Part Design Specification

7/27/2019 Part Design Specification

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T.C. Chang

Chapter 2

PART DESIGN SPECIFICATION

Dr. T.C. Chang

School of Industrial EngineeringPurdue University


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THE DESIGN PROCESS

Design Process

1. Conceptualization

2. Synthesis

3. Analysis4. Evaluation

5. Representation

Design Process

(VDI)

1. Clarification of the task

2. Conceptual design

3. Embodiment design

4. Detailed design

Functional requirement -> Design

Steps 1 & 2 needs creativity, sketch is sufficient3 mathematical, engineering analysis4 simulation, cost, physical model5 formal drawing or modeling


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DESIGN REPRESENTATION

Design Representation Manufac-turing

Verbal

Sketch

Multiview orthographic drawing (drafting) CAD draft ing

CAD 3D & surface model

Solid model

Feature based design

Requirement of the representation method

precisely convey the design concept easy to use


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A FREE-HAND SKETCH


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A FORMAL DRAWING

0.9444"

4 holes 1/4" diaaround 2" dia , firsthole at 45

A

2.0000.001


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DESIGN DRAFTING

Third angle projection

P r o f ile p la n e

Y

Z

XI I I

H o r i z o n t a l

F ro n t a l p la n e

I

I V

I I

top

front

side

a

b c d ef

g

h i

j

Drafting in the third angle


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INTERPRETING A DRAWING


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DESIGN DRAFTING

Partial view

Cut off view and auxiliary view

Provide more local details

A

2.0000.001

AA

A - A


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DIMENSIONING

Requirements

1. Unambiguous

2. Completeness

3. No redundancy

0.83 ' 0.95 ' 1.22 '

3.03 '

Redundant dimensioning

0.83 ' 1.22 '

3.03 '

1.72 '

0.86 '

Adequate dimensioning

Incompletedimensioning


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TOLERANCE

Dimensional tolerance - conventional

Geometric tolerance - modern

unilateral

bilateral

1.00 0.05+-

nominal dimension

tolerance

0.95+ 0.10- 0.00 1.05

+ 0.00- 0.10

1.00 0.05+-

0.95 - 1.05means a range

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TOLERANCE STACKING

"TOLERANCE IS ALWAYS ADDITIVE" why?

What is the expected dimension and tolerances?

d = 0.80 +1.00 + 1.20 = 3.00

t = (0.01 + 0.01 + 0.01) = 0.03

0.80 ' 0.01 1.20 ' 0.01

1.00 ' 0.01

?

1. Check that the tolerance & dimension specifications arereasonable - for assembly.

2. Check there is no over or under specification.

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TOLERANCE STACKING (ii)

What is the expected dimension and tolerances?

d = 3.00 - 0.80 - 1.20 = 1.00

t = (0.01 + 0.01 + 0.01) = 0.03

0.80 ' 0.01 1.20 ' 0.01

3.00 ' 0.01

?

T C Chang


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TOLERANCE STACKING (iii)

Maximum x length = 3.01 - 0.79 - 1.19 = 1.03Minimum x length = 2.99 - 0.81 - 1.21 = 0.97

Therefore x = 1.00 0.03

0.80 ' 0.01 1.20 ' 0.01

3.00 ' 0.01

?

x

T C Chang


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TOLERANCE GRAPH

G(N,d,t)

N: a set of reference lines, sequenced nodes

d: a set of dimensions, arcs

t: a set of tolerances, arcs

A B C D Ed,t d,t d,t

d,t

d : dimension between references i & j

t : tolerance between references i & jij

ij

Reference i is in front of reference j in the sequence.

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EXAMPLE TOLERANCE GRAPH

A B C D E


d,t

different propertiesbetween d & t

dDE

= dDA

+dAE

= dAD

+dAE

= (dAB

+dBC

+dCD) +d

AE

tDE =

tAB+

tBC+

tCD +

tAE

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g

OVER SPECIFICATIONIf one or more cycles can be detected in the graph, we say that the

dimension and tolerance are over specified.

A B C

A B C

A B C

d1 d2

d3d1,t1 d2,t2

d3,t3

t1 t2

t3

Redundant dimension

Over constraining tolerance(impossible to satisfy) why?


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PROPERLY TOLERANCED

A B C D E


d,t

dDE

= dDA

+dAE

= dAD

+dAE

= (dAB

+dBC

+dCD) +d

AE

tDE = tAB+tBC+ tCD +tAE

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TOLERANCE ANALYSISFor two or three dimensional tolerance analysis:

i. Only dimensional tolerance

Do 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?

true position

diameter & tolerance

A circular tolerance zone, the size is influenced

by the diameter of the hole. The shape of thehole is also defined by a geometric tolerance.

T.C. Chang


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3-D GEOMETRIC TOLERANCE

PROBLEMS

t

datum surfacedatumsurface

Referenceframe

perpendicularity

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TOLERANCE ASSIGNMENT

Tolerance is money

Specify as large a tolerance as possible as long as functional andassembly requirements can be satisfied.

(ref. Tuguchi, ElSayed, Hsiang, Quality Engineering in ProductionSystems, McGraw Hill , 1989.)

function

cost

Tolerance value

d ( no mina l d im e ns io n)

Q u a l i t yC o s t

- t

+ t

Quality cost

T.C. Chang


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REASON OF HAVING TOLERANCE

No manufacturing process is perfect.

Nominal dimension (the "d" value) can not beachieved exactly.

Without tolerance we lose the control and as aconsequence cause functional or assemblyfailure.

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EFFECTS OF TOLERANCE (I)

1. Functional constraints

e.g.

d t

flow rate

Diameter of the tube affects the flow. What is the allowedflow rate variation (tolerance)?

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EFFECTS OF TOLERANCE (II)

2. Assembly constraints

e.g. peg-in-a-hole dp

dh

How to maintain theclearance?

Compound fitting

The dimension ofeach segmentaffects others.

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RELATION BETWEEN

PRODUCT & PROCESSTOLERANCES

S e t u pl o c a t o r s

0 . 0 0 5

0 . 0 0 5

0 . 0 0 5

Design specifications

Process tolerance

Machine uses the locators as

the reference. The distancesfrom the machine coordinatesystem to the locators areknown.

The machining tolerance ismeasured from the locators.

In order to achieve the 0.01tolerances, the processtolerance must be 0.005 or

better. When multiple setups are used,

the setup error need to be takeninto consideration.

A0 .0 1 t o le rance s

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TOLERANCE CHARTINGA method to allocate process tolerance and verify that the processsequence and machine selection can satisfy the design tolerance.

0 .0 1 0 .0 1

0 . 0 1

s t o c k

b oundary

Dim tol

1 . 0 0 . 0 11 . 0 0 . 0 13 . 0 0 . 0 1

Op co de

10 la the

10 la the

20 la the

20 la the

1 0

1 2

2 0

2 2

blue print

Operationsequence

Not shown areprocess toleranceassignment andbalance

produced tolerances:

process tol of 10 + process tol of 12

process tol of 20 + process tol 22

process tol of 22 + setup tol

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SURFACE FINISH

waviness widt h

roughness width

waviness

roughness

63 0.010

0.005

0.002 - 2roughnessheight

waviness height

waviness width

roughness width cutoffdefault is 0.03" (ANSI Y14.36-1978)

roughness widthLay

( inch)

(inch)

63

Usuallysimplified:

T.C. Chang


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PROBLEMS WITH DIMENSIONAL

TOLERANCE ALONE

1 . 0 0 1

1 . 0 0 11 . 0 0 1

6 . 0 0

1 .000 .001

6 .000 .001

As designed:

As manufactured:

Will you accept the partat right?

Problem is the control ofstraightness.

How to eliminate theambiguity?

T.C. Chang


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GEOMETRIC TOLERANCES

FORM

straightness

flatness

Circularity

cylindricity

ORIENTATION

perpendicularity

angularity

parallelism

LOCATION

concentricity

true positionsymmetry

RUNOUT

circular runouttotal runout

PROFILE

profileprofile of a line

ANSI Y14.5M-1994 GD&T (ISO 1101, geometric tolerancing;ISO 5458 posit ional tolerancing; ISO 5459 datums;and others)

Squareness

roundness

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DATUM &

FEATURE CONTROL FRAMEDatum: 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 oneor more surfaces such as holes, faces, screw threads, profiles, orslots.

Feature Control Frame:

A

// 0.005 M A

symbol tolerance valuemodifier

datum

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MODIFIERS

M Maximum material condition MMC assembly

Regardless of feature size RFS (implied unless specified)

L Least material condition LMC less frequently usedP Projected tolerance zone

O Diametrical tolerance zone

T Tangent plane

F Free state

maintain criticalwall thickness orcritical location of

features.

MMC, RFS, LMC

MMC, RFS

RFS

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SOME TERMS

MMC : Maximum Material Condition

Smallest hole or largest peg (more material left on the part)

LMC : Least Material Condition

Largest 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 pointsshould be located. Three for primary datum, two for secondarydatum and one or tertiary datum.

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DATUM REFERENCE FRAMEThree perfect planes used to

locate the imperfect part.

a. Three point contact on theprimary plane

b. two point contact on thesecondary plane

c. one point contact on the tertiaryplane

O 0.001 M A B C

primary Secondary

Tertiary

P r i m a r y

S e c o n d a r y

Te r t ia r y

A

B

C

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STRAIGHTNESS

Value must be smallerthan the size tolerance.

1.000 ' 0.002

0 . 0 0 1

Me as ure d e rro r 0 .0 0 1

1.000 ' 0.002

0 . 0 0 1

0 . 0 0 1

Design Meaning

Tolerance zone between two straightness l ines.

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FLATNESS

1.000 ' 0.002

0 . 0 0 1

0 . 0 0 1

p a r a lle lp la n e s

Tolerance zone defined by two parallel planes.

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CIRCULARITY (ROUNDNESS)

1.00 ' 0.05

0.01

0.01 Tole rance zone

At any section along the cylinder

a. Circle as a result of the intersection by any plane perpendicular toa common axis.

b. On a sphere, any plane passes through a common center.

Tolerance zone bounded by two concentric circles.

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CYLINDRICITY

1.00 ' 0.05

0.01

0.01

Rotate in a V

Rotate between points

Tolerance zone bounded by two concentric cylinderswithin which the cylinder must lie.

T.C. Chang

C


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PERPENDICULARITYA surface, median plane, or axis at a right angle to the datum planeor axis.

0 . 0 0 2

tolerancezone perpendicularto the da tum plane

. 0 0 2 A

O 1 .00 0 .01

A

0 .002 d i amete r t o l

zone is perpendicularto the da tum plane

1.000 ' 0.005

.0 0 2 A

0.500 ' 0.005

2.000 ' 0.005

A

.0 0 2 T A

T.C. Chang

ANGULARITY


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ANGULARITYA surface or axis at a specified angle (orther than 90) from a datumplane or axis. Can have more than one datum.

0.005 to lerance zonewhich is exactly 40from the datum plane

3.500 ' 0.005

1 .5 0 0 0 .0 0 5

4 0

0 .0 0 5 A

A

T.C. Chang

PARALLELISM


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PARALLELISM

1.000 " 0.005

2.000 " 0.005

.0 0 1 A

A

The condition of a surface equidistant at all points from a datum plane,or an axis equidistant along its length to a datum axis.

0 . 0 0 1

T.C. Chang

PROFILE


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PROFILEA uniform boundary along the true profile within whcihthe elements of the surface must lie.

A

B

0 .0 0 5 A B

0.001

T.C. Chang

RUNOUT


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RUNOUT

0.361 " 0.002

1.500 " 0.005A

0 . 0 0 5 A

A composite tolerance used to control the functional relationshipof one or more features of a part to a datum axis. Circular runoutcontrols the circular elements of a surface. As the part rotates360 about the datum axis, the error must be within the tolerancelimit.

Datuma x i s

De viat ion on e achcircula r che ck ringis le ss t han t het o l e r a n c e .

T.C. Chang

TOTAL RUNOUT


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TOTAL RUNOUT

Datuma x i s

De viat io n on t het ot al s we pt whe nt he part is rot at ingis le ss t han t het o l e r a n c e .

0.361 " 0.002

1.500 " 0.005A

0 . 0 0 5 A

T.C. Chang

TRUE POSITION


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TRUE POSITION

1 . 2 0 0 . 0 1

1 . 0 0 0 . 0 1

1 . 2 0

1 . 0 0

To le ra nc e z on e

0 . 0 1 d i a

O 0 .0 1 M A B

O .8 0 0 .0 2

Dimensionaltolerance

True position

tolerance

Hole center tolerance zone

A

B

Tolerance zone

0 .02 2

T.C. Chang

HOLE TOLERANCE ZONE


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HOLE TOLERANCE ZONE

Tolerance zone for dimensional tolerancedhole is not a circle. This causes some assemblyproblems.

For a hole using true position tolerancethe tolerance zone is a circular zone.

T.C. Chang

TOLERANCE VALUE MODIFICATION


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TOLERANCE VALUE MODIFICATION

Produced True Pos tol

hole size

0.97 out of diametric tolerance

0.98 0.01 0.05 0.01

0.99 0.02 0.04 0.01

1.00 0.03 0.03 0.01

1.01 0.04 0.02 0.01

1.02 0.05 0.01 0.01

1.03 out of diametric tolerance

1 . 2 0

1 . 0 0

O 0 .0 1 M A B

O 1 .00 0 .02

M L S

The default modif ier fortrue position is MMC.

MMC

LMC

For M the allowable tolerance = specified tolerance + (produced holesize - MMC hole size)

A

B

T.C. Chang

MMC HOLE


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MMC HOLE

Given the same peg (MMC peg), when the produced hole sizeis greater than the MMC hole, the hole axis true positiontolerance zone can be enlarged by the amount of differencebetween the produced hole size and the MMC hole size.

hole axis tolerance zone

MMC holeLMC hole

MMC pe g will fit in t he ho leaxis must be in the tolerance zone,

T.C. Chang

PROJECTED TOLERANCE ZONE


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PROJECTED TOLERANCE ZONEApplied for threaded holes or press fit holes to ensure interchangeabilitybetween parts. The height of the projected tolerance zone is the thicknessof the mating part.

O .0 1 0 M A B C

.2 5 0 p

.375 - 16 UNC - 2B

Projected tolerancezone0 .25

0 .01

Produced part

T.C. Chang

SOME NUMBERS


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SOME NUMBERSKrulikowski, A., GD&T Challenges the Fast Draw, MFG ENG, feb 1994.

GD&T drawings are more expansive to make, however, saves revisioncost.

Drawing revision costs $500 - $2000 on the paper work

Documents

Part Design Specification