Chap 2 Design

7/31/2019 Chap 2 Design

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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. Synthesis3. Analysis

4. 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 drafting

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" dia

arou nd 2 " dia , first

hole at 45

A

2.0000.001


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DESIGN DRAFTING

Third angle projection

Profile plane

Y

Z

X

I I I

Horizontal

Frontal plane

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

A

A

A - A


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DIMENSIONING

Requirements1. Unambiguous

2. Completeness

3. No redundancy0.83 ' 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

?


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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


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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,td,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

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

d,t

different propertiesbetween d & t

dDE= d

DA+ d

AE=

dAD+ d

AE

= (dAB+ d

BC+ d

CD) + d

AE

tDE= tAB+ tBC+ tCD + tAE


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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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UNDER SPECIFICATION

A B C D E

A B C D Ed1 d2

d3

C D is disconnected from the

rest of the graph.

No way to find dBC and dDE

When one or more nodes are disconnected from the graph, the

dimension or tolerance is under specified.


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PROPERLY TOLERANCED

A B C D E

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

d,t

dDE= d

DA+ d

AE= d

AD+ d

AE

= (dAB+ d

BC+ d

CD) + d

AE

tDE= tAB+ tBC+ tCD + tAE


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TOLERANCE ANALYSIS

For 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?

t rue posit ion

diamet er & t olerance

A circular tolerance zone, the size is influencedby the diameter of the hole. The shape of thehole is also defined by a geometric tolerance.

C C


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3-D GEOMETRIC TOLERANCEPROBLEMS

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 (nominal dimension)

Quality

Cost

-t

+t

Quality cost

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

dh

How to maintain theclearance?

Compound fitting

The dimension ofeach segmentaffects others.

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RELATION BETWEENPRODUCT & PROCESS

TOLERANCES

Setup

locators

0.005

0.005

0.005

Design specifications

Process tolerance

Machine uses the locators asthe reference. The distancesfrom the machine coordinatesystem to the locators are

known. The machining tolerance is

measured 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.

A

0 . 0 1 t o l e r an c e s

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TOLERANCE CHARTINGA method to allocate process tolerance and verify that the process

sequence and machine selection can satisfy the design tolerance.

0 .01 0 .0 1

0 .01

stock

boundary

Dim t ol

1.0 0.01

1.0 0.01

3.0 0.01

Op code

10 lathe

10 lathe

20 lathe

20 lathe

10

12

20

22

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 width

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 width

Lay

( inch)

(inch)

63

Usuallysimplified:

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PROBLEMS WITH DIMENSIONALTOLERANCE ALONE

1.001

1.0011.001

6.00

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?

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GEOMETRIC TOLERANCES

FORM

straightness

flatness

Circularity

cylindricity

ORIENTATION

perpendicularity

angularity

parallelism

LOCATION

concentricity

true positionsymmetry

RUNOUT

circular runouttotal runout

PROFILEprofileprofile of a line

ANSI Y14.5M-1994 GD&T (ISO 1101, geometric tolerancing;

ISO 5458 positional tolerancing; ISO 5459 datums;and others)

Squareness

roundness

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g

DATUM &FEATURE CONTROL FRAME

Datum: a reference plane, point, line, axis where usually a planewhere 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 value

modifier

datum

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g

MODIFIERS

M Maximum material condition MMC assembly

Regardless of feature size RFS (implied unless specified)

L Least material condition LMC less frequently used

P Projected tolerance zone

O Diametrical tolerance zone

T Tangent plane

F Free state

maintain critical

wall thickness orcritical location offeatures.

MMC, RFS, LMC

MMC, RFS

RFS

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SOME TERMS

MMC : Maximum Material ConditionSmallest 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 the

primary 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

Primary

Secondary

Te r t iar y

A

B

C

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STRAIGHTNESS

Value must be smallerthan the size tolerance.

1.000 ' 0.002

0.001

Measured error 0.001

1.000 ' 0.002

0.001

0.001

Design Meaning

Tolerance zone between two straightness lines.

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FLATNESS

1.000 ' 0.002

0.001

0.001

parallel

planes

Tolerance zone defined by two parallel planes.

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CIRCULARITY (ROUNDNESS)

1.00 ' 0.05

0.01

At any section along the cylinder

a. Circle as a result of the intersection by any plane perpendicular to

a 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.

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

or axis.

1.000 ' 0.005

. 0 0 2 A

0.500 ' 0.005

2.000 ' 0.005

A

. 0 0 2 T A

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ANGULARITYA surface or axis at a specified angle (orther than 90) from a datum

plane or axis. Can have more than one datum.

3.500 ' 0.005

1.5000.005

40

0.005 A

A

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PARALLELISM

1.000 " 0.005

2.000 " 0.005

.001 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.

0.001

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PROFILEA uniform boundary along the true profile within whcih

the elements of the surface must lie.

A

B

0.005 A B

0.001

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RUNOUT

0.361 " 0.002

1.500 " 0.005A

0.005 A

A composite tolerance used to control the functional relationshipof one or more features of a part to a datum axis. Circular runout

controls the circular elements of a surface. As the part rotates360 about the datum axis, the error must be within the tolerancelimit.

Datum

axis

Deviation on each

circular check ring

is less than the

tolerance.

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TOTAL RUNOUT

Datum

axis

Deviation on the

total swept when

the part is rotating

is less than the

tolerance.

0.361 " 0.002

1.500 " 0.005A

0.005 A

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TRUE POSITION

1.20

0.01

1.00 0.01

1.20

1.00

Tolerance zone

0.01dia

O0.01MA B

O.800.02

Dimensionaltolerance

True positiontolerance

Hole center tolerance zone

A

B

Tolerance zone0.022

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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.

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TOLERANCE VALUE MODIFICATION

Produced True Pos tol

hole size0.97 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

1.20

1.00

O 0.01 M A B

O 1.00 0.02

M L S

The default modifier fortrue position is MMC.

MMC

LMC

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

A

B

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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 peg will fit in t he hole

axis must be in the tolerance zone,

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PROJECTED TOLERANCE ZONEApplied for threaded holes or press fit holes to ensure interchangeability

between parts. The height of the projected tolerance zone is the thicknessof the mating part.

O .01 0 M A B C

.250 p

.375 - 16 UNC - 2B

Project ed t olerance

zone0.25

0.01

Produced part

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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

Chap 2 Design

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