Download presentation
Presentation is loading. Please wait.
Published byRandall Bond Modified over 7 years ago
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 problemsynthesis (putting together)analysisIteration 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 systemelectrical 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 ideasfrustrationincubationeurekaiterate 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 designbasic 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
Similar presentations
© 2025 SlidePlayer.com Inc.
All rights reserved.