INTRODUCTION TO
MECHANICAL
ENGINEERING
DESIGN
CHAPTER 1
Wednesday, February 01, 2017
Mohammad Suliman Abuhaiba, Ph.D., P.E. 1
CHAPTER OUTLINE
Mohammad Suliman Abuhaiba, Ph.D., P.E. Wednesday, February 01, 2017 2
1. Design
2. Mechanical Engineering Design
3. Phases and Interactions of the Design Process
4. Design Tools and Resources
5. The Design Engineer’s Professional Responsibilities
6. Standards and Codes
7. Economics
8. Safety and Product Liability
9. Stress and Strength
10.Uncertainty
11.Reliability
12.Dimensions and Tolerances
13.Calculations and Significant Figures
14.Power Transmission Case Study Specifications
DESIGN
Formulate a plan for the satisfaction of a
specified need
Requires innovation, iteration, and decision-
making
Products should be
Functional
Safe
Reliable
Mohammad Suliman Abuhaiba, Ph.D., P.E.Wednesday, February 01, 2017
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Competitive
Usable
Manufacturable
Marketable
MECHANICAL ENGINEERING
DESIGN (MED)
MED involves all disciplines of mechanical
engineering
Example - Journal bearing
fluid flow
heat transfer
Friction
energy transport
material selection
thermo-mechanical treatments
Mohammad Suliman Abuhaiba, Ph.D., P.E. Wednesday, February 01, 2017 4
DESIGN CONSIDERATIONS
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Functionality Cost Thermal properties
Strength / stress Friction Surface
Distortion / deflection / stiffness Weight Lubrication
Wear Life Marketability
Corrosion Noise Maintenance
Safety Styling Volume
Reliability Shape Liability
Manufacturability Size Remanufacturing /
resource recoveryUtility Control
COMPUTATIONAL TOOLS
Computer-Aided Engineering (CAE): Any use of
computer & software to aid in the engineering
process
Computer-Aided Design (CAD)
Drafting, 3-D solid modeling, etc.
Computer-Aided Manufacturing (CAM)
CNC, rapid prototyping, etc.
Engineering analysis and simulation
FEA, fluid flow, dynamic analysis, motion, etc.
Math solvers: Spreadsheet, procedural
programming language, equation solver, etc.
MatLab, Mathematica, Maple, etc..
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ACQUIRING TECHNICAL INFORMATION
Libraries
• Engineering handbooks, textbooks, journals, patents, etc…
Government sources
• Government agencies, U.S. Patent & Trademark
• National Institute for Standards and Technology
Professional Societies (conferences, publications, etc.)
• American Society of Mechanical Engineers
• Society of Manufacturing Engineers
• Society of Automotive Engineers
Commercial vendors
• Catalogs, technical literature, test data, etc…
InternetMohammad Suliman Abuhaiba, Ph.D., P.E. Wednesday, February 01, 2017 8
USEFUL INTERNET SITES
www.globalspec.com
www.engnetglobal.com
www.efunda.com
www.thomasnet.com
www.uspto.gov
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THE DESIGN ENGINEER’S
PROFESSIONAL RESPONSIBILITIES
Satisfy needs of the customer in a
competent, responsible, ethical, and
professional manner.
Some key advise for a professional engineer
• Be competent
• Keep current in field of practice
• Keep good documentation
• Ensure good and timely communication
• Act professionally and ethically
Mohammad Suliman Abuhaiba, Ph.D., P.E. Wednesday, February 01, 2017 10
ETHICAL GUIDELINES FOR
PROFESSIONAL PRACTICE
National Society of Professional Engineers(NSPE) publishes a Code of Ethics forEngineers and an Engineers’ Creed.
www.nspe.org/ethics
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ETHICAL GUIDELINES FOR
PROFESSIONAL PRACTICE
Six Fundamental Canons Engineers, in thefulfillment of their professional duties, shall:
1. Hold paramount safety, health, and welfare of the public
2. Perform services only in areas of their competence
3. Issue public statements only in an objective & truthfulmanner
4. Act for each employer or client as faithful agents ortrustees
5. Avoid deceptive acts
6. Conduct themselves honorably, responsibly, ethically,and lawfully so as to enhance the honor, reputation, andusefulness of the profession.
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STANDARDS AND CODES
Standard
• A set of specifications for parts, materials, or processes
• Intended to achieve uniformity, efficiency, and a specified
quality
• Limits the multitude of variations
Code
• A set of specifications for the analysis, design,
manufacture, and construction of something
• To achieve a specified degree of safety, efficiency, and
performance or quality
• Does not imply absolute safety
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1. Aluminum Association (AA)
2. American Bearing Manufacturers Association
(ABMA)
3. American Gear Manufacturers Association
(AGMA)
4. American Institute of Steel Construction
(AISC)
5. American Iron and Steel Institute (AISI)
6. American National Standards Institute
(ANSI)
7. American Society of Heating, Refrigerating
and Air-Conditioning Engineers
8. (ASHRAE)
9. American Society of Mechanical Engineers
(ASME)
10.American Society of Testing and Materials
(ASTM)
11.American Welding Society (AWS)
12.ASM International
STANDARDS AND CODES
Some organizations that establish standards and codes:
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13.British Standards Institution (BSI)
14. Industrial Fasteners Institute (IFI)
15. Institute of Transportation
Engineers (ITE)
16. Institution of Mechanical
Engineers (IMechE)
17. International Bureau of Weights
and Measures (BIPM)
18. International Federation of
Robotics (IFR)
19. International Standards
Organization (ISO)
20.National Association of Power
Engineers (NAPE)
21.National Institute for Standards
and Technology (NIST)
22.Society of Automotive Engineers
(SAE)
ECONOMICS
Cost is an important factor in engineering
design
Use of standard sizes is a first principle of
cost reduction.
Table A-17: some typical preferred sizes
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TOLERANCES
Close tolerances
generally increase
cost & require:
• additional
processing steps
• additional
inspection
• machines with
lower production
rates
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BREAKEVEN POINTS
A cost comparison between two possible production methods
There is a breakeven point on quantity of production
Mohammad Suliman Abuhaiba, Ph.D., P.E.
Automatic screw
machine
25 parts/hr
3 hr setup
$20/hr labor cost
Hand screw machine
10 parts/hr
Minimal setup
$20/hr labor cost
Breakeven at 50 units
EXAMPLE
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SAFETY & PRODUCT LIABILITY
Manufacturer is liable for damage or harm
that results because of a defect.
Negligence need not be proved.
Calls for good engineering in analysis and
design, quality control, and comprehensive
testing.
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STRESS AND STRENGTH
Strength
•An inherent property of a material or of a
mechanical element
•Depends on treatment and processing
•May or may not be uniform throughout the part
•Examples: Ultimate strength, yield strength
Stress
•A state property at a specific point within a body
•Primarily a function of load and geometry
•Sometimes also a function of temperature and
processingMohammad Suliman Abuhaiba, Ph.D., P.E. Wednesday, February 01, 2017 2
0
UNCERTAINTY
Common sources of uncertainty in stress or strength
Composition of material and the effect of variation on properties
Variations in properties from place to place within a bar of stock
Effect of processing locally, or nearby, on properties
Effect of nearby assemblies such as weldments and shrink fits on
stress conditions
Effect of thermo-mechanical treatment on properties
Intensity and distribution of loading
Validity of mathematical models used to represent reality
Intensity of stress concentrations
Influence of time on strength and geometry
Effect of corrosion and wear
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UNCERTAINTY
Stochastic method
•Based on statistical nature of the design
parameters
•Focus on the probability of survival of the
design’s function (reliability)
•Often limited by availability of statistical data
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Wednesday, February 01, 2017
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RELIABILITY
Reliability, R: statistical measure of the
probability that a mechanical element will not
fail in use
Probability of Failure, pf : number of instances
of failures per total number of possible
instances
Example: If 1000 parts are manufactured, with
6 of the parts failing, the reliability is
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RELIABILITY
Overall reliability of a series system = product
of reliabilities of individual components
Example: A shaft with two bearings having
reliabilities of 95% & 98% has an overall
reliability of
R = R1 R2 = 0.95 (0.98) = 0.93 or 93%
Mohammad Suliman Abuhaiba, Ph.D., P.E.
1
(1-5)n
i
i
R R
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DIMENSIONS AND TOLERANCES
Nominal size: size we use in speaking of an
element.
Is not required to match actual dimension
Limits: stated max & min dimensions
Tolerance: difference between the two limits
Bilateral tolerance: variation in both
directions from basic dimension, e.g. 1.005 ±
0.002 in.
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DIMENSIONS AND TOLERANCES
Unilateral tolerance: basic dimension is taken
as one of the limits, and variation is permitted
in only one direction, e.g.
Clearance: difference in sizes of two mating
cylindrical parts such as a bolt and a hole.
Diametral clearance
Radial clearance
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DIMENSIONS AND TOLERANCES
Interference: opposite of clearance, where
internal member is larger than the external
member
Allowance: minimum stated clearance or
maximum stated interference of mating parts
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CALCULATIONS AND
SIGNIFICANT FIGURES
Accuracy of a real number depends on number of
significant figures describing the number
Unless otherwise stated, no less than three
significant figures should be used in your
calculations.
# of significant figures is usually inferred by # of
figures given.
706, 3.14, and 0.00219 are assumed to be
numbers with three significant figures
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CALCULATIONS AND
SIGNIFICANT FIGURES
Consider a number such as 91600.
For three significant figures express the
number as 91.6 × 103
For four significant figures express it as
91.60 × 103
Never report a number of significant
figures of a calculation any greater than
smallest number of significant figures of
the numbers used for the calculation.
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LINKED END-OF-CHAPTER PROBLEMS
Mohammad Suliman Abuhaiba, Ph.D., P.E.
Wednesday, February 01, 2017
30
Mohammad Suliman Abuhaiba, Ph.D., P.E.
POWER TRANSMISSION CASE STUDY
SPECIFICATIONS
Design Requirements Power to be delivered = 20 hp
Input speed = 1750 rpm
Output speed = 85 rpm
Targeted for uniformly loaded applications, such as
conveyor belts, blowers, and generators
Output shaft and input shaft in-line
Base mounted with 4 bolts
Continuous operation
6-year life, 8 hours / day, 5 days / week
Low maintenance
Competitive cost
Nominal operating conditions of industrialized locations
Input and output shafts standard size for typical
couplings