PART DESIGN SPECIFICATION

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PART DESIGN SPECIFICATION. Fall 2008 Dr. R. A. Wysk. Go over engineering specifications Functional requirements Form, fit and function Dimensioning Tolerancing Engineering drawings datum. Agenda. Read Chapter 2 and 3 from Computer Aided manufacturing (3 rd Edition)

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PART DESIGN SPECIFICATION

Fall 2008

Dr. R. A. Wysk

Go over engineering specifications

Functional requirements

Form, fit and function

Dimensioning

Tolerancing

Engineering drawings

datum

Agenda

Overview of engineering design

Mechanical design representations

Engineering drawing

Geometric dimensioning and tolerancing

AMSE Y14.5

Materials
Design Process

How can this be accomplished?

1. Clarification of the task

2. Conceptual design

3. Embodiment design

4. Detailed design

THE DESIGN PROCESSProduct Engineering

Design Process

Off-road bicycle that ...

1. Conceptualization

2. Synthesis

3. Analysis

4. Evaluation

5. Representation

Functional requirement -> Design

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

• Verbal

• Sketch

• Multi-view orthographic drawing (drafting)

• CAD 3D & surface model

• Solid model

• Feature based design

DESIGN REPRESENTATION

Design

Engineering

Representation

Manufac-

turing

Requirement of the representation method

• precisely convey the design concept

• easy to use

0.9444"

A FORMAL 3-VIEW DRAWING

4 holes 1/4" dia

around 2" dia , first

hole at 45°

±

2.000

0.001

A

X

I

I

I

DESIGN DRAFTING

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Third angle projection

Drafting in the third angle

A

A

±

2

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0

0

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1

A

DESIGN DRAFTING

Partial view

A

-

A

Cut off view and auxiliary view

Provide more local details

Requirements

1. Unambiguous

2. Completeness

3. No redundancy

1.22 '

0.98 '

3.03 '

1.72 '

1.22 '

3.03 '

DIMENSIONING

Incomplete

dimensioning

0.83 '

Redundant dimensioning

0.86 '

0.83 '

Dimensional tolerance - conventional

Geometric tolerance - modern

TOLERANCE

nominal dimension

+

means a range

0.95 - 1.05

1.00 0.05

-

tolerance

+ 0.10

- 0.00

+ 0.00

- 0.10

0.95

1.05

unilateral

bilateral

+

1.00 0.05

-

1.20 '

±0.01

1.00 '

±0.01

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

?

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

3.00 '

±0.01

TOLERANCE STACKING (ii)

?

0.80 '

±0.01

1.20 '

±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

1.20 '

±0.01

3.00 '

±0.01

TOLERANCE STACKING (iii)

x

?

0.80 '

±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

G(N,d,t)

N: a set of reference lines, sequenced nodes

d: a set of dimensions, arcs

t: a set of tolerances, arcs

TOLERANCE GRAPH

d,t

d,t

d,t

A B C D E

d,t

d : dimension between references i & j

t : tolerance between references i & j

ij

ij

Reference i is in front of reference j in the sequence.

EXAMPLE TOLERANCE GRAPH

d,t

d,t

d,t

A B C D E

d,t

different properties

between d & t

If one or more cycles can be detected in the graph, we say that the dimension and tolerance are over specified.OVER SPECIFICATION

d1

d2

A B C

d1,t1

d2,t2

d3

Redundant dimension

d3,t3

A

B

C

t1

t2

A B C

t3

Over constraining tolerance

(impossible to satisfy) why?

UNDER SPECIFICATION

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

dimension or tolerance is under specified.

d2

d1

A B C D E

d3

A

B

C

D

E

C D

is disconnected from the

rest of the graph.

No way to find

PROPERLY TOLERANCED

A

B

C

D

E

d,t

d,t

d,t

A B C D E

d,t

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?

TOLERANCE ANALYSIS

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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.

t

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t

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3-D GEOMETRIC TOLERANCEPROBLEMS

datum surface

datum

surface

± t

Reference

frame

perpendicularity

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.)

TOLERANCE ASSIGNMENT

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t

function

cost

+

t

-

t

d

(

n

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d

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s

i

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)

Tolerance value

Quality cost

• 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.

REASON OF HAVING TOLERANCE
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)?

EFFECTS OF TOLERANCE (II)

2. Assembly constraints

e.g. peg-in-a-hole

dp

How to maintain the clearance?

dh

Compound fitting

The dimension of each segment affects others.

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.

A

RELATION BETWEENPRODUCT & PROCESSTOLERANCES

±

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Design specifications

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±

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±

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±

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5

Process tolerance

A method to allocate process tolerance and verify that the process sequence and machine selection can satisfy the design tolerance.TOLERANCE CHARTING

Not shown are

process tolerance

assignment and

balance

blue print

Operation

sequence

produced tolerances:

process tol of 10 + process tol of 12

process tol of 20 + process tol 22

process tol of 22 + setup tol

SURFACE FINISH

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Usually

simplified:

waviness height

63

waviness width

roughness

height

0.002 - 2

63

roughness width cutoff

default is 0.03" (ANSI Y14.36-1978)

0.010

0.005

(m inch)

roughness width

(inch)

Lay

PROBLEMS WITH DIMENSIONALTOLERANCE ALONE

As designed:

1

.

0

0

±

0

.

0

0

1

6

.

0

0

±

0

.

0

0

1

As manufactured:

1

.

0

0

1

1

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0

0

1

Will you accept the part

at right?

Problem is the control of

straightness.

How to eliminate the

ambiguity?

1

.

0

0

1

6

.

0

0

FORM

straightness

flatness

Circularity

cylindricity

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

ORIENTATION

perpendicularity

angularity

parallelism

Squareness

roundness

LOCATION

concentricity

true position

symmetry

RUNOUT

circular runout

total runout

PROFILE

profile

profile of a line

Datum: 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 more surfaces such as holes, faces, screw threads, profiles, or slots.

Feature Control Frame:

DATUM & FEATURE CONTROL FRAME

A

datum

// 0.005 M A

modifier

tolerance value

symbol

Maximum material condition MMC assembly

Regardless of feature size RFS (implied unless specified)

Least material condition LMC less frequently used

Projected tolerance zone

Diametrical tolerance zone

T Tangent plane

F Free state

MODIFIERS

maintain critical wall thickness or critical location of features.

MMC, RFS, LMC

MMC, RFS

RFS

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.

SOME TERMS
Three perfect planes used to locate the imperfect part.

a. Three point contact on the primary plane

b. two point contact on the secondary plane

c. one point contact on the tertiary plane

primary

Tertiary

O 0.001 M A B C

DATUM REFERENCE FRAME

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Secondary

C

B

A

1.000 '

±0.002

1.000 '

±0.002

STRAIGHTNESS

Tolerance zone between two straightness lines.

Value must be smaller than the size tolerance.

0

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0

0

1

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0

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0

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1

Design

Meaning

1.000 '

±0.002

FLATNESS

Tolerance zone defined by two parallel planes.

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0

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1

1.00 '

±0.05

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

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0

1

0

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1

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At any section along the cylinder

1.00 '

±0.05

CYLINDRICITY

Tolerance zone bounded by two concentric cylinders within which the cylinder must lie.

0

.

0

1

Rotate in a V

0

.

0

1

Rotate between points

A

.

0

0

2

T

1.000 '

±0.005

0.500 '

±0.005

2.000 '

±0.005

PERPENDICULARITY

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

or axis.

.

0

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2

A

0

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0

0

2

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A

A

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±

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0

0

2

A

3.500 '

±0.005

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

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5

A

1

.

5

0

0

±

0

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0

0

5

4

0

°

A

1.000 "

±0.005

2.000 "

±0.005

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

A

0

.

0

0

1

B

PROFILE

A uniform boundary along the true profile within whcih

the elements of the surface must lie.

0

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0

0

5

A

B

0

.

0

0

1

A

1.500 "

±0.005

0.361 "

±0.002

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

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0

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5

A

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1.500 "

±0.005

0.361 "

±0.002

TOTAL RUNOUT

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0

5

A

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TRUE POSITION

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2

Dimensional

tolerance

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±

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1

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2

0

±

0

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0

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O

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8

0

±

0

.

0

2

Hole center tolerance zone

O

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1

M

A

B

True position

tolerance

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0

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d

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B

1

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2

0

A

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.

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

TOLERANCE VALUE MODIFICATION

O

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.

0

0

±

0

.

0

2

O

0

.

0

1

M

A

B

1

.

0

0

M L S

B

1

.

2

0

MMC

LMC

A

The default modifier for

true position is MMC.

For M the allowable tolerance = specified tolerance + (produced hole

size - MMC hole size)

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.MMC HOLE

,

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

U

N

C

-

2

B

O

.

0

1

0

M

A

B

C

.

2

5

0

p

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.

SOME NUMBERS

Krulikowski, A., GD&T Challenges the Fast Draw, MFG ENG, Feb 1994.