1. Mechanical Engineering Design Shigley • Mischke • Budynas
Chapter 1
Introduction
Mechanical Engineering Design
Seventh Edition
Shigley • Mischke • Budynas
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. What Is Design?
Engineering design is a systematic process by which solutions to the needs of humankind are obtained
Examples
Efficient lawn mulching machine
Lightweight,compact wireless communication devices
High-temperature resistance material for reentry vehicle

3. What Is Design?; cont’
Teamwork with engineers, scientists, environmentalists, economists, sociologists, legal personnel, marketing personnel, etc
Public sentiments as executed through government regulations and political influence (e.g. new transportation vehicle banned in downtown, etc)
Engineers must be beware of the impact of our actions on society and the environment

4. What Is Design? Object’s aesthetic appearance; Like clothes
The process of applying the various techniques and scientific principles for the purpose of designing a device, a process or a system in sufficient detail to permit its realization
Define, calculate motions, forces, and changes in energy  sizes, shapes, materials
Failure—stress and deflection analysis needed
Applied, inertial loads; Parts geometry; Analysis of the forces, moments, and torques; Dynamics of the system

5. Engineering Design Designare; To designate, mark out Mechanism Machine
To outline, plan or plot, as action or work; To conceive, invent, contrive
Mechanism
A device which transforms motion to some desirable pattern and typically develops low forces and transmits little power
Machine
Contains mechanism which are designed to provide significant forces and transmit power

6. ABET Definition of Design
The engineering design component of a curriculum must include most of the following features:
development of student creativity,
use of open-ended problems,
development and use of modern design theory and methodology,
formulation of design problem statements and specifications,
consideration of alternative solutions,

7. ABET Definition of Design
feasibility considerations,
production processes,
concurrent engineering design,
and detailed system descriptions.
Further, it is essential to include a variety of realistic constraints such as economic factors, safety, reliability, aesthetics, ethics, and social impact.

8. Engineering Design Pencil sharpener Camera shutter Analog clock
Folding chair
Adjustable table
Lamp
Umbrella
Hood linkage
Food blender
Bank vault door
Transmission
Bull dozer
Robot
Amusement park ride

9. Introduction to Kinematics
Kinetics
The study of forces on systems in motion
Kinematics
Study of motion without regard to forces
F=ma, a=ÿ  Obtain y
Create (design) the desired motion of mechanical part; compute position, velocity, and acceleration

10. Introduction to Kinematics
James Watt ( )
Straight-line linkage to guide very long stroke pistons in the new steam engine
Oliver Evans ( )
U.S. steam engine
Euler ( )
Separation of dynamic analysis problem into geometrical and mechanical P B A O4 O2

11. Kinematics, continued D’Alembert, Kant Ampere (1775-1836)
Proposed the same idea; Kinematics, kinetics
Ampere ( )
Cinematique (greek; motion)
Father of modern kinematics
Franz Reuleaux ( )
Alexander Kennedy ( ) translated into English textbook

12. Design Process Design Process Identify the need
Unstructured problem
Blank paper syndrome; Don’t know how to begin!
structuring the unstructured problemsynthesis (putting together)analysisIteration
Identify the need
e.g. we need a better lawn mower
Background research
Patented? GT?

13. 4. Performance Specification
3. Goal Statement
Functional visualization
Design a better lawn mower Design a mean to shorten grass
State problem generally, clearly, concisely
4. Performance Specification
Define what the system must do. (Design specification define how it must do it)
Example of lawn mower
self-contained power supply
corrosion resistance
cost less than $150
Emit less than 80 db at 50 ft away
to shorten ¼ acre of grass per hour, etc

14. Case Study; Lawn Mowers
During the mid-1960s, a gardening equipment firm was losing market share due to increased competition
Design engineers generated a number of new lawn mower such as installing new safety guard, automatic shut-off switches, or with multiple blades for more effective cutting, or mower that could be folded into a compact shape for storage

15. Case Study; Lawn Mowers
But none were so revolutionary to make a resounding success in the market
One senior engineer suggested that the original problem statement should be changed to “design an effective means of maintaining lawns”
Brainstorming resulted in 50 ideas that include a chemical additive for lawns

16. Case Study; Lawn Mowers
One engineer commented that his 3-year-old son playing with yo-yo on the lawn, swinging horizontally. He said maybe a high-speed spinning cord could be used to cut grass
Focus upon the functions that are desired in a solution to the problem and formulate the problem statement in terms of these functions

17. Design Process, cont’ 5. Ideation and Invention Creative process
Idea generation
Brainstorming
Use analogy (mechanical systemelectrical system)
Inversion
Synonyms
Move x from A to B  push, pull, shove, throw, eject, jump, spill, ???

18. Design Process; Ideation
Ideation, continued
Large number of ideasfrustrationincubationeurekaiterate
Fascination with a problem (motivation)saturation with the facts, technical ideas, data, and the background of the problem A period of reorganization

19. Design process, Continued
6. Analysis
7. Selection
Decision Matrix
Weight factor
8. Detailed Design
Cad, Iteration
9. Prototyping and testing
10. production

20. Advice to Design Process
KISS; Keep it simple, stupid
There are multiple solutions!!!!!!!
No one has right answer
Physical test is expensive Do as much analysis on paper, computer as possible. Use Mathematical Model
Human factors
Ergonomics (Human factors engineering)
Steps, car (clutch, brake distance, etc), utilities
Uncomfortable to use, tiring, dangerous

21. *10-step Design Process. 1. Identification of a need
2. Problem definition
3. Search
4. Constraints
5. Criteria
6. Alternative solutions
7. Analysis
8. Decision
9. Specification
10. Communication

22. Iterative Design Process
1.Identify the need
10. communication
2. Define problem
9. Specification
3. search
Iterative Design Process
8. Decision
4. Constraints
7. Analysis
6. Alternative solutions
5. criteria

23. Design Process Design is a structured problem-solving activity
Process is a phenomenon identified through step-by-step changes that lead toward a required result
Cyclic and iterative process

24. Design Process; cont’ All projects have time and budget constraints
Example a new car must come to the market in a limited time frame even though engineers like to do more
Design phases
Definition of a problem (step 1 identify need and step 2 define problem)

25. Design Process; cont’ Design Phases Conceptual design phase
Information is gathered (step 3 search)
Constraints are established (step 4 constraints)
Multitude of possible solutions are generated (step 6 alternatives)
Preliminary design phase
Development of criteria (step 5 criteria)
Analysis of potential solutions (step 7 analysis)
Select best solution (step 8 decision)

26. Design Process; cont’ Design Phases Detailed design phase
Selection of stock parts, the design of all other components, and the optimization of the solution (step 9; specification)
Optimization considering cost, materials, performance, manufacturability and feasibility
Example; moving product from East Coast to the West Coast; airplanes, trucks and airplanes? New factory?

27. Design Process; cont’ Design Phases Prototype design phase
Extensive tests before mass production
Final Design (Mass production)
Communicated (step 10) to manufacturing for production

28. Design and the Customer
The result of the execution of the design process is a new product, process or system
Identification of need starts from customer’s suggestions or requests
Final design must satisfy customer requirements or exceed expectation

29. Design and the Customer
If customer requirements are not clear, engineers must consult with customers
Customers must be informed of the design status at all times
Both design team and customers may have to modify their requirements in order to meet time, cost, performance and manufacturing constraints

30. Kano Model
Relationship between degree of achievement and customer satisfaction
Basic; customer requirements are simply expected by the customer and assumed to be available
Exciting; customer requirements are generally suggested by the design team; usually outside of customer knowledge or vision

31. Customer Satisfaction
Performance Related
Exciting
Degree of Achievement
Basic

32. Example of Kano Model New electric –powered barbeque grill
Design team starts from existing successful designbasic
Customer may specify performance-related items such as ease of cleaning, ease of setting the controls; cooking time, cooking effectiveness
New concept, such as programmable cooking cycle, can give unexpected bonus to customer, make it selling point and create excitement.

33. The Nature of Engineering Design
Is engineering design an art?
It is an cognitive process that requires a broad knowledge base, intelligent use of information, and logical thinking
Design team consists of engineers, marketing personnel, economists, management, customers, etc

34. Cognitive Process Benjamin Bloom (1950s); Bloom’s taxonomy
Knowledge; the ability to recall information, facts, or theories
Example; what was the date of the Challenger space shuttle accident?
Comprehension; ability to make sense (understand)the material
Explain the cause of the Challenger accident

35. Cognitive Process
Application; ability to use knowledge and comprehension in a new situation and to generalize the knowledge
What would have you done to prevent the Challenge accident?
Analysis; ability to break learned material into its component parts so that the overall structure may be understood

36. Cognitive Process Analysis; cont’
It includes part identification, relationships of the parts each other and to the whole, and recognize of the organizational principles involved
Example; what lessons did we learn about the space program from the Challenger accident?

37. Cognitive Process Analysis; cont’
The highest level of convergent thinking, whereby the individual recalls and focuses on what is known and comprehended to solve a problem through application and analysis

38. Cognitive Process Divergent thinking
The individual process information and produces new insights and discoveries that were not part of the original information
Synthesis; ability to put parts together to form a new plan or idea
Example; propose an alternative to the Challenger O-Ring design that would perform the required function

39. Cognitive Process
Evaluation; ability to judge the value of material based on specific criteria
Usually the individual is responsible for formulating the criteria to be used in the evaluation
Example; assess the impact of the Challenger accident on the U.S. space program

40. Bloom’s Taxonomy Divergent Thought complexity Evaluation Synthesis
Analysis
Convergent Thought
Application
Comprehension
Knowledge

41. Design Steps 1. Identification of a Need
Usually other than the engineer decides that a need exists
Products have life cycle. New profitable products must be developed
The consumers are ultimately the judges of whether there is truly a need; any product that doesn’t satisfy customers are doomed
Citizens of a community decide to have roads, libraries, buildings, etc. Engineers can help decision makers by providing information

42. 1. Identification of a Need, cont’
Example
Dormitory rooms are crowded with beds, desks, shelving units, etc.
There is a need to utilize better dormitory living space for college students
Maybe lofts (elevated beds) that can be a combined system with desk, closet, dresser and shelves could be a solution

43. 2. Problem Definition
A loft can be built with a few boards, nails, and a hammer
How about stability? Efficiency of assembly? Efficient use of space? Regulation of the college and government?
Brainstorming all possibilities that might satisfy the need

44. 2. Problem Definition; cont’
Symptom vs. Cause
Rainfall drain of a new development
Storm sewer systems? It only transport the water problem to downstream for someone else to handle
Holding ponds; onsite treatment
Real problem is not how to get rid of the rainfall as rapidly as possible, but how to control the water

45. 2. Problem Definition; cont’
Solving the Wrong Problem
In the 1970s, to reduce auto accident fatalities, using lap and shoulder belts were required
The solution technique that was implemented was an interlock system that requires the belts be latched before the auto could be started
Driver’s attitude was the real problem; it failed

46. 2. Problem Definition; cont’
Broad definition of problem may show
Purchase a prefabricated loft system
Purchase parts and assemble after sketching a possible solution
Rent two rooms and cut a connecting door, so on
Obtain the most concise and complete problem definition
State A (Undesirable situation) State B (Desirable situation )

47. 2. Problem Definition; cont’
Crowded living conditions Uncrowded living conditions
Too broad
Existing dorm furnishings  Existing furnishings with lofted beds
Complete considerations needed; time constraints
Existing dorm beds Lofted beds

48. Case Study; PS vs DS
State the present or problem state (PS) and the desired state (DS)
Then engineers modify either PS statement, the DS statement, or both until there is a satisfactory correlation between the two
Example; a student currently enrolled in both engineering design and a physics course
PS: I need to study physics
DS: I want to earn an A in engineering design

49. Case Study; PS vs DS There is no common between them
PS: I need to study physics because I have an exam next week
DS: I want to earn an A in engineering design
PS: I need to study physics because I have an exam next week, but the only extra time that I can devote to physics is already scheduled for my term project in engineering design
DS: I want to earn an acceptable grades in both engineering design and physics

50. Case Study; PS vs DS
PS: I am not sufficiently prepared for my upcoming physics exam and I also need to work on my term project in engineering design
DS: I want to earn an acceptable grades on both my engineering design term project and my physics exam
Now a direct and obvious correlation can be seen and solutions can be investigated

51. Case Study; PS vs DS Possible solutions I must become more efficient
I will speak with my professor
Seek tutoring help
I will decrease time to watch Television and devote this time to study
I will reformulate my term project so that less time is needed to complete

52. Design Steps 3. Search
Locating, applying, and transferring information; lots of information is needed
Open to many alternative solutions
Gathering information may help for a better definition of the problem and a better solution

53. 3. Search; cont’ Type of Information What has been written about it?
Is something already on the market that may solve the problem? (already patented? Group technology?)
What is wrong with the way it is being done?
What is right the way it is being done?

54. 3. Search; cont’ Type of Information
Who manufactures the current ‘solution’?
How much does it cost?
Will people pay for a better one if it costs more?
How much will they pay (or how bad is the problem)?

55. 3. Search; Source of Information
Existing solutions; reverse engineering
Internet search
Library search
Government documents
Professional organizations
Trade journals
Vendor catalog
From experts

56. 3. Search; Example Project
Loft bed state or other government state codes
Assemble with simple tools
Standard parts as possible
Preferred wood construction
No guard rail or ladder
No need for handicap access

57. 3. Search; Example Project; cont’
Survey
If students like loft bed and why
If students like current bed and why
How much students are willing to pay
List of important factors such as durability, accessibility, stability, cost, appearance, easy of assembly, safety and maintenance

58. 4. Constraints
There could be many solutions, but there are physical and practical limitations (constraints)
Examples
Market competition
Too expensive
Thin laptop or cell phone
Legal restriction
Boundary conditions

59. 4. Constraints; Example Project
Cost must not exceed $1500
Must meet safety codes
Must accommodate a unit bed size of 78 X 36 inches
Must be freestanding and cannot affect the existing structure of the room

60. 5. Criteria
Criteria are desirable characteristics of the solution which are established from experience, research, market studies, and customer preferences
Criteria are used to judge alternative solutions on a qualitative basis, unless quantitative evaluation by mathematical model is available

61. 5. Criteria; cont’ Weighting factor for criteria
Typical design criteria
Cost
Reliability
Weight (either heavy or light)
Ease of operation and maintenance
Appearance
Compatibility

62. 5. Criteria; cont’ Typical design criteria Safety features Noise level
Effectiveness
Durability
Feasibility
Acceptance

63. 5. Criteria; Example Project
Stability 15%
Easy of assembly 35%
Cost 25%
Functionality 25%

64. 6. Alternative Solutions
It is just like selecting the best person among the candidates for a new management position. A list of candidates must be made for interview and review processes
Likewise we need a list of possible answers to our problem before selecting the best one

65. 6. Alternative Solutions; cont’
The word “invention” strikes fear into the minds of many people
We learned that if we were like the other kids, no one laughed at us
If not already done well, few people are willing to try new
Fear that people laugh at us
Fear of failure (new experiments fails a lot)

66. 6. Alternative Solutions; cont’
There are techniques that can be used to assist us in developing a list of possible solutions
Checkoff lists;
The list suggest possible ways that an existing solution to your problem might changed and used
Use modify and rearrange to guide or focus on the efforts to obtain a new solution

67. 6. Alternative Solutions; cont’
Checkoff lists (cont’)
Modify?
Use laminates instead of solid wood
Use glue instead of bolts and screws
Rearrange?
Bed on the floor, desk and shelves above
Ladder on side of bed instead of end
Ask yourself; Why is the solution like it is? Will change make it better or worse?

68. 6. Alternative Solutions; cont’
Brainstorming
The leader states the problem clearly and ideas about its solution are invited
About 3-15 people, usually 4-8 works well
Free expression is essential; no discouraging word, no evaluation during brainstorming about the idea
The leader sets the tone and tempo of the session and provides a stimulus when things begin to drag

69. 6. Alternative Solutions; cont’
Brainstorming (cont’)
The members of the group should be equals; no reason to impress or support any other member
Recorders are necessary

70. Design Steps 7. Analysis
In order to find the best solution in light of available knowledge and criteria, we must analyze the alternative solutions to determine performance capability
Use of mathematical and engineering principles
The goal is to obtain quantitative information for the decision step in the design process
The time required to produce an analysis is critical

71. 7. Analysis; cont’
Many laws of nature; conservation of mass, momentum, energy, etc
Mathematical model
Graphics
Cardboard cutouts
Subscale model or pilot plants
Balance between accuracy and time & money

72. Design Steps 8. Decision There may be no perfect one solution
Trade-offs; many alternatives to satisfy criteria
Decision is very hard part
You need information in order to evaluate each alternative against each of the criteria

73. 8. Decision; cont’ Analysis can provide basis for decision
If time and money permits, experiment or prototype can help
Poor research, a less than adequate list of alternatives, or inept analysis would prevent good decision
Decision making is an art and a science

74. 8. Decision; cont’
There has been a lot of efforts to make decision process as a science
Probability
Statistics
Optimization (pay-off function)
Utility theory

75. Design Steps 9. Specification
After designing, it must be clearly defined to others in detail specifically
Drawings, database, bill of materials
A sufficient number of databases describing the size and shape of each part
Layouts to delineate clearance and operational characteristics
Assembly and subassemblies to clarify the relationship of parts

76. 9. Specification; cont’ Database; cont’
Written notes, standards, specifications, and so on, concerning quality and tolerances
A complete bill of materials
Local or national codes and standard must be satisfied
Utilize written, spoken, and graphical language in order to develop and interplete specifications

77. Design Steps 10. Communication
Great emphasis nowadays
Selling your design and idea
If if your design is superb, you have to convince other people

78. 10. Communication; cont’ Written report Appropriate cover page
Abstract
Table of contents
Body
Conclusion and recommendation
appendixes

79. 10. Communication; cont’ Oral Presentation Be prepared;
rehearse
use adequate audio/visual equipment
Stand in such a way so that you do not detract from what you are saying or showing
Look at your audience and maintain eye contact

80. 10. Communication; cont’
Project your voice by consciously speaking to the back row
Speak clearly

81. Approaches to Product Development
(a) Over-The-Wall Engineering Approach (From Kalpakjian [1997]).
(b) Concurrent Engineering Approach (adapted from Pugh [1996]).
Text Reference: Figure 1.1, page 5

82. Design of Mechanical Systems
If your only tool is a hammer, then every problem is a nail.
Concurrent Engineering
Failure
Breaking
Completely inoperable
Unable to perform the intended function
Unreliable or unsafe; need service

83. Design for Manufacture
Effect of manufacturing and assembly on design of reciprocating power saw.
(a) Original design, with 41 parts and 6.37 min assembly time. (b) modified design, with 29 parts and 2.58 min assembly time. [From Boothroyd (1992)].
Text Reference: Figure 1.2, page 14

84. Safety Factor Ns=allowable/design Ns>1 Safety factor
Code, experience level, tested?, manned?
Ns=N A,B,C * N C, D
A: Quality of Materials, workmanship, maintenance, and inspection
B: Control over load applied to part
C: Accuracy of analysis, experimental data
D:Danger to personnel
E: Economic impact

85. Example 1.1. A Wire Rope in Elevator to 20th Floor; 50% Overload; Safety Factor?
A (Quality of Materials, workmanship, maintenance, and inspection) should be very good; life threatening
B (Control over load applied to part) can be fair to poor because overload is permitted
C (Accuracy of analysis, experimental data) should be good as highly regulated; ASME code

86. D (Danger to personnel)very serious
E (Economic impact) serious, possible lawsuit
Ns=1.6*1.5 = 2.4; but code >7.6

87. Puglsey Safety Factor Approach
Table 1.1 Safety Factor Characterisics A, B, and C
Table 1.2: Safety Factor Characteristics D and E
Usage:
ns=ns,xns,y
ns=safety factor
ns,x is obtained from Table 1.1
ns,y from Table 1.2
Text Reference: Tables 1.1 and 1.2, page 9

88. Codes and Standards ANSI American National Standard Institute
ASME American Society of Mechanical Engineers
ASTM American society of testing and Materials
AGMA American Gear Manufacturers Association
AISI American Iron and Steel Construction
AISC American Institute of Steel Construction
ISO International standards Organization
NFPA National Fire Protection Association

89. Design for Safety Redundancy Fail-Safe Manifest Danger
Active-e.g., two deadbolt locks on a door
Passive-e.g.,one deadbolt lock plus a chain
Fail-Safe
If something goes wrong, it goes wrong to a safe way.
Manifest Danger
e.g.,Break system noise, leaking gas tank

90. SI Units and Prefixes Table 1.3 SI units and prefixes
Text Reference: Table 1.3, page 19

91. Conversion Factors and Definitions
Table 1.4 Conversion factors and definitions.
Text Reference: Table 1.4, page 20

92. Fig.1.3

93. Design Considerations
Functionality
Strength/stress
Deflection
wear
Corrosion
Safety
Reliability
Maintainability
Utility
Cost
Friction
Weight
Life
Noise
Styling
Shape
Size
Control
Thermal properties
Surface
Lubrication
Marketability
Maintenance
Volume
Liability
recycling

94. Fig. P1.5

95. Fig. P1.6

96. Fig. P1.10