Presentation on theme: "Product specification Dimensioning and tolerancing"— Presentation transcript:
1 Product specification Dimensioning and tolerancing It is impossible to make a perfect component so when we design a part we specify the acceptable range of features that make-up the part.
2 Chapter 2 Suppliment DIMENSIONS, TOLERANCES, AND SURFACES Dimensions, Tolerances, and Related AttributesSurfacesASME Y14.5 Form GeometryEffect of Manufacturing ProcessesIE 316 Manufacturing Engineering I - Processes
3 THE DESIGN PROCESS Product Engineering How can this be accomplished?1. Clarification of the task2. Conceptual design3. Embodiment design4. Detailed designDesign ProcessOff-road bicycle that ...1. Conceptualization2. Synthesis3. Analysis4. Evaluation5. RepresentationFunctional requirement -> DesignSteps 1 & 2 Select material and properties, begin geometricmodeling (needs creativity, sketch is sufficient)mathematical, engineering analysissimulation, cost, physical modelformal drawing or modeling
4 DESIGN REPRESENTATION EngineeringRepresentationManufac-turing• Verbal• Sketch• Multi-view orthographic drawing (drafting)• CAD drafting• CAD 3D & surface model• Solid model• Feature based designRequirement of the representation method• precisely convey the design concept• easy to use
12 TOLERANCE STACKING1. Check that the tolerance & dimension specifications arereasonable - for assembly.2. Check there is no over or under specification."TOLERANCE IS ALWAYS ADDITIVE" why?1.20 '±0.010.80 '±0.011.00 '±0.01?What is the expected dimension and tolerances?d = = 3.00t = ± ( ) = ± 0.03
13 TOLERANCE STACKING (ii) ?0.80 '±0.011.20 '±0.013.00 '±0.01What is the expected dimension and tolerances?d = = 1.00t = ± ( ) = ± 0.03
14 TOLERANCE STACKING (iii) x1.20 '±0.01?0.80 '±0.013.00 '±0.01Maximum x length = = 1.03Minimum x length = = 0.97Therefore x = ± 0.03
15 TOLERANCE GRAPH d,t d,t d,t A B C D E d,t G(N,d,t) N: a set of reference lines, sequenced nodesd: a set of dimensions, arcst: a set of tolerances, arcsd : dimension between references i & jt : tolerance between references i & jijijReference i is in front of reference j in the sequence.
16 EXAMPLE TOLERANCE GRAPH d,td,td,tA B C D Ed,tdifferent propertiesbetween d & t
17 OVER SPECIFICATIONIf one or more cycles can be detected in the graph, we say that the dimension and tolerance are over specified.d1d2A B Cd1,t1d2,t2d3Redundant dimensiond3,t3ABCt1t2A B Ct3Over constraining tolerance(impossible to satisfy) why?
18 UNDER SPECIFICATIONWhen one or more nodes are disconnected from the graph, thedimension or tolerance is under specified.d1d2A B C D Ed3ABCDEC Dis disconnected from therest of the graph.No way to find
20 TOLERANCE ANALYSIS For two or three dimensional tolerance analysis: i. Only dimensional toleranceDo one dimension at a time.Decompose into X,Y,Z, three one dimensional problems.ii. with geometric tolerance? Don't have a good solution yet. Use simulation?diameter&toleranceA circular tolerance zone, the size is influencedby the diameter of the hole. The shape of thehole is also defined by a geometric tolerance.trueposition
21 3-D GEOMETRIC TOLERANCE PROBLEMS datum surfacedatumsurface± tReferenceframeperpendicularity
22 TOLERANCE ASSIGNMENT Tolerance is money • Specify as large a tolerance as possible as long as functional and assembly requirements can be satisfied.(ref. Tuguchi, ElSayed, Hsiang, Quality Engineering in Production Systems, McGraw Hill, 1989.)QualityfunctionCostcost+t-td(nominaldimension)Tolerance valueQuality cost
23 REASON OF HAVING TOLERANCE • No manufacturing process is perfect.• Nominal dimension (the "d" value) can not be achieved exactly.• Without tolerance we lose the control and as a consequence cause functional or assembly failure.
24 EFFECTS OF TOLERANCE (I) 1. Functional constraintse.g.flow rated ± tDiameter of the tube affects the flow. What is the allowedflow rate variation (tolerance)?
25 EFFECTS OF TOLERANCE (II) 2. Assembly constraintse.g. peg-in-a-holedpHow to maintain the clearance?dhCompound fittingThe dimension of each segment affects others.
26 RELATION BETWEEN PRODUCT & PROCESS TOLERANCES Machine uses the locators as the reference. The distances from the machine coordinate system to the locators are known.The machining tolerance is measured from the locators.• In order to achieve the 0.01 tolerances, the process tolerance must be or better.• When multiple setups are used, the setup error need to be taken into consideration.A.1tolerancesDesign specificationsSetuplocators.5.5.5Process tolerance
27 TOLERANCE CHARTINGA method to allocate process tolerance and verify that the process sequence and machine selection can satisfy the design tolerance.Not shown areprocess toleranceassignment andbalanceblue printOperationsequenceproduced tolerances:process tol of 10 + process tol of 12process tol of 20 + process tol 22process tol of 22 + setup tol
28 PROBLEMS WITH DIMENSIONAL TOLERANCE ALONE As designed:1..16..1As manufactured:1.1Will you accept the partat right?Problem is the control ofstraightness.How to eliminate theambiguity?1.11.16.
29 GEOMETRIC TOLERANCESANSI Y14.5M-1977 GD&T (ISO 1101, geometric tolerancing;ISO positional tolerancing; ISO 5459 datums;and others), ASME YFORMstraightnessflatnessCircularitycylindricityORIENTATIONperpendicularityangularityparallelismSquarenessroundnessLOCATIONconcentricitytrue positionsymmetryRUNOUTcircular runouttotal runoutPROFILEprofileprofile of a line
30 DATUM & FEATURE CONTROL FRAME Datum: a reference plane, point, line, axis where usually a plane where you can base your measurement.Symbol:Even a hole pattern can be used as datum.Feature: specific component portions of a part and may include one or more surfaces such as holes, faces, screw threads, profiles, or slots.Feature Control Frame:Adatum// M Amodifiersymboltolerance value
31 MODIFIERS Maximum material condition MMC assembly Regardless of feature size RFS (implied unless specified)Least material condition LMC less frequently usedProjected tolerance zoneDiametrical tolerance zoneT Tangent planeF Free statemaintain critical wall thickness or critical location of features.MMC, RFS, LMCMMC, RFSRFS
32 SOME TERMS MMC : Maximum Material Condition Smallest hole or largest peg (more material left on the part)LMC : Least Material ConditionLargest hole or smallest peg (less material left on the part)Virtual condition:Collective effect of all tolerances specified on a feature.Datum target points:Specify on the drawing exactly where the datum contact points should be located. Three for primary datum, two for secondary datum and one or tertiary datum.
33 DATUM REFERENCE FRAME.Three perfect planes used to locate the imperfect part.a. Three point contact on the primary planeb. two point contact on the secondary planec. one point contact on the tertiary planePrimaryTertiarySecondarySecondaryO M A B CprimaryTertiaryCBA
34 STRAIGHTNESS Tolerance zone between two straightness lines. . 1 .1Value must be smaller than the size tolerance.1.000 '±0.002MeasurederrorŠ.1.11.000 '±0.002.1DesignMeaning
35 Dimensions and Tolerances In addition to mechanical and physical properties, other factors that determine the performance of a manufactured product include:Dimensions - linear or angular sizes of a component specified on the part drawingTolerances- allowable variations from the specified part dimensions that are permitted in manufacturingIE 316 Manufacturing Engineering I - Processes
36 SurfacesNominal surface - intended surface contour of part, defined by lines in the engineering drawingThe nominal surfaces appear as absolutely straight lines, ideal circles, round holes, and other edges and surfaces that are geometrically perfectActual surfaces of a part are determined by the manufacturing processes used to make itThe variety of manufacturing processes result in wide variations in surface characteristicsIE 316 Manufacturing Engineering I - Processes
37 Why Surfaces are Important Aesthetic reasonsSurfaces affect safetyFriction and wear depend on surface characteristicsSurfaces affect mechanical and physical propertiesAssembly of parts is affected by their surfacesSmooth surfaces make better electrical contactsIE 316 Manufacturing Engineering I - Processes
38 Surface Technology Concerned with: Defining the characteristics of a surfaceSurface textureSurface integrityRelationship between manufacturing processes and characteristics of resulting surfaceIE 316 Manufacturing Engineering I - Processes
39 Figure 5.2 ‑ A magnified cross‑section of a typical metallic part surface IE 316 Manufacturing Engineering I - Processes
40 Surface Texture The topography and geometric features of the surface When highly magnified, the surface is anything but straight and smooth. It has roughness, waviness, and flawsIt also possesses a pattern and/or direction resulting from the mechanical process that produced itIE 316 Manufacturing Engineering I - Processes
41 Surface IntegrityConcerned with the definition, specification, and control of the surface layers of a material (most commonly metals) in manufacturing and subsequent performance in serviceManufacturing processes involve energy which alters the part surfaceThe altered layer may result from work hardening (mechanical energy), or heating (thermal energy), chemical treatment, or even electrical energySurface integrity includes surface texture as well as the altered layer beneathIE 316 Manufacturing Engineering I - Processes
42 Figure 5.3 ‑ Surface texture features Repetitive and/or random deviations from the nominal surface of an objectFigure 5.3 ‑ Surface texture featuresIE 316 Manufacturing Engineering I - Processes
43 Four Elements of Surface Texture Roughness - small, finely‑spaced deviations from nominal surface determined by material characteristics and process that formed the surfaceWaviness - deviations of much larger spacing; they occur due to work deflection, vibration, heat treatment, and similar factorsRoughness is superimposed on wavinessIE 316 Manufacturing Engineering I - Processes
44 Figure 5.4 ‑ Possible lays of a surface 3. Lay - predominant direction or pattern of the surface textureFigure 5.4 ‑ Possible lays of a surfaceIE 316 Manufacturing Engineering I - Processes
45 4. Flaws - irregularities that occur occasionally on the surface Includes cracks, scratches, inclusions, and similar defects in the surfaceAlthough some flaws relate to surface texture, they also affect surface integrityIE 316 Manufacturing Engineering I - Processes
46 Surface Roughness and Surface Finish Surface roughness - a measurable characteristic based on roughness deviationsSurface finish - a more subjective term denoting smoothness and general quality of a surfaceIn popular usage, surface finish is often used as a synonym for surface roughnessBoth terms are within the scope of surface textureIE 316 Manufacturing Engineering I - Processes
47 Surface RoughnessAverage of vertical deviations from nominal surface over a specified surface lengthFigure 5.5 ‑ Deviations from nominal surface used in the two definitions of surface roughnessIE 316 Manufacturing Engineering I - Processes
48 Surface Roughness Equation Arithmetic average (AA) is generally used, based on absolute values of deviations, and is referred to as average roughnesswhere Ra = average roughness; y = vertical deviation from nominal surface (absolute value); and Lm = specified distance over which the surface deviations are measuredIE 316 Manufacturing Engineering I - Processes
49 An Alternative Surface Roughness Equation Approximation of previous equation is perhaps easier to comprehend:where Ra has the same meaning as above; yi = vertical deviations (absolute value) identified by subscript i; and n = number of deviations included in LmIE 316 Manufacturing Engineering I - Processes
50 Cutoff LengthA problem with the Ra computation is that waviness may get includedTo deal with this problem, a parameter called the cutoff length is used as a filter to separate waviness from roughness deviationsCutoff length is a sampling distance along the surface. A sampling distance shorter than the waviness width eliminates waviness deviations and only includes roughness deviationsIE 316 Manufacturing Engineering I - Processes
51 Figure 5.6 ‑ Surface texture symbols in engineering drawings: the symbol, and (b) symbol with identification labelsValues of Ra are given in microinches; units for other measures are given in inchesDesigners do not always specify all of the parameters on engineering drawingsIE 316 Manufacturing Engineering I - Processes
52 TRUE POSITION T o l e r a n c e z o n e Dimensional tolerance . 2 2 1 .221..11.2.1O.8.2Hole center tolerance zoneO.1MABTrue positiontoleranceTolerancezone.1dia1.BA1.2
53 HOLE TOLERANCE ZONE Tolerance zone for dimensional toleranced hole is not a circle. This causes some assemblyproblems.For a hole using true position tolerancethe tolerance zone is a circular zone.
54 TOLERANCE VALUE MODIFICATION 1..2O.1MABProduced True Pos tolhole sizeout of diametric toleranceout of diametric tolerance1.M L SB1.2MMCLMCAThe default modifier fortrue position is MMC.For M the allowable tolerance = specified tolerance + (produced holesize - MMC hole size)
55 MMC HOLE,Given the same peg (MMC peg), when the produced hole size is greater than the MMC hole, the hole axis true position tolerance zone can be enlarged by the amount of difference between the produced hole size and the MMC hole size.
56 PROJECTED TOLERANCE ZONE Applied for threaded holes or press fit holes to ensure interchangeabilitybetween parts. The height of the projected tolerance zone is the thicknessof the mating part..375-16UNC-2BO.1MABC.25p
57 Surface IntegritySurface texture alone does not completely describe a surfaceThere may be metallurgical changes in the altered layer beneath the surface that can have a significant effect on a material's mechanical propertiesSurface integrity is the study and control of this subsurface layer and the changes in it that occur during processing which may influence the performance of the finished part or productIE 316 Manufacturing Engineering I - Processes
58 Surface Changes Caused by Processing Surface changes are caused by the application of various forms of energy during processingExample: Mechanical energy is the most common form in manufacturing. Processes include metal forming (e.g., forging, extrusion), pressworking, and machiningAlthough primary function is to change geometry of workpart, mechanical energy can also cause residual stresses, work hardening, and cracks in the surface layersIE 316 Manufacturing Engineering I - Processes
59 Surface Changes Caused by Mechanical Energy Residual stresses in subsurface layerCracks ‑ microscopic and macroscopicLaps, folds, or seamsVoids or inclusions introduced mechanicallyHardness variations (e.g., work hardening)IE 316 Manufacturing Engineering I - Processes
60 Surface Changes Caused by Thermal Energy Metallurgical changes (recrystallization, grain size changes, phase changes at surface)Redeposited or resolidified material (e.g., welding or casting)Heat‑affected zone in welding (includes some of the metallurgical changes listed above)Hardness changesIE 316 Manufacturing Engineering I - Processes
61 Surface Changes Caused by Chemical Energy Intergranular attackChemical contaminationAbsorption of certain elements such as H and Cl in metal surfaceCorrosion, pitting, and etchingDissolving of microconstituentsAlloy depletion and resulting hardness changesIE 316 Manufacturing Engineering I - Processes
62 Surface Changes Caused by Electrical Energy Changes in conductivity and/or magnetismCraters resulting from short circuits during certain electrical processing techniquesIE 316 Manufacturing Engineering I - Processes
63 Tolerances and Manufacturing Processes Some manufacturing processes are inherently more accurate than othersExamples:Most machining processes are quite accurate, capable of tolerances = 0.05 mm ( in.) or betterSand castings are generally inaccurate, and tolerances of 10 to 20 times those used for machined parts must be specifiedIE 316 Manufacturing Engineering I - Processes
64 Surfaces and Manufacturing Processes Some processes are inherently capable of producing better surfaces than othersIn general, processing cost increases with improvement in surface finish because additional operations and more time are usually required to obtain increasingly better surfacesProcesses noted for providing superior finishes include honing, lapping, polishing, and superfinishingIE 316 Manufacturing Engineering I - Processes