introduction to machine component design

Course description
The objective of this course is to
facilitate the students in the
development of mechanical
design methodology through
analysis and application of
engineering concepts and enable
the students in designing various
machine elements
Course outcome
1. Know about the types of materials and
material properties, Application of
materials, Limits, fits, tolerance, and
clearances.
2. Understand and Apply Engineering
Design process.
3. Apply engineering principles and
analytical techniques in the design
process.
4. Design the Machine Components like
Shafts and Springs Gear Design
Flywheels and Bearings.
Machine Component Design U15AUT502

Machine Component Design
1. Fundamentals of Machine elements by Bernard Hemrock Tata McGraw Hill
Publishing
2. Machine Design by Dr. Sadhu Singh
3. Hajra choudry “ Workshop Technology Vol I”
4. U Jindal ,”Machine Design” Tata McGraw Hill Publishing
5. Bhandari,v.B., "Design of Machine Elements", Tata McGraw Hill Publishing Co. Ltd.,
New Delhi.
6. T J Prabhu. ”Fundamentals of machine Design “
7. RS Khurmi and JK Gupta “A Text book of Machine Design “ Eurasia Publishing House
NPTEL : Design of Machine Elements – I [ Prof B Maiti ] IIT Khargpur
https://www.youtube.com/watch?v=mzWMdZZaHwI&list=PL3D4EECEFAA99D9BE
I Introduction
II Design of shafts and
springs
III Gear Design
IV Flywheels
V Design of Bearings
Important Dates
CAT I - 10.09.18
CAT II - 22.10.18
Units

Introduction
• Design
• Classification of Design
• Morphology of Design
• Machine Design
• Machine Element Design

Modelling/ Design tools are used to
communicate/ represent the design
How Do We Design ?

Definition of Design
• Iterative process to convince and implement optimum
systems to solve society problems and needs – 1965
• Finding the right physical components of a physical structure
- 1963
• Design Simulating what we want to make , before we
make , it as many times as may be necessary to feed
confident in final result – 1964 booker
• A creative activity which involves bringing into being
something new and useful that has not existed
previously -1965 resurch
Ref: Machine Design by Dr. Sadhu Singh.

Engineering design
• Concerns with
• Physical reliability
• Economic feasibility
• Financial feasibility
• High level of sophistication required
• Manipulation and application of tech
• High level of understanding physical
phenomenon is necessary
Design
• Two methods of design
• Design by craft evolution
• Design by drawing ( leads to design
engg where much process is shifted
from shop floor to design floor )
• Level of complexity is way less
• Routine technology is used to
accomplish goals
• Transforms concepts and ideas
into useful machinery

Classification of design
1. Adaptive design.
The designer only
makes minor alternation or
modification in the existing
designs of the product.

2.Development design.
The designer starts from the
existing design, but the final
product may differ quite markedly
from the original product.

3. New design.
Needs lot of research, technical ability and creative
thinking.
(a) Rational design.
(b) Empirical design:
(c) Industrial design:

Rational Design
This type of design depends upon
mathematical formulae of
principle of mechanics.

Empirical Design
• Design using the Empirical formulae.
• The empirical formulae could be derived on the basis of data obtained
from past experience and from the experimental results.

Industrial design
• Production aspects to manufacture any machine component in the
industry
• This design deals with the process of operation inside a industry and
about machining of a component.

OVER THE WALL AND CONCURRENT ENGINEEIRNG
Designer and Concurrent Engineering

Designers should listen to ?
Over the wall engineering ( monarchy )
• Like our schooling { 1-2-3-4-5}
• Since designs are ideas and to make it real we
need a process where lot of members involve,.
• Material engg
• Manufacturing engg
• Some times designs are complicated to
manufacture and so the manufacturer returns
the product back to designer to accommodate
the change in order to machine it
• And material engineer would suggest a different
material for such manufacturing process
• And so the cost of the product become higher
Concurrent Engineering ( democratic )
• The draw backs of the OTW are
• Simply that the designer has to work for all
other considering the reality / physical ,
economical and financial feasibility
• This could be done only when the designer
could get council from his fellow associates
regarding the solution to the problem
• This leads to concurrent engineer thus
makes the design engineer to rely on
experts for the rest and should be aware of
other discipline knowledge

Machine Design
• Machine design process of achieving/ developing a plan for construction
of a machine.
• A machine is a combination of mechanisms and components that
transforms , transmits , uses energy , load motion for a specific task
• A Machine comprises several different components , elements designed
and connected and constrained in away to perform the desired task

introduction to machine component design

Design of mechanical System
• Mechanical system is synergetic collection of machine elements
• Design of mechanical system comprises thousand and millions of machine
elements and so to design a mechanical system a designer should be more
sophisticated and experience in machine elements.

General Considerations in Machine Design
1. Type of load and stresses caused by the load.
2. Motion of the parts or kinematics of the machine.
3. Selection of materials.
4. Frictional resistance and lubrication.
5. Convenient and economical features.
6. Use of standard parts.
7. Safety of operation.

Machine elements
• A Machine is Made up of numerous Machine elements .
• A Machine parts which would have motion with respect to the
neighbouring parts are called as machine elements
• A Machine element can also have several parts assembled together to
perform the intended task Ex: Roller Bearing

Steps involved in Design of Machine Elements
1. Function of Elements
2. Determination of forces
I. Construction of free diagram of forces acting on element
3. Selection of material
I. Availability
II. Cost
III. Properties
IV. Manufacturing process
4. Possible type of failure
5. Determination of dimension

Procedure In Designing Machine Elements
• Selecting a Suitable type of machine elements from consideration of
its function
• Estimating the size of the machine element that is to be satisfactory
• Evaluating machine element performance against requirement
• Modifying the design and dimension until performance is neared to
whoever is consider most important.

Failure and Factor of safety
Ref: Fundamentals of Machine Design by Bernard Hamrock
• Failure
• FMEA [ Failure mode Effect Analysis ]
• FTA [fault tree analysis]
• Benefit of FMEA and FTA
• Factor of Safety
• Problems on Factor of safety

Failure
Failure of machine elements in service
• completely inoperable
• operable but unable to perform intended fn
• unreliable and unsafe for continuous usage
The Design analysis attempts to predict the
strength of a machine elements so that it could
exercise its duty under safe condition for the
provided load as long as required

Theories Of Failure
• Maximum Principle Stress theory
• Failure occurs when the maximum normal stress equals the tensile yield strength
• Maximum Shear Stress Theory
• Failure occurs when maximum shear stress in the machine element equals the
maximum shear stress at yielding due to tension
• Maximum strain Theory
• Failure occurs when the maximum strain in the member equals the tensile yield
strain
• Distortion energy theory
• Failure occurs when strain energy of distortion per unit volume becomes equal to
the strain energy of distortion per unit volume at the yield point.

Failure Mode and Effects Analysis and Fault
trees
• FMEA make designers To possibly
think and reason the foreseeable
and reasonable failure mode for
every component and Provide its
alternative solution .
• In FTA is statistical hard data are
considered to identify failure.

Benefits of FMEA and Fault Tree Analysis
• It makes the designer to think of minimizing the catastrophic event
due to failure of single component.
• Redundancy in design
• Active
• Passive
• Fail safe Feature
• Doctrine of Manifest danger

Redundancy in Design
Active
• Two are more component is
used though one is sufficient
• All the employed components
will actively take part in
functioning
Passive
• Two are more component is used
though one is sufficient
• The second / alternative component
will function only at the failure of the
component that is in function
Hudson cactus 1549

Doctrine of Manifest Danger
• It’s a powerful method used by the designer to detect the single component
failure before its leads to a catastrophic event
• Where the failure of the single component could be detected earlier by
means of sound or vibration.
Generally in Drum braking , the braking
shoe is riveted with long rivet such that
after a period of time , nearer to the
failure, the long rivet would produce a
squeaking sound while braking

Fundamental considerations in Design of machine elements – Safety

Safety factor / factor of safety
The Factor of Safety is defined as the ratio of yield stress to the working stress / permissible stress
= in case of ductile Material = in case of Brittle Material
[Failure ]Max stress based on material = * Stress at the component works possible maximum stress developed under load
Where
represents A B C where
A= quality of material , workmanship and maintenance inspection
B= Control over load applied to part
C= accuracy of stress analysis experimented data and experience with similar devices
is given by D and E
D – Danger to personnel
E – Economic impact

Material Selection in Design
Ref: Material Selection in Mechanical Design by Michael F Ashby
• Engineering Materials
• Selection of Materials
• Properties
• Single Parameter Chart
• Two Parameter Chart

Engineering materials
• Metals
• Ceramics and glasses
• Polymers and elastomers
• Composites

Metals
• Large no of free electrons
• Good conductors of electricity and
heat
• Non transparent to visible light
• Well deformable and ductile
• It can be made stronger by alloying and
also by treating
• Since metals are usually ductile and so
employed in cyclic load environment
and they can fail from fatigue
• Resistant to corrosion

Elasticity range and
Plastic deformation

Ceramics and glasses
• Compound of metallic and non-
metallic elements
• Good insulators
• More resistant to high temperature
• Brittle in nature ( material that
fractures below 5% of strain )
• 15 time stronger in compression than
in tension
• Highly stiff, hard and abrasive resistant
• The stress strain diagram is not
determined by the tensile test

Polymers and Elastomers
• Polymers- thermoplastic and
thermosets
• Thermoplastic are more ductile than
thermosets and they soften at high
temp
• Thermosets are britle
• Elastomer – large elastic
deformation but brittle fracture
• Polymer and elastomer property
greatly vary with temperature and
five times less dense than metals
Challenger Space shuttle Disaster – rubber O ring – temperature

Selection of materials
1. Availability of the materials,
2. Properties
3. Suitability of the materials for the working conditions in service, and
4. The cost of the materials.

Properties of solid Material
• Strength
• Elasticity
• Stiffness
• Ductility
• Malleability
• Toughness
• Thermal conductivity
• Specific heat capacity

• Strength.
It is the ability of a material to resist the externally applied forces without breaking or yielding. The
internal resistance offered by a part to an externally applied force is called stress.
• Stiffness.
It is the ability of a material to resist deformation under stress. The modulus of elasticity is the
measure of stiffness.
• Elasticity.
Ability to regain its original shape after deformation when the external forces are removed. This
property is desirable for materials used in tools and machines. It may be noted that steel is more elastic
than rubber.

• Plasticity.
Deformation produced under load permanently. This property of the
material is necessary for forgings, in stamping images on coins and in
ornamental work.
• Ductility.
It is the property of a material enabling it to be drawn into wire with
the application of a tensile force. A ductile material must be both strong and
plastic.
Ability of the material to undergo greater deformation under axial load
• Brittleness.
It is the property of breaking of a material with little permanent
distortion. Brittle materials when subjected to tensile loads snap off without
giving any sensible elongation. Cast iron is a brittle material.

Malleability.
• A malleable material has ability of
deforming greater under action of
compressive load.
• The malleable materials
commonly used in engineering
practice (in order of diminishing
malleability) are lead, soft steel,
wrought iron, copper and
aluminum.

Toughness
It is the property of a material to resist fracture due to high impact
loads like hammer blows.
• The toughness of the material decreases when it is heated.
• This property is desirable in parts subjected to shock and impact loads.

• Machinability.
It is the property of a material which refers to a relative case with
which a material can be cut.
The machinability of a material can be measured by the energy
required to remove a unit volume of the material. It may be noted that
brass can be easily machined than steel.

• Resilience. the capacity to recover quickly from difficulties
Property of a material to absorb energy and to resist shock and
impact loads. It is measured by the amount of energy absorbed per unit
volume within elastic limit.
• Creep
When a part is subjected to a constant stress at high
temperature for a long period of time, it will undergo a slow and permanent
deformation called creep. Polymer products ( plastic water bottle , water
bucket )
• Fatigue.
When a material is subjected to repeated stresses, it fails at
stresses below the yield point stresses. Such type of failure of a material is
known as *fatigue. The failure is caused by means of a progressive crack
formation which are usually fine and of microscopic size.

Archard wear constant
• When solids slide , the volume of the material lost from one surface
per unit distance slid
The wear resistance of material is characterized by Archard wear
constant
A= Area of the surface
p=normal pressure pressing together

• Hardness.
The ability of a metal to cut another metal.
The hardness of a metal may be determined by the following tests:
(a) Brinell hardness test,
(b) Rockwell hardness test,
(c) Vickers hardness (also called Diamond Pyramid) test, and
(d) Shore scleroscope.

Single parameter chart

MODULUS OF ELASTICITY
𝐸=
𝑘
𝑟𝑜
𝐸=
𝜎
𝜀
Covalent bond = 20 to 200
Metallic and ionic bond = 15 to 100
Possion ratio
Max 0.5 for rubber
Minimum could not be less than zero
For steel 0.30
For Al 0.33
For Mg 0.33
Cast iron 0.26

Specific Heat Capacity
Heat capacity of the material @ 1 g of mass at 1 degree Celsius
Qty of heat energy taken or given up by a material, when
there is change in temperature ,
is proportional to the mass of the object, difference in temp
and the characteristic constant specific heat capacity
Different material at same temperature range on
cooling would likely to give up different amount of
heat

Two parameter chart

Primary consideration for material selection
in designing machine elements
1. Stiffness versus density
2. Strength versus density
3. Stiffness versus strength
4. Wear rate versus limiting pressure

Modulus of Elasticity (stiffness ) vs Density

Stiffness ( modulus of elasticity ) Vs Strength

Wear Constant vs Limiting pressure

Fits , Tolerance and allowances
• Need for Tolerance
• Types of Tolerance
• Terminologies in tolerance and allowances
• Types of Fit
• Tolerance Designation system
• Methods for Calculating Tolerance , allowance and identifying Fits
Ref: Workshop Technology by Hajra Choudhry

Fits , Tolerance and allowances
Design and Manufacturing relied and one another , there are two most
important facts
1. No component can be manufactured for accurate Dimension
2. Even though the component can be manufactured for such
accurate dimension no system is to measure it.
3. And also if machined for such accuracy the cost of the product
would be very high.

Method of Assigning Tolerance
• Unilateral
• The tolerance value would be
unidirectional, i.e the size would
have limits in positive or negative
• Bilateral
• The tolerance value would be in
bidirectional, i.e the size would
have limits in both positive and
negative

Terminologies in limits, fits and tolerance

Types of Fit
• Clearance fit
• Allowance would be Positive
• The component can be assembled
easily
• Interference Fit
• Allowance would be in Neagtive
• The Component could be
assembled by force / pressuring
• Transition Fit
• Could be in between of both
clearance and interference fit

Designation system for Tolerance

Two Types of System for calculating Limits
• Hole Basis system
• In hole basis system the size of hole is
kept constant and size of the shaft is
varied
• Shaft Basis System
• In shaft Basis System the Size of the
Shaft is kept constant and size of the
hole is varied
• Generally the hole basis system is
followed as the shaft size could be
altered easier than that of hole.

introduction to machine component design

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