STRESS ANALYSIS ON POWER DRIVE GEAR OF BFU-5 MILLING MACHINE USING FINITE ELEMENT METHOD

7/27/2019 STRESS ANALYSIS ON POWER DRIVE GEAR OF BFU-5 MILLING MACHINE USING FINITE ELEMENT METHOD

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STRESS ANALYSIS ON POWER DRIVE GEAR OF

BFU-5 MILLING MACHINE USING FINITE

ELEMENT METHODA PROJECT REPORT

Submitted by

D. MANJU

I. LAKME @ ASHYA

Inpartial fulfillment for the award of the degree

of

BACHELOR OF TECHNOLOGYIN

MECHANICAL ENGINEERING

Under the guidance of

Mr.S. GUNABALAN,

Assistant Professor- Mechanical Department

BHARATHIYAR COLLEGE OF ENGINEERING AND

TECHNOLOGYKARAIKAL

PONDICHERRY UNIVERSITY: PUDUCHERRY

MAY 2010

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ACKNOWLEDGEMENT

Several people have directly or indirectly contributed towards the development and

success of this project. It is indeed of a great pleasure to acknowledge the help of all these

individuals.

We wish to express our sincere thanks to our beloved Principal,

Prof. Dr. V.JAYARAMAN and Prof. C.RAVICHANDRAN our Head of Department of

Mechanical Engineering for his kind permission to work on this project.

We are greatly indebted to our project guide Mr.S.GUNABALAN,Asst. Professor

of the Department of Mechanical Engineering for his valuable guidance, advice and highly

useful suggestion without which this project would not have been brought to this successful

completion.

Last but not the least, we take great pleasure and consider it a proud privilege to

express our indebtedness and gratitude to our Senior Lecturers Mr.K.MARIMUTHU

,Ms.S.SRIDEVI ,Mr.VIJAYANAND and Staff Mr.JAGADESH ,Mr. JOSEPH

,Mr.GANESH of the department of mechanical engineering for their support in successful

completion of this project.

We also thank all the teaching and non-teaching staffs of our department for providing

us with valuable suggestion and kind cooperation for the project without any inhibition.

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ABSTRACT

From smaller watches an instruments to heaviest and most powerful machineries

like lifting cranes spur gear is used to transmit the power from negligibly small values

thousands of KW using gears of diameter from a few mm to many meters. They are used in

automobiles, hoisting machineries rolling mills, machining tools such as lathes, milling

machines, shaping machines and so on.

Gear drives should be designed in such a way that they should overcome the

following gear failures:

Tooth breakage is caused due to over loads of either impact or static action

,repeated overloads causes low endurance fatigue .To overcome this gear material of

sufficient beam strength may be selected.

Pitting of tooth surface is caused due to over pressing of the tooth of one gear to the

tooth of mating gear. During continuous operation a crack may be formed which may

increase in size and change into pits .To prevent pitting the tooth are checked for

surface endurance.

Abrasive wear is the principle reason for the failure of open and closed gearing of

machineries operated in media, polluted by abrasive materials. This increases

dynamic load, noise, weakens the tooth and finally leads to breakage. To prevent this

gear can be protected from corrosive atmosphere.

Seizing of the tooth is due to crushing of oil film on the tooth surface under high

pressure leading to scores and scratches on its surface. To prevent this operating

temperature and properties of lubricants are properly maintained.

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CHAPTER I

INTRODUCTION:

1.1 What is Gear:

A gear is a toothed wheel designed to transmit torque to another gear or toothed

component .This simple mechanism is well known since humankind started to deal with

machineries.

Early engineers developed wood gears with cylindrical pegs for cogs to multiply

torque and to change speed properties of different shafts. Subsequently cogs were replaced

by teeth and many archaeological discoveries had revealed that ancient civilizations (100

b.c.) used gears for a large variety of purposes,

From a single spur gear pair in water mill, to differential gear systems in very

complex astronomical calculating device, such as the Antikythera mechanism.

1.2 TYPES OF GEARS:

The following are the main types of gears:

Spur gear

Helical gear

Bevel gear

Worm gear

Rack and Pinion ,and so on

.

1.3 Spur Gear:

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Spur gear is cylindrical in shape, with teeth on the outer circumference that

are straight and parallel to the axis (hole).There are a number of variations of the basic spur

gear ,including pinion wire, stem pinions, rack and internal gears.

Gears are used in many mechanical devices. Gears are a simple machine that

can give you a mechanical advantage. The components of any mechanical devices could be

broken down into simple machines. There are six basic simple machines: lever, pulley, wheel

and axle, inclined plane, wedge, and screw. The gear is considered to be within the wheel and

axle category of simple machines. Gears

(1) transmit motion,

(2) increase/decrease speed, and

(3) increase/decrease torque (power).

Gears can be divided into three major classes: parallel-axis gears, nonparallel but

coplanar gears, and nonparallel and non-coplanar gears. Parallel-axis gears are the simplest

and the most universal type of gear. They may transfer very much power and the high

efficiency in this classification, while spur gear is the main kind of gears.

1.4 Gear nomenclature:

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fig 1.1

Addendum:

The radial distance between the Pitch Circle and the top of the teeth.

Centre Distance:

The distance between centres of two gears.

Circular Pitch:

Inches of Pitch Circle circumference per tooth.

Circular Thickness:

The thickness of the tooth measured along an arc following the Pitch Circle

Clearance:

The distance between the top of a tooth and the bottom of the space into

which it fits on the meshing gear.

Dedendum:

The radial distance between the bottom of the space between teeth and the top

of the teeth.

Diametral Pitch:

Teeth per inch of diameter. Sometimes written (incorrectly) as Diametrical

Pitch.

Face:

The working surface of a gear tooth, located between the pitch diameter and

the top of the tooth.

Face Width:

The width of the tooth measured parallel to the gear axis.

Flank:The working surface of a gear tooth, located between the pitch diameter and

the bottom of the space between gear teeth

Module:

Teeth per millimeter of Pitch Diameter

Pitch Circle:

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The circle, the radius of which is equal to the distance from the center of the

gear to the pitch point.

Pitch Diameter:

Diameter of the pitch circle

Pressure Angle:

Angle between the Line of Action and a line perpendicular to the Line of

Centres

Root Circle:

The circle that passes through the bottom of the tooth spaces.

Root Diameter:

The diameter of the Root Circle

Pitch) for a given Pitch Diameter.

Whole Depth:

The distance between the top of the teeth and the bottom of the spaces

between teeth.

Working Depth:

The depth to which a tooth extends into the space between teeth on the mating

gear.

1.5 SPUR GEAR APPLICATIONS:

From smaller watches an instruments to heaviest and most powerful machineries

like lifting cranes spur gear is used to transmit the power from negligibly small values

thousands of KW using gears of diameter from a few mm to many meters.They are used in

automobiles,hoisting machineries rolling mills,machining tools such as lathes ,milling

machines,shaping machines and so on.

1.6 COMMON FAILURE WITH SPUR GEAR:

Gear drives shoud be designed in such a way that they should overcome the

following gear failures:

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Tooth breakage is caused due to over loads of either impact or static action

,repeated overloads causes low endurance fatigue .To overcome this gear material of

sufficient beam strength may be selected.

Pitting of tooth surface is caused due to overpressing of the tooth of one gear to the

tooth of mating gear.During continous operation a crack may be formed which may

increase in size and change into pits .To prevent pitting the tooths are checked for

surface endurance.

Abrassive wear is the principle reason for the failure of open and closed gearing of

machineries operated in media,polluted by abrassive materials. This increases

dynamic load, noise, weakenes the tooth and finally leads to breakage.To prevent this

gear can be protected from corrosive atmosphere.

Seizing of the tooth is due to crushing of oil flim on the tooth surface under high

pressure leading to scores and cratches on its surface.To prevent this operating

temperature and properties of lubricants are properly maintained.

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CHAPTER II

PROBLEM IDENTIFICATION

2.1 PROBLEM IDENTIFICATION:

The common failure encountered in spur gear is tooth failure.Spur gear found wide

application in all machining parts. Therfore gear failure cause heavy loss and economic loss

to end users.

Spur gear clip(fig 2.1)

The main cause of spur gear tooth failure are

i. Continous usage

ii. Due to wear

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iii. Fracture

Hence it is felt that a detail study is required to find out the cause for tooth failure and

FEA is required to overcome the set failures. In this project a detailed modeling and FEA

was done to address the above problem.

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CHAPTER III

METHODOLOGY

3.1 METHODOLOGY:

To execute the project study we have followed the methodology given below:

a) REVERSE ENGINEERING:

To find out geometrical and mechanical properties of the spur gear which is under

study.

a. Calculating dimensions using Profile Projector and Vernier Calliper.

b. Microstructure Analysis Material properties identification.

c. Hardenability test to measure depth of hardness for identifying whether the

material is case hardened.

b) MODELLING:

1. AUTOCAD 2000 is used to draw Spur gear.

2. The drawn Spur gear is imported in PRO-E3. IGES conversion is made and the PRO-E diagram is imported to

Ansys

c) FEA:

FEM tool provides exact gear geometry, relative positioning and the automatic

FEM discretization for a wide family of spur gears.

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3.2 REVERSE ENGINEERING:

3.2.1 VERNIER MEASUREMENTS:

Vernier calliper is used to measure the dimensions of the Spur Gear accurately inmm .The measured dimensions are

No of teeth = 64

Addendum circle = 99mm

Inside diameter = 25mm

Face width = 20mm

Bush outside diameter = 25mm

Bush inside diameter = 22mm

Key width = 6mm

We cant find the tooth depth and tooth thickness using Vernier calliper. Hence we

have to go for Profile measurement using profile Projector.

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3.2.2 PROFILE MEASUREMENTS:

Profile projectors magnification is 10 times larger than the original size .Small

objects are magnified and it is drawn in a paper and its dimensions are measured and the final

value divided by 10 gives the original value.

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Gear Tooth with defects (fig 3.1)

Comparing the above 3 profile diagrams we conclude that

Tooth depth = 3.5mm

Tooth thickness = 1mm

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3.2.3 MICROSTRUCTURE ANALYSIS:

Microstructure analysis is used to find the structure of the given specimen.

The surface of the specimen is polished using emery papers of grade 1/0,2/0,3/0,4/0.

Etchant nital 4% is applied on the polished surface.

The specimen is mounted on the telescopic microscope but the structure is not

identified due to continous usage of the gear.

So the surface is grinded for 0.5mm and the above procedure is done again.

Finaly by viewing in telescopic microspe we identified that the structure is Gray Cast

Iron.

Microstructure of Gray CI (fig 3.2)

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3.2.4 HARDENABILITY TEST:

Rockwell hardness testing machine is used for testing the hardness of the

material . A straight line is drawn along the grinded surface of the gear and is divided into 6

equal parts measuring 5 mm each and readings are taken applying a load of 1500N (specified

for Cast iron).The following table shows the hardness value of the material.

Hardenability (fig 3.3)

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ROCKWELL HARDNESS TEST:

Specimen Indenter Load

(kg f)

Dial gauge reading

Gray Cast Iron Diamond

(1/16 steel ball)

150

63.5

64.9

61.9

62.9

63.8

64

The readings obtained from the dial gauge are irregular so we conclude that the

surface is not case hardened,but the surface of the gear is somewhat hardened due to

machining.

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3.2.5 DESIGN CALCULATION (manual):

INPUT:

Power(P)=1.1kw

Speed(N)=1400rpm

No of teeth pinion(Z1)=64

No of teeth of Gear(Z2)=84

Addendum circle diameter()=99mm

Inside diameter=25mm

Face width(F)=20mm

Tooth thickness=1mm

Tooth height=3.5mm

Pressure angle( )=20

SOLUTION:

MODULE(m)

Outer diameter=(No of teeth+2)Module

99=(64+2)m

m=1.5mm

ADDENDUM(a)

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Addendum=module

a=1.5mm

DEDENDUM(b)

Dedendum=1.25*Addendum

b=1.25*1.5

b=1.8mm

CENTER DISTANCE(C)

m=2C/(Z1+Z2)

1.5=(2*C)/(64+84)

C=111mm

BOTTOM CLEARENCE(c)

c=0.25*m

c=0.25*1.5

c=0.2

c=0.3mm

PITCH DIAMETER(D)

D=m*Z1

D=1.5*64

D=96mm

DIAMETREL PITCH(Pd)

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Pd=Z1/D

Pd=64/96

Pd=0.6mm

CIRCULAR PITCH(p)

p=D/Z1

p=(*96)/64

p=4.7mm

ROOT DIAMETER(df1)

df1=(Z1-2f )m-2c

df1=(64-2)1.5-2*0.2

df1=92.6mm

PITCH LINE VELOCITY(V)

V=DN/60

V=(mZ1N)/60

V=(*1.5*64*90)/60

V=0.452m/sec

TANGENTIAL LOAD(Wt)

Wt=(P/V)*Cs

Wt=(1.1*10^3/0.452)*1

Wt=2444.44m/sec

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3.3 MODELLING:

Gear calculation values from MITCALC:

Since it is very difficult to draw a gear tooth exactly we downloaded a Gear

calculation software from MITCALC.

This gear calculation is already done by a person called JOHN DOE. In that

software we changed his input values and gave our calculated values from reverse

engineering and click the button Calc which automatically calculates the other parameters

which is needed for our designing.

SYMBOL EXPANSION VALUES UNITS

M Module 1.5 mm

A Addendum 1.5 mm

B Dedendum 1.8 mm

C Center distance 111 mm

C Bottom clearance 0.2 mm

D Pitch diameter 96 mm

P Diametral pitch 0.6 mm

P Circular pitch 4.7 mm

df1 Root diameter 92.6 mm

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The values of manual calculation coincides with the MITCALC values. So we

conclude that our dimensional analysis is correct. Lets move to modelling.

3.3.1 DRAFTING - 2D:

CAD involves the designer's use of the computer as a versatile alternative to

more traditional modes of drawing and modelling and is today an indispensable tool for

graphic and product designers, engineers, interior designers, and architects.

Computer-aided design (CAD) is the use of computer technology for the

design of objects, real or virtual. CAD often involves more than just shapes. As in the manual

drafting of technical and engineering drawings, the output of CAD often must convey also

symbolic information such as materials, processes, dimensions, and tolerances, according to

application-specific conventions.

CAD may be used to design curves and figures in two-dimensional ("2D")

space; or curves, surfaces, and solids in three-dimensional ("3D") objects.

3.3.2 Design of Gear tooth:

Importing 2D drawing of gear tooth to Autocad by using MITCALC is shown

below

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2D drawing of gear(fig 3.4)

Pinion model(fig 3.5)

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Spur gear using autocad(fig 3.6)

3.3.3 INTRODUCTION TO PRO-E

In recent years, the computer has become a powerful tool in design and

manufacturing. CAD/CAM systems (Computer Aided Designing and Computer Aided

Manufacturing) can increase design accuracy, reduce lead times and improve overall

engineering productivity in the design and manufacturing industry.

Pro/Engineer is one of new CAD/CAE/CAM software in the world, featuring

the best operation in the design. The advantages are listed as the following:

1 Formidable, parameter design function permission, superior product

differentiated and manufacturability.

2 Integrates the application to develop out from the concept to the manufacture

within one kind of application.

3 The design change system allows you to float variable.

4 Completes the virtual simulation function to enable you to improve the

product performance and to surpass the product quality goal.

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3.3.4 IMPORTING AUTOCAD DRAWING:

First setting the working directory, the file which is required is saved in

working directory that can be opened from any folder as we prefer . This is the main use of

setting working directory.

Now with the help of working directory the autocad drawing is opened in Pro-

e and necessary changes were made and is saved. Extrude the saved drawing for 20mm width

and save in IGES file.

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Pro-e model(fig 3.7)

3.3.5 IGES

The Initial Graphics Exchange Specification (IGES) (pronounced eye-jess) defines

a neutral data format that allows the digital exchange of information among Computer-aided

design (CAD) systems

Using IGES, a CAD user can exchange product data models in the form of circuit

diagrams, wireframe, freeform surface or solid modeling representations. Applications

supported by IGES include traditional engineering drawings, models for analysis, and other

manufacturing functions

3.3.6. ANSYS:

INTRODUCTION TO ANSYS:

Ansys is a modeling software used in engineering drawings.The following

procedure is used for modelling in ansys.

First level in Ansys is Environment ie, file setting. Set the environment where

we are going to work.

Second level is analysis. It has four main menus, they are

PREFERENCES

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What type of experiment we are going to do

Preference for GUI filtering -Structural

PREPROCESSOR

It is the key thing for any analysis .It includes modeling ,material properties

,load and so on.

ELMENTAL TYPE

Shell 93

MATERIAL PROPERTIES

Youngs Modulus=113000N/mm2

Poissons Ratio=0.25

SOLUTION

It solves the problem in preprocessor and gives the solution.

POSTPROCESSOR

It gives the report of the analysed model.

3.3.7 IMPORTING PRO-E MODEL:

The pro-e model in IGES form is imported to ANSYS and the procedures mentioned

above are done. The results are as shown below.

3.4 FINITE ELEMENT ANALYSIS:

The main part of the present work deals with the modeling of a spur gear and try to

give a unique approach to design gears, joining static and dynamics analyses.

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FEM tool provides exact gear geometry, relative positioning and the automatic FEM

discretization for a wide family of spur gears. The code generates gear profiles based on

parameters describing the cutting tool and particular attention is paid on simulating the

enveloping process

In order to provide a FE model, a parametric routine is used to generate automatically

the mesh according to the teeth profiles geometry. This tool allows a fast and accurate static

analysis of the gear and the calculation of the main source of dynamic excitation, such as the

transmission error. The transmission error is strictly related to the variable global mesh

stiffness, which depends on the gear position, materials and teeth geometry.

A correct FEA can provide the value of the mesh stiffness, i.e. the transmission error.

In the second part of the work a single degree of freedom oscillator with clearance

type nonlinearity is considered. Such an oscillator represents the simplest model able to

analyze a single teeth gear pair.

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Arresting all degrees of freedom(fig 3.8)

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Meshing (fig 3.9)

The model is also able to predict the effect of detailed profile modifications and

manufacturing errors on the vibration of the spur gear .

3.4.1 SOLUTION OF FEA:

Von Mesis stress(fig 3.10)

Von Mesis stress analysis shows very less and well below the ultimate stress, so the

failure may not be due to working stress.

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Drawing using profile projector(fig 3.11)

Shear stress(fig 3.12)

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Breakage area

Breakage area


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The figure 2.2 shows two main variations, ie dark blue and navy blue which has

values as -271.2 and +118.09.

The positive value represents tensile shear sress and negative value represents

compressive shear stress. When the gear revolves, changes occurs as compressive to tensile

and tensile to compressive alternatively.

Due to continuous change in shear stress, breakage occurs as shown in figure 2.2

along the boundary of the dark blue area.

Since this happens below the ultimate stress the breakage is due fatigue fracture after

150 to 200 hours of usage.

This is proved practically in the figure 2.1.

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CHAPTER IV

CONCLUSION AND FUTURE SCOPE

4.1 CONCLUSION:

Project study reports on an extensive stress analysis of the toothed gear.

Particular interest is devoted to a study of the observed movement of the maximum-stress

position around the edge of the gear tooth associated with the variations due to shear loads.

A theoretical finite element model of spur gear system was developed. The research result

shows that the theoretical methods presented in this thesis have, good simulation accuracy.

This method could also be applied to many other engineering problems.

This study shows the Von Mesis stress analysis shows very less deviation.The

same way in this analysis it shows less deviation on the gear tooth except the edge of the

tooth where the load is applied and it is exceptional.

So from the following analysis we conclude that breakage occurs mainly due to

Fatigue fracture and not due to material properties.Wear fracture possibility is more due to no

surface hardening.

4.2 FUTURE SCOPE:

The present study can be applied to other types of gears such as Worm gear, Helical

gear and so on. The shear stress analysis can be further extended to other kind of analysis

such as wear , temperature distribution and so on.

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CHAPTER V

BIBLIOGRAPHY:

5.1 REFERENCES:

i .Mechanical Engineering Design:Joseph Edward Shigley(MCGraw-Hill Book

Company).

ii.A Text Book Of Machine design:R.S Khurmi,J.K.Gupta(Eurasia publishing house

Pvt. Ltd)

iii.Design Of Transmission System:V.Jayakumar(Lakshmi publications,Nagapattinam

District,Tamil Nadu).

iv.Design Data:Faculty of Mechanical Engineering(PSG College Of

Technology,Coimbatore).

v.Design of Transmission elements:T.J.prabu

vi.Mechanical engineering design:Joseph E.Shigley ,Charles R.Misckke

5.2 WEBSITE

i.School.mech.uwa.edu.au

ii.Gizmology.net/gears.htm

iii.swiftdsl.com

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STRESS ANALYSIS ON POWER DRIVE GEAR OF BFU-5 MILLING MACHINE USING FINITE ELEMENT METHOD

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