Chapter 1
Introduction to
Mechanical
Engineering Design
ME307 Lecture Notes
Chapter 1-1-Introduction
ME307 Lecture Notes
Chapter 1-1-Introduction
What is Design ?
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Fundamentally, design the process of problem solving.
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Design problems have no unique answer (Open-ended problems).
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To design is to formulate a plan for the satisfaction of a human need.
Decision and Engineering Judgment
Designed product should be:
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Functional
Safe
Reliable
Competitive
Usable
Manufacturable
Marketable
ME307 Lecture Notes
Chapter 1-1-Introduction
What is Mechanical Design ?
Against human need,
e.g. clothing design,
interior design
Problem Solving
Design
Engineering Design
Mechanical
Design
Machine
Design
Highway, building, ship, car, heating
cooling, IC design, telecommunication
system
ME307 Lecture Notes
Ship, car, heating/cooling
process, power generation,
process plant, pump, turbine
Chapter 1-1-Introduction
What is Machine Design ?
Mechanical Design
Energy System
Difference
Structure & Machine Design
between STRUCTURE and MACHINE
Mechanical
System: Motor vehicle drive line
Engine with flywheel  Clutch
 Gearbox Propshaft
AxleWheel
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Machine Elements: Shafts, gears, belts, clutch, brake, wheel etc.
Chapter 1-1-Introduction
What is Mechanical Design ?
Multi Disciplinary knowledge may be involved
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Design of a Journal Bearing
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Fluid Flow,
Friction,
Heat Transfer,
Material Selection,
Thermo-mechanical
Treatment.
Building Environment
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Heating,
Ventilation,
Air-Conditioning
ME307 Lecture Notes
Machine Component Design:
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Shafts,
gears,
belts,
clutch,
brake,
wheel
Mechanical System Design:
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Automobile
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Selection of sub-systems (e.g. Engine)
Design of Components (Suspension
System)
Chapter 1-1-Introduction
Design
Process
Iterative Approach
ME307 Lecture Notes
Chapter 1-1-Introduction
The Traditional Design Process
ME307 Lecture Notes
Chapter 1-1-Introduction
Standards and Codes
Standards and codes represent a regulatory approach to design that may be
incorporated into a design process.
Standards
A standard is a set of specifications for parts, materials, or processes
intended to achieve uniformity, efficiency, and a specified quality.
- Standards provide a reasonable inventory of tooling, sizes, shapes, and
varieties.
Code
A set of specifications for the analysis, design, manufacture, and
construction of something. Purpose is to achieve a specified degree of
safety, efficiency, and performance or quality.
ME307 Lecture Notes
Chapter 1-1-Introduction
Organizations and societies have established specifications
for standards and safety or design codes.
Aluminum Association (AA)
American Gear Manufacturers Associations (AGMA)
American Institute of Steel Construction (AISC)
American Iron and Steel Institute (AISI)
American National Standards Institute (ANSI)
ASM International
American Society of Mechanical Engineers (ASME)
American Society of Testing and Materials (ASTM)
Society of Automotive Engineers (SAE)
And others
ME307 Lecture Notes
Chapter 1-1-Introduction
Design Considerations
The design of a component or system may be influenced by a number of
requirements. If a requirement affects design, it is called a design
consideration
For example, if the ability to carry large loads without failure is important, we say that
strength is a design consideration.
Most product development projects involve a number of design considerations:
- Strength/stress
- Distortion/stiffness
- Wear
- Corrosion
- Safety
- Reliability
- Friction
- Usability/utility
ME307 Lecture Notes
- Cost
- Processing requirements
- Weight
- Life
- Noise
- Aesthetic considerations
- Shape
- Size
Chapter 1-1-Introduction
- Thermal properties
- Surface finish
- Lubrication
- Marketability
- Maintenance
- Volume
- Liability
- Scrapping/recyclability
Economics
Strength, safety, reliability, and cost are perhaps the most important
design considerations.
In general the design
alternative that satisfies other
design considerations at the
lowest costs is to be preferred.
Issues affecting the “cost” of a
design include:
 Product development costs
 Material choice
 Manufacturing processes
involved
 Economies of scale
 Tolerances specified
 Use of standard sizes and
components
ME307 Lecture Notes
Breakeven point for two different screw manufacturing processes
Chapter 1-1-Introduction
bud21932_0102.jpg
Tolerance
Among the effects of design
specifications on costs,
tolerances are perhaps most
significant.
Tolerances, manufacturing
processes, and surface
finish are interrelated and
influence the producibility of
the end product.
ME307 Lecture Notes
Chapter 1-1-Introduction
Safety
Safety is paramount, most importantly because it is an ethical issue.
 Safety is also related to function.
 Safe designs tend to function well and perform reliably.
The best approaches to the prevention of product liability are good
engineering in analysis and design, quality control, and
comprehensive testing procedures.
Advertising managers often make glowing promises in the
warranties and sales literature for a product.
The statements should be reviewed carefully by the engineering
staff
 To eliminate excessive promises and,
 To insert adequate warnings and instructions for use.
ME307 Lecture Notes
Chapter 1-1-Introduction
Reliability
The statistical measure of the probability that a mechanical element
will not fail in use is called the reliability of that element
The reliability R can be expressed by a number having the range
0 ≤ R ≤ 1.
A reliability of R = 0.90 means that there is a 90 percent chance that
the part will perform its proper function without failure
The failure of 6 parts out of every 1000 manufactured might be
considered an acceptable failure rate for a certain class of products.
This represents a reliability of:
R = 1 −(6/1000) = 0.994
or 99.4 percent.
ME307 Lecture Notes
Chapter 1-1-Introduction
Uncertainty – Inherent in Engineering Design
Sources of Uncertainty
• Random variables associated with material processing result in
strength distributions that vary from sample to sample.
• Some samples will have strengths greater than the specified
value.
• Others – hopefully a very few – will have strengths lower than
the specified value.
• Statistical scatter in critical dimensions specified into the design during
the detail design phase due to imperfections in manufacturing
processes.
• Approximations used in the analytical expressions used to perform
design calculations.
ME307 Lecture Notes
Chapter 1-1-Introduction
Dealing With Uncertainty
Design Factor or Factor of Safety
• There is a difference between a design goal, which may be based upon
experience (often involving load) and design realization which is based
upon a specific failure criterion (often involving stress) quantified by a
strength value:
Material: Strength
Loading: Stress
Failure Theory
Strength( S )
Design Factor (nd ) 
Allowable Stress ( )
ME307 Lecture Notes
Chapter 1-1-Introduction