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Project report on redesigning of split ring for holding the crank journal for fatigue testing, bending and torsion
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INDIANINSTITUTEOFTECHNOLOGY(BHU),VARANASI
IIT(BHU),VARANASI
INTERNSHIPPROJECTREPORTON
FEASIBLESOLUTIONFORTHEPROBLEMOFSLIPPINGOFCRANKJOURNALFROMTHEGRIP
OFSPLIT-RINGDURINGFATIGUETESTING
WITH
BHARATFORGELTD.
UNDERTHEGUIDANCEOF
MrRAJESHMANE
SUBMITTEDBY
ARPITGUPTA
AND
PIYUSHRAJ
DURING
MAY2013-JUNE2013
Preface
Each and every report is prepared with a purpose. This report is also prepared
focusing on interpreting the relevant information of my summer internship
training. This report aims at providing brief details about an ongoing project in
the company regarding a feasible solution for the problem of slipping of crank
journal from the grip of split-ring during fatigue testing. The project report
focuses on exploring ways to implement the various engineering innovations in
order to combat the problem of slipping of crank during fatigue testing of it.
The prime objective of this project is to study the force distribution in the
present scenario using engineering simulation software like Ansys, which make
use of FEA (Finite Element Analysis) to calculate stress, force and
displacement fields and provide suggestions to redesign the ring for better
performance.
This report has been prepared to provide the answers to all these questions and
also discuss the various upcoming technologies. All the facts and figures
mentioned in this report are non-manipulative, true and unbiased to the best of
my knowledge.
The diagrams and explanatory text in each section provide definitive,
irrefutable knowledge about the fatigue testing of crankshaft. This internship
report will provide few solutions to the problem faced by the company
regarding the slippage of crankshaft during fatigue testing of it.
This report also includes the detailed profile of the Bharat Forge Ltd. as per the
various sources within the company itself.
It is hoped that this book will be able to answer all the questions of the given
context.
Finally, the successful completion of this project is attributed to my mentor Mr.
Rajesh Mane. The internship training in Bharat Forge Ltd. was the great
learning experience both at my academic & professional level.
Looking forward to the replies of my readers, mentors, and my teachers that
has always been a great source of inspiration and motivation for me.
ACKNOWLEDGEMENT
The experience at Bharat Forge Ltd. has certainly been full of learning and
numerous people are to thank for it.
First of all, we would like to thank Mrs. Leena Deshpande for providing us
with this valuable opportunity here at Bharat Forge. We would also like to
thank Ms. Shobha Ronimath and Ms. Sapna Gadh for their guidance during our
induction and after and for helping us with every process.
We extend our gratitude to Mr. Rajesh Mane for giving us this project and for
being our supervisor. His guidance and encouragement has made it possible for
us to complete this project and learn a lot from the experience. A token of our
gratitude also goes to all the people working in CAE/Fatigue testing lab for
their perpetual support in our times of need. Without their help, this project
would not have been possible.
A special thanks to all our co-interns for making this experience enriching and
memorable.
CONTENTS
ABOUT BHARAT FORGE LTD.
BHARAT FORGE IN PUNE (MUNDHWA)
INTERNSHIP MAIN REPORT
Introduction
Problem faced in split ring arrangement
Procedure opted for analysis
Requirement of clamping force
Analysis of actual clamping force
Redesigning of split ring
PERSONAL LEARNINGS AND EXPOSURE
REFERENCES
ABSTRACT The objective of this project is to find a feasible solution for the problem of
slippage of crank journal from the grip of split-ring during fatigue testing. The
split-ring and collar arrangement is used to clamp the crankshaft journal in the
inertia plates for bending fatigue testing. The grip is jarred open by the
vibrations induced by the Electrodynamic shaker. In case of torsion, only one
inertia plate is hung from the support while the other is hung on the crankshaft
itself. This arrangement can be fatal if the grip comes loose and the inertia
plate, being very heavy, falls and hence, split-rings are not used in this test at
present.
In case of bending, no such risk is present but erroneous results may still result
from this and in case of slippage, the operator has to do the assembly again.
Another difficulty is regarding the non-uniform distribution of forces on the
journal by the split-ring. It is observed that the fretting marks on the split-ring
are concentrated only on diametrical ends. Split-rings also pose the problem of
very long lead times as it is very difficult to assemble and disassemble the
specimen using them. Numerous bolts have to be tightened and loosened in
order to change the specimen. Another problem is that the target load cannot be
applied directly in one go. It has to be applied in small steps which take time to
actually start the test.
A new design for the journal clamp is undoubtedly required. The prime
objective of this project is to study the force distribution on the surface of the
journal in the present scenario using engineering simulation software like
Catia, which make use of FEA (Finite Element Analysis) to calculate stress,
force and displacement fields and also provide the amount of surface stress
applied on the journal by the split ring.
The project also contains detail theoretical calculation of the amount of
clamping force required by the journal to prevent the problem of slippage. The
report also provides various modified model with their detail force analysis
using Catia V5 in order to improve the performance of the fatigue testing
fixture. Thus various suggestions for the redesigning of the split ring for better
performance has been made with detail data analysis obtain using simulation
software.
ABOUT BHARAT FORGE
A PREFERRED TECHNOLOGY & ENGINEERING
DRIVEN DEVELOPMENT PARTNER
Bharat Forge is a forging company based in Pune, India. Bharat Forge Ltd.
(BFL) is a subsidiary of the Kalyani group which was founded by Nilkanthrao
Kalyani. Currently the chairman of the company is B.N. Kalyani, son of Dr. N
Kalyani. The company's international operations are carried out by its
subsidiary Carl Dan Peddinghaus GmbH.
Bharat Forge came into existence in year 1961. Forging began in 1967. The
forging was carried out through hammer forging. In 1991, first Forging
Modernization Division (FMD I) was established. It was based on hydraulic
presses which were bought from Muller-Weingarten and was the first robotic
division in India at the time. The second FMD (FMD II) was established in
1997, which was similar to the previous one apart from the capacity of the
presses which was enhanced to produce heavier and quicker output. Similarly,
the 3rd
FMD (FMD III) was established in 2005 and houses the largest press in
Pune plant (16500 MT).
BFL today has the largest repository of metallurgical knowledge in the region
and offers full service supply capability to its geographically dispersed
marquee customers from concept to product design, engineering,
manufacturing, testing and validation.
The world's largest forging company with manufacturing facilities spread
across India, Germany and Sweden, Bharat Forge manufactures a wide range
of high performance, critical & safety components for the automotive & non-
automotive sector. It is India's largest manufacturer and exporter of automotive
components and leading chassis component manufacturer in the world. BFL's
customer base includes virtually every global automotive backed by several
decades of experience in component manufacturing & metallurgy, the company
is now looking beyond automotive and has embarked on an ambitious and
exciting journey to redefine its already existing presence across several critical
business verticals such as oil & gas, power, locomotive & marine, aerospace,
metals & mining, construction and general engineering.
Bharat Forge will use its strong platform of metallurgical knowledge, design &
engineering capability and manufacturing prowess, to create a strong position
for itself in these sectors. Expanding into new horizons will give Bharat
Forge a completely new growth perspective.
Bharat Forge's machining facilities are world-class and comparable to the best
in the industry. Their state-of-the-art machining facility is the largest of its kind
and has a crankshaft machining capacity of 650,000 units per annum. In
addition, the facility also has the capacity to machine 500,000 Front Axle
Beams and 750,000 Steering Knuckles per annum.
Bharat Forge's Machining facilities include Crankshaft Machining, Front Axle
Beam Machining, Steering Knuckle Machining, Oil and Gas Sector Machining.
Bharat forge Ltd annual turnover is around $2.5 billion. The company follows a
derisked model where if any of the sector is down then it is stabilized by the
other sectors of the company.
It has nine manufacturing plants in India, Germany, Sweden, United States,
Scotland, United Kingdom and mainland China. Backed by a full service
supply capability and dual-shore manufacturing model, Bharat Forge provides
end-to-end solutions from product conceptualization to designing and finally
manufacturing, testing and validation.
In Bharat Forge Ltd. products are produced both by
Closed Die Forging process
Open Die Forging process
Generally closed die forging process is used to produce automobile
components like Crankshafts, Connecting Rods, and Axle Beam etc. While
open die forging is used for producing components of various sectors like
Marine, Defence, Aerospace, and Oil & Gas.
In Bharat Forge, Forging began right from the manufacturing of Die till the
production of the finished product as per the customers requirement. Bharat
Forge LTD has joint ventures with companies like ArvinMeritor, Carpenter
Technology Corporation, FAW Corporation etc.
BFL CORE OBJECTIVE
To be committed to listening and responding to the needs of our customers,
associates and business partners and honoring their individual value.
To be committed to an entrepreneurial spirit that fuels the growth of our
companies and increases shareholder value.
BHARAT FORGE LTD. PUNE
(Mundhwa)
Bharat Forge has 4 plants in India, all of which are in Maharashtra region. They
are:
Mundhwa : Its the main plant of BFL and has all types of forgings
techniques available within .
Baramati : This plant is specialized in ring-rolling process mainly
Chakan : In this Mostly machining processes are prevalent
Satara : Largest plant for heavy forging (Open-die forging)
BHARAT FORGE IS ONE OF THE FEW GREEN FORGING
COMPANIES IN THE WORLD, WITH MAJORITY OF ITS
POWER PRODUCED BY RENEWABLE RESOURCES.
Over the years Bharat Forge has created world-class capacities and
capabilities. Our forging facilities consists of fully automated forgings
press lines ranging from 1600T to 16000T. With a global installed
forging capacity of 560,000 TPA, BFL India (Mundhwa Plant) is the
world's largest single location forging facility with an installed capacity
of 300,000 TPA. All forging press lines are highly flexible, which gives
the company the inherent advantage to simultaneously meet different
customer demands and optimize production. This allows Bharat Forge to
meet the growing demands of its customers continuously.
Bharat Forge Ltd (BFL) Mundhwa plant is divided into following major
departments:
Sales/ITD (International Trade Dept.)
Profit Planning Control (PPC)
Material Dept.
Finance
Human Resource (HR)/ IR
Safety
Closed die forging division (CDFD) Engg.
Die Shop
Forge Shop (FMD I/II/III, HFD I/II)
Heat Treatment
Machine Control Division I/II
MTB
Metallurgical Quality Control
Security
Different types of Forging processes are performed in different departments of
the BFL starting from the designing of the component till the quality &
validation of the components. Whole process of production, from procuring
material to delivery of goods, goes schematically through various departments.
These departments are interlinked with one another for efficient production and
faster problem-solving. These departments are as follows:
Closed Die Forging Division Engg:
In order to produce a customers product, it first has to be designed virtually.
This task comes under CDFD Engg. which makes use of many designing and
simulating softwares to estimate, design and optimize a given specimen. The
process starts with estimation of force and energy required for the job by using
Ansys which is determined by the 2-D or 3-D drawings given by the customer.
Then it is sent to the design team which designs the tooling and die required for
the job with the help of AutoCAD. Once the die is designed, it is sent to CAD
department for its 2-D drawings to be generated which is carried out with the
help of softwares like Unigraphics, Catia and ProE. Afterwards, a 3-D
simulation software (Forge or Deform) gives necessary data about the thermal,
defect, stress and energy distribution in the forging. Finally, the drawing and
model are sent to the CAM department which writes the program for the CNC
machines to produce the required die. Finally the drawing is optimized using
various software.
Die Shop
Once the CDFD Engg. has issued the programs for CNC machines, the dies are
manufactured in the die shop. The general process outlook is as follows.
Firstly planning of the die to be manufactured for the given product is made i.e.
the amount of time required for the manufacturing of the die prior to product
manufacturing. . Finally dies are manufactured as per the required
specifications in High Speed Milling Machines (HSM). After this if there is
any wear or irregularities are there in the dies, then it is removed either through
welding (in case of smaller dies) or CNC machines (for bigger dies). Finally
surface finishing of the dies are made through Electron Discharge Machine
(EDM) followed by Benching (i.e. polishing of the die). Then the die is
checked in CMM and LMM machine for any defect present in the die after
final finishing of the die.
Heat Treatment
After press forging, the products are quenched and thus, develop brittleness or
sometimes, a customer has a special demand of heat treatment of the product.
Whatever the case maybe, all the heat treatments are carried out by this
department. Various processes available are annealing, normalizing, hardening,
nitriding (exclusively for dies), carbo-nitriding, iso-annealing and carbon
restoration. Annealing is process by which any residual stress due to thermal or
mechanical loading is relieved by heating. Carbo-nitriding is the process by
which case hardening is achieved for gears and other products. The shop has both batch-type and continuous-type furnaces. Various quenching media are
used which include water, oil, polymer and even air.
Forge Modernization Division I (FMD I)
This department came into existence in 1991. It is a press forge and houses 5
presses namely,
PTS 900 (16500 MT): It is a mechanical press and is the largest in BFL.
PSH 4.560 (4560 MT): It is a screw press and uses a large flywheel for energy transfer.
LKM 400 (4000 MT)
LKM 2.500 (2500 MT)
LMZ 2500 (2500 MT)
The general process of the division is as follows:
First billets are cut into suitable sizes and heated in an oil-fired surface to a temperature of 1280 degrees Celsius.
The heated billets are de-scaled with water jets at high pressure.
Then they are put into dies and pressed till they take the shape completely.
Forge Modernization Division II
This shop also follows the same process of forging as that of the FMD I/III.
Firstly raw material as per the given specification of the product are sorted and
cut in a band saw to the required dimensions. Then similar to FMD I here also
the cut billet is heated in the oil furnace where 72 billets are heated
simultaneously. After this the same procedure as that of FMD I/III is followed
of that of upsetting, trimming and padding. FMD II shop contains screw
presses of different capacity
1. 16000 ton
2. 6000 ton
3. 5000 ton
4. 2500 ton
Forge Modernization Division III
This division of Bharat Forge Ltd. comes under closed die Forge division.
Generally in this division the process used for forging is similar to that of FMD
I/II. This shop contains three screw presses, which are of following capacity
12500 metric ton
8000 metric ton
5500 metric ton
In this division firstly the raw materials in the forms of billets are cut into the
required dimensions as per the customers specifications for the product. Then
after this jobs were heated simultaneously in the oil furnace for a temperature
range of 1230-1300 Celsius. Then we pass the heated job through rolling
machine in order to increase its length and reduces the cross sectional area.
After that job is sent to main press where firstly job is placed in the blocker die
followed by finishing die in order to give the required shape. Then it is sent to
trimming press where the flash produced during the forging is cut out. After
this job is moved to padding press where it is straightened i.e. any bending that
is present in it is removed. Finally finishing is performed using short blasting or
short peening.
Heavy Forge Division I/II
This division comes under open die forging. These two shop is generally used
to produce products of critical shapes , which cannot be produced by the closed
die forging method. The products which are usually produced in this shop are
wind mill shafts, gear blanks, mining manifolds, camshafts etc. HFD I shop
contains a hydraulic press of 1600 Ton capacity (ZDAS). The shop also
contains QKK12T manipulator having carrying capacity of 12 Ton and travel
speed of 20-40 m/min. Similarily HFD II contains hydraulic press of 4000
metric ton as well as manipulator similar to that of HFD I. The shop also contains various types of furnaces like
1. Slow cooling furnace
2. Normalizing furnace
3. Tempering furnace
Forge Shop
This the oldest forging shop in Bharat Forge which uses Manual forging
technique unlike FMD I/II/III which uses automatic forging machines. This
shop contains Hammer Machine that is used for the forging of the job.
Generally it is used to produce heavy or complex shape products, which cannot
be manufactured, by FMD I/II/III shop. This shop can forge the given job both
vertically as well as horizontally unlike FMD in which only vertical forging is
done. Hammer used for forging in this shop is around 25000 pound. Hence it is
not used for mass production but only for the production of the complex
shapes.
Machined Components Division (MCD I)
MCD I is responsible for the grinding and finishing of the crankshafts that
come out of the pressing shops. This shop has 11 lines for crankshaft finishing
and 6 lines for non-crankshaft products (such as FAB assembly, knuckle,
reinforcement brackets and Al forgings). All the output of this shop is for
domestic sales only.The processes carried out on each line are roughly the
same which include milling of crank pin and journal, grinding of pin, journal,
flange and thrust collar, cutting of key-slot, drilling of centre holes and super-
finishing of the pin and journal to an average roughness of 0.07m. Finally it is
checked for the correct dimension using different types of gauges.
Machined Components Division II(MCD II)
This department was set up in 2004 and is fully automated. It has 4 production
lines and produces fully- finished crankshafts exclusively for export. The gantry system is fully automatic which reduces production time and lot
rejection, even with 24 machines per line. The process sequence is similar to
that of MCD I which includes grinding of flange, pin, journal, thrust collar,
super-finishing of pin and journal, cutting of keyways, drilling of end-holes.
The division produces 800 jobs per day. Tac time is 6.88 minutes per job.
Metallurgical Quality Control Division
MQC division is responsible for the control of material quality that is used in
the forging, both for dies and forgings. It houses apparatus for Jominy end-
quench test, Kinematic viscosity test, Universal tensile test machine, Hardness
machine etc. It carries out various tests on materials to find out the different
physical and chemical properties of raw materials which are different grades of
steels. Physical properties are also determined through microstructures which
are seen through high magnification microscopes. Chemical properties are
determined from the composition of the forging material.
Machine Tool Building (MTB)
MTB is a research and development department which caters to the needs of
the other departments. Its main objectives are to procure machinery for BFL,
re-condition grinding and milling, make super-finishing, gear-cutting and
hobbing machines. Another important objective of this division is to procure
old machines and repair them for further usage. A brand-new machine is very
expensive whereas an old machine can be bought and repaired quite cheaply.
These machines are for BFL plants only and are not sold outside the company.
A2 Line
This shop is generally performed the final machining and painting of the
products like crankshafts and front axle. Firstly the parting line grinding of the
job is done through a robotic machine (special purpose machine). Then end
grinding of the job is done followed by straightening and untwisting of the job.
After this job is sent for visual inspection in MPI (Magnetic Particle
Inspection) where job is magnetized and then seen under UV rays in order to
find whether there is any crack is present in work piece or not.
Environment Management Systems
BFL is an ISO-14001 certified company. It has five waste treatment plants
which are Effluent, Coolant, Acid, Graphite and Sewage Treatment Plant.
BFL also has air and noise monitoring to keep the air and noise pollution to a
minimum as they pose a threat to the environment as well.
Finance
This department handles all the checks and balances of the company. It has
some major sections as follows:
Cash and Bank Responsible for small cash payments and bank dealings.
Expense Keeps an account of expenditure incurred on companys behalf like travels, stationary etc.
Salary Processing payrolls and all other employee-related issues.
Payable Accounts for raw materials, machines and job contracts expenditures.
Receivables Accounts for payments made to the company.
Costing It controls job costings, budget and inventory.
Treasury Maintains investments and arranges long-term and short-
term finance.
Fixed Assets It accounts for the fixed assets (land, machines etc.),
their depreciation and other projects.
International Trade Division (ITD)/Sales
The marketing and sale of products to overseas buyers is carried out by the
ITD. BFL exports automotive parts to North and South America, Europe,
China and Japan and non-automotive parts worldwide. There are teams to
coordinate such sales, which are:
Documentation and Logistics team: They handle all the documentation and transport of the products. 99% of the product sold overseas is
shipped through cargo ships.
Sales and Marketing team: This team is responsible for capturing clients and expanding the companys foreign clientele. It markets the
companys products to potential buyers.
The domestic marketing and sale of the product is carried out by the sales
deptt. The procedure of sales deptt. Is similair to that of ITD starting from
product purchase till the dispatch of the of the product to the customer.
Safety
It employs 39 safety engineers and 23 fire engineers which are trained in fire-
fighting and safety measures should the need arise. Each department has an
HSE (Health, Safety and Environment) Representative who is responsible for
the safety regulations to be followed.
For safety regulations to be employed, one needs HIRA (Hazard Identification
and Risk Assessment). BFL employs Croners method for HIRA. Another lever
is the BBS or the Behaviour Based Safety which divides workers behaviours
into two categories Safe and Atrocious. Safe behaviour is what the worker
should exhibit as is expected from him/her as per the guidelines.
Each department is to carry out the following safety drills:
1. Plant safety inspection of one line per section per week.
2. Identification of two hazards per line per section and
implementation of its control.
3. One safety meeting per month.
4. Weekly tool box talk per line per section.
5. Reduction of oil consumption by eliminating oil leakage and
spillage.
6. One department of fire audit per month.
7. Fire Risk Assessment of one line per section per week
8. One equipment audit per month.
9. One safety Kaizen or suggestion per line per section per month.
Security
Bharat forge Ltd is in 86 acres Surrounded with 6 feet high stonewalls and
barbed wire. There are 100 guards in total at Bharat forge working in groups of
30 in 3 shifts. The next step in the security is the access control where each of
the employees are given the smart card and the visitors as well as the contract
workers are given the manual or smart passes. There is DFMA and Security
gate in order to check the access of the individuals coming inside the premises
Internship Main Report
INTRODUCTION
Crankshaft is a large component with a complex geometry in the engine,
which converts the reciprocating displacement of the piston to a rotary motion
with a four link mechanism. The crankshaft is one of the most critically loaded
components as it experiences cyclic loads in the form of bending and torsion
during its service life, fatigue performance and durability of this component has
to be considered in the design process.
Fatigue is a localized damage process of a component produced by cyclic
loading. It is the result of the cumulative process consisting of crack initiation,
propagation, and final fracture of a component. During cyclic loading,
localized plastic deformation may occur at the highest stress site. This plastic
deformation induces permanent damage to the component and a crack
develops. As the component experiences an increasing number of loading
cycles, the length of the crack increases. After a certain number of cycles, the
crack will cause the component to fail. Applied stresses may be axial (tension-
compression), flexural (bending) or torsional (twisting) in nature. In general
there are three possible fluctuating stress-time modes possible. The simplest is
completely reversed constant amplitude where the alternating stress varies from
a maximum tensile stress to a minimum compressive stress of equal magnitude.
The second type, termed repeated constant amplitude, occurs when the maxima
and minima are asymmetrical relative to the zero stress level. Lastly, the stress
level may vary randomly in amplitude and frequency which is merely termed
random cycling.
During fatigue testing, the test specimen is subjected to completely reversed
constant amplitude alternating loads until failure. The loads applied to the
specimen are defined by either a constant stress range (r) or constant stress
amplitude (a). The stress range is defined as the algebraic difference between
the maximum stress (max) and minimum stress (min) in a cycle:
r = (max - min )
The stress amplitude is equal to one-half of the stress range:
a= r/2= (max- min)/2
Typically, for fatigue analysts, it is a convention to consider tensile stresses
positive and compressive stresses negative.
The mean stress ( m) is defined as
m= ( max+ min)/2
The stress ratio is defined as the ratio of minimum stress to maximum stress:
R= max/min
When load ratio R=-1 then tensile & compressive stresses are same. This is the
kind of cyclic loading is given to the test specimen during fatigue testing of
crankshaft.
The setup of the vertical Bending Fatigue testing of crankshaft consists of
Inertia plates, Electrodynamic Shaker and Split ring along with a single throw
of crankshaft which when assembled together are put to completely reversed
constant amplitude cyclic loading with the help of the shaker which works
within the given frequency range as controlled by its controller in order to
provide a constant resonating condition to the test fixture. Resonating condition
to the specimen provide the worst case scenario for fatigue test as maximum
amplitude of vibration is attained during resonance condition to the fixture and
the specimen.
The electrodynamic shaker used for the test is a device that excites the
specimen or structure according to its amplified input signal. Several input
signals are available for modal testing, but the sine sweep and random
frequency vibration profiles are by far the most commonly used signals.
Test specimen is attached directly to the inertia plate. With some types of
shakers, an armature is often attached to the body to be tested by way of piano
wire (pulling force) or stringer (Pushing force). When the signal is transmitted
through the piano wire or the stinger, the specimen responds the same way as
impact testing, by attenuating some and amplifying certain frequencies. These
frequencies are measured as modal frequencies.
There are two methods that are used for the validation criteria of the crankshaft,
which are:
1. Maximum Bending Moment applied 2. Maximum stress at pin fillet
To measure either of the above, calibration is required to find the correct
arrangement for the test. Usually a load cell is placed between the shaker and
the structure to obtain the excitation force at the pin fillet. Then providing the
given bending moment to the test specimen does the calibration of the force
and then using linear interpolation or extrapolation the required force is
obtained and checked for the test failure criteria. Secondly, a strain gauge is
also placed on the pin fillet of the crankshaft in order to measure the micro
strain produce during the fatigue testing. Then the calibration of the strain for
given bending moment applied on the machine is done in order to obtain the
maximum stress on the pin fillet. Then using linear interpolation or
extrapolation the required stress at the fillet is obtained and checked for the
fatigue failure criteria for the given number of cycle which is given to the
specimen as per the customer or the company requirement. If the specimen
passes the failure criteria for the given number of cycles, then another
specimen of the same batch is tested for much harsh conditions by increasing
the bending moment. Shaker is connected to the inertia plate through the
stringer in which the crankshaft is fixed and as the vibration by the shaker to
the inertia plate is provided. Due to vibration the bending moment is produced
in the crankshaft and since vibration is of fluctuating nature an alternating
bending moment is produced which is measured using load cell for a given
number of cycles.
SPLIT-RING ARRANGEMENT
A split ring is a ring with a slit in its circumference to allow for easy elongation
and/or compression as per the external load. This range of deformation allows a
shaft or a journal (with diameter in a particular range) to be clamped in a
circular housing. It is a friction-type of clamping mechanism which eliminates
the use of keyways. It is useful in cases where notches are to be avoided at all
costs. One such example is the fatigue testing of crankshafts where the journal
is to be clamped in the fixture but without any keyways as they may err the
results of the test. Its arrangement is as shown below.
PROBLEMS FACED IN SPLIT RING
ARRANGEMENT
The two of the major problems faced in the mounting of crankshafts and their
testing are:
Non-uniform gripping of the journal by the ring After observing the fretting marks on the surface of the split ring, one
can clearly see that the forces are not distributed uniformly. Rather, they
tend to be concentrated on diametrically opposite ends. The marks can
be seen in the following picture.
Slipping of the journal from the ring during the test This is the major problem of the current split ring arrangement. For
certain crankshafts (KV-12 and KV-16), the crankshaft tends to slip out
of the ring due to improper clamping. It leads to erroneous results and
dangerous circumstances. Further, due to this phenomenon, the torsion
fatigue test does not employ the split rings. Rather, it depends on shrink
fits of the journals in collars which fit into inertia plate. While being
reliable, this method is time consuming as the company has to get it
fitted from other sources which add to the expenditure of the testing
facility.
Due to excessive fretting, the ring sometimes gets stuck in the collar and
during dis-assembly, has led to bolt failures. It can be seen in the
following pictures.
The solution of these problems requires redesigning of the ring so as to
increase the clamping force with minimal effort from the operator.
PROCEDURE OPTED FOR
ANALYSIS
Firstly the amount of force required for the clamping of the journal in
the test fixture is studied and calculated using basic mechanical theory
taking into consideration the different parameters which will affect the
clamping of the journal into the split ring. Having solved the problem of
clamping force required, then we look for the force which is actually
applied by the split ring on the journal in the original test arrangement
using Finite Element Analysis (FEA).
Once the applied clamping force is obtained for the given arrangement
of split ring and journal, we move towards the theoretical aspect of it
and calculate the amount of force experienced by the journal using basic
mathematical technique.
After doing so, we look for the redesigning of the split ring with the sole
objective of increasing the clamping force between the ring and the
journal so that we would be able to get the required amount of force as
calculated earlier. After doing so, we perform the job of redesigning of
the split ring. Different models were prepared and analysed for the
clamping force using FEA and checked with respect to the required
force.
We also find into the pros and cons of different models which we
designed and the one which is presently used in our analysis in order to
combat the problem of slippage between ring and journal.
REQUIREMENT OF CLAMPING
FORCE SIMPLIFIED STATIC ANALYSIS
To find the clamping force required by the fixture, we make the following
assumptions to simplify the mathematics involved and obtain a rough estimate
of the force. The assumptions made are as follows:
The plate remains vertical at all times. The journal is subjected to pure bending and thus, the pivot is at the
centre of the journal.
The journal, although subjected to bending, remains perfectly horizontal.
Friction is uniform around the circumference of the journal. Effect of gravity is neglected.
After applying these assumptions, the free body diagram of the plate is shown
in the figure.
Taking the moments about point A,
D x f = B.M.
D is the diameter of the shaft (or journal)
f is the friction force on journal by the ring
B.M. is the Bending Moment applied
For the given journal (KV-12), the bending moment required was found (via
calibration using load cell) to be 16000 N-m.
This gives the required friction f = (16000) / (0.165) = 96.9 kN
However, one must remember that this is a simplified static solution. The
conditions imposed are dynamic and the assumptions made may not hold true
every time. Thus, a design factor of safety needs to be included to avoid any
complications during the running of test.
STATIC ANALYSIS (CONSIDERING THE BENDING OF JOURNAL)
A little detailed analysis can be made while considering the bending of journal
to obtain a better estimate of the force required. It, however, still includes
assumptions from before but the bending of the journal is considered.
The journal is taken as a cylinder with diameter of 165 mm and the free body
diagram of the plate considering bending of journal is shown in the figure.
To find the angle made by the bent journal with the horizontal axis, we use the
deflection formula for pure bending,
|
E (Youngs Modulus) = 210 GPa (for steel)
I (Area moment of inertia)
L (Length of assumed journal) = 318.77 mm
M (Bending Moment) = 16000 N-m
On solving, one obtains = 0.019
Now we can solve the equations obtained from the free body diagram of the
plate.
On solving for friction, one obtains,
N (req) = Clamping force required
M = Bending moment applied
D = Diameter of the journal
= Coefficient of friction between ring and journal
= Angle made by the bent shaft with the horizontal
FACTOR OF SAFETY
Since the calculations made are for static case, a factor of safety needs to be
included to account for the dynamic load conditions. The factor is chosen as
per the following procedure.
FS(overall) = FS(material) x FS(geometry) x FS(stress) x FS(failure analysis) x
FS(reliability)
FS(material) = 1.1 (Material properties are known from a handbook or
manufacturers values)
FS(geometry) = 1.05 (Tolerances are average)
FS(Stress) = 1.25 (Nature of loads defined in an average manner with,
overloads of 20-50%, and the stress analysis may result in errors less than 50%)
FS(failure analysis) = 1.3 (Failure analysis is not well-developed)
FS(reliability) = 1.1 (Average reliability of about 92%)
Thus, FS (overall) = 1.1 x 1.05 x 1.25 x 1.3 x 1.1 = 2.065
The modified clamping force plot (with FOS = 2) is as follows,
Coefficient of friction
Force (in kN) (With FoS = 2)
0.1 1945.865889
0.2 971.3171267
0.3 647.1864751
0.4 485.2556143
0.5 388.1400838
0.6 323.4142977
0.7 277.190358
0.8 242.5271952
0.9 215.5697967
1 194.0056663
ANALYSIS OF ACTUAL
CLAMPING FORCE
The major problem with this arrangement is that it relies solely on friction
between the journal and the inner surface of the ring. Due to lack of any
positive contact, the journal is susceptible to slippage which has been quite
frequently observed in several tests. To circumvent this problem, one may
intuitively propose the increase of friction coefficient between the journal and
the ring. The following section explores various parameters which affect the
clamping force and can be modified to achieve maximum possible force.
Many other factors, other than friction between the ring and journal, include:
Friction between collar housing and split-ring,
Tapped holes misalignment,
Flexibility of the split-ring and the bolts,
Weight of the split ring,
Taper angle of the split-ring.
We now try to study and analyse each aspect and provide a suggestion to get
the better of the problem of slippage.
Friction between collar and split-ring & Taper of ring
and collar
An analysis of forces between the collar and the ring using elementary methods
of force balance yields the following relation between the radial force exerted
by the collar on the ring and the friction coefficient between the two,
(neglecting any other force or deformation)
[
]
is the taper angle of the ring and collar (1.9 degrees)
F(bolts) is the total axial force applied by the eight bolts screwed into the
assembly. The axial load can be easily found as the tightening torque is known
to be 85 N-m (specified by the wrench). This yields an axial force of 35 kN per
bolt (by the relation T = 0.2*F*d). This relation implies that the radial force
increases if the friction (or the taper angle ) is reduced.
Since a complete mathematical analysis is very complicated in this case, we
use FEA (Finite Element Analysis) to study the effect of friction coefficient
between the collar and ring and between ring and journal. Following is the
variation of clamping force with the two coefficients of friction obtained
through FEA.
(collar and ring) 0.7 (Collar and ring) 0.5
( ring &
journal)
C22
(MPa)
C33
(MPa)
Avg.
(MPa)
Clamping
force(kN)
C22
(MPa)
C33
(MPa)
Avg.
(MPa)
Clamping
force(kN)
0.05 5.537 5.524 5.5305 342.891 7.408 7.375 7.3915 458.273
0.1 5.3 5.274 5.287 327.794 6.791 6.744 6.7675 419.585
0.2 4.969 4.942 4.9555 307.241 6.235 6.19 6.2125 385.175
0.3 4.813 4.793 4.803 297.786 5.878 5.839 5.8585 363.227
0.5 4.48 4.458 4.469 277.078 5.37 5.339 5.3545 331.979
0.7 4.247 4.23 4.2385 262.787 4.957 4.929 4.943 306.466
0.9 4.09 4.074 4.082 253.084 4.61 4.584 4.597 285.014
*C22 and C33 represent normal surface stresses in non-axial directions of the
journal
The variations can be plotted graphically as shown,
0
50
100
150
200
250
300
350
400
450
500
0 0.5 1
0.7
0.5
Thus, we see that clamping force increases on reducing either of the two
friction coefficients. But, as we have seen before, the required clamping force
increases drastically as the friction between the journal and the clamp is
reduced. Hence, the friction coefficient needs to be optimized in order get
minimum requirement and maximum output.
However, the friction coefficient between collar and ring is to be made as low
as possible. Various ways to reduce friction includes:
Introduce lubrication, liquid or solid.
Improve the surface texture of the outer surface of the ring and inner surface of collar.
Thus, it is advised that the outer surface of the ring should be lubricated.
Note: Only outer surface should be lubricated, not the inner surface.
Tapped-holes misalignment
This is probably the major reason for low clamping force on the journal,
however, a rigorous mathematical calculation still eludes us. The tapped holes
in the ring and the collar are aligned when the ring is not tightened. As the ring
travels into the collar, the taper deforms the ring and shortens its diameter. This
tends to misalign the holes and thus, exerts a bending force on the bolts. Thus,
bolts act as cantilever beams under partially-uniform load and bend inwards
and consequently, act as leaf springs which push the ring outside, reducing
the actual force transmitted to the journal clamp. The evidence for this
phenomenon is the worn out threads of the bolts as seen the picture.
This theory is supported by the observation that the bolts used for tightening
the ring have worn-out threads in the region which enters into the split-ring
tapped hole. A rigid mathematical equation to define this phenomenon is
quite cumbersome and thus, an FEA model is proposed to account for this
factor. Possible remedies include; larger tolerance for tapped holes, flexible
material for bolts and, if possible, reduction in the number of bolts.
An analysis for reducing the number of bolts in the original test fixture was
carried out using FEA. The results are as follows,
NOTE: The following data has been evaluated taking coefficient of friction
between collar and ring as 0.7
Assembly with 8 bolts Assembly with 6 bolts
(Ring and
journal)
C22 C33 Avg. Clamping
force (kN)
C22 C33 Avg. Clamping force
(kN)
0.1 5.3 5.274 5.287 327.794 3.827 3.941 3.884 240.808
0.2 4.969 4.942 4.9555 307.241 3.481 3.409 3.445 213.59
0.3 4.813 4.793 4.803 297.786 3.397 3.259 3.328 206.336
0.5 4.48 4.458 4.469 277.078 3.361 3.118 3.2395 200.849
0.7 4.247 4.23 4.2385 262.787 3.358 3.061 3.2095 198.989
0.9 4.09 4.074 4.082 253.084 3.3 2.975 3.1375 194.525
C22 and C33 are normal surface stresses in non-axial directions of the journal
The plotted graph shows the variation between clamping force and friction
between ring and journal for assembly with 6 and 8 bolts. It is quite evident
that the number of bolts cannot be reduced as the clamping force reduces very
sharply with reduction in bolts.
Flexibility of the split rings and bolts
Just like the previous case, the ring also acts as a spring. And thus, it resists
any deformation and exerts a restoring force back on the collar. This force also
consumes a large part of the radial force exerted by the collar. Thus, there is a
need to increase the flexibility of the ring so that it can transmit maximum
force and can deform easily so that better wrapping can be achieved over the
journal.
0
50
100
150
200
250
300
350
0 0.2 0.4 0.6 0.8 1
8 bolts
6 bolts
This problem is very complex to be solved mathematically as it is a case of
uniform load on a curved circular beam. Thus, it also requires an FEA model
and calculation.
Possible remedies are: Adding kerfs or partial slits in the ring and
changing the material to a much flexible one (for instance spring steel).
An FEA analysis was carried out to see the effects of additional partial slits on
the gripping force. Following are the clamping forces for various coefficient of
friction between ring and journal with the friction between collar and ring
being 0.7.
(Between
ring and
journal)
C22
(MPa)
C33
(MPa)
Avg.
(MPa)
Clamping force (kN)
(With kerfs)
Clamping force(kN)
(Without kerf)
0.1 5.42 5.413 5.4165 335.823 327.794
0.2 5.094 5.097 5.0955 315.921 307.241
0.3 4.912 4.895 4.9035 304.017 297.786
0.5 4.617 4.634 4.6255 286.781 277.078
0.7 4.389 4.375 4.382 271.684 262.787
0.9 4.117 4.078 4.0975 254.045 253.084
The comparison can be seen on the following graph.
The difference in the clamping force is not appreciable. But, since, the
evaluation is only theoretical; its actual performance may be different. Thus,
the ring with kerf model may or may not be beneficial.
Weight of the split ring
This factor is not so imposing on its own but definitely has some contribution.
Another elementary analysis reveals that weight, in fact, can affect the radial
force. The relation is as follows,
0
50
100
150
200
250
300
350
400
0 0.2 0.4 0.6 0.8 1
With kerf
Without kerf
[ [
]] {
}
Here, M is the mass of the split-ring and Mc is the half of the weight of the
crankshaft.
From the relation, the weight also reduces the clamping force, even so slightly.
Since, it is not possible to reduce the weight of the specimen, decreasing the
weight of the split ring can thus, increase the clamping force.
Another advantage of reducing the weight is that it will also reduce the
stiffness of the ring.
Friction between split ring and journal
This is perhaps the easiest of the solutions but has very little scope for
improvement. There are many ways to increase friction between the two
surfaces. Apart from friction coefficient, other ideas can also be employed.
Some of the remedies include:
Increase inner surface roughness of the split ring
Change the surface texture of inner surface of the ring. Circumferential machining marks can enhance the gripping efficiency.
A thin rubber or asbestos gasket may be used (if possible) to increase the contact between the surfaces.
A mild adhesive can be used in a similar fashion.
The friction between the journal and ring has two counteracting effects on
the clamping. Increasing the coefficient of friction reduces the required
clamping force but it also reduces the clamping force transmitted by the
split-ring. Thus, the value of coefficient of friction needs to be optimized.
Following is the plot of required clamping force and available force at = 0.7
and 0.5. The optimized value would undoubtedly the point where the two
curves intersect.
For (Collar & Ring) = 0.7, critical value comes out (Ring & Journal) = 0.75
while, for (Collar & Ring) = 0.5, the critical value reduces to (Ring
Journal) = 0.6
Thus, as the friction between the collar and ring is reduced, the critical
friction coefficient required between the journal and ring also falls down.
0
500
1000
1500
2000
2500
0 0.2 0.4 0.6 0.8 1
(Collar & Ring) = 0.7
(Collar & Ring) = 0.5
Required Clamping force
REDESIGNING OF SPLIT RING
Since, we did not achieve any substantial improvement in the clamping force,
we tried to redesign the split ring. We tried to find out other types of clamping
collars available for holding shafts and journals. We then designed rings which
were coherent with present collar bush so that replacement would not be
required.
One of those ideas was of the muff-type collar bush which employs a
circumferential bolt to clamp the shaft. Since, all the axial load of the pre-
tension of bolt would be utilized in clamping, the number of bolts required to
hold the ring in the collar would be reduced. Thus, the flexibility of the ring
can be increased and mounting time can be reduced. Further, the tightening
torque required would also be reduced substantially.
Following is the crude design of the muff-type clamping ring. The outer
surface has the same taper as the collar already in use.
The muff may either have just one tightening bolt or two. A single bolt reduces
the number of bolts but the clamping force obtained is distributed non-
uniformly over the journal. Thus, we designed with two through bolts and the
ring split in two pieces as shown. It promises a much more uniform force
distribution on the journal.
The comparison between the 8-bolt assembly and muff-type assembly is as
follows,
Friction
Coefficient
C22 (MPa) C33(MPa) Avg.(MPa) Clamping force
Double muff (kN)
Clamping Force Split
ring ( = 0.7) (kN)
0.1 5.901 5.64 5.7705 357.771 327.794
0.2 5.534 5.075 5.3045 328.879 307.241
0.3 5.408 5.072 5.24 324.88 297.786
0.5 5.213 4.804 5.0085 310.527 277.078
0.7 4.998 4.542 4.77 295.74 262.787
0.9 4.786 4.283 4.5345 281.139 253.084
A major disadvantage of this design is the aligning of bolt holes while
assembly. While using split rings, any misalignment is taken care of using a
wedge driven in the slit which loosens the ring on the journal. While, the
wedge is stuck, the ring can be rotated to accommodate any misalignment. This
convenience will not be available in muff-type which will be tightened using
bolts and spring action of a solid split ring.
PERSONAL LEARNINGS AND EXPOSURE
With the culmination of the project, following conclusions/ derivations can be
made with regard to what I learnt, the tasks I performed, and my contribution to
the company and the novelty of the idea behind the project.
TASKS PERFORMED
Since the project was about the feasible solution for the problem of slipping
of crank journal from the grip of split-ring during fatigue testing. It was
initially required to get familiar with the brief & basic knowledge of the Finite
Element Analysis. The complete study carried out by me throughout the
internship training includes developing a strong foundation in the area of
redesigning and stress analysis using FEA with the help of Catia software. The
organised & focussed approach begins with the most basic architecture of split
ring along with the collar and the journal.
Moreover, some basic mechanical and software techniques were also
implemented that were significantly used during the course of our training.
These technologies feature the most significant part of my project. It was
therefore, necessary to learn about these technologies in details.
The most interesting and informative task that we had performed was visiting
the full BFL plant, and gain the knowlegde regarding the different
manufacturing technique in a much better way and also gained bulk of
fascinating knowledge about different types of robotic forging machine.
ACHIEVEMENTS AND BENEFITS
Being a part of well-established company like Bharat Forge Ltd. proved to be
a great learning experience for us. The internship has not only helped us to
polish our academic knowledge but has also refined & brushed-up our
communication skills.
Apart from this we gained an adequate and detailed knowledge of the Catia,
Ansys software. These add to our skill set which will definitely help us later on
in our professional lives.
Briefly, the training experience with Bharat Forge Ltd. enabled us to gain an
ultimate professional knowledge. Moreover, we learned how the academic
world differs from the professional. The responsibilities, tasks, colleague
interaction, interaction with the workers are some of our learnings in Bharat
Forge Ltd. worth mentioning.
Not only this, we learned about the strength & importance of working in a
team. Moreover, we understood the various leadership and management
qualities that a professional should have.
The entire internship experience with Bharat Forge Ltd. was like an
opportunity that one should definitely aspire for. Looking forward to work with
company like BFL in future.
REFERENCES
http://www.udco.com/sseries.shtml
Design & Analysis of Crankshaft Bending Test
Mechanical Engineering Design By Joseph Shigley
Mechanical of Material by Beer & Johnston
Practical finite element Analysis By Nitin S Gokhale
http://en.wikipedia.org/wiki/Split-ring_resonator
http://www.ruland.com/shaft-collars.asp
http://www.udco.com/sseries.shtml
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