Introduction to design

Introduction to Design
by
S. Thanga Kasi Rajan
Assistant Professor,
Department of Mechanical Engineering,
Kamaraj College of Engineering and Technology
Virudhunagar - 625 701.
Tamil Nadu, India
Email :stkrajan@gmail.com

Design
Creating
Plan or
Drawing
Design
Intellectual ability
Scientific Knowledge
The products thus obtained should meet
 Economic Manufacture
 Specification requirement
S. Thanga Kasi Rajan, Assistant Professor 2

Machine Design
Machine :
Combination of Stationary and moving parts constructed for the
useful purpose of generating, transforming or utilizing the mechanical
energy
Machine Design:
- Defining and calculating the different types of motions,
forces and energy transformations
- determining the shapes, size and materials needed for each
of the interrelated parts in a machine

Types of Machine design
According to the demand created by people
1. Adaptive Design (Slightly modifying the existing design)
Ex: watches, bicycle, clocks, television etc,
2. Developed Design (Implementing ideas of one over another)
Ex: Electronic watch, IC engine in a cycle
3. New Design (Inventive or creative design)
Ex: Qualis MUV, train, aircraft etc.,

Types of Machine design
According to the methods used
1. Rational design – (mathematical formula, scientific technique
and Principles of mechanics)
2. Empirical design – (empirical formulae and experience)
3. Industrial design – (production aspects)
4. Functional design – (design based on defined parameters)
5. Optimum design – (best design, max. efficiency and economy
design Men, material, and money)

Design process
RECOGNITION OF NEED
DEFINE THE PROBLEM
DEVELOPMENT OF PLAN
MODAL FORMATION
ANALYTICAL/EXPERIMENTAL
APPLICATIONS GATHERING
OF PHYSICAL DATA
PRINCIPLES
COMPUTATION
CHECKING
EVALUATION
OPTIMISATION
PRESENTATION
SYNTHESIS
AND ANALYSIS

Safety design
 Should provide covers and enclosures
 Parts causing injury should not be projected out
 Have safety proof parts (mishandled – not function)
 Easy maintenance – lubrication, adjustments
 Sharp corners and edges should be avoided.
 Electrical equipments should properly sealed and
grounded
 Provide natural or forced ventilation (for fumes, dust
etc.,)
 Provisions made to avoid x-rays,uv rays, α β γ rays

Engineering parameters
 Mass
 Weight
 Density
 Specific gravity
 Force
 Load
 Moment
 Couple
 Inertia
 Moment of Inertia
 Mass Moment of Inertia
 Area moment of Inertia
 Polar Moment of Inertia
 Stress
 Strength
 Pressure
 Work
 Power
 Energy
 Linear momentum
 Angular momentum
 Temperature
 Heat

Optimum design
Finding best solution from all feasible solutions
maximizing desired quantity
minimizing undesired quantity
 Optimization by evaluation (improve existing design)
Optimization by intuition (improve due to self
inducement)
Optimization by trial and error (by iterations)
Optimization by numerical algorithm (linear,
nonlinear, Arithmetic and geometric progression)

Classification of Material
MATERIALS
Solids Liquids Gases
Metals Non Metals
Ferrous Non Ferrous Organics Ceramics
Metals Metals
1. Water
2. Oil
(i) Vegetable oil
(ii) Mineral oils
3. Acids
4. Alkalies etc.,
1. Air
2. Oxygen
3. Nitrogen
4. Hydrogen
5. Helium
6. Steam
(Vapour)
7. Plasma
(Ionised gas)
1. Wrought iron
2. Steel
3. Cast iron
1. Plastics
2. Textiles
3. Wood etc.,
1. Glass
2. Cement1. Copper
2. Aluminium
3. Nickel
4. Zinc
5. Lead
6. Gold etc.,

Types of Properties
1. Mechanical Properties
2. Thermal Properties
3. Magnetic Properties
4. Electrical Properties
5. Physical Properties
6. Chemical Properties
7. Optical Properties etc.,

Thermal Property
1. Specific heat
2. Thermal expansion of solid
3. Thermal Conductivity
4. Thermal diffusivity
5. Thermal resistance
6. Thermal fatigue
7. Thermal stress etc.,

Mechanical Property
1. Strength - resist deformation
2. Elasticity - regain initial shape when force removed
3. Plasticity - Do not regain initial shape
4. Ductility - to draw into wire
5. Malleability - to form thin sheets
6. Toughness - resist fracture
7. Brittleness - fail by small deformation
8. Hardness - resistance to wear, scratching,
penetration.
9. Creep - const stress at high temp for long period
of time
10. Fatigue - variable load, fail before stipulated time

Engineering Materials
Ferrous Metals
1. Wrought iron
2. Steels
(i). Carbon steels
(ii). Alloy steels
(iii). Cast steels
3. Cast iron
(i) Grey Cast iron
(ii) White cast iron
(iii) Malleable cast iron

Wrought iron
99.5 to 99.9 % pure iron + silicate slag
Cannot be casted
Shaping by hammering, pressing, forging
Property ductility , corrosion resistance
Carbon 0.02 to 0.03%
Ultimate tensile strength
250 Mpa to 500 Mpa
Ultimate Compressive Strength
300 MPa

Steel
Casting Mechanical
(ingots) Treatment
Heated to 1095 to 1425° C
Process - hot rolling, pressing hammering
1. Low Carbon steel ( C < 0.20 %)
2. Medium Carbon steel (C - 0.20 to 0.50 %)
3. High carbon steel (C - 0.50 to 1.8 %)
4. Low alloy steel (alloying < 8%)
5. High alloy steel (alloying > 8%)
Steel

Designation Steel
On the basis of Chemical Composition:
Old Indian Standard (IS: 1570 – 1961)
C15 – Avg. % of Carbon is 0.15
C30 – Avg. % of Carbon is 0.30
New Indian Standard (IS: 1570 (Part II) – 1979)
20C8 – Avg % of C 0.20 & Mn 0.80
On the Basis of Mechanical Properties:
Fe 290 – Min Tensile strength 290 N/mm2
Fe E 290 – yield strength 290 N/mm2

Alloy steels
Steel Alloy Steel
When % > than
Mn - 1 %
Si - 0.7. %
Ca - 0.50 %
Cr - 0.25 %
Mo - 0.10 %
V - 0.05 %
Ti - 0.05 %

Effect of alloying elements on steel
Chromium
Improve Corrosive resistance, wear and abrasion
 improves hardenability
 improve mechanical properties when added with nickel
 improve strength at temperature when added with
Molybdenum
Applications:
ball and rollar bearing
gears
crushers

Nickel
(Not more than 5 %)
Improves hardness, toughness, Corrosive resistance,
wear and elastic limit
 high hardenability
 It is costlier than chromium
Applications:
Axle & propeller shafts,
Connecting rods, springs, bolts and keys etc.,

Vanadium
(0.16 to 0.25%)
Increases elastic limit and resilience
 higher resistance to repeated loads
Applications:
Heavy duty application
such as leaf spring, gears etc.,

Manganese
Increase in Mn decreases ductility and weldability
 moderate effect on hardenability
Applications:
alloyed with other elements and used at which high
elastic and fatigue limits are required

Silicon
Increases Oxidation resistance (deoxidizer)
 gives higher elastic and fatigue limits
Applications:
Exhaust valves

Tungsten
(5 to 15 %)
Forms hard and abrasion resistance – tool steels
 increases hardness and strength at elevated temperature
 very hard to grind and machine.
Applications:
Used in high speed steels, cutting tools

Molybdenum
(0.1 to 0.6 %)
Increases creep strength and red hardness
Forms abrasion resistance particles
Applications:
Boiler, Firebox, cutting tools (drills, taps milling, etc.,)

Cast Iron
Iron + Carbon + silicon + alloying elements
(2 – 4 %) (0.25 – 3%)
Advantages:
Low cost,
Good casting Characteristic,
high compressive strength,
high wear resistance
Disadvantage:
It cannot absorb shock load
tensile strength - 100 to 200 Mpa
Compressive Strength - 400 to 1000 Mpa
Shear Strength - 120 Mpa

Factors Influencing Machine Design
1. Type of Loading
2. Size and shape of the object
3. Material properties required
4. Environmental conditions
5. Human safety
6. Cost
7. Service life
8. Appearance
9. Quantity required
10. Handling provisions
11. Workshop facilities and manufacturing methods

Need For Standardization
For economic manufacturing
1. min. manufacturing process
2. use of cheaper materials
3. min. number of components
4. use of standard parts

Standardization
Standardization is defined as the adoption of
prescribed regulations and establishment of
mandatory standards covering the types, grades,
parameters like dimensions, quality characteristics, test
methods, and rules of marking, packing and storage of
finished products, raw materials and semi-finished
products.
standardization is accompanied by
simplification or elimination of unnecessary variations
in sizes

Standardization
Advantages:
 Better product quality, reliability and longer service
life.
 Mass production of components at lower cost
 Easy availability of parts for replacement and
maintenance
 Less time and effort required to manufacture
 Reduction in variation in size

Standards
AISI - American Iron and Steel Institute
ASM - American Society of Metals
ASTM- American Society for Testing of Materials
BS - British Standards
BIS - Bureau of Indian Standards
DIN - German Standards
GOST - Russian Standards
JIS - Japanese Standards
SAE - Society of Automotive Engineers

Preferred numbers
• preferred numbers are numbers formulated
based on geometric series and used in
standardization.
Parameters like shaft size, speed, diameter of
pulleys etc., are specified by preferred numbers

Preferred numbers
A geometrical series provides small steps for small numbers, large
steps for large numbers and this meets most requirements
A geometric series is defined by one term and the ratio of each
term to the proceeding.
the base term is 1
the multiplication factor -
ie , , , , ……………
The above series is called R series R5, R10, R20, R40 ……..
R stands for Charles Renard, a French scientist.

Illustration
• Step ratio Φ for R20 series
first number is 1
Second number 1 x 1.12 = 1.12
Third number 1.12 x 1.12 =1.25
Fourth number 1.25 x 1.12= 1.40

Interchangeability
The standard parts are manufactured by mass
production. The parts produced by mass
production must be interchangeable.
ie.,
A part picked up by random must fit properly with
its counterpart which is also picked randomly, and
both of them must function satisfactorily.
The above character of proper fitting of matting
parts is called interchangeability.

Fits and tolerance
Interrelationship between Tolerance and limit

Basic Terminology
Zero line - St. line corresponding to basic size
(The deviations are measured from this line)
Basic Size - Theoretical size derived from design also called Nominal
size
Limits - Basic size with permitted variations in dimensions
Max. Permissible size – Upper limit
Min. Permissible size – Lower Limit
Actual Size - Size obtained after machining
Deviation - difference between actual size and basic size
Upper deviation – upper limit ~ basic size
Lower deviation – lower limit ~ basic size
Mean deviation – arithmetic mean of both deviations

Tolerance
Difference between maximum and minimum
dimensions ie., between upper and lower limits.
Unilateral - Tolerance present on one side of the
nominal size
Bilateral - Tolerance present on both the sides of
the nominal size

Tolerance
Allowance : difference of dimensions between
hole and shaft is called allowance
Clearance : If the size of hole is larger than the
shaft then the allowance is called
clearance
Interference: if the size of hole is smaller than
the shaft then the allowance is
called interference

Fit – the degree of tightness or looseness of the
engagement of mating parts

Illustration
Hole diameter is Shaft Diameter is
Max permissible diameter of hole = 50.05 mm
Min. permissible diameter of hole = 49.97 mm
Max permissible diameter of shaft = 50.03 mm
Min. permissible diameter of hole = 49.98 mm
Tolerance of hole = 0.08 mm
Tolerance of shaft = 0.07 mm
Maximum clearance = 0.07 mm
Minimum clearance = 0.02 mm
Maximum interference = 0.06 mm
Minimum interference = 0.01 mm

Introduction to design

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