2. Course Objectives
The main learning objective of this course is to prepare the students for:
1. To introduce the students to the fundamentals of machine
design, material selection and to solve the basic design problems.
2. To learn to derive various parameters for modelling links and
joints in a robot.
3. To learn about Fundamentals of Computer Graphics
4. To learn and understand curves and surfaces in robot modelling.
5. To learn to derive various parameters for modelling end-
effectors of a robot
3. Syllabus
Fundamentals of Machine Design-Engineering
Design, Phases of Design, Design Consideration
- Standards and Codes - Design against Static
and Dynamic Load –Modes of Failure, Factor of
Safety, Principal Stresses, Theories of Failure-
Stress Concentration, Stress Concentration
Factors, Variable Stress, Fatigue Failure,
Endurance Limit, Design for Finite and Infinite
Life, Soderberg and Goodman Criteria.
4. Engineering design-Definition
Engineering design is a systematic, intelligent process in which engineers
generate, evaluate, and specify solutions for devices, systems, or processes
whose form(s) and function(s) to achieve clients’ objectives and users’
needs
In other words, engineering design is a thoughtful process for generating
plans or schemes for devices, systems, or processes that attain given
objectives while adhering to specified constraints.
6. Objectives of designing a portable ladder
• Ladder should be compact and portable
• It should be stable on smooth surfaces
• Should stand safely without a support
• Can be used for house hold requirements
• Should be reasonably stiff and comfortable for users
• Must be safe and durable
• Should be relatively economical
• Should be reduce space requirements while packing by
means of detachable parts
• The ladder should be marketable
• Useful for electrical and maintenance work
7. Measure weight of objects
up to 120 kg
Support weight up to 70 kg
Hold on wall without failure
Control pointer on a computer
Design functions
8. Design functions
Project Images
(Primary/Basic Function)
Converting Energy
(Secondary function)
Generation of Light
(Desirable)
Generation of Heat
(Undesirable)
Secondary functions are prerequisites
11. Machine Design
Machine design is defined as the 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.
22. Rubber as Washer
Steel as structure support
Polythene as bag
Thermocol for packing Leather as Belt
Titanium alloy for Medical Implants
Material Selection
26. Factors To Be Considered While Material Selection
•Availability
•Cost
•Mechanical Properties
•Manufacturing Considerations
27. Use Of Standards In Design
Code is a collection of laws and rules that assists a government agency in meeting
its obligation to protect the general welfare by preventing damage to property or
injury or loss of life to persons.
Standard is defined as obligatory norms, to which various characteristics of a
product should conform. The characteristics include materials, dimensions and shape
of the component, method of testing and method of marking, packing and storing of
the product.
28. USE OF
STANDARDS IN
DESIGN
Standards for materials, their chemical compositions,
mechanical properties and heat treatment
Standards for shapes and dimensions of commonly used
machine elements
Standards for fits, tolerances and surface finish of component
Standards for testing of products
Standards for engineering drawing of components
National standards These are the IS (Bureau of Indian
Standards), DIN (German), AISI or SAE (USA) or BS (UK)
standards
International standards These are prepared by the
International Standards Organization (ISO)
29. PREFERRED
SIZES
Preferred numbers are used to specify the ‘sizes’ of the
product
French balloonist and engineer Charles Renard first
introduced preferred numbers in the 19th century.
The system is based on the use of geometric progression to
develop a set of numbers
There are five basic series, denoted as R5, R10, R20, R40
and R80 series, which increase in steps of 58%, 26%, 12%,
6%, and 3%, respectively
30. Ergonomic Considerations In Design
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.
31. •Anatomical factors in the design of a driver’s seat
•Layout of instrument dials and display panels for
accurate perception by the operators
•Design of hand levers and hand wheels
•Energy expenditure in hand and foot Operations
•Lighting, noise and climatic conditions in machine
environment
Ergonomic Considerations In Design
32. Design For Manufacture And Assembly (DFMA)
The design effort makes up only about
5% of the total cost of a product.
However, it usually determines more
than 70% of the manufacturing cost of
the product.
33. Design For Manufacture And Assembly (DFMA)
(i) Reduce the Parts Count
(ii) Use Modular Designs
(iii) Optimize Part Handling
(iv) Assemble in the Open
(v) Do not Fight Gravity
(vi) Design for Part Identity
(vii)Design Parts for Simple Assembly
(viii)Reduce, Simplify and Optimize
Manufacturing Process
35. Material of the component
Cost of manufacture
Geometric shape of the component
Surface finish and tolerances required
Volume of production
Manufacturing Considerations in Design
36. Tolerance
• Due to the inaccuracy of manufacturing methods, it is not
possible to machine a component to a given dimension
• The components are so manufactured that their dimensions lie
between two limits - maximum and minimum
• Tolerance is defined as permissible variation in the dimensions
of the component
• The two limits are sometimes called the upper and lower
deviations
38. Types of Fits
• When two parts are to be assembled, the relationship resulting
from the difference between their sizes before assembly is
called a fit
• Clearance fit is a fit which always provides a positive clearance
between the hole and the shaft over the entire range of
tolerances. In this case, the tolerance zone of the hole is entirely
above that of the shaft.
• Interference fit is a fit which always provides a positive
interference over the whole range of tolerances. In this case, the
tolerance zone of the hole is completely below that of the shaft.
39. Types of Fits
• Transition fit is a fit which may provide either a clearance or
interference, depending upon the actual values of the individual
tolerances of the mating components.
40. Stress
• When a mechanical component is subjected to an
external static force, a resisting force is set up within
the component.
• The internal resisting force per unit area of the
component is called stress.
σ t= tensile stress (N/mm2)
P = external force (N)
A = cross-sectional area (mm2)
41. Types of stresses-Strain
• The strain is deformation per unit length. It given by
• According to Hooke’s law, the stress is directly proportional
to the strain within elastic limit. Therefore,
δ = elongation of the tension rod (mm)
l = original length of the rod (mm)
E = Young’s modulus or modulus of
elasticity (N/mm2)
42. Types of stresses-Poisson’s ratio
• Provided the load on the material is retained within the elastic range the
ratio of the lateral and longitudinal strains will always be constant. This
ratio is termed Poisson's ratio.
43. Types of stresses-Direct or normal stress
• If, a bar is subjected to a uniform tension or compression, i.e. a direct force,
which is uniformly or equally applied across the cross section, then the
internal forces set up are also distributed uniformly and the bar is said to be
subjected to a uniform direct or normal stress, , the stress being defined as
44. Types of stresses-Direct or normal stress
• If, a bar is subjected to a uniform tension or compression, i.e. a direct force,
which is uniformly or equally applied across the cross section, then the
internal forces set up are also distributed uniformly and the bar is said to be
subjected to a uniform direct or normal stress, , the stress being defined as
45. Types of stresses-Direct or normal stress
• If a bar is subjected to a direct load, and hence a stress, the bar will change in
length. If the bar has an original length L and changes in length by an amount
δL, the strain produced is defined as follows:
46. Types of stresses-Shear stress
• There is then a tendency for one layer of the material to slide over another to
produce the form of failure. If this failure is restricted, then a shear stress is set
up. This shear stress will always be tangential to the area on which it acts;
direct stresses, however, are always normal to the area on which they act.
48. Types of stresses-Double Shear stress
• When load is applied to the plates the rivet is subjected to shear forces tending
to shear it on one plane as indicated. In the butt joint with two cover plates ,
however, each rivet is subjected to possible shearing on two faces, i.e. double
shear. In such cases twice the area of metal is resisting the applied forces so
that the shear stress set up
49. Types of stresses-Bending stress
• A straight beam subjected to a bending moment ,the beam is subjected to a
combination of tensile stress on one side of the neutral axis and compressive
stress on the other. the outside fibers are in tension, while the inside fibers are
in compression. The bending stress at any fiber is given by
50. Types of stresses-Bending stress
• The bending stress at any fiber is given by
σb = bending stress at a distance of y from the
neutral axis (N/mm2 or MPa)
Mb = applied bending moment (N-mm)
I = moment of inertia of the cross-section about
the neutral axis (mm4)
51. Types of stresses-Bending stress
• The bending stress at any fiber is given by
σb = bending stress at a distance of y from the
neutral axis (N/mm2 or MPa)
Mb = applied bending moment (N-mm)
I = moment of inertia of the cross-section about
the neutral axis (mm4)
52. Types of stresses-Torsional stress
• The internal stresses, which are induced to resist the action of twist, are called
torsional shear stresses. The torsional shear stress is given by
τ= torsional shear stress at the fi bre (N/mm2
or MPa)
Mt = applied torque (N-mm)
r = radial distance of the fi bre from the axis of
rotation (mm)
J = polar moment of inertia of the cross-section
about the axis of rotation (mm4)
53. Types of stresses-Principal stresses
• There are many components, which are subjected to several types of load
simultaneously. A transmission shaft is subjected to bending as well as
torsional moment at the same time. In design, it is necessary to determine the
state of stresses under these conditions.
54. Types of stresses-Principal stresses
• Principal planes-Plane where no shear stress acts
• Principal stresses-Plane where normal stress acts
• σ1 –Maximum Principal stress
• σ2 –Minimum Principal stress
• τmax –Principal shear stress
59. 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 (fs or n).
• The factor of safety is defined as the ratio of ultimate
strength to the allowable or permissible stress
(fs) or n = Ultimate stress /allowable stress or permissible
stress
60. Factor of safety
Design without fos
Material-Mild steel (σyt = 380 N/mm2)
Stress- Tensile stress (σt=P/A)
380 = 10000/A
380 =10000/(𝜋/4)*d2
D=5.78mm
10000N
d = ?
61. Factor of safety
Design with fos
Material-Mild steel (σyt = 380 N/mm2)
Permissible stress=Yield stress/factor of safety
Permissible stress= 190N/mm2
Stress- Tensile stress (σt=P/A)
190 = 10000/A
190 =10000/(𝜋/4)*d2
D=8.18mm
10000N
d = ?
62. Factors influencing FoS
• Effect of Failure
• Type of Load
• Degree of Accuracy in Force Analysis
• Material of Component
• Reliability of Component
• Cost of Component
• Testing of Machine Element
• Service Conditions
• Quality of Manufacture
