Introduction to Machine Design Machine Design

1 1 August 15, 2007 August 15, 2007P N RaoP N Rao11330:148 (g)330:148 (g) Machine DesignMachine DesignNageswara Rao Posinasetti Nageswara Rao Posinasetti August 15, 2007 August 15, 2007P N RaoP N Rao22 Introduction to Machine Introduction to Machine DesignDesignObjectivesObjectives Field of activities in Machine DesignField of activities in Machine Design Course DetailsCourse DetailsAugust 15, 2007 August 15, 2007P N RaoP N Rao33 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 products Product is any manufactured item Product is any manufactured item including Machine , structure, tool and including Machine , structure, tool and People who Design are called Design People who Design are called Design 15, 2007 August 15, 2007P N RaoP N Rao44 What is Good Design ?

2 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 solving OptimizationOptimization Cost containment/ reductionCost containment/ reduction System analysisSystem analysisAugust 15, 2007 August 15, 2007P N RaoP N Rao55 August 15, 2007 August 15, 2007P N RaoP N Rao662 August 15, 2007 August 15, 2007P N RaoP N Rao77 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.

3 (ABET)mankind. (ABET)August 15, 2007 August 15, 2007P N RaoP N Rao88 Background for Machine Background for Machine DesignDesign Technical drawingTechnical drawing KinematicsKinematics MechanicsMechanics Materials engineeringMaterials engineering Strength of materialsStrength of materials Manufacturing processesManufacturing processesAugust 15, 2007 August 15, 2007P N RaoP N Rao99 Philosophy of Machine Philosophy of Machine DesignDesign Requires fundamentals of knowledgeRequires fundamentals of knowledge No memorisation of formulae or tables of No memorisation of formulae or tables of datadata Build upon old ideasBuild upon old ideas Be innovative and search for ideasBe innovative and search for ideasAugust 15, 2007 August 15, 2007P N RaoP N Rao1010 Check list for DesignersCheck list for Designers Does it satisfy the need?

4 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?August 15, 2007 August 15, 2007P N RaoP N Rao1111 Major areas in Machine Major areas in Machine DesignDesign Initial Design conceptionInitial Design conception Strength analysisStrength analysis Material selectionMaterial selection AppearanceAppearance ManufacturabilityManufacturabilityAugust 15, 2007 August 15, 2007P N RaoP N Rao1212 Major areas in Machine Major areas in Machine DesignDesign EconomyEconomy SafetySafety Environmental effectsEnvironmental effects Reliability and lifeReliability and life Legal considerationLegal consideration3 August 15, 2007 August 15.

5 2007P N RaoP N Rao1313 Design process elementsDesign process elements Decide on a number alternativesDecide on a number alternatives Evaluate each alternative and discard the Evaluate each alternative and discard the unsatisfactory onesunsatisfactory ones Choose the optimum one from the Choose the optimum one from the alternativesalternatives Implement the designImplement the designAugust 15, 2007 August 15, 2007P N RaoP N Rao1414 Stages in the Design processRecognition of needDefinition of problemSynthesisAnalysis and optimisationEvaluationPresentationIterat ionIterationAugust 15, 2007 August 15, 2007P N RaoP N Rao1515 Design considerationsDesign considerationsStrength/stressStrength/st ressDeflection/stiffnessDeflection/stiff nessWearWearCorrosionCorrosionSafetySafe tyReliabilityReliabilityFrictionFriction UsabilityUsabilityUtilityUtilityCostCost ProcessingProcessingWeightWeightLifeLife NoiseNoiseAugust 15, 2007 August 15, 2007P N RaoP N Rao1616 Design considerationsDesign considerationsStylingStylingShapeShapeSi zeSizeControlControlThermal propertiesThermal propertiesSurfaceSurfaceLubricationLubri cationMarketabilityMarketabilityMaintain abilityMaintainabilityVolumeVolumeLiabil ityLiabilityRecyclingRecyclingAugust 15, 2007 August 15.

6 2007P N RaoP N Rao1717 Material PropertiesMaterial Properties Yield strengthYield strength Ultimate strengthUltimate strength Modulus of ElasticityModulus of Elasticity DuctilityDuctility Thermal expansionThermal expansionStress, SSuSyStrain, eProportional limitE =SeAugust 15, 2007 August 15, 2007P N RaoP N Rao1818 Design problemDesign problem Select 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 selected Yield stress = 61,000 Yield stress = 61,000 psipsi4 August 15, 2007 August 15, 2007P N RaoP N Rao1919 Design problemDesign problem Cantilever beamCantilever beam Max bending moment = 300 Max bending moment = 300 3636= 10,800 in= 10,800 in--lblb Stress in the beam, S = M/ZStress in the beam, S = M/Z S = 10,800 S = 10,800 32 / (32 / ( dd33)) Allowable stress = 61,000 / 2 = 30,500 Allowable stress = 61,000 / 2 = 30,500 psipsi Equating the above two, and solvingEquating the above two, and solving d = in = in (preferred size)d = in = in (preferred size) Deflection = Deflection = --FLFL33/ (3EI) = in/ (3EI)

7 = inAugust 15, 2007 August 15, 2007P N RaoP N Rao2020 Information in Machine Information in Machine DesignDesign CataloguesCatalogues Catalogue services Catalogue services --CDROMCDROM InternetInternet Yellow pagesYellow pages Trade publicationsTrade publications Trade showsTrade shows Product registersProduct registersAugust 15, 2007 August 15, 2007P N RaoP N Rao2121 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. 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 of some 15, 2007 August 15, 2007P N RaoP N Rao2222 Standard InstitutionsStandard Institutions Professional Professional societiessocieties AGMAAGMA AISIAISI AFBMAAFBMA ASMASM ASMEASME ASTMASTM AWSAWS National StandardsNational Standards ANSIANSI DINDIN JISJIS BISBIS ISOISOA ugust 15, 2007 August 15, 2007P N RaoP N Rao2323 EconomicsEconomics Standard sizesStandard sizes Large tolerancesLarge tolerances Breakeven pointsBreakeven points Cost estimatesCost estimatesAugust 15, 2007 August 15.

8 2007P N RaoP N Rao2424 Break even chartBreak even chartBreak even chart0204060801101001000 Production QuantityAverage cost per pieceOpen die forgingClosed die forging5 August 15, 2007 August 15, 2007P N RaoP N Rao2525 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 Good EngineeringGood Engineering AnalysisAnalysis DesignDesign Quality controlQuality controlAugust 15, 2007 August 15, 2007P N RaoP N Rao2626 August 15, 2007 August 15, 2007P N RaoP N Rao2727 Computational toolsComputational tools MathCadMathCad MATLABMATLAB TK SolverTK Solver Excel or Lotus 1 Excel or Lotus 1--22--33 CAD and FEACAD and FEAA ugust 15, 2007 August 15, 2007P N RaoP N Rao2828 Module 1-3aProperties of Rectangular Cross Sectionsb = = = = = = = : Design of Machine ElementsAugust 15, 2007 August 15, 2007P N RaoP N Rao2929 Courtesy: Design of Machine ElementsModule 1-3aProperties of Rectangular Cross Sectionsb = = = = 2in4Iy = = = 15, 2007 August 15, 2007P N RaoP N Rao3030 Problem using Finite Element Analysis (FEA)Start with 2 in dia; Max stress = 13,751 lower than the allowable 30,500 psi6 August 15, 2007 August 15, 2007P N RaoP N Rao3131 Problem using FEA ( )Next try in dia; Max stress = 32,599 higher than the allowable 30,500 psiAugust 15, 2007 August 15, 2007P N RaoP N Rao3232 Problem using FEA ( )Next try in dia.

9 Max stress = 25,635 lower than the allowable 30,500 psi - AcceptableAugust 15, 2007 August 15, 2007P N RaoP N Rao3333 Problem using FEA ( )For in dia; Max displacement = in Compare this to analytical solution of in, a 3% errorAugust 15, 2007 August 15, 2007P N RaoP N Rao3434 Why Calculating Moments is Why Calculating Moments is Important?Important? 15, 2007 August 15, 2007P N RaoP N Rao3535 August 15, 2007 August 15, 2007P N RaoP N Rao3636 7 August 15, 2007 August 15, 2007P N RaoP N Rao3737 August 15, 2007 August 15, 2007P N RaoP N Rao3838 August 15, 2007 August 15, 2007P N RaoP N Rao3939 August 15, 2007 August 15, 2007P N RaoP N Rao4040 August 15, 2007 August 15, 2007P N RaoP N Rao4141 August 15, 2007 August 15, 2007P N RaoP N Rao4242 8 August 15, 2007 August 15, 2007P N RaoP N Rao4343 August 15, 2007 August 15, 2007P N RaoP N Rao4444 August 15, 2007 August 15, 2007P N RaoP N Rao4545 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.

10 The Machine elements that would be The Machine elements that would be covered are gears, bearings, shafts, 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 materialsAugust 15, 2007 August 15, 2007P N RaoP N Rao4646 Text BookText Book WentzellWentzell, T. H. , T. H. -- Machine Machine Design , Delmar Design , Delmar Learning, 2004, Learning, 2004, ISBN ISBN 15, 2007 August 15, 2007P N RaoP N Rao4747 ReferenceReferenceBookBookss A. Esposito and A. Esposito and -- Machine Design , Machine Design , 22ndndEdition, Delmar Publishers, Albany, 1991, Edition, Delmar Publishers, Albany, 1991, 480 pages, 480 pages, ISBN 0 ISBN (No more in (No more in print)print) Mott Mott Machine Elements in Mechanical Machine Elements in Mechanical Design , 4 Design , 4ththEdition, Prentice Hall, New Jersey, Edition, Prentice Hall, New Jersey, 2004, ISBN 2004, ISBN AnselAnselC.