2103-314Mechanical System Design IIBy Asst. Prof. Dr. Kaukeart Boonchukosol

The Product Design Process

Design Process; the basic moduleSpecificInformationDesign OperationGeneral InformationOutcomeEvaluationFeedback loopNoYesGo toThe NextStep

Example of Design OperationExploring the alternating systemFormulating the mathematical modelSpecifying specific partsSelecting a material

Some kind of InformationManufacturers catalogueHandbook dataNational standardTechnical paperExperience

Problem Solving MethodologyDefinition of the problemGathering of informationGeneration of alternative solutionsEvaluation of alternativesCommunication of the result

Definition of the Problem

Gathering InformationWhat do I need to find out?Where can I find it and how can I get it?How credible and accurate is the information?How should the information be interpreted for my specific need?When do I have enough information?What decision result from the information?

Detailed Description of Design Process

Morphology of DesignPhase I:Conceptual DesignPhase II:Embodiment DesignPhase III:Detail DesignPhase IV:Planning for ManufacturePhase V:Planning for DistributionPhase VI:Planning for UsePhase VII:Planning for Retirement of the Product

Phase I: Conceptual DesignIdentification of customer needsProblem definitionGathering informationConceptualizationConcept selectionRefinement of the PDSDesign review

Phase II: Embodiment DesignProduct architectureConfiguration design of parts and componentsParametric design of parts and components

Conceptual DesignEmbodiment Design

Phase IV: Planning for ManufactureDesigning specialized tools and fixturesSpecifying the production plant that will be usedPlanning the work schedules and inventory controlPlanning the quality assurance systemEstablishing the standard time and labor costs for each operationEstablishing the system of information flow necessary to control the manufacturing operation

Need Identification

Types of Design ProjectVariation of an existing productImprovement of an existing productDevelopment of a new product for a low-volume production runDevelopment of a new product for mass productionOne-of-a-kind design

How to Gathering Information from CustomerInterview with customerFocus groupCustomer surveysCustomer complaints

Levels of Customer RequirementsExpecters: the basic attribute that one would expect to see in the productSpokens: the specific features that the customers say they want in the productUnspokens: the product attributes the customer does not generally talk about, but are nevertheless are important to him or herExciters or delighters: the features that make the product unique and distinguish it from the competition

Quality Function DeploymentQFD is a planning and problem-solving tool that is finding growing acceptance for translating customer requirements into the engineering characteristics of a product.Group decision-making activityGraphical representation using a diagram called House of Quality

Engineering Characteristics

Relationship Matrix

Customer Requirement

What

Competitive assessment

Absolute Importance

Relative Importance

Technical Competitive Assessment

Technical Difficulty

Target Value

Correlation Matrix

Importance Rating

Engineering Characteristics

Customer Requirements

Target Values

Engineering Characteristics

Target Values

Customer Requirements

Engineering Characteristics

Target Values

Customer Requirements

ProcessParameters

PartCharacteristics

ProductPlanning

PartDeployment

ManufacturingPlanning

ProductionPlanning

Concept Generation and Evaluation

Problem decompositionExplore fore ideasExplore systematicallyMorphological chartExternal to teamInternal to teamBrain-stormingAbsolute criteriaGo-no-go screeningRelative criteriaPugh concept selectionDecision matrixAnalytical hierarchy processBest conceptConcept GenerationEvaluation

CreativityDevelop a creative attitudeUnlock your imaginationBe persistentDevelop an open mindSuspend your judgmentSet problem boundary

Vertical and lateral thinking

InventionInvention is something novel and useful, being the result of creative thought.Classified into 7 categoriesThe simple or multiple combinationLabor-saving conceptDirect solution to a problemAdaptation of an old principle to an old problem to achieve a new resultApplication of a new principle to an old problemApplication of a new principle to a new useSerendipity

Psychological View of Problem SolvingFour-stage modelPreparation: The element of the problem are examined and their relations are studied. Incubation: You sleep on the problem.Inspiration: A solution or a path toward the solution suddenly emerges.Verification: The inspired solution is checked against the desired result.

Creativity Methods

Mental BlockPerceptual blocksStereotypingInformation overloadLimiting the problem unnecessarilyCultural blocksEnvironmental blocksEmotional blocksFear of risk takingUnease with chaosAdopting a judgmental attitudeUnable or unwilling to incubateIntellectual blocks

BrainstormingFour fundamental brainstorming principlesCriticism is not allowed.Ideas brought forth should be picked up by other people present.Participants should divulge all ideas entering their minds without any constraint.A key objective is to provide as many ideas as possible within a relatively short time.

Stimulation of ideasCombination: What new ideas can arise from combining proposes and functions?Substitution: What else? Who else? What other place? What other time?Modification: What to add? What to subtract? Change color, material, motion, shape?Elimination: Is it necessary?Reverse: What would happen if we move it backward? Turn it upside down? Inside out?Other use: Is there a new way to use it?

Creative Idea Evaluation

Theory of Inventive Problem Solving (TRIZ)TRIZ is Russian acronymDeveloped by Genrich Altshuller and his coworkers in Russia, since 1946About 1.5 million patents were studied, and discovered that only a few dozen inventive principles were used for solving the problems

Five levels of problem solutionsLevel 1:Routine design solutions arrived at methods well known in the specialty area. 30%Level 2:Minor correction to an existing system by methods know in the industry. 45%Level 3:Fundamental improvement to an existing system which resolve contradictions within the industry. 20%Level 4:Solution based on application of new scientific principle to perform the primary function of the design. 4%Level 5:Pioneering inventions based on rare scientific discovery. 1%TRIZ is aimed at improving design concept at levels 3 and 4

Engineering Parameters usedWeight of moving objectWeight of nonmoving objectLength of moving objectLength of nonmoving objectArea of moving objectArea of nonmoving objectVolume of moving objectVolume of nonmoving objectSpeedForceTension, PressureShapeStability of objectStrengthDurability of moving objectDurability of nonmoving objectTemperatureBrightnessEnergy spent by moving objectEnergy spent by nonmoving object

Engineering Parameters usedPowerWaste of energyWaste of substanceLoss of informationWaste of timeAmount of substanceReliabilityAccuracy of measurementAccuracy of manufacturingHarmful factors acting on objectHarmful side effectsManufacturabilityConvenience of useRepairabilityAdaptabilityComplexity of deviceComplexity of controlLevel of automationProducibility

The Inventive PrinciplesSegmentationExtractionLocal qualityAsymmetryCombiningUniversalityNestingCounterweightPrior counteractionPrior actionCushion in advanceEquipotentialityInversionSpheroidalityDynamicityPartial or overdone action

The Inventive PrinciplesMoving to a new dimensionMechanical vibrationPeriodic actionContinuity of useful actionRushing throughConvert harm into benefitFeedbackMediatorSelf-serviceCopyingAn inexpensive short-lived object instead of an expensive durable oneReplacement of a mechanical system

The Inventive PrinciplesUse of a pneumatic or hydraulic constructionFlexible film or thin membranesUse of porous materialChange the colorHomogeneityRejecting and regenerating partTransformation of physical and chemical states of an objectPhase transitionThermal expansionUse strong oxidizersInert environmentComposite materials

ExampleA metal pipe was used to pneumatically transport plastic pellets. A change in the process required that metal powder now be used with the pipe instead of plastic. The harder metal powder causes erosion of the inside of the pipe at the elbow where the metal particles turn 90o. Conventional solutions to this problem might include reinforcing the inside of the elbow with an abrasion-resistant hard-facing alloy, providing for an elbow that could be easily replaced after it has corroded, or redesigning the shape of the elbow. However, all of these solutions require significantly extra costs, so a more creative solution was sought.

SolutionWhat is the main function of our elbow?To change the direction of flow of metal particleWhat we want to improve?Increase the delivered particles speed (parameter 9)Reduce the energy required (parameter 19)

SolutionImproving speedImproving energy

SolutionBy counting the frequency of inventive principles suggested, the Principle 28 is the most cited (4 times).The others Principles cited are 13(3), 15(3), and 38(3).Then Principle 28 shall be firstly considered.

SolutionThe full description of Principle 28 is28 Replacement of a mechanical systemReplace a mechanical system by an optical, acoustical, or odor system.Use an electrical, magnetic, or electromagnetic field for interaction with the object.Replace fields. Example: (1) stationary field change to rotating field; (2) fixed fields become fields that change in time; (3) random fields change to structural one.Use a field in conjunction with ferromagnetic particles.Then possible solution may be placing a magnet at the elbow to attract and hold a thin layer of powder that will serve to absorb the energy of particles navigating the 90o bend, thereby preventing erosion of the inside wall of the elbow.

Algorithm of Inventive Problem SolvingFormulate initialphysical contradictionOriginal problemstatementFormulate technicalcontradictionAnalysis of conflictdomain & resourceFormulate idealsolutionFormulate maincontradictionMethod of eliminationofPhysical contradictionReformulation of problem statementNO SOLUTIONSOLUTIONKnowledge baseof effects

Conceptual DecompositionIt is common tactic to decompose the problem into smaller parts.Connections of elements in terms of structure and function within the blocks shall be stronger than those between the blocks.There are two main approachesDecomposition in the physical domainFunctional decomposition

Decomposition in the Physical DomainDecompose the product into subassemblies and components that are essential for the all functioning of the product.Need to understand the interactions and connections that each of these subassemblies and elements has with each other. The connection can be physical, energy, or force connection.

Functional DecompositionFunction is in the nature of a physical behavior or actionFunction tells us that what the product must do.The process of functional decomposition describes the design problem in term of a flow of energy, material, and information.

Functionality of some common device

Generating Design Concept

Morphological ChartProposed by Zwicky Steps to followArrange the functions and subfunctions in logical orderList for each subfunction howCombine concepts

Example CD case

Example CD case

Example CD caseThe combinations of these concepts generate many possible solutions for the design. There are 162,000 combinations in this design.

Assume that 5 concepts are drawn from the previous chart.Concept 1: Conventional square box (1), with the incline plane lock (2) and a slide-out matchbox (3) for a hinge. The CD is secured with a conventional rosetta (1) while the leaflet is secured with tab (1).Concept 2:A streamline curved box to fit the hand (3), with a friction lock (2) and a conventional hinge (3). The CD is secured in padded elastomer cradle (3) and the CD case are designed to stack flat (2).Concept 3:The box is grooved to the shape of the finger (2), with a magnetic lock (3) and conventional hinges (1). A new lift/lock secures the CD (2). The leaflet fits in a slot in the top of the case (2).Concept 4:A standard square box (1) with magnetic lock (3) and conventional hinges (1). The CD is secured with a padded cradle (3), while the leaflet is secured with Velcro straps (3).Concept 5: A curved box (3) with inclined plane lock (2), with a slide-out matchbox (3). The CD is held by a rosetta (1) and the leaflet fits into a slot (2). The cases are designed to stack (2).

Axiomatic DesignDeveloped by Professor Nam Suh and his colleagues at MITFocus around 2 design axiomsAxiom 1:The independent axiomMaintain the independence of functional requirements (FRs).Axiom 2:The information axiomMinimize the information content.

Mapping process of Suhs conceptFunctionalRequirementsFR1FR2FR3DesignParametersDP1DP2DP3DP4

Hierarchy of FRs for a metal cutting latheMetalremovaldevicePowersupplyWorkpiecerotationsourceSpeed-changingdeviceWorkpiecesupport andtoolholderSupportstructureToolpositionerSupportstructurePositionerToolholderToolholderRotationstopLongitudinalclamp

Hierarchy of lathe design in physical domainLatheMotordriveHeadstockGearboxTailstockBedCarriageFrameFeedscrewSpindleassemblyBoltHandleClampTaperedborePin

7 corollaries are derived from the 2 axioms mentioned before

Evaluation

Comparison Based on Absolute CriteriaEvaluation based on judgment of feasibility of the design. Concept should be into one of three categories:It is not feasible? Next question is Why is it not feasible?It is conditional it might work if something else happen?Looks as if it will work, then it seems worth to work further.

Comparison Based on Absolute CriteriaEvaluation based on assessment of technology readiness. The technology used in the design must be mature enough not to need any additional research. Their indicators areCan the technology be manufactured with known processes?Are the critical parameters that control the function identified?Are the safe operating latitude and sensitivity of the parameters known?Have the failure modes been identified?Does hardware exist that demonstrates positive answers to the above four questions?

Comparison Based on Absolute CriteriaEvaluation based on go-no-go screening of the customer requirements.After a design concept has passed filters 1 and 2, the emphasis shifts to establishing whether it meets the customer requirements framed in the QFDEach requirement must be transformed into a question to be addressed to each concept.The questions should be answerable as either yes (go), maybe (go), or no (no-go).The emphasis is not on a detail examination but on eliminating any design concepts that clearly not able to meet an important customer requirement.

Pughs Concept Selection MethodChoose the criteria by which the concepts will be evaluatedFormulate the decision matrixClarify the design conceptChoose the datum conceptRun the matrixEvaluate the ratingEstablish a new datum and rerun the matrixPlan further workSecond working session

Example of CD case

Measurement ScalesPairwise Comparison methodAssume 5 design objectives to be compared

Weighted Decision Matrix

Example of Steel Crane HookA heavy steel crane hook, for use in supporting ladles filled with molten steel as they are transported through the steel mill, is being designed. Three concepts have been proposed: (1) built-up from steel plates, welded together; (2) built-up from steel plates, riveted together; (3) a monolithic cast-steel hook.The design criteria investigated are (1) material cost, (2) manufacturing cost, (3) time to produce another if one fails. (4) durability, (5) reliability, (6) reparability.Crane hookO1=1.0CostO11=0.6Quality in serviceO12=0.4Matl costO111=0.3Mfg. CostO112=0.5ReparabilityO113=0.2DurabilityO121=0.6ReliabilityO122=0.3Time to produceO123=0.1Oxyz here are weighted factors

Weighted Decision Matrix for a steel hookMag. = MagnitudeExp. = ExperienceExcell. = Excellent

Design criterionWeight factorsUnitBuilt-up plates weldedBuilt-up plates rivetedCast steel hookMag.ScoreRatingMag.ScoreRatingMag.ScoreRatingMaterial cost0.18/lb6081.446081.445091.62Mfg. cost0.60$250072.1220092.70300041.20Reparability0.12ExpGood70.84Excell.91.08Fair50.60Durability0.24Exp.High81.92High81.92Good61.44Reliability0.12Exp.Good70.84Excell.91.08Fair50.60Time to produce0.04Hr.4070.282590.366050.207.428.585.66

Analytical Hierarchy Process, AHPMulticriteria decision process introduced by SaatySuited to hierarchically structural systemCan work with both numerical and intangible and subjective factorsUse pairwise comparison of the alternatives

Example of crane hook design using AHP approach Crane hook designMaterialcostManufacturingcostReliability

Durability

Reparability

Time toproduceBuilt-up plates,welded steelBuilt-up steelplates, rivetedCast steelHierarchical structure of a crane hook design

Saatys fundamental scale for pairwise comparison

Square matrix to determine weighting factors

Normalized values for square matrix

Now construct the decision matrix using previous values given.

Built-up welded platesBuilt-up riveted platesCastManufacturing cost250022003000$/crane hook400454333Reciprocal x 10-60.340.380.28Fraction of total

Built-up welded platesBuilt-up riveted platesCastReparability6101Ranking0.350.590.06Fraction of total

DurabilityWelded plateRiveted plateCastTotalRating (Avg.)Welded plate1.000.231/30.223.000.330.780.26Riveted plate3.000.691.000.655.000.561.900.63Cast1/30.081/50.131.000.110.320.11Total4.331.001.531.009.001.003.001.00

Final Decision Matrix for the Crane Hook ProblemThen riveted plate is the most appropriate alternative for this design

Design criterionWeight factorWelded plateRiveted plateCastWelded plateRiveted plateCastMaterial cost0.140.310.310.380.0430.0430.053Manufacturing cost0.390.340.380.280.1330.1480.109Reparability0.060.350.590.060.0210.0350.004Durability0.250.260.630.110.0650.1570.027Reliability0.120.330.430.240.0400.0520.029Time to produce0.030.310.490.200.0080.0130.005Total1.000.310.450.23