The stator rings are

bolted together at the flanges.

54

fig 4.3 compressor section

4.2.5 DIFFUSER CASING

Casing is bolted to the Compressor stator ring stage 3. The inner and outer

casings are joined by 4 radial struts. Stator Ring Stage 4 is bolted at the front of the

diffuser casing.

At the rear, the casing has a flange for the combustion chamber outer casing.

The engine front mounting and the air start adaptor are positioned on the diffuser

casing rear flange.

fig 4.4 diffuser casing

55

4.2.6 COMBUSTION SECTION

Combustion Section consists of an annular combustion chamber, an external

casing, fuel manifold with 16 fuel nozzles and an Igniter plug. The combustion

chamber outer casing (CCOC) houses the flame tube assembly and provides bosses

for fixing the igniter plug, air impingement tubes, fuel manifold and air tapping for

mist generation and A/C fuel tank pressurization.

fig 4.5 combustion section

4.2.7 TURBINE SECTION

This comprises a single stage axial turbine rotor with integral blades and a

nozzle guide vane assembly. The turbine rotor is an integrally cast rotor blade and

disc unit. The front of the turbine rotor is bolted to the CT shaft and the rear is

supported by a roller bearing in the exhaust cone assembly.

56

Fig. 4.6 turbine section

4.2.8 ROTOR ASSEMBLY

The compressor rotors, the thrust balancing disc, a front shaft, compressor

turbine shaft (CT shaft) and the tie rod along with the turbine rotor form the main

rotating assembly. Curvic couplings are present on the ends of the compressor

turbine shaft (CT shaft), the rear end of front shaft and the front end of the turbine

rotor.

4.2.9 EXHAUST SECTION

The exhaust cone is secured to the rear of the combustion chamber outer

casing. The inner cone and the outer cone are joined by three radial hollow struts.

The inner cone accommodates the rear bearing housing.

57

fig. 4.7 exhaust section

4.3 SPECIFICATION

CONDITION : ISA – SEA LEVEL – STATIC

THRUST : 380 kgf (373 daN)

SFC : 1.18 kg/kgf-h

AIR MASS FLOW : 6.65 kg/s

COMPRESSOR

PRESSURE RATIO : 4.6

TET : 1200 K

ENGINE SPEED : 29,500 rpm

COMPRESSOR : 4 STAGE AXIAL

TURBINE : 1 STAGE AXIAL

COMBUSTOR : ANNULAR

OVERALL LENGTH : 1400 mm

MAXIMUM DIAMETER : 330 mm

WEIGHT : 72 kg58

4.4 MAJOR COMPONENTS OF THE ENGINE

Airintake casing

4 Stage Compressor to achieve Pressure Ratio of 4.65 and Integrally Bladed

Compressor Rotors and Stators in Aluminium Alloy.

Short Annular Combustor.

Integrally Bladed Precision Investment Casting for Turbine Stator and Rotor

in Super alloy to Meet Uncooled Turbine Operation upto 1200K.

High Speed (29,500 rpm) Rotor on Flexible Bearing Supports.

4.5TECHNOLOGICAL HIGHLIGHTS

 

Successful Flight of the Totally Indigenously Designed Aero Jet Engine

marks an Important Milestone in the History of Indian Aviation.

The Engine incorporates a microprocessor controlled closed loop hydro-

mechanical Fuel System.

The unit delivers fuel scheduled through an electronically controlled

metering system in response to the speed demand.

The engine control system consists of the Digital Electronic Control Unit

(DECU), Fuel Metering Unit and the Fuel Pump.

4.6 ABOUT QUILL SHAFT

59

4.6.1 CONSTRUCTIONAL DETAILS

Air Intake section consists of an Air Intake Casing (AIC) which carries the

front rotor bearing. The alternator and the fuel pump are mounted on the front of

the AIC in that order. A quill shaft connects the alternator rotor to the front of the

compressor-turbine shaft (CT shaft) tie rod and another quill shaft connects fuel

pump drive gear to the alternator rotor.

4.6.2 DESIGN CONDITION

Torque required to rotate alternator rotor should withstand the quill shaft.

The quill shaft should be less stronger in order to save the engine.

Quill shaft should have proper splines so that it could mate properly with the

main shaft.

4.6.3 FUNCTION OF THE QUILL SHAFT

Main function of the quill shaft is to transfer the power from the Alternator

shaft to the Compressor– Turbine shaft (CT shaft).

It is also used for the safety of the engine when excessive load is produced.

4.6.4 DEFINITION OF THE PROBLEM

The quill shaft that is used in the Turbojet Engines has

1. Taper teeths i.e., un even addendum and deddendum

2. Tooth parallelism error is beyond drawing limit(0.0002”)

3. Chattering marks appeared on the splines due to which profile error goes

beyond the drawing limit (+0.0002”/-0.0004”, zero at pitch point)

4. Bending occurs during the various operations like lathe, grinding.

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The manufacture of a quill shaft cannot be done in one process. It involves

variety of processes like turning, grinding gear cutting. etc. These processes are

determined based on the component drawing. These processes have to be carried in

a specific order.

4.6.5 SPECIFICATION OF QUILL SHAFT

4.6.5.1 MATERIAL SPECIFICATION

Material : Chromium Steel

Specification :AMS 5622

Heat Treatment : Heat Treatment at 5500C +/-50C for 4 hours and

cool in air

Non- Destructive Test : Magnetic Particle Inspection

4.6.6 PROCESS BEFORE MODIFICATION

PROCESS:-1

Machine Tool : INCINNATI C’less Grinder

Operational Description : Centerless Grind Dia

134

15.57

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PROCESS:-2

Machine Tool:-HMT C’lathe

Operational Description:-Load To Soft Jaws And Machine As Per Sketch Process

PROCESS:-3

Machine Tool:-HMT C’lathe

Operational Description:-Load To Soft Jaws And Machine As Per Sketch Process

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PROCESS:-4

Machine Tool:-HMT C’lathe

Operational Description:-Load Between Center Machine As Per Sketch

PROCESS:-5

Machine Tool:-HMT C’lathe

Operational Description:-Load Between Center Machine As Per Sketch

PROCESS:-6

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Machine Tool:-Technical Center Correction Machine

Operational Description:- Center Corection Both Ends

PROCESS:-7

Machine Tool:-Studer Universal Grinder

Operational Description:-Load Between Center Grind Dia

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PROCESS:-8

Machine Tool:-Studer Universal Grinder

Operational Description:-Load Between Center Grind Dia

PROCESS:-9

Machine Tool:-Dowding And Dool Hobber

Operational Description:-Load To Fixture Hob Splines

PROCESS:-1065

Machine Tool:-Dowding And Dool Hobber

Operational Description:-Load To Fixture Separtions

4.6.7 PROCESS AFTER MODIFICATION

PROCESS:-1

Operation description:-grind OD as shown

Machine tool:-CINCINNATI C’less grinder

PROCESS:-2

Machine tool:-Schaublin centre lathe

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Operation Description:-Hold in soft jaws. Face end face and form centre as shown

PROCESS:-3

Machine tool:-Schaublin centre lathe

Operation Description:- Hold in soft jaw. Face end face and form centre as shown

PROCESS:-4

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Machine tool:-Schaublin centre lathe

Operation Description:-Hold between centre.Machine as shown

PROCESS:-5

Machine tool:-Technical centre correction machine

Operation Description:- Correct centres as shown

PROCESS:-6

Machine tool:-Studer universal grinder

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Operation Description:-Hold between centers, grind dia as shown.

INVOLUTE SPLINE DATA FOR 3/8”NOM.FILLET ROOT SIDE FIT

No of splines 17

Diametral Pitch 48/96

Pressure angle 300

Major dia 0.375”/0.372”

Minor dia 0.3125”/0.3050”

Form dia 0.3293”

Pitch dia 0.3542”

Base dia 0.3067”

Circular spline thick max eff 0.312”max act 0.0299” (ref)

min eff 0.03”(ref) min act 0.0287”

Involute profile error +0.0002”

(zero at pitch point) -0.0004”

Max pitch error 0.0013”

Measurement over pins 0.04081”/0.4098”

PROCESS:-7

Machine tool: Dowding and doll hobber

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Operation Description:-Form splines as shown

PROCESS: 8

Machine tool:-Schaublin centre lathe

Operation Description:-Load between centre machine as shown

PROCESS: 9

Machine tool:-Technical centre correction machine

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Operation Description:-centre correct as shown

PROCESS:10

Machine tool: Studer universal grinder

Operation Description: Hold between centre grinder outer dia as shown

PROCESS: 11

Machine tool: Dowding and dool hobber71

Operation Description: form splines as shown

EXTERNAL SERRATION DATA

No of teeth 15

Diametral pitch 80/160

Pressure angle 450

Pitch circle diameter 0.1875”

Nominal diameter 0.200”/0.198”

Minor diameter 0.173”/0.175”

Dimensions over pins 0.2246”/0.2236”

Measuring pin diameter 0.244”

Circular tooth thickness with gauge 0.0216”max eff

Tooth parallelism error across face

within

0.0004”max

Eccentricity of pitch dia. with axis of

centres

0.0015”fir max

PROCESS: 12

Machine tool:-Schaublin centre lathe

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Operation Description:-Hold between centre machine as shown

4.6.7 THE REQUIRED QUILL SHAFT

CHAPTER 5

CONCLUSION

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The modified design was studied and the inspections on all the surfaces

including splines were done. The modified designing of the quill shaft reduced the

errors in the gear profiles and proper meshing of splines is made for the successful

power trabsmission.

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CHAPTER 6

BIBLIOGRAPHY

In the process of finding a solution we went through several books

and websites. These are mentioned below

BOOKS

Practical Gear Design by D.W.Dudley

Modern gear production by H.J.Watson

Gear Engineering by H.E.Merit Pitman publications

WEBSITES

www.firstgear.com

www.efunda.com

www.adamsmachinery.com

www.ansi.org

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