1、GD&T for BodyCourse content Introduction to GD&T 5 Step ProcessIntroduction What is GD&T How it affects Ford Motor CompanyWhat is GD&TGeometric Dimensioning and Tolerancing is a technical data base through which our Product Design and Manufacturing Organisations can talk to one another via Product D
2、ata,whether on paper or the computer graphics screenIt is the engineering product definition standard that geometrically describes design intent and provides the documentation base for the design of the quality and production system.It is a technique of communication between Product Engineering and
3、Manufacturing Engineering that promotes a uniform interpretation of the requirements for making a component.What is GD&TGDT provides the dimensions of the component and the tolerances in a language that eliminates confusing and inconsistent notes,datum lines,and location point identifications,and re
4、places them with standard symbols that refer to a universal code.This code describes the dimensions and tolerances of the component with reference to the relationships of the features to each other and their functional interfaces with mating parts,assemblies,etc.AuthorisationIn 1990 Ford World-wide
5、adopted the American National Standard for Dimensioning and Tolerancing,currently the ASME Y14.5M 1994.The authorisation for the above is documented in Standard D-1 of the Ford Engineering CAD and Drafting Standards and is referenced on all our released data.This information can be accessed via Ford
6、 intranet;www-wise.ford/non-regulatory.htmlThe above document also contains an electronic copy of the ASME Y14.5M 1994 Dimensioning and Tolerancing Standard.ApplicationThe application of GDT is initially the responsibility of the relevant Component Engineer,however teamwork is the key to the correct
7、 application through the component Core Team.This provides the opportunity for all disciplines to contribute their part of the total design package.It ensures part data will satisfy design intent as well as manufacturing and inspection requirements based on function,machine capability and available
8、technology.ApplicationIt provides the opportunity for proper Datum selection and has the potential to significantly reduce product changes,especially those changes following final product release.The Core Team should consist at a minimum of representatives from Product Engineering,Design Engineering
9、,Manufacturing Engineering,and Quality Engineering.More informationFord Engineering CAD and Drafting Standardswww-wise.ford/non-regulatory.htmlGDT Applicationcadmethods.fordHow GD&T Relates to FordThe correct application has the potential to;Influence Fit and Finish Reduce Reworks Increase Reliabili
10、ty Affects Assembly Process Reduce costThe 5 Step Process1 2 3 4 55 Step Process1 Utilise the new Design Concept2 Establishment of the Datum Reference Frame3 Establish GD&T Controls4 Establish Tolerances5 Final Approval of GD&T on Cad DataStep 1Utilise new design conceptUtilise new design conceptThe
11、 1st step involves making decisions at the basic design stage that will ultimately effect the design,manufacture and verification of the final component.This can only be successfully achieved by the relevant PD representative attending the Master Control Plan(MCP)Meetings.Master Control PlanWhat is
12、the purpose of the MCP meeting in relation to PDTo establish a common understanding for the verification process of the major panels,e.g.Bodyside,Hood,Deck Lid,Door,Roof,Underbody,etc.To obtain agreement at an early stage of the design for the datum reference frame,die approach,etc.Who attends the M
13、eetingPD and Manufacturing,i.e.Body Engineering,DCD,Stamping,Body and Assembly.Master Control PlanWhen should the Meeting take place.Initial design concept stage,knowing the components parameters such as size and function Current methods use;Past evidence,past experience,can sometimes hinder rather
14、than assist the new design conceptResult of meetingMay be documented in CAD,or paper formStep 2Establish Datum Reference FrameEstablish Datum Reference FrameAs part of the Master Control Plan(MCP)Process meeting,Body Engineering and Manufacturing agreed to the definition of the Datum Features and th
15、eir location.PD have Ownership of the Datum Features.Datum Reference Frame(Reference Pocket Guide,Page 8)Consists of a set of three mutually perpendicular planesThe reference frame exists in theory only and is not on the partSufficient datum features are used to position the part in relation to the
16、Datum Reference Frame.Datum FeaturesAn actual feature of the part used to stage/position the part in the equipment for purposes of relating its geometry to the Datum Reference Frame.Primary Datum PlaneAchieved by establishing a minimum of three Points to define a plane Primary Datum PlanePrimary Dat
17、um Plane should be Parallel to Die PlanePrimary Datum PlaneWhen Datum Target Areas defining Primary Datum Plane are not on one single planar surface,they must be controlled one to another using the PROFILE of a SURFACE geometric control.Supporting a panel only on the designated Datum Target Areas,ef
18、fectively removes 3 degrees of freedom,i.e.1 Linear and 2 Rotational.Datum Target AreasDatum Target Areas should wherever possible be planar and parallel to the die plane.Primary Datum PlaneDatum Target AreasDedicated Datum Target Areas makes both the part,and gauge/fixture more robust,cost effectiv
19、e and Improves repeatabilitySecondary Datum FeatureGenerally a Datum Feature of Size is used,i.e.Single circular Hole,positioned on a surface that is parallel to the Primary datum Plane,and is ultimately used as a four way locator.Secondary Datum FeatureControlled relative to the Primary Datum Plane
20、 using the Geometric control PERPENDICULARITY.Secondary Datum FeatureThe intersection of the derived axis of the feature perpendicular to the Primary Datum Plane,and the design side of the component is the local origin of all basic dimensions;0,0,0Supporting a panel on the designated Datum Target Ar
21、eas,and using the four way locator removes another 2 Linear degrees of freedom,resulting in all 3 Linear,and 2 Rotational degrees of freedom constrained.Tertiary Datum FeatureGenerally the width of a Slotted Feature of Size is used as a two way locator.Tertiary Datum FeatureTo eliminate tolerance of
22、 Datum Shift on one of the theoretical axis of the cartesian coordinate system,the orientation of the slot(length)should point to the axis of the Secondary Datum Feature.Tertiary Datum FeatureThe slotted features width must be positioned on a surface with the slot width axis parallel to the primary
23、datum plane,and controlled using the geometric control of POSITION and nominated as the Tertiary Datum Feature.Supporting a panel on the designated Datum Target Areas,using the four way,and two way locators removes all six degrees of freedom.Step 3Establish GD&T ControlsCommon Terms and DefinitionsR
24、eference Pocket GuidePage 2Material Conditions MMCMaximum Material Condition LMC Least Material Condition RFS Regardless of Feature Size Virtual ConditionMaximum Material ConditionThe condition in which a feature of size contains the maximum amount of material within the stated limits of size.The He
25、aviest PartMinimum Hole Diameter(10.0)Maximum Shaft Diameter(11.0)M10.0+1.0 0Least Material ConditionThe condition in which a feature of size contains the least amount of material within the stated limits of size.The Lightest partMaximum Hole Diameter(11.0)Minimum Shaft Diameter(10.0)To date no appl
26、ication in the Feature Control Frame for this symbol has been identified in Body Engineering.L10.0+1.0 0Regardless of Feature SizeThere is no symbol for Regardless of Feature Size.If a material modifier is not used then Regardless of Feature Size is assumed.The term used to indicate that a geometric
27、 tolerance or datum reference applies at any increment of size of the feature within its size toleranceRegardless of Feature Size is expensive to verify,and rarely reflects the relevant feature function,and therefore should not be used in a Body application without the agreement of the entire core t
28、eam.10.0+1.0 01.0Virtual Condition A constant Boundary generated by the collective effects of a size features specified MMC or LMC material condition and the geometric tolerance for that condition.The VIRTUAL CONDITION of features of mating parts must be matched,guaranteeing component features at th
29、eir worst case for assembly will always assemble.The Virtual condition envelope is the worst condition offered to the mating part.Virtual Condition(Shaft)Virtual condition(Shaft)=MMC+Tolerance zone value=12.0MMCLMCM1.010.0+1.0-0=10.0=11.0Virtual ConditionVirtual Condition(Hole)MMCLMCM1.010.0+1.0-0=1
30、1.0=10.0Virtual ConditionVirtual condition(Hole)=MMC-Tolerance zone value=9.0Geometric ControlsReference Pocket GuidePage 1Feature Control Frame(Reference Pocket Guide,page 3)MAB0.5MC MGeometric characteristic symbols,the tolerance value,Material Modifiers,and Datums of Reference,where applicable,ar
31、e combined in a feature control frame to express a geometric tolerance.GeometricCharacteristicSymbolMaterial Condition SymbolWhere applicableMAB0.5MC MToleranceTolerance ZoneShape where applicableDatum Reference LettersGeometric ControlsEach feature of the component must be controlled for SIZE,FORM,
32、ORIENTATION and LOCATION.In the American National Standard there are fourteen geometric controls.Body Engineering use just three;1PERPENDICULARITY2POSITION3PROFILEPERPENDICULARITYReference Pocket GuidePage 29PERPENDICULARITYThe main Application for PERPENDICULARITY within Body Engineering is to cont
33、rol a single Secondary Datum Feature of size(a hole)to be perpendicular to the Primary Datum Plane.Generally used only once within each component to define the secondary datum feature.Any other use of this control for other features would be an additional requirement,because PERPENDICULARITY does no
34、timply any location LMCThe Cylindrical Tolerance Zone diameter is dependant on the actual feature sizeBAPERPENDICULARITYMA019.0+0.1 0A cylindrical tolerance zone perpendicular to a datum plane within which the axis of a feature must lie.POSITIONReference Pocket GuidePage 33POSITION Definition Positi
35、on Tolerance Zones Zero at MMC Concept Boundary Concept Composite Tolerance Zones Projected Tolerance ZoneThe term to describe the perfect(theoretical exact)location of individual features in relationship with a datum reference or other feature(s).In general the POSITION control is used to locate un
36、iform features of size,e.g.holes,shafts,slots etc.POSITIONVerificationAs with all Features of Size;First to be verified is that the top and bottom limits of size have not been violated(Taylors Principle).A full form check at the MMC and a two pointed instrument check at the LMC.Secondly the features
37、“Position”must be verified.GD&T does not dictate the method of verification.The decision on the gauging technique employed is the responsibility of the core team.Position Tolerance ZonesPositional Tolerance Zone 1(Cylindrical)20.0+1.0 0To specify a Cylindrical Tolerance Zone,a diameter sign must pre
38、cede the tolerance value,followed by the material Modifier MMC unless Regardless of Feature Size is intended.M0.5A cylindrical zone within which the centre axis of a feature of size is permitted to vary from its true(theoretically exact)position.Positional Tolerance Zone 2(Non Cylindrical)A zone wit
39、hin which the centre,axis,of centre plane of a feature of size is permitted to vary from its true(theoretically exact)position.20.0+2.0 0The tolerance value is followed by the material Modifier MMC unless Regardless of size is intended.To specify a total width Tolerance Zone,No diameter symbol prece
40、des the tolerance value.M0.5BOUNDARYReference Pocket GuidePage 37BOUNDARYIn Body Engineering controlling the centre plane of a slotted feature is rarely a priority.As no Diameter symbol precedes the positional tolerance,a non cylindrical zone is inferred.BOUNDARYBOUNDARYBOUNDARYWhat we are intereste
41、d in is controlling the BOUNDARY of the feature.12.0 +2.0 02.0 M1.0 M5.0+1.0 0BOUNDARY 5.0 MMC Width of Hole-1.0 Positional Tolerance 4.0 Wide Boundary4BOUNDARY1.0 MBOUNDARY5.0+1.0 0Virtual Condition12.0 MMC Width of Hole-2.0 Positional Tolerance10.0 Wide Boundary102.0 M12.0 +2.0 0BOUNDARYNo portion
42、 of the slot surfaces are permitted to lie within the area described by the Virtual Condition when the part is positioned within the Datum Reference FrameThe POSITION control+BOUNDARY controls both Location and Orientation12.0 +2.0 02.0 MBOUNDARY1.0 MBOUNDARY5.0+1.0 0BOUNDARY12.0 +2.0 02.0 MBOUNDARY
43、2.0 MBOUNDARY5.0+1.0 0If the same Positional Tolerance value applies to both the Length and Width limits of size,then the Feature Control Frame is separated from the Limits of Size,and points directly to the slotted feature.BOUNDARY12.0 +2.0 02.0 MBOUNDARY5.0+1.0 0If the same Positional Tolerance va
44、lue applies to both the Length and Width limits of size,then the Feature Control Frame is separated from the Limits of Size,and points directly to the slotted feature.BOUNDARY The BOUNDARY note only applies to non cylindrical features.The POSITION control+BOUNDARY controls both Location and Orientat
45、ionIn this case the word BOUNDARY must be added below the FCF and the material Modifier MMC specified after the POSITION tolerance value.No diameter symbol precedes the tolerance value in the Feature Control FrameThe positional tolerance specified for the length may differ from that specified for th
46、e width.To SummariseZero at MMC conceptReference Pocket GuidePage 44Zero at MMC conceptThe Zero at MMC concept applies only to features whos sole function is CLEARANCEM10.0L11.51.02.59.010.310.510.811.21.31.51.82.29.09.09.09.09.0Actual Mating EnvelopeTolerance Zone(Dia)Virtual Condition10.0+1.5 0Wha
47、t is the smallest diameter hole permissible?Question?10AnswerExample of current specificationM1.0AMMBCExample of current specificationYesAnswerQuestion?If a feature of the part was measured,and the hole was found to be Dia 9.6,would this part be reject?M10.0L11.51.02.59.010.310.51.31.510.811.21.82.2
48、9.09.09.09.09.0Actual Mating EnvelopeTolerance Zone(Dia)Virtual Condition10.0+1.5 0M1.0AMMBCExample of current specificationBut,would the rejected part be functional?Question?AnswerTo make the part acceptable we would need to change the data specification.10.0+1.5 0If the part meets the functional g
49、auge requirements,we know the part is functional.The part has been rejected because of feature size alone.Therefore it must have been manufactured to a tighter specification than that stated on the data.M1.0AMMBCExample of current specificationWhat needs to change?Question?The specification for the
50、hole needs to change,by adopting the“Zero at MMC”conceptAnswerM10.0L11.51.02.59.010.310.51.31.510.811.21.82.29.09.09.09.09.0Actual Mating EnvelopeTolerance Zone(Dia)Virtual Condition10.0+1.5 0M1.0AMMBCZero at MMC concept+2.5 09.0Example:To comply with the“Zero at MMC”concept for clearance holes;The
