Part Design Specification
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Transcript of 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
?
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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,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
A B C D Ed,t d,t d,t
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
A B C D Ed,t d,t d,t
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.
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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
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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:
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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?
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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.
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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
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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
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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
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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
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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 .
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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
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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
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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.
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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
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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,
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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
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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