Transcript Chapter 2 PART DESIGN SPECIFICATION

IE550 - Manufacturing Systems
PART DESIGN SPECIFICATION
Spring 2011
Dr. R. A. Wysk
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Agenda
• Go over engineering specifications
• Functional requirements
• Form, fit and function
–
–
–
–
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Dimensioning
Tolerancing
Engineering drawings
datum
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Materials
• Read Chapter 2 and 3 from Computer Aided
manufacturing (3rd Edition)
• Overview of engineering design
• Mechanical design representations
• Engineering drawing
• Geometric dimensioning and tolerancing
• AMSE Y14.5
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THE DESIGN PROCESS
Product Engineering
Design Process
Design Process
Off-road bicycle that ...
How can this be
accomplished?
1. Conceptualization
2. Synthesis
3. Analysis
4. Evaluation
5. Representation
1. Clarification of the task
2. Conceptual design
3. Embodiment design
4. Detailed design
Functional requirement -> Design
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Steps 1 & 2 Select material and properties, begin geometric
modeling (needs creativity, sketch is sufficient)
3
mathematical, engineering analysis
4
simulation, cost, physical model
5
formal drawing or modeling
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DESIGN REPRESENTATION
Design
Engineering
Representation
Manufacturing
• Verbal
• Sketch
• Multi-view 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
Orthographic Projection
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A FORMAL 3-VIEW DRAWING
0.9444"
4 holes 1/4" dia
around 2" dia , first
hole at 45°

2.000 0.001
A
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DESIGN DRAFTING
Y
t op
Pr o f ile
b
d
c
f
p lan e
e
g
a
H o r iz o n t a l
h
i
side
j
I I
I
X
I I I
Z
I V
Fr o n t a l
p lan e
front
Drafting in the third angle
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Third angle projection
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INTERPRETING A DRAWING
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DESIGN DRAFTING
A
Partial view
A
2.0000.001
A-A
A
Cut off view and auxiliary view
Provide more local details
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DIMENSIONING
Requirements
1. Unambiguous
Incomplete
dimensioning
2. Completeness
3. No redundancy
0.83 '
0.98 '
1.22 '
3.03 '
1.72 '
Redundant dimensioning
0.86 '
1.22 '
0.83 '
3.03 '
Adequate dimensioning
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TOLERANCE
Dimensional tolerance - conventional
Geometric tolerance - modern
nominal dimension
1.00 +
- 0.05
means a range
0.95 - 1.05
tolerance
unilateral
bilateral
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0.95
+ 0.10
- 0.00
1.05
+ 0.00
- 0.10
1.00+
- 0.05
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TOLERANCE STACKING
1. Check that the tolerance & dimension specifications are
reasonable - for assembly.
2. Check there is no over or under specification.
"TOLERANCE IS ALWAYS ADDITIVE" why?
0.80 ' ±0.01
1.20 ' ±0.01
1.00 ' ±0.01
?
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
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TOLERANCE STACKING (ii)
0.80 ' ±0.01
?
1.20 ' ±0.01
3.00 ' ±0.01
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
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TOLERANCE STACKING (iii)
x
0.80 ' ±0.01
?
1.20 ' ±0.01
3.00 ' ±0.01
Maximum x length = 3.01 - 0.79 - 1.19 = 1.03
Minimum x length = 2.99 - 0.81 - 1.21 = 0.97
Therefore x = 1.00 ± 0.03
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TOLERANCE GRAPH
A
d,t
B
d,t
d,t
C
D
E
d,t
G(N,d,t)
N: a set of reference lines, sequenced nodes
d: a set of dimensions, arcs
t: a set of tolerances, arcs
d
t
ij
ij
: dimension between references i & j
: tolerance between references i & j
Reference i is in front of reference j in the sequence.
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EXAMPLE TOLERANCE GRAPH
A
A
d,t
B
B
C
d,t
D
C
d,t
E
D
E
d,t
d DE = d DA + d AE = – d AD + d AE
= – (d AB + d BC + d CD) + d AE
different properties
between d & t
t DE = t AB + t BC + tCD + t AE
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OVER SPECIFICATION
If one or more cycles can be detected in the graph, we say that the
dimension and tolerance are over specified.
A
d1,t1
d2,t2
B
B
d2
C
d3
Redundant dimension
d3,t3
A
d1
C
A
t1
B
t2
C
t3
Over constraining tolerance
(impossible to satisfy) why?
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UNDER SPECIFICATION
When one or more nodes are disconnected from the graph, the
dimension or tolerance is under specified.
A
d1
B
C
d2
D
E
d3
A
B
C
D
E
C
D
is disconnected from the
rest of the graph.
No way to find dBC and dDE
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PROPERLY TOLERANCED
A
A
d,t
B
B
C
d,t
D
C
d,t
E
D
E
d,t
d DE = d DA + d AE = – d AD + d AE
= – (d AB + d BC + d CD) + d AE
t DE = t AB + t BC + tCD + t AE
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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?
diamet er & t olerance
t rue posit ion
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A circular tolerance zone, the size is influenced
by the diameter of the hole. The shape of the
hole is also defined by a geometric tolerance.
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3-D GEOMETRIC TOLERANCE
PROBLEMS
datum surface
datum
surface
±t
Reference
frame
perpendicularity
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TOLERANCE ASSIGNMENT
Tolerance is money
• Specify as large a tolerance as possible as long as functional and
assembly requirements can be satisfied.
(ref. Tuguchi, ElSayed, Hsiang, Quality Engineering in Production
Systems, McGraw Hill, 1989.)
function
Qu al it y
Co st
cost
+t
-t
Tolerance value
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d ( nom inal dim ensio n)
Quality cost
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REASON OF HAVING TOLERANCE
• No manufacturing process is perfect.
• Nominal dimension (the "d" value) can not be
achieved exactly.
• Without tolerance we lose the control and as a
consequence cause functional or assembly
failure.
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EFFECTS OF TOLERANCE (I)
1. Functional constraints
e.g.
flow rate
d±t
Diameter of the tube affects the flow. What is the allowed
flow 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 the
clearance?
Compound fitting
The dimension of
each segment
affects others.
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RELATION BETWEEN
PRODUCT & PROCESS
TOLERANCES
•
A
± 0 .0 1 t olerances
Design specifications
•
•
Set up
lo cat o r s
± 0 .0 0 5
•
± 0 .0 0 5
± 0 .0 0 5
Machine uses the locators as
the reference. The distances
from the machine coordinate
system to the locators are
known.
The machining tolerance is
measured from the locators.
In order to achieve the 0.01
tolerances, the process
tolerance must be 0.005 or
better.
When multiple setups are used,
the setup error need to be taken
into consideration.
Process tolerance
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TOLERANCE CHARTING
A method to allocate process tolerance and verify that the process
sequence and machine selection can satisfy the design tolerance.
st ock
boundary
± 0 .0 1
± 0 .0 1
± 0 .0 1
blue print
Dim
t ol
1 .0
1 .0
3 .0
0 .0 1
0 .0 1
0 .0 1
Not shown are
process tolerance
assignment and
balance
Op code
Operation
sequence
10
lat he
10
lat he
20
lat he
20
lat he
10
12
process tol of 10 + process tol of 12
20
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produced tolerances:
22
process tol of 20 + process tol 22
process tol of 22 + setup tol
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SURFACE FINISH
waviness
roughness
roughness widt h
waviness
widt h
Usually
simplified:
roughness
height
63
(m inch)
waviness height
waviness width
0.002 - 2
0.010
0.005
Lay
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roughness width cutoff
default is 0.03" (ANSI Y14.36-1978)
roughness width
(inch)
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PROBLEMS WITH DIMENSIONAL
TOLERANCE ALONE
As designed:
1 .00±0.0 01
6.00±0.001
As manufactured:
1 .0 0 1
Will you accept the part
at right?
1 .0 0 1
1 .0 0 1
Problem is the control of
straightness.
How to eliminate the
ambiguity?
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6 .0 0
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GEOMETRIC TOLERANCES
ANSI Y14.5M-1977 GD&T (ISO 1101, geometric tolerancing;
ISO 5458 positional tolerancing; ISO 5459 datums;
and others), ASME Y14.5 - 1994
FORM
ORIENTATION
straightness
perpendicularity
Squareness
flatness
angularity
Circularity
parallelism
roundness
cylindricity
LOCATION
RUNOUT
circular runout
total runout
concentricity
true position
symmetry
PROFILE
profile
profile of a line
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DATUM &
FEATURE CONTROL FRAME
Datum: a reference plane, point, line, axis where usually a plane
where you can base your measurement.
A
Symbol:
Even a hole pattern can be used as datum.
Feature: specific component portions of a part and may include one
or more surfaces such as holes, faces, screw threads, profiles, or
slots.
Feature Control Frame:
//
symbol
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datum
0.005 M A
modifier
tolerance value
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MODIFIERS
M Maximum material condition
MMC
assembly
Regardless of feature size
RFS
(implied unless specified)
LMC
less frequently used
L Least material condition
P Projected tolerance zone
maintain critical
wall thickness or
critical location of
features.
O Diametrical tolerance zone
T Tangent plane
F Free state
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 points
should be located. Three for primary datum, two for secondary
datum and one or tertiary datum.
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DATUM REFERENCE FRAME
Pr i m a r y
Three perfect planes used to
locate the imperfect part.
T
e
rt
ia
r
y
a. Three point contact on the
primary plane
Sec on dar y
C
b. two point contact on the
secondary plane
c. one point contact on the tertiary
plane
primary
O 0.001 M A
Secondary
B C
Tertiary
B
A
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STRAIGHTNESS
Tolerance zone between two straightness lines.
0.0 01
1.000 '
Value must be smaller
than the size tolerance.
±0.002
Measured error Š 0 .0 0 1
0.0 01
0.0 01
1.000 '
Design
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±0.002
Meaning
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FLATNESS
Tolerance zone defined by two parallel planes.
0.0 01
1.000 '
±0.002
p ar al l e l
p lanes
0.0 01
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CIRCULARITY (ROUNDNESS)
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.
0.01
1.00 ' ±0.05
0 .0 1 Tolerance zone
At any section along the cylinder
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CYLINDRICITY
Tolerance zone bounded by two concentric cylinders
within which the cylinder must lie.
0.01
1.00 ' ±0.05
Rotate in a V
0.01
Rotate between points
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PERPENDICULARITY
A surface, median plane, or axis at a right angle to the datum plane
or axis.
A
.0 0 2 T
.0 0 2
A
1.000 '
0.500 '
±0.005
0.0 0 2
t olerance
zone perpendicular
t o t he dat um plane
±0.005
A
2.000 '
±0.005
A
O 1 .0 0 ± 0 .01
.0 02
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A
0 .0 0 2 diamet er t ol
zone is perpendicular
t o t he dat um plane
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ANGULARITY
A surface or axis at a specified angle (orther than 90°) from a datum
plane or axis. Can have more than one datum.
0 .0 0 5
A
1.5 0 0 ± 0 .0 05
40°
3.500 '
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±0.005
A
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PARALLELISM
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 1 A
1.000 "
±0.005
A
2.000 "
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±0.005
0.0 01
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PROFILE
A uniform boundary along the true profile within whcih
the elements of the surface must lie.
0 .0 05 A B
B
A
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0.0 01
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RUNOUT
A composite tolerance used to control the functional relationship
of one or more features of a part to a datum axis. Circular runout
controls the circular elements of a surface. As the part rotates
360° about the datum axis, the error must be within the tolerance
limit.
A
1.500 "
±0.005
0 .0 0 5 A
0.361 "
±0.002
Dat um
ax is
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Deviat ion on each
circular check ring
is less t han t he
t olerance.
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TOTAL RUNOUT
A
1.500 "
±0.005
0 .0 0 5 A
0.361 "
±0.002
Dat um
axis
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Deviat ion on t he
t ot al swept when
t he part is rot at ing
is less t han t he
t olerance.
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TRUE POSITION
Tolerance zone
0.0 2 2
Dimensional
tolerance
1 .00 ± 0 .0 1
1.2 0
± 0 .0 1
O .8 0 ± 0 .02
Hole center tolerance zone
O 0 .0 1 M A B
True position
tolerance
Tolerance zone
0 .0 1 dia
1 .0 0
B
A
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1.2 0
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HOLE TOLERANCE ZONE
Tolerance zone for dimensional toleranced
hole is not a circle. This causes some assembly
problems.
For a hole using true position tolerance
the tolerance zone is a circular zone.
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TOLERANCE VALUE MODIFICATION
O 1.0 0 ± 0 .0 2
O 0 .0 1 M A B
Produced
1 .00
hole size
B
1 .2 0
A
The default modifier for
true position is MMC.
0.97
MMC
LMC
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S
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
For M
True Pos tol
M
L
out of diametric tolerance
the allowable tolerance = specified tolerance + (produced hole
size - MMC hole size)
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MMC HOLE
LMC hole
MMC hole
hole axis t olerance zone
MMC peg will f it in t he hole ,
axis must be in t he t olerance zone
Given the same peg (MMC peg), when the produced hole size
is greater than the MMC hole, the hole axis true position
tolerance zone can be enlarged by the amount of difference
between the produced hole size and the MMC hole size.
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PROJECTED TOLERANCE ZONE
Applied for threaded holes or press fit holes to ensure interchangeability
between parts. The height of the projected tolerance zone is the thickness
of the mating part.
.3 7 5 - 1 6 UNC - 2 B
O .0 1 0 M A B C
.2 5 0 p
0.01
0.25
Project ed
zone
t olerance
Produced part
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SOME NUMBERS
Krulikowski, A., GD&T Challenges the Fast Draw, MFG ENG, Feb 1994.
GD&T drawings are more expansive to make, however, saves revision
cost.
Drawing revision costs $500 - $2000 on the paper work
How much does it cost to “put a part number” onto a part? Estimates
range from $1,000 -$10,000.
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