Engineering Product Specification

8/12/2019 Engineering Product Specification

1/39

Chapter 2 Chang, Wysk & Wang, Computer Aided Manufacturing, 3rd Ed,Prentice Hall, 2006

1

Chapter 2Engineering Product

Specification


2/39


2

Evolution/realization of a product


3/39


3

Idea sketch prepared by Leonardoda Vinci (1452-1519). (Courtesy of Institut de France.)


4/39


4

Perspective projection andorthographic projection

a. Perspectiveprojection

b. Orthographicprojection

Vanishing point Vanishing point


5/39


5

Isometric project axes

120

120

120


6/39


6

Multiview drawing of a bracket


7/39


8/39


8

Reconstruct a three-dimensionalgeometry from the three view

drawing in Figure 2-5

Refine thedrawing


9/39


9

Partial views. (a) Sectional view,(b) auxiliary view on the A-A

direction

A

A

2 . 0 0 0 0 . 0 0 1

A A

A - A

B


10/39


10

Dimension specification

2.500

Dimension line Extensionline

Dimension value


11/39


11

Adequate dimension

0.83 1.22

3.03

1.72

0.86


12/39


12

Redundant dimension on X-axis,and incomplete dimension on Y-

axis

0.83 0.95 1.22

3.03


13/39


13

Tolerancing: bilateral andunilateral. Dashed lines show the

tolerance limits


14/39


14

Tolerance stacking example 1

0.80 0.01 1.20 0.01

1.00 0.01

?


15/39


15

Tolerance stacking example 2

0.80 0.01 1.20 0.01

3.00 0.01

?


16/39


16

Illustration of unidirectional lay surfacecharacteristics (ANSI Standard B46.1-1978)


17/39


17

Surface roughness symbol

a = roughness value Ra in micrometersb = production method, treatment, coating,other text or note calloutc = roughness cutoff or sampling length inmillimetersd = direction of laye = minimum material removal requirementin millimeters

f = roughness value other than Ra inmicrometers preceded by its parametersymbol (e.g. Rz 0.4)


18/39


18

Lay symbols and examplesLay Symbol Meaning Example

Lay approximately parallel to the line representing the surface to which thesymbol is applied.

Lay approximately perpendicular to the line representing the surface towhich the symbol is applied.

Lay angular in both directions to the line representing the surface to whichthe symbol is applied.

Lay multidirectional.

Lay approximately circular relative to the center of the surface to which thesymbol is applied.

Lay approximately radial relative to the center of the surface to which thesymbol is applied.

Lay particulate, non-directional, or protuberant.


19/39


19

Examplesof the

surfacetexturesymbol

application

Basic Surface Texture Symbol. Surface may be produced by any method except when the bar or circle (Symbol b or d) is specified.

Material Removal By Machining Is Required. The horizontal bar indicates material removal by machining is required to produce the surface and material must be provided for that purpose.

Material Removal Allowance. Value in millimeters for "X" defines the minimum materialremoval requirement.

Material Removal Prohibited. The circle in the vee indicates the surface must be produced by processes such as casting, forging, hot finishing, cold finishing, die casting, powdermetallurgy and injection molding without subsequent removal of material.

Surface Texture Symbol. To be used when any surface texture values, production method,

treatment, coating or other text are specified above the horizontal line or to the right of thesymbol. Surface may be produced by any method except when bar or circle (Symbol b or d)is specified or when the method is specified above the horizontal line.

Roughness average rating is placed at the left of the long leg and the roughness cutoff ratingor sampling length is placed at the right. The specification of only one rating for roughnessaverage shall indicate the maximum value and any lesser value shall be acceptable. Specifythe roughness average in micrometers.

The specification of maximum and minimum roughness average values indicates a permissible range of roughness. Specify in micrometers.

Removal of material prohibited.

Roughness sampling length or cutoff rating is placed below the horizontal extension and ismandatory in all cases when values are applied to the symbol. Specify in millimeters.

Lay designation is indicated by the lay symbol placed at the right of the long leg.


20/39


20

Roughness profile

Roughness width cutoff


21/39


21

Recommended Height Values


22/39


23/39


23

A tolerance graph

A B C D E d AB,t AB d BC ,t BC d CD ,t CD

d AE,t AE


24/39


24

Example

A B C D E


25/39


25

Solution

d AB,t AB d DE ,t DE d CD ,t CD

d AE,t AE

A B C D E


26/39


26

Over specification of dimensionand tolerance

A B C

d1,t1 d2,t2

d3,t3


27/39


27

Tolerance graph for example inFigure 2-24

A B C d1,t1 d2,t2

d3,t3


28/39


28

Under specification

A B C D E


29/39


29

Tolerance graph for drawing inFigure 2-26.

A B C D E d1,t1 d2,t2

d3,t3


30/39


30

Design specification

3.00 0.01

1.00 0.01

1.00 0.01

A B C D


31/39


31

Process Plan

Process Plan

1 Chuck on the left side,use A as reference. CutC and D.

2 Turn the workpiece

around, use D (newlycut surface) asreference. Cut B and A.


32/39


32

Tolerance chart (Not shown are processtolerance assignment and balance)

0 .0 1 0 .01

0 . 01

stockboundary

Dim t ol

1.0 0.011.0 0.013.0 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


33/39


33

Accuracy versus precision in process.Dots in targets represent location of

shots. Cross represent location of theaverage position of all shots

(a) Accurate andprecise

(b) Not accurate but precise

(c) Accurate but notprecise

(d) Precise within sample, notprecise between samples, not

accurate.


34/39


34

(A) A frequency curve of 50 measurements on screw machine part. (B)Relative position of frequency curve of the process relative to the

specification limits shows good statistical control

(A) F f h i


35/39


35

(A) Frequency curve of a process that is notcentralized. (B) Frequency curve of a process that

has too large a spread of variation.


36/39


36

Chart reflecting average and rangeover a period of time


37/39


37

Frequency distribution of OD of hubdiameter.


38/39


38

Mortality curve based on RobertLussers concepts.

Mortality curve on product designed and


39/39

Ch 2 Ch W k & W C Aid d M f i 3 d Ed 39

Mortality curve on product designed andbuilt on a well-conceived quality-control and

reliability program.

Documents

Engineering Product Specification