Unit-I Theory.ppt

OMachine Design:
O “ Use of scientific principles, technical
information and imagination in the
description of a machine or a mechanical
system to perform specific functions with
maximum economy and efficiency”

O Basic Requirements of Machine Element:
O Strength
O Rigidity
O Wear Resistance
O Min. Dimensions and weight
O Manufacturability
O Safety
O Conformance of standards
O Reliability
O Maintainability
O Min. Life cycle cost

O Basic Procedure of Design of Machine
Element Specify Functions of
Element
Determine Forces Acting on
Element
Select Suitable Material for
Element
Determine the failure mode of Element
Determine Geo. Dimensions of
Element
Modify the dimensions for Assembly and
manufacture and
Check Design at critical Cross sections
Prepare Working Drawing of Element

Design synthesis
O Defined as the process of creating or selecting
configurations, materials, shape and
dimensions for a product.
O Decision making process with objective of
optimization.
O Difference between design analysis and
design synthesis.

O In design synthesis the designer has fix
objective.
O Objective can be min. cost, min. weight, or
volume, max. reliability or max. life.
O Mathematical formulation of these objectives
and requirements.
O Final step is mathematical analysis for
optimization and interpretations of these
result.
Design synthesis

O Concurrent Engineering:
1. Conventional Design Process.

O Concurrent Engineering:
“ Concurrent Engineering is defined as the
design process that brings both design and
manufacturing engineers together during the
early phases of the design process.”

Aesthetic Considerations in Design
O Each product has definite purpose.
O It has to perform specific functions to the
satisfaction of customer.
O The contact between product and people is
arises due to sheer necessity of this functional
requirement.
O E.g. Automobile Car, domestic refrigerator.

O When there are a number of products in the
market having same qualities of efficiency,
durability and cost, customer attracted towards
the most appealing product.
O External appearance is an important feature.
O The growing realization of the need of the
aesthetic considerations in product design has
given rise to a separate disciple known as
‘Industrial design’.

O The job of an industrial designer has to create
new forms and shapes, which are aesthetically
pleasing.
O There are five basic forms;
1. Step form
2. Stream or stream line form
3. Taper form
4. Shear form
5. Sculpture form

O The ‘step form’ is similar to the shape of
‘skyscraper’ or multistory building.
O This involves shapes with a vertical accent
rather than a horizontal.
O The ‘stream or streamline form’ is seen in
automobiles and aeroplane structure.
O The ‘taper form’ consists of tapered blocks
interlocked with tapered plinth or cylinders.
O The ‘shear form’ has a square outlook, which
is suitable for free standing engineering
product.

O The ‘ Sculpture form’ consists of ellipsoids,
paraboloids and hyperboloids.
O The sculpture and stream forms are suitable for
mobile products like vehicles.
O Step and shear forms suitable for stationary
products.

O There is relationship between functional
requirement and appearance of the product.
O Selection of proper colour is an important
consideration in product aesthetics.
O The choice of colour should be compatible
with the conventional ideas of the operator.
O Many colours are associated with different
moods and conditions.

O Meaning of colours:
Colour Meaning
Red Danger- Hazard-Hot
Orange Possible danger
Yellow Caution
Green Safety
Blue Caution-Cold
Grey Dull

O The external appearance of the product does not
depend upon only the two factors of form and
colour.
O It is cumulative effect of a number of factors such
as,
O Rigidity and resilience, tolerance and surface
finish, motion of individual components, materials,
manufacturing methods and noise.

O The industrial designer should select form which
is in harmony with the functional requirements of
the product.
O The economics and availability of surface-
treating processes like anodizing, plating,
blackening and painting should be taken into
account before finalizing the external
appearance of the product.

O Plain carbon steel is designated according to
BIS as follows:
1. The first one or two digits indicate the 100
times of the average percentage content of
carbon.
2. Followed by letter “C”
3. Followed by digits indicates 10 times the
average percentage content of Manganese “Mn”.
B.I.S DESIGNATIONS OF THE PLAIN CARBON STEEL:

B.I.S DESIGNATIONS OF ALLOY STEEL:
O Alloy carbon steel is designated according to BIS as
follows:
1. The first one or two digits indicate the 100 times of
the average percentage content of carbon.
2. Followed by the chemical symbol of chief alloying
element.
3. Followed by the rounded off the average percentage
content of alloying element as per international
standards.
4. Followed by the chemical symbol of alloying
elements followed by their average percentage content
rounded off as per international standards in the
descending order.
5. If the average percentage content of any alloying
element is less than 1%, it should be written with the
digits up to two decimal places and underlined.

Ergonomics Considerations
 Ergonomics is defined as the relationship
between man and machine and the application
of anatomical, physiological and psychological
principles to solve the problems arising from
man machine relationship.
 Ergonomics means natural laws of work

From design considerations, the topic of topics
of ergonomic studies are as follows:
1. Anatomical factors in the design of drivers
seat.
2. Layout of instrument dials and display
panels for accurate perception by the
operators
3. Design of hand levers and hand wheels.
4. Energy expenditure in hand and foot
operations.
5. Lighting, noise and climatic conditions in
machine environment.

The visual display instruments are classified in
three groups:
1. Display giving quantitative measurements
such as speedometers, voltmeter.
2. Display giving state of affairs, such as red
and green lamp indicator
3. Displays indicating predetermined settings
e.g. a lever which can be set at 1440 rpm,
720 rpm or off position for a 2 speed
electric motor.

The ergonomic consideration in design of display are as
follows:
1. The scale on dial indicator should be divided in
suitable numerical progression like 0-10-20-30 and
not 0-5-30-55.
2. The number of subdivisions between numbered
divisions should be minimum.
3. The size of letters or numbers on the indicator
should be as on the indicator should be as follows:
4. Height of letter or number=reading distance/200
5. Vertical figures should be used for stationary dials,
while radially oriented figures are suitable for
rotating dials.
6. The pointer should have knife edge with a mirror in
the dial to minimize parallax error.

The ergonomics considerations in the design of
controls are as:
1. The control should be easily accessible and
logically positioned.
2. The control operation should involve min.
motions and avoid awkward movements.
3. The shape of control component, which comes
in contact with hands, should be in conformity
with anatomy of human hands
4. Proper colour produces beneficial
psychological effects.

Standardization is defined as obligatory norms to
which various characteristics of a product should
confirm. The characteristics include materials,
dimensions and shape of the component, method
of testing, method of making, packing and storing
of the product.
OStandards for materials
OStandards for shapes and dimensions
OStandards for fits tolerances and surface finish
OStandards for testing of product
OStandards for engineering drawing of component
Use of Standardization in Design

OStandard is defined as a set of specifications for
parts materials or processes. The objective of
standard is to reduce variety and limit the number
of items to a reasonable level.
OCode is defined as set of specifications for the
analysis, design, manufacture, testing and
erection of the product. The purpose of code is to
achieve a specified level of safety.

O Types of Standards Used In Machine Design:
Based on the defining bodies or organization, the
standards used in the machine design can be divided
into following three categories:
(i) Company Standards: These standards are
defined or set by a company or a group of
companies for their use.
(ii) National Standards: These standards are defined
or set by a national apex body and are normally
followed throughout the country. Like BIS, AWS.
(iii) International Standards: These standards are
defined or set by international apex body and are
normally followed throughout the world. Like ISO,
IBWM
Standards and Standardization:

Advantages of Standardization:
OReduction in types and dimensions of identical
components.
ORelieves from designing and manufacturing of
individual machine parts.
OStandard parts are easy to replace when worn
out due to interchangeability.
OImproves quality and reliability.

Manufacturing Methods:
OCasting
ODeformation
OMaterial removal
OJoining
Selection of Manufacturing Methods:
OMaterial of the Component
OCost of manufacture
OGeometric shape of component
OSurface finish and tolerance required
OVolume of production
Manufacturing Consideration in Design

Poor shaping of cast-iron component can
adversely affect its strength more than the
composition of the material. Before designing
castings the designer should consult the
foundryman and patternmaker.
The general principle of design of casting are as
follow:
1. Always keep the stressed
areas of the part in
compression
Design Consideration of Castings

2. Round all External Corners

3. Whenever possible Section thickness
throughout should be held uniform as
compatible with overall design considerations

4. Avoid concentration of metals at the junctions

5. Shot blast the parts whenever possible
6. Other

6. Other

Forged Components are used under following
circumstances:
1. Moving components requiring light weight to
reduce inertia forces, e.g. connecting rod of I C
Engine.
2. Components subjected to excessive stresses, e.g.
aircraft structure
3. Small components that must be supported by other
structure or part, e.g. hand tools and handle
4. Components requiring pressure tightness where
the part must be free from internal cracks e.g.
valve bodies
5. Components whose failure would cause the injury
and extensive damage are forged for safety.
Design Consideration of Forgings

In order to obtain maximum benefits from forged
components , following principle should be adopted
1. While designing a forging advantage should be
taken of direction of fiber lines

2. Forged component should be provided with an
adequate draft

3. The Parting line should be in one plane as far as
possible and it should divide the forging in two
equal halves.

4. The forging should be provided with adequate
fillet and corner radii.
5. Thin sections and ribs should be avoided in
forged components.
A properly designed forging is not only sound with
regard
to strength but it also helps to reduce the forging
forces,
improves the die-life and simplifies die design. If the
design is poor the best of steel and forging methods
will
not give a satisfactory component.

Design Consideration of Machined parts
Machined components are useful under following
circumstances:
1. Components requiring precision and high
dimensional accuracy.
2. Components requiring flatness, roundness,
parallelism or circularity for their proper
functioning.
3. Components of interchangeable assembly
4. Components which are in relative motion with
each other or with some fixed part.

Design Consideration of Machined parts
The general principles for the design of machined
parts are as follows:
1. Avoid machining
2. Specify liberal tolerances
3. Avoid sharp corners
4. Use stock dimensions
5. Design rigid parts
6. Avoid shoulders and undercuts
7. Avoid hard materials

Tolerance
Tolerance is defined as permissible variation in the
dimension of the component.
Two types Unilateral and bilateral

Fit
When two parts are to be assembled, the relationship
resulting from the difference between their sizes
before
assembly is called a fit. Depending upon limits of
shaft
and hole, fits are broadly classified in three groups:
O Clearance Fit
O Transition Fit
O Interference Fit

Fit
Hole Basis System
Shaft Basis System

Factor of Safety
While designing a component it is necessary to
provide
sufficient reserve strength in case of an accident.
This is
achieved by taking a suitable factor of safety.
FOS= failure stress/allowable stress
FOS=failure load/working load
σ = Syt/FOS ---(Ductile material)
σ = Sut/FOS ---(Brittle material)

Factor of Safety
Factor of safety ensures certainty against following
uncertain factors:
 Uncertainty in the magnitude of external force
acting on the component
 Variation in the properties of materials like yield
strength or ultimate strength
 Variation in the dimension of the component due
to imperfect workmanship.
 Assumptions made in design analysis to simplify
calculations

Factor of Safety
Magnitude of factor of safety depends on following
factors:
 Effect of failure
 Type of load
 Degree of accuracy in force analysis
 Material of component
 Reliability of component
 Cost of material of component
 Testing of machine element
 Service conditions
 Quality of Manufacture

Unit-I Theory.ppt

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