Position and Profile v2 Embedded

8/2/2019 Position and Profile v2 Embedded

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Def in i t i on o f Posi t i on and Pr o f i l e

Position Profile of a Surface

Profile of a line

[x ] [g ]

[u ]


2/11

Advan t ages o f Posi t i on an d Pr o f i l e

Position

1) Accurately represent Design Intent

2) Optimally use available tolerance

-Feature Bonus

3) More reliable PASS/FAIL analysis

-less likely to reject a good part oraccept a bad part

Profile

1) Accurately represent Design Intent

2) Optimally use available tolerance

-Datum Bonus

3) Eliminates measurement errorcaused by feature calculation

-i.e. small arc radii

4) More reliable PASS/FAIL analysis

-less likely to reject a good part oraccept a bad part

[x ] [g ]


3/11

Cr i t i ca l Com pon en t s t o Accu r a t e

Measu r em en t o f Posi t i on and Pr o f i l e( a l l GD& T)

Position

1) Datum Simulation

2) Bonus Calculation Feature Bonus

Datum Bonus

3) Feature calculation Actual Mating Envelope

(AME)

Profile

1) Datum Simulation

2) Bonus Calculation Datum Bonus

3) Fitting Remaining Degrees of

Freedom (if any) afterDatum constraints

[x ] [g ]


4/11

Co m p on en t 1 - Dat u m Sim u lat i on

( Posi t i on and Pro f i l e ) Planar Datum

Need to fit to True Geometric Counter-part (TGC) Either by using a surface plate or an algorithm that simulates the ASME fit

As a primary datum, constrains 3 degrees of freedom

2 rotational, 1 translation

Cylindrical Datum Need to fit to True Geometric Counter-part (TGC)

By creating a max-inscribed cylinder on a hole, or a min-circumscribed cylinderon a stud (if a primary datum @ RFS)

Bonus allowed As a primary datum, constrains 4 degrees of freedom (DOF)


As a secondary datum, datum must be simulated at nominal orientationto primary datum

If perp to primary, constrains 2 additional DOF, otherwise 3

Conical Datum Need to fit to True Geometric Counter-part (TGC) As a primary datum, constrains 5 degrees of freedom



5/11

Co m p on en t 1 - Dat u m Sim u lat i on

( Posi t i on and Pro f i l e )

Compound Datums Need to fit to True Geometric Counterpart

Most common

2 inline cylinders, as a primary datum

Multiple cylinders (pattern), as a secondary datum

Allows for Bonus if at MMC All features of a compound datum are equal

i.e. cannot zero on one and rotate to another


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Co m p o n e n t 2 - Bo n u s Cal cu l at i on

( Posi t i on and Pro f i l e )

Position Bonus on a Feature As feature (hole, stud, or slot) departs from its Maximum

Material Condition (MMC), feature receives position bonustolerance

Calculated based on Actual Mating Size (AMS)

Bonus on Datums Only allowed on Datums that are features of size

Bonus is calculated the same as with position, but not added totolerance

Calculated bonus is an allowable part shift from Datum

Part shift must be used at the same time for all simultaneouscallouts, not an individual shift per callout

[x ]a .005m]A]

[x ]a .005m]A ]B m] [g ].005]A ]B m]


7/11

Com ponen t 3 - Feat u r e Ca lcu la t i on

(Pos i t i on )

Position of a hole, stud, or slot is calculated basedon the axis or mid-plane of the AME (Actual

Mating Envelope).


8/11

Co m p on en t 4 - Op t im al Fi t t in g

(P ro f i l e )

Any remaining degrees of freedom after Datumconstraints

i.e. or

Most commonly used Least Squares algorithm does notprovide optimal fit.

We are not concerned with averaging the errors, but need todetermine whether or not the part will fit within the specifiedtolerance zone.

Inspection software needs to provide a fitting algorithm that

provides optimal fit (Minimizing Maximum error with respect

to profile tolerance) for all simultaneous callouts

[g ].005]A ] [g ].005]A ]B m]


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Ex am p le 1


10/11

Ex am p le 2


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* Co r r ect m e thods f o r evalua t i ng t he i t em s l i st ed above a reabso lu te l y cr i t i ca l i n p rov id ing accu ra te resu l t s . I m p rope r ana l ysi so f any o f t h e above has t h e po ten t i a l t o resu l t i n e r ro r s s ign i f i can t l y

l ar g e r t h a n t h e e r r o r o f t h e m e asu r e m e n t e q u ip m e n t u s ed .

Position

1) Datum Simulation

2) Bonus Calculation On holes, studs or slots

Datums (Feature of Size)

3) Feature creation Actual Mating Envelope

(AME)

Profile

1) Datum Simulation

2) Bonus Calculation Datum (Feature of Size)

3) Fitting

Remaining Degrees ofFreedom after Datumconstraints

Rev iew o f Measu r em en t Com ponen t s o f

Posi t i on and Pr o f i l e

[x ] [g ]

Position and Profile v2 Embedded

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