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Product specification
Dimensioning and tolerancing
It is impossible to make a perfectcomponent so when we design a part
we specify the acceptable range offeatures that make-up the part.
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IE 316 ManufacturingEngineering I - Processes
Chapter 2 Suppliment
DIMENSIONS, TOLERANCES, AND
SURFACES
Dimensions, Tolerances, and Related Attributes
Surfaces
ASME Y14.5 Form Geometry
Effect of Manufacturing Processes
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THE DESIGN PROCESS
Product Engineering
Design Process
Off-road bicycle that ...
1. Conceptualization
2. Synthesis3. Analysis
4. Evaluation
5. Representation
Design ProcessHow can this be
accomplished?
1. Clarification of the task
2. Conceptual design
3. Embodiment design
4. Detailed design
Functional requirement -> Design
Steps 1 & 2 Select material and properties, begin geometricmodeling (needs creativity, sketch is sufficient)
3 mathematical, engineering analysis4 simulation, cost, physical model5 formal drawing or modeling
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DESIGN REPRESENTATION
Design EngineeringRepresentation
Manufac-turing
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 SKETCHOrthographic Projection
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A FORMAL 3-VIEW DRAWING
0.9444"
4 holes 1/4" dia
around 2" dia , first
hole at 45
A
2.0000.001
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DESIGN DRAFTING
Third angle projection
Profile plane
Y
Z
XIII
Horizontal
Frontal plane
I
IV
II
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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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,td,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,td,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,td,t d,t
d,t
dDE= d
DA+ d
AE= dAD+ dAE
= (dAB+ d
BC+ d
CD) + 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 influencedby 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 and assemblyrequirements can be satisfied.
(ref. Tuguchi, ElSayed, Hsiang, Quality Engineering in Production Systems,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) cannot be achieved exactly.
Without tolerance we lose the control andas a consequence cause functional orassembly failure.
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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 of eachsegment affectsothers.
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RELATION BETWEEN
PRODUCT & PROCESS
TOLERANCES
Setuplocators
0.005
0.005
0.005
Design specifications
Process tolerance
Machine uses the locators as thereference. The distances from themachine coordinate system to thelocators are known.
The machining tolerance is measuredfrom the locators.
In order to achieve the 0.01tolerances, the process tolerancemust be 0.005 or better.
When multiple setups are used, the
setup error need to be taken intoconsideration.
A
0.01 t olerances
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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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PROBLEMS WITH DIMENSIONAL
TOLERANCE 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 position
symmetry
RUNOUT
circular runouttotal runout
PROFILEprofileprofile of a line
ANSI Y14.5M-1977 GD&T (ISO 1101, geometric tolerancing;
ISO 5458 positional tolerancing; ISO 5459 datums;and others), ASME Y14.5 - 1994
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 one or moresurfaces such as holes, faces, screw threads, profiles, or slots.
Feature Control Frame:
A
// 0.005 M A
symbol tolerance value
modifier
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 used
P Projected tolerance zone
O Diametrical tolerance zone
T Tangent plane
F Free state
maintain critical wall
thickness or criticallocation of features.
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 points should belocated. Three for primary datum, two for secondary datum and one ortertiary datum.
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STRAIGHTNESS
Value must be smaller than
the size tolerance.
1.000 '0.002
0.001
Measurederror0.001
1.000 '0.002
0.001
0.001
Design Meaning
Tolerance zone between two straightness lines.
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IE 316 ManufacturingEngineering I - Processes
Dimensions and Tolerances
In addition to mechanical and physical
properties, other factors that determine the
performance of a manufactured product
include: Dimensions - linear or angular sizes of a
component specified on the part drawing
Tolerances- allowable variations from the specifiedpart dimensions that are permitted in
manufacturing
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IE 316 ManufacturingEngineering I - Processes
Surfaces
Nominalsurface - intended surface contour ofpart, defined by lines in the engineeringdrawing
The nominal surfaces appear as absolutely straightlines, ideal circles, round holes, and other edgesand surfaces that are geometrically perfect
Actual surfaces of a part are determined by
the manufacturing processes used to make it The variety of manufacturing processes result in
wide variations in surface characteristics
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IE 316 ManufacturingEngineering I - Processes
Why Surfaces are Important
Aesthetic reasons
Surfaces affect safety
Friction and wear depend on surface
characteristics
Surfaces affect mechanical and physical
properties
Assembly of parts is affected by their surfaces
Smooth surfaces make better electrical contacts
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IE 316 ManufacturingEngineering I - Processes
Surface Technology
Concerned with:
Defining the characteristics of a surface
Surface texture
Surface integrity
Relationship between manufacturing processes
and characteristics of resulting surface
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IE 316 ManufacturingEngineering I - Processes
Figure 5.2 - A magnified cross-section of a typical metallic part surface
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IE 316 ManufacturingEngineering I - Processes
Surface Texture
The topography and geometric features of the
surface
When highly magnified, the surface is
anything but straight and smooth. It has
roughness, waviness, and flaws
It also possesses a pattern and/or direction
resulting from the mechanical process thatproduced it
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IE 316 ManufacturingEngineering I - Processes
Surface Integrity
Concerned with the definition, specification, andcontrol of the surface layers of a material (mostcommonly metals) in manufacturing andsubsequent performance in service
Manufacturing processes involve energy whichalters the part surface
The altered layermay result from work hardening(mechanical energy), or heating (thermal energy),
chemical treatment, or even electrical energy Surface integrity includes surface texture as well
as the altered layer beneath
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IE 316 ManufacturingEngineering I - Processes
Four Elements of Surface Texture
1. Roughness - small, finely-spaced deviations
from nominal surface determined by material
characteristics and process that formed the
surface
2. Waviness - deviations of much larger spacing;
they occur due to work deflection, vibration,
heat treatment, and similar factors Roughness is superimposed on waviness
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IE 316 ManufacturingEngineering I - Processes
3. Lay-predominantdirection or
pattern of thesurface texture
Figure 5.4 - Possible
lays of a surface
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IE 316 ManufacturingEngineering I - Processes
4. Flaws - irregularities that occur occasionally
on the surface Includes cracks, scratches, inclusions, and
similar defects in the surface
Although some flaws relate to surface texture,
they also affect surface integrity
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IE 316 ManufacturingEngineering I - Processes
Surface Roughness
Average of vertical deviations from nominalsurface over a specified surface length
Figure 5.5 - Deviations from nominal surface used inthe two definitions of surface roughness
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IE 316 ManufacturingEngineering I - Processes
Surface Roughness Equation
Arithmetic average (AA) is generally used, based onabsolute values of deviations, and is referred toas average roughness
where Ra = average roughness; y= vertical deviation
from nominal surface (absolute value); and Lm =specified distance over which the surfacedeviations are measured
dxL
yR
m
a
L
m0
A Al i S f R h
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IE 316 ManufacturingEngineering I - Processes
An Alternative Surface Roughness
Equation
Approximation of previous equation is perhapseasier to comprehend:
where Ra has the same meaning as above; yi=
vertical deviations (absolute value) identifiedby subscript i; and n = number of deviationsincluded in Lm
n
i
ianyR
1
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IE 316 ManufacturingEngineering I - Processes
Cutoff Length
A problem with the Ra computation is thatwaviness may get included
To deal with this problem, a parameter called
the cutoff length is used as a filter to separatewaviness from roughness deviations
Cutoff length is a sampling distance along thesurface. A sampling distance shorter than thewaviness width eliminates waviness deviationsand only includes roughness deviations
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IE 316 ManufacturingEngineering I - Processes
Figure 5.6 - Surface texture symbols in engineering drawings:
(a) the symbol, and (b) symbol with identification labels
Values ofRa are given in microinches; units for other measures are given
in inchesDesigners do not always specify all of the parameters on engineering
drawings
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TRUE POSITION
1.200.01
1.000.01
1.20
1.00
Tolerancezone0.01dia
O0.01MABO.800.02
Dimensionaltolerance
True position
tolerance
Hole center tolerance zone
A
B
Tolerancezone0.022
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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 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
1.20
1.00
O0.01MABO1.000.02
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 size is greaterthan the MMC hole, the hole axis true position tolerance zone can beenlarged by the amount of difference between the produced hole sizeand 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.010MABC.250p
.375-16UNC-2B
Project ed t olerance
zone0.25
0.01
Produced part
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IE 316 Manufacturing
Engineering I - Processes
Surface Integrity
Surface texture alone does not completelydescribe a surface
There may be metallurgical changes in the altered
layer beneath the surface that can have asignificant effect on a material's mechanicalproperties
Surface integrityis the study and control of this
subsurface layer and the changes in it that occurduring processing which may influence theperformance of the finished part or product
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IE 316 Manufacturing
Engineering I - Processes
Surface Changes Caused by Processing
Surface changes are caused by the applicationof various forms of energy during processing
Example: Mechanical energy is the most common
form in manufacturing. Processes include metalforming (e.g., forging, extrusion), pressworking,and machining
Although primary function is to change geometry
of workpart, mechanical energy can also causeresidual stresses, work hardening, and cracks inthe surface layers
Surface Changes Caused by
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IE 316 Manufacturing
Engineering I - Processes
Surface Changes Caused by
Mechanical Energy
Residual stresses in subsurface layer
Cracks - microscopic and macroscopic
Laps, folds, or seams
Voids or inclusions introduced mechanically
Hardness variations (e.g., work hardening)
Surface Changes Caused by
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IE 316 Manufacturing
Engineering I - Processes
Surface Changes Caused by
Thermal Energy
Metallurgical changes (recrystallization, grain
size changes, phase changes at surface)
Redeposited or resolidified material (e.g.,
welding or casting)
Heat-affected zone in welding (includes some
of the metallurgical changes listed above)
Hardness changes
Surface Changes Caused by
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IE 316 Manufacturing
Engineering I - Processes
Surface Changes Caused by
Chemical Energy
Intergranular attack
Chemical contamination
Absorption of certain elements such as H and
Cl in metal surface
Corrosion, pitting, and etching
Dissolving of microconstituents
Alloy depletion and resulting hardness
changes
Surface Changes Caused by
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IE 316 Manufacturing
Engineering I - Processes
Surface Changes Caused by
Electrical Energy
Changes in conductivity and/or magnetism
Craters resulting from short circuits during
certain electrical processing techniques
Tolerances and Manufacturing
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IE 316 Manufacturing
Engineering I - Processes
Tolerances and Manufacturing
Processes
Some manufacturing processes are inherently
more accurate than others
Examples:
Most machining processes are quite accurate,
capable of tolerances = 0.05 mm ( 0.002 in.) or
better
Sand castings are generally inaccurate, andtolerances of 10 to 20 times those used for
machined parts must be specified
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Surfaces and Manufacturing Processes
Some processes are inherently capable of
producing better surfaces than others
In general, processing cost increases with
improvement in surface finish because additionaloperations and more time are usually required to
obtain increasingly better surfaces
Processes noted for providing superior finishes
include honing, lapping, polishing, and
superfinishing