Introduction to Machine Design Machine Designrao/Md-00intro.pdf · 1 August 15, 2007 P N Rao 1 330:148 (g) Machine Design Nageswara Rao Posinasetti August 15, 2007 P N Rao 2 Introduction

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August 15, 2007August 15, 2007 P N RaoP N Rao 11

330:148 (g)330:148 (g)Machine DesignMachine Design

Nageswara Rao Posinasetti Nageswara Rao Posinasetti


Introduction to Machine Introduction to Machine DesignDesign

ObjectivesObjectivesField of activities in Machine DesignField of activities in Machine DesignCourse DetailsCourse Details


What is machine design?What is machine design?

Application of science and technology to Application of science and technology to devise new or improved productsdevise new or improved productsProduct is any manufactured item Product is any manufactured item including machine, structure, tool and including machine, structure, tool and instruments.instruments.People who design are called design People who design are called design engineers.engineers.


What is Good Design?What is Good Design?

Activity done by engineers (includes Activity done by engineers (includes technologists) to create devices, technologists) to create devices, structures, processes to fill a needstructures, processes to fill a need

Problem solvingProblem solvingOptimizationOptimizationCost containment/ reductionCost containment/ reductionSystem analysisSystem analysis

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Definition of EngineeringDefinition of Engineering

…….that profession in which knowledge of .that profession in which knowledge of the mathematical and natural sciences the mathematical and natural sciences gained by study, experience and practice gained by study, experience and practice is applied with judgement to develop ways is applied with judgement to develop ways to utilise, economically, the materials and to utilise, economically, the materials and forces of nature for the benefit of the forces of nature for the benefit of the mankind. (ABET)mankind. (ABET)


Background for Machine Background for Machine DesignDesign

Technical drawingTechnical drawingKinematicsKinematicsMechanicsMechanicsMaterials engineeringMaterials engineeringStrength of materialsStrength of materialsManufacturing processesManufacturing processes


Philosophy of Machine Philosophy of Machine DesignDesign

Requires fundamentals of knowledgeRequires fundamentals of knowledgeNo memorisation of formulae or tables of No memorisation of formulae or tables of datadataBuild upon old ideasBuild upon old ideasBe innovative and search for ideasBe innovative and search for ideas


Check list for DesignersCheck list for Designers

Does it satisfy the need?Does it satisfy the need?Will it be competitive?Will it be competitive?Is it economical to produce?Is it economical to produce?Can it be readily maintained?Can it be readily maintained?Will it sell and make a profit?Will it sell and make a profit?


Major areas in Machine Major areas in Machine DesignDesign

Initial design conceptionInitial design conceptionStrength analysisStrength analysisMaterial selectionMaterial selectionAppearanceAppearanceManufacturabilityManufacturability


Major areas in Machine Major areas in Machine DesignDesign

EconomyEconomySafetySafetyEnvironmental effectsEnvironmental effectsReliability and lifeReliability and lifeLegal considerationLegal consideration

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Design process elementsDesign process elements

Decide on a number alternativesDecide on a number alternativesEvaluate each alternative and discard the Evaluate each alternative and discard the unsatisfactory onesunsatisfactory onesChoose the optimum one from the Choose the optimum one from the alternativesalternativesImplement the designImplement the design


Stages in the design process

Recognition of need

Definition of problem

Synthesis

Analysis and optimisation

Evaluation

Presentation

Iteration

Iteration


Design considerationsDesign considerations

Strength/stressStrength/stress Deflection/stiffnessDeflection/stiffnessWearWear CorrosionCorrosionSafetySafety ReliabilityReliabilityFrictionFriction UsabilityUsabilityUtilityUtility CostCostProcessingProcessing WeightWeightLifeLife NoiseNoise


Design considerationsDesign considerations

StylingStyling ShapeShapeSizeSize ControlControlThermal propertiesThermal properties SurfaceSurfaceLubricationLubrication MarketabilityMarketabilityMaintainabilityMaintainability VolumeVolumeLiabilityLiability RecyclingRecycling


Material PropertiesMaterial Properties

Yield strengthYield strengthUltimate strengthUltimate strengthModulus of ElasticityModulus of ElasticityDuctilityDuctilityThermal expansionThermal expansion

Stress, S

Su

Sy

Strain, e

Proportional limit

E = Se


Design problemDesign problemSelect a round bar to be constructed from an AISI 1020 Select a round bar to be constructed from an AISI 1020 coldcold--drawn steel to support the 300drawn steel to support the 300--pound ball. Assume pound ball. Assume a safety factor of 2, and determine the deflection for the a safety factor of 2, and determine the deflection for the size selectedsize selectedYield stress = 61,000 Yield stress = 61,000 psipsi

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Design problemDesign problemCantilever beamCantilever beamMax bending moment = 300 Max bending moment = 300 ×× 3636

= 10,800 in= 10,800 in--lblbStress in the beam, S = M/ZStress in the beam, S = M/ZS = 10,800 S = 10,800 ×× 32 / (32 / (ΠΠ dd33))Allowable stress = 61,000 / 2 = 30,500 Allowable stress = 61,000 / 2 = 30,500 psipsiEquating the above two, and solvingEquating the above two, and solvingd = 1.533 in = 1.625 in (preferred size)d = 1.533 in = 1.625 in (preferred size)Deflection = Deflection = --FLFL33 / (3EI) = 0.455 in/ (3EI) = 0.455 in


Information in Machine Information in Machine DesignDesign

CataloguesCataloguesCatalogue services Catalogue services -- CDROMCDROMInternetInternetYellow pagesYellow pagesTrade publicationsTrade publicationsTrade showsTrade showsProduct registersProduct registers


Codes and standardsCodes and standards

Standard is a set of specifications for Standard is a set of specifications for parts, materials or processes intended to parts, materials or processes intended to achieve uniformity, efficiency and a achieve uniformity, efficiency and a specified quality.specified quality.Code is a set of specifications for the Code is a set of specifications for the analysis, design, manufacture and analysis, design, manufacture and construction of some thing.construction of some thing.


Standard InstitutionsStandard Institutions

Professional Professional societiessocietiesAGMAAGMAAISIAISIAFBMAAFBMAASMASMASMEASMEASTMASTMAWSAWS

National StandardsNational StandardsANSIANSIDINDINJISJISBISBISISOISO


EconomicsEconomics

Standard sizesStandard sizesLarge tolerancesLarge tolerancesBreakeven pointsBreakeven pointsCost estimatesCost estimates


Break even chartBreak even chart

Break even chart

0

20

40

60

80

1 10 100 1000

Production Quantity

Ave

rage

cos

t per

pi

ece Open die forging

Closed die forging

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Safety and product liabilitySafety and product liability

Manufacturer of an article is liable for any Manufacturer of an article is liable for any damage or harm that results because of a damage or harm that results because of a defect.defect.Good EngineeringGood Engineering

AnalysisAnalysisDesignDesignQuality controlQuality control



Computational toolsComputational tools

MathCadMathCadMATLABMATLABTK SolverTK SolverExcel or Lotus 1Excel or Lotus 1--22--33CAD and FEACAD and FEA


Module 1-3aProperties of Rectangular Cross Sections

b = 2.000 in widthh = 1.000 in height

Area = 2.000 in

I x = 0.166667 in4

I y = 0.666667 in4

k x = 0.288675 in

k y = 0.333333 in

A = bh

y

3

I = hb12

x

3

I = bh12

xxk = I

A

yyk = I

A

h

b

h/2

b/2

Cx

Courtesy: M.F.Spotts – Design of Machine Elements


Courtesy: M.F.Spotts – Design of Machine Elements

Module 1-3aProperties of Rectangular Cross Sections

b = 3.000 in widthh = 2.000 in height

Area = 6.000 in

I x = 2 in4

I y = 4.5 in4

k x = 0.57735 in

k y = 0.75 in

A = bh

y

3

I = hb12

x

3

I = bh12

xxk = I

A

yyk = I

A

h

b

h/2

b/2

Cx


Problem using Finite Element Analysis (FEA)

Start with 2 in dia; Max stress = 13,751 lower than the allowable 30,500 psi

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Problem using FEA (contd..)

Next try 1.5 in dia; Max stress = 32,599 higher than the allowable 30,500 psi



Next try 1.625 in dia; Max stress = 25,635 lower than the allowable 30,500 psi - Acceptable



For 1.625 in dia; Max displacement = 0.47 in Compare this to analytical solution of 0.455 in, a 3% error


Why Calculating Moments is Why Calculating Moments is Important?Important?

http://www.sv.vt.edu/classes/ESM2204/EShttp://www.sv.vt.edu/classes/ESM2204/ESM2204_kriz_NoteBook/moments/momentsM2204_kriz_NoteBook/moments/moments.html.html


http://www.sv.vt.edu/classes/ESM2204/ESM2204_kriz_NoteBook/moments/moments.html



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Objectives of the courseObjectives of the course

Develop understanding of the design Develop understanding of the design principles involved in the design of various principles involved in the design of various machine elements.machine elements.The machine elements that would be The machine elements that would be covered are gears, bearings, shafts, etc.covered are gears, bearings, shafts, etc.We will develop methods of applying We will develop methods of applying principles learned in previous courses on principles learned in previous courses on mechanics and strength of materialsmechanics and strength of materials


Text BookText Book

WentzellWentzell, T. H. , T. H. -- Machine Machine Design, Delmar Design, Delmar Learning, 2004, Learning, 2004, ISBN ISBN 140180517140180517--5.5.


ReferenceReference BookBookss

A. Esposito and J.R.Thrower A. Esposito and J.R.Thrower -- Machine Design, Machine Design, 22ndnd Edition, Delmar Publishers, Albany, 1991, Edition, Delmar Publishers, Albany, 1991, 480 pages, 480 pages, ISBN 0ISBN 0--82738273--40814081--8.8. (No more in (No more in print)print)R.L. Mott R.L. Mott –– Machine Elements in Mechanical Machine Elements in Mechanical Design, 4Design, 4thth Edition, Prentice Hall, New Jersey, Edition, Prentice Hall, New Jersey, 2004, ISBN 2004, ISBN 00--1313--06188530618853..AnselAnsel C. C. UguralUgural, Mechanical Design: An , Mechanical Design: An Integrated Approach, Integrated Approach, McGraw Hill, New York, McGraw Hill, New York, 2004, ISBN 02004, ISBN 0--0707--2921854.2921854.


ReferenceReference BookBookss

J.E. J.E. ShigleyShigley, C.R. , C.R. MischkeMischke, and R G , and R G BudynasBudynas -- Mechanical Engineering Design, Mechanical Engineering Design, 77thth Edition, McGraw Hill, New York, 2004, Edition, McGraw Hill, New York, 2004, ISBN 0ISBN 0--0707--292193292193--5.5.Bernard J. Bernard J. HamrockHamrock, Bo O. Jacobson, and , Bo O. Jacobson, and Steven R. Steven R. SchmidSchmid, F, Fundamentalsundamentals ofofMMachineachine EElementslements, McGraw Hill Publishing, , McGraw Hill Publishing, ISBN: 0ISBN: 0--0707--297682297682--9, 2005 / Hardcover / 9, 2005 / Hardcover / 980 pages980 pages

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Evaluation procedure

Examinations (3)Examinations (3) 35%35%Home work (10)Home work (10) 40%40%Design projectDesign project 15%15%Class participation Class participation 10%10%and class workand class work


ExaminationsExaminations

Examinations during the semester are not Examinations during the semester are not comprehensive. comprehensive. Final examination is comprehensive.Final examination is comprehensive.Questions may be in the form of problems, short Questions may be in the form of problems, short answers, fill in the blank and/or True/False. answers, fill in the blank and/or True/False. During the tests you can make use of the textbook During the tests you can make use of the textbook for referring the equations or any data required for for referring the equations or any data required for solving the problems. solving the problems. You may also bring one sheet on which the You may also bring one sheet on which the necessary equations are written. (see p. 497 necessary equations are written. (see p. 497 ––502)502)


ExaminationsExaminations

The coverage of the examinations will be The coverage of the examinations will be announced in the class prior to the tests and announced in the class prior to the tests and generally include the lectures, text, homework, generally include the lectures, text, homework, etc. etc. There will be no chance to makeup for the There will be no chance to makeup for the missed examinations, unless arrangements missed examinations, unless arrangements have been made have been made beforebefore the examination that is the examination that is considered reasonable by the professor.considered reasonable by the professor.


Design ProjectDesign Project

The aim of this is to combine the various The aim of this is to combine the various principles being studied in the course for a principles being studied in the course for a final product design. final product design. You are expected to go through the design You are expected to go through the design procedures that are being studied and procedures that are being studied and apply them to a particular product.apply them to a particular product.Submission: December 8Submission: December 8thth


Design Project Design Project -- ReportReport

Functions of the projectFunctions of the projectDesign requirementsDesign requirementsSelection criteria usedSelection criteria usedDesign alternatives examined for the various Design alternatives examined for the various componentscomponentsDetailed design of the individual components Detailed design of the individual components in the system such as housing, gears, shafts, in the system such as housing, gears, shafts, bearings, seals, etc.bearings, seals, etc.Final assembly of the designed power Final assembly of the designed power transmissiontransmission


Research Paper Research Paper (Graduate students only)(Graduate students only)They are expected to do a detailed study They are expected to do a detailed study of a topic relevant to the course content, of a topic relevant to the course content, subject to the approval of the instructor. subject to the approval of the instructor. The topic and a brief written description The topic and a brief written description are to be submitted to the instructor by are to be submitted to the instructor by September, 15September, 15thth. . The type written, 8 to 12 page APA format The type written, 8 to 12 page APA format paper is to be submitted by December 8paper is to be submitted by December 8thth

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GradingGrading

FF< 60< 60DD--60 60 –– 6363D D 64 64 –– 6666D+D+67 67 –– 6969CC--70 70 –– 7373CC74 74 –– 7676C+C+77 77 –– 7979BB--80 80 –– 8383BB84 84 –– 8686B+B+87 87 –– 8989AA--90 90 –– 9494AA95 95 –– 100100

GradeGradePercentage Percentage rangerange

GradeGradePercentage Percentage rangerange


SummarySummary

Design is an exciting and fulfilling activity Design is an exciting and fulfilling activity for an engineer.for an engineer.Design requires basic knowledge in a Design requires basic knowledge in a number of disciplines.number of disciplines.Design engineer should be a person with Design engineer should be a person with sound judgement and wide experience.sound judgement and wide experience.

Documents

Introduction to Machine Design Machine Designrao/Md-00intro.pdf · 1 August 15, 2007 P N Rao 1 330:148 (g) Machine Design Nageswara Rao Posinasetti August 15, 2007 P N Rao 2 Introduction