ME 422 Machine Design I

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ME 422 Machine Design I
Glen Prater, Jr. Associate Professor and
ChairmanSH 200, 588-6331, gprater_at_louisville.edu
Office hours M, W, F, 1000-1050, or by
appointment Mechanical Engineering
Department University of LouisvilleLouisville,
KentuckyFall Semester 2001
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Course Overview

• Topics
• The engineering design process
• Fundamental concepts related to the designof
  mechanical components and machines
• Design for strength and reliability
• Machine component design (fasteners,weldments,
  springs)
• Open-ended design projects
• Textbook
• Mechanical Engineering Design, Shigley and
  Mischke, 6th Edition

Stress distributions in an axially loaded
rectangular bar with different stress raisers
filleted shoulder, central circular hole,
U-notches
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Course Outcomes

• Ability to apply knowledge of mathematics,
  science, and engineering in the field of
  mechanical engineering
• Ability to design a system, component, or process
  to meet desired needs in the field of mechanical
  engineering
• Ability to identify, formulate and solve
  mechanical engineering problems
• Understanding of professional and ethical
  responsibility in the field of mechanical
  engineering
• Ability to communicate effectively
• Recognition of the need for, and an ability to
  engage in, life-long learning in the field of
  mechanical engineering
• Ability to use the techniques, skills, and modern
  tools necessary for the practice of mechanical
  engineering

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Grading
Course grades will be based on selectively graded
homework, four quizzes, two midterm examinations,
three design projects, and a final
examination Homework 10 Quizzes 3_at_5 Midt
erm Exams 2_at_15 Design Projects 2_at_12.5 Final
Exam 20 The scale below will be used to assign
letter grades. These percentages may be lowered,
depending upon the class score distribution. 90
-100 A 80-89 B 65-79 C 50-64 D
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Code of Ethics for Engineers (1)

• Fundamental Principles
• Engineers uphold and advance the integrity,
  honor, and dignity of the Engineering profession
  by
• using their knowledge and skill for the
  enhancement of human welfare
• being honest and impartial, and serving with
  fidelity the public, their employers and clients,
  and
• striving to increase the competence and prestige
  of the engineering profession.

The American Society of Mechanical Engineers
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Code of Ethics for Engineers (2)

• Fundamental Canons
• Engineers shall hold paramount the safety, health
  and welfare of the public in the performance of
  their professional duties.
• Engineers shall perform services only in the
  areas of their competence.
• Engineers shall continue their professional
  development throughout their careers and shall
  provide opportunities for the professional
  development of those engineers under their
  supervision.
• Engineers shall act in professional matters for
  each employer or client as faithful agents or
  trustees, and shall avoid conflicts of interest.
• Engineers shall build their professional
  reputations on the merit of their services and
  shall not compete unfairly with others.
• Engineers shall associate only with reputable
  persons or organizations.
• Engineers shall issue public statements only in
  an objective and truthful manner.

The American Society of Mechanical Engineers
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Machine Design

• Machine Design
• is an iterative process that has as its primary
  objective the synthesis of machines in which the
  critical problems are based upon material
  sciences and engineering mechanics sciences.
• This synthesis involves the creative conception
  of mechanisms, and optimization with respect to
  performance, reliability and cost.
• Machine design does not encompass the entire
  field of mechanical engineering. Design where the
  critical problems involve the thermal/fluid
  sciences fall under the broader category of
  mechanical engineering design.
• The primary objective of machine design is
  synthesis, or creation, not analysis. Analysis is
  a tool that serves as a means toward an end.

Finite element model of a pickup truck floorpan
assembly
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The Traditional Design Process
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Preliminary Design Phase

• Often the first step in which a designer becomes
  involved, and may not involve intense iteration.
  In this phase, we deal with the entire machine
• Define function
• Identify constraints involving cost, size, etc.
• Develop alternative conceptions of
  mechanism/process combinations that can satisfy
  the constraints
• Perform supporting analyses (thermodynamic, heat
  transfer, fluid mechanics, kinematics, force,
  stress, life, cost, compatibility with special
  constraints)
• Select the best mechanism
• Document the design

Concept 1 Two longitudinal members, one
trans-verse split-end cross member, small
transverse member in transmission tunnel, rear
transverse member similar to original, gauge
reduction.
Concept 6 Two integrated, split transverse cross
members, rear transverse member similar to
original, reduced sheet thickness in cross
members.
Alternative design concepts for cross members in
a light-duty truck floorpan assembly
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Intermediate Design Phase

• Generally occurs after preliminary design, but
  the two phases may overlap. Intermediate design
  always involves iterations. In this phase, we
  deal with individual components of the machine
• Identify components
• Define component functions
• Identify constraints involving cost, size, etc.
• Develop tentative conceptions of the components
  mechanism/process combinations using good form
  synthesis principles
• Perform supporting analyses (including analyses
  at each critical point in each component)
• Select the best component designs
• Document component designs prepare a layout
  drawing

FrontReinforcement
CornerReinforcement
A-pillar component geometries
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Detail Design Phase

• Subsequent to intermediate and. In this phase, we
  deal with individual components of the machine
  and the machine as a whole
• Select manufacturing and assembly processes
• Specify dimensions and tolerances
• Prepare component detail drawings
• Prepare assembly drawings

Line rendering of a pickup box assembly showing
geometric details such as wheel well openings,
cross members, and bed corrugation
Lecture material in this course focuses on the
preliminary and intermediate phases. The design
projects will involve elements of detail design
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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 - Cost - Thermal properties -
Distortion/stiffness - Processing requirements -
Surface finish - Wear - Weight - Lubrication -
Corrosion - Life - Marketability - Safety -
Noise - Maintenance - Reliability - Aesthetic
considerations - Volume - Friction - Shape -
Liability - Usability/utility - Size -
Scrapping/recyclability
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Standards and Codes
Standards and codes represent a prescriptive
approach to design that may be incorporated into
a design process. Standards A set of technical
definitions and guidelines for designers and
manufacturers. Standards are written by experts
and are considered voluntary. ASME groups
develops and maintains standards using
committees. Code A set of standards that has
been adopted by one or more governmental bodies
or incorporated into a contract. Essentially, a
code is a set of standards with the force of law
behind it. According to its web site, ASME
maintains and distributes 600 codes and
standards used around the world for the design,
manufacturing and installation of mechanical
devices.
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ASME Standards and Codes Related to
Standardization
A112 Plumbing Materials and Equipment B1 Screw
Threads B5 Machine Tools - Components,
Elements, Performance, and Equipment B18
Standardization of Fasteners B29 Chains,
Attachments and Sprockets for Power Transmission
and Conveying B32 Metal and Metal Alloy
Wrought Mill Product Nominal Sizes B40
Standards for Pressure and Temperature
Instruments and Accessories B46 Classification
and Designation of Surface Qualities B47 Gage
Blanks B73 Chemical Standard Pumps B89
Dimensional Metrology B94 Cutting Tools,
Drivers, and Bushings B107 Hand Tools and
Accessories B133 Gas Turbine Procurement HST
Overhead Hoists MFC Measurement of Fluid Flow
in Closed Conduits MH1 Pallets, Slip Sheets,
and Other Bases For Unit Loads SRB Slew Ring
Bearing STS Steel Stacks Y14 Engineering
Drawing and Related Documentation Practices
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ASME Standards for Screw Threads (1)
B1.1-1989 Unified Inch Screw Threads (UN and UNR
Thread Form) B1.2-1983 (R1991) Gages and Gaging
for Unified Inch Screw Threads B1.3-1992 Screw
Thread Gaging Systems for Dimensional
Acceptability Inch and Metric Screw Threads
(UN, UNR, UNJ, M, and MJ) B1.5-1997 Acme Screw
Threads B1.7M-1984 (R1992) Nomenclature,
Definitions and Letter Symbols for Screw Threads
B1.8-1988 (R1994) Stub Acme Screw Threads
B1.11-1958 (R1994) Microscope Objective Thread
B1.12-1987 (R1998) Class 5 Interference-Fit
Thread B1.13M-1995 Metric Screw Threads M
Profile B1.15-1995 Unified Inch Screw Threads
B1.16M-1984 (R1992) Gages and Gaging for Metric
M Screw Threads B1.20.1-1983 (R1992) Pipe
Threads, General Purpose (Inch) B1.20.7-1991
(R1998) Hose Coupling Screw Threads (Inch)
B1.21M-1997 Metric Screw Threads MJ Profile
B1.22M-1985 (1992) Gages And Gaging Practice For
"MJ" Series Metric Screw Threads B1.30M-1992
Screw Threads Standard Practice for Calculating
and Rounding Dimensions
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ASME Standards for Screw Threads (2)
B1.1-1989 Unified Inch Screw Threads (UN and UNR
Thread Form) Scope This Standard specifies the
thread form, series, class, allowance, tolerance,
and designation for unified screw threads. (In
order to emphasize that unified screw threads are
based on inch modules, they may be denoted
unified inch screw threads.) Several variations
in thread form have been developed for unified
threads however, this Standard covers only UN
and UNR thread forms. For easy reference, a
metric translation of this Standard has been
incorporated as Appendix C. Appendices A through
C contain useful information that is
supplementary to the sections of this Standard.
Order No. M020889 55.00
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ASME Standards for Screw Threads (3)

• B1.7M-1984 (R1992) Nomenclature, Definitions and
  Letter Symbols for Screw Threads
• Scope The purpose of this Standard is to
  establish uniform practices for standard screw
  threads with regard to the following
• Screw thread nomenclature, and
• Letter symbols for designating features of screw
  threads for use on drawings, in tables of
  dimensions which set forth dimensional standards
  and in other records, and for expressing
  mathematical relationship.
• This Standard consists of a glossary of terms,
  and illustrated table showing the application of
  symbols, and a table of thread series
  designations. Many of the terms and symbols
  specified in this Standard vary considerably from
  those of previous issues because ISO terms and
  symbols have been adopted where the intended
  definition is the same.
• Order No. L00011 32.00

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Economics

• Strength, safety, reliability, and cost are
  perhaps the most important design
  considera-tions. 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 andcomponents

Breakeven point for two different screw
manufacturing processes
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Safety and Reliability
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 United States law
recognizes the concept of strict reliability. The
manufacturer of a product is responsible for any
damage or harm that arises due to a defect in the
product. It doesnt matter how long after
manufacture the damage occurs, or if the defect
is due to a design flaw or manufacturing error.
Negligence does not have to be proven. A
plaintiff only has to establish that the product
was defective and that the defect caused damage
or harm.
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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.
• Inexact knowledge of the magnitude and tie
  history of external loads.
• Effect of corrosion and wear on strengths.

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Dealing With Uncertainty (1)

• Permissible Stress Method
• Permissible stress in a design is based upon a
  fraction of material strength. The actual
  fraction is based upon experience with successful
  designs. Still used by civil engineers and for
  the design of weldments.
• Design Factor Method
• 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

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Dealing With Uncertainty (2)

• Stochastic Design Factor Method
• Stochastic means involving random variables, and
  uncertainty in strength and stress can be
  statistically quantified.
• The design factor equation can then be adapted to
  use to determine a mean design factor. For a
  linear load stress relationship

• Stochastic Method
• Does not use a design factor. Based upon the
  concept of reliability, R