Download - Product specificationDimensioning and tolerancing

7/28/2019 Product specificationDimensioning and tolerancing

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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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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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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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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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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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Figure 5.2 - A magnified cross-section of a typical metallic part surface


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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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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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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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3. Lay-predominantdirection or

pattern of thesurface texture

Figure 5.4 - Possible

lays of a surface


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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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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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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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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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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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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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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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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)



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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



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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



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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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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

Download - Product specificationDimensioning and tolerancing

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