7/22/2019 Dimensions, Tolerances, And Surfaces
1/38
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals o f Mod ern Manufac tur ing 3/e
5. Dimensions, Tolerances, and Surfaces
1. Dimensions, Tolerances, and Related Attributes
2. Surfaces
3. Effect of Manufacturing Processes
7/22/2019 Dimensions, Tolerances, And Surfaces
2/38
ME 3631
Manufacturing Processes I
Lecture Objective
Dimensions, Tolerances, and Surfaces
Dimensions and TolerancesSurfaces
Characteristics of Surfaces
Surface Texture
Surface Integrity
Tolerances and m anufactur ing Processes
Surfaces and manufactur ing Processes
Lecture No. 03
7/22/2019 Dimensions, Tolerances, And Surfaces
3/38
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals o f Mod ern Manufac tur ing 3/e
Dimensions, Tolerances, and Surfaces
1. Dimensions, Tolerances, and Related Attributes
2. Surfaces
3. Effect of Manufacturing Processes
7/22/2019 Dimensions, Tolerances, And Surfaces
4/38
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals o f Mod ern Manufac tur ing 3/e
Dimensions and Tolerances
Factors that determine the performance of amanufactured product, other than mechanicaland physical properties, include :
Dimensions - linear or angular sizes of acomponent specified on the part drawing
Tolerances - allowable variations from thespecified part dimensions that are permitted
in manufacturing
7/22/2019 Dimensions, Tolerances, And Surfaces
5/38
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals o f Mod ern Manufac tur ing 3/e
Dimensions (ANSI Y14.5M-1982):
A dimension is "a numerical value expressed inappropriate units of measure and indicated on adrawing and in other documents along with lines,symbols, and notes to define the size or
geometric characteristic, or both, of a part or partfeature"
Dimensions on part drawings represent nominalor basic sizes of the part and its features
The dimension indicates the part size desired bythe designer , if the part could be made with noerrors or variations in the fabrication process
7/22/2019 Dimensions, Tolerances, And Surfaces
6/38
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals o f Mod ern Manufac tur ing 3/e
Tolerances (ANSI Y14.5M-1982):
A tolerance is "the total amount by which aspecific dimension is permitted to vary. Thetolerance is the difference between themaximum and minimum limits"
Variations occur in any manufacturing process,which are manifested as variations in part size
Tolerances are used to define the limits of the
allowed variation
7/22/2019 Dimensions, Tolerances, And Surfaces
7/38
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals o f Mod ern Manufac tur ing 3/e
Bilateral Tolerance
Variation is permittedin both positive andnegative directionsfrom the nominal
dimension Possible for a
bilateral tolerance tobe unbalanced; for
example, 2.500+0.010, -0.005
Figure 5.1 Ways to specifytolerance limits for anominal dimension of 2.500:(a) bilateral
7/22/2019 Dimensions, Tolerances, And Surfaces
8/38
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals o f Mod ern Manufac tur ing 3/e
Unilateral Tolerance
Variation from thespecified dimension ispermitted in only onedirection
Either positive ornegative, but not both
Figure 5.1 Ways to specifytolerance limits for anominal dimension of 2.500:(b) unilateral
7/22/2019 Dimensions, Tolerances, And Surfaces
9/38
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals o f Mod ern Manufac tur ing 3/e
Limit Dimensions
Permissiblevariation in a partfeature size consistsof the maximum and
minimumdimensions allowed
Figure 5.1 - Ways to specifytolerance limits for anominal dimension of 2.500:(c) limit dimensions
7/22/2019 Dimensions, Tolerances, And Surfaces
10/38
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals o f Mod ern Manufac tur ing 3/e
Other Geometric Attributes
Angularity. The extent to which a part featuresuch as a surface or axis is at a specified anglerelative to a reference surface
Circularity. Circularity is the degree to which allpoints on the intersection of the surface and aplane perpendicular to the axis of revolution areequidistant from the axis.
Concentricity . The degree to which any two (ormore) part features, such as a cylindrical surfaceand a circular hole have a common axis.
7/22/2019 Dimensions, Tolerances, And Surfaces
11/38
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals o f Mod ern Manufac tur ing 3/e
Flatness. The extent to which all points on a surfacelie in a single plane.
Parallelism. The degree to which all points on a partfeature, such as a surface, line, or axis, areequidistant from a reference plane or line or axis.
Perpendicularity. The degree to which all points on apart feature, such as a surface, line, or axis, are 90o
from a reference plane or line or axis.
Straightness. The degree to which a part featuresuch as a line or axis is a straight line.
7/22/2019 Dimensions, Tolerances, And Surfaces
12/38
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals o f Mod ern Manufac tur ing 3/e
Dimensions, Tolerances, and Surfaces
1. Dimensions, Tolerances, and Related Attributes
2. Surfaces
3. Effect of Manufacturing Processes
7/22/2019 Dimensions, Tolerances, And Surfaces
13/38
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals o f Mod ern Manufac tur ing 3/e
Why Surfaces are Important
Aesthetic reasonsSurfaces affect safety
Friction and wear depend on surface
characteristicsSurfaces affect mechanical and physicalproperties
Assembly of parts is affected by their surfaces
Smooth surfaces make better electricalcontacts
7/22/2019 Dimensions, Tolerances, And Surfaces
14/38
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals o f Mod ern Manufac tur ing 3/e
Surfaces
Nominal surface designers intended surfacecontour of part, defined by lines in theengineering drawing
The nominal surfaces appear asabsolutely straight lines, ideal circles,round holes, and other edges andsurfaces that are geometrically perfect
Actual surfaces of a part are determined bythe manufacturing processes used to make it
Variety of processes result in widevariations in surface characteristics
7/22/2019 Dimensions, Tolerances, And Surfaces
15/38
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals o f Mod ern Manufac tur ing 3/e
Surface Technology
Concerned with:Defining the characteristics of a surface
Surface texture
Surface integrity
Relationship between manufacturing processes and characteristics of resulting
surface
7/22/2019 Dimensions, Tolerances, And Surfaces
16/38
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals o f Mod ern Manufac tur ing 3/e
Surface Texture
The topography and geometric features of thesurface
When highly magnified, the surface is anythingbut straight and smooth
It has roughness, waviness, and flaws
It also possesses a pattern and/or directionresulting from the mechanical process that
produced it
7/22/2019 Dimensions, Tolerances, And Surfaces
17/38
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals o f Mod ern Manufac tur ing 3/e
Metallic Part Surface
Figure 5.2 A magnified cross-section of a typical metallic part surface
7/22/2019 Dimensions, Tolerances, And Surfaces
18/38
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals o f Mod ern Manufac tur ing 3/e
Surface Texture
Repetitive and/or random deviations from thenominal surface of an object
Figure 5.3 Surface texture features
7/22/2019 Dimensions, Tolerances, And Surfaces
19/38
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals o f Mod ern Manufac tur ing 3/e
Four Elements of Surface Texture
1. Roughness - small, finely-spaced deviationsfrom nominal surface
Determined by material characteristics and processes that formed the surface
2. Waviness - deviations of much larger spacing
Waviness deviations occur due to workdeflection, vibration, heat treatment, andsimilar factors
Roughness is superimposed on waviness
7/22/2019 Dimensions, Tolerances, And Surfaces
20/382007 John Wiley & Sons, Inc. M P Groover, Fundamentals o f Mod ern Manufac tur ing 3/e
Four Elements of Surface Texture
3. Lay -predominantdirection orpattern of thesurface texture
Figure 5.4 Possiblelays of a surface
7/22/2019 Dimensions, Tolerances, And Surfaces
21/38
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals o f Mod ern Manufac tur ing 3/e
Four Elements of Surface Texture
4. Flaws - irregularities that occur occasionally onthe surface
Includes cracks, scratches, inclusions, andsimilar defects in the surface
Although some flaws relate to surfacetexture, they also affect surface integrity
7/22/2019 Dimensions, Tolerances, And Surfaces
22/38
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals o f Mod ern Manufac tur ing 3/e
Surface Texture
Repetitive and/or random deviations from thenominal surface of an object
Figure 5.3 Surface texture features
7/22/2019 Dimensions, Tolerances, And Surfaces
23/38
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals o f Mod ern Manufac tur ing 3/e
Surface Roughness
Average of vertical deviations from nominalsurface over a specified surface length
Figure 5.5 Deviations from nominal surface used in the twodefinitions of surface roughness.
7/22/2019 Dimensions, Tolerances, And Surfaces
24/38
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals o f Mod ern Manufac tur ing 3/e
Surface Roughness Equation
Arithmetic average (AA) based on absolutevalues of deviations, and is referred to asaverage roughness
where R a = average roughness; y = verticaldeviation from nominal surface (absolutevalue); and L m = specified distance over whichthe surface deviations are measured
dx Ly
R
mL
ma 0=
7/22/2019 Dimensions, Tolerances, And Surfaces
25/38
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals o f Mod ern Manufac tur ing 3/e
Alternative Surface Roughness Equation
Approximation of previous equation is perhapseasier to comprehend
where R a has the same meaning as above; y i =
vertical deviations (absolute value) identified bysubscript i ; and n = number of deviationsincluded in Lm
n
i
i a
n
y R
1
7/22/2019 Dimensions, Tolerances, And Surfaces
26/38
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals o f Mod ern Manufac tur ing 3/e
Cutoff Length
A problem with the R a computation is thatwaviness may get included
To deal with this problem, a parameter calledthe 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 eliminates waviness deviationsand only includes roughness deviations
7/22/2019 Dimensions, Tolerances, And Surfaces
27/38
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals o f Mod ern Manufac tur ing 3/e
Surface Roughness Specification
Figure 5.6 Surface texture symbols in engineeringdrawings: (a) the symbol, and (b) symbol with
identification labels
7/22/2019 Dimensions, Tolerances, And Surfaces
28/38
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals o f Mod ern Manufac tur ing 3/e
Surface Integrity
Surface texture alone does not completelydescribe a surface
There may be metallurgical changes in thealtered layer beneath the surface that can havea significant effect on a material's mechanicalproperties
Surface integrity is the study and control of thissubsurface layer and the changes in it thatoccur during processing which may influencethe performance of the finished part or product
7/22/2019 Dimensions, Tolerances, And Surfaces
29/38
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals o f Mod ern Manufac tur ing 3/e
Surface Changes Caused by Processing
Surface changes are caused by the applicationof various forms of energy during processing
Example: Mechanical energy is the mostcommon form in manufacturing
Processes include forging, extrusion,and machining
Although its primary function is to change
geometry of workpart, mechanical energycan also cause residual stresses, workhardening, and cracks in the surface layers
7/22/2019 Dimensions, Tolerances, And Surfaces
30/38
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals o f Mod ern Manufac tur ing 3/e
Energy Forms in Surface Integrity
Mechanical energyThermal energy
Chemical energy
Electrical energy
7/22/2019 Dimensions, Tolerances, And Surfaces
31/38
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals o f Mod ern Manufac tur ing 3/e
Surface Changes by Mechanical Energy
Residual stresses in subsurface layerExample: bending of sheet metal
Cracks - microscopic and macroscopic
Example: tearing of ductile metals inmachining
Voids or inclusions introduced mechanically
Example: centerbursting in extrusion
Hardness variations (e.g., work hardening)
Example: strain hardening of new surface inmachining
7/22/2019 Dimensions, Tolerances, And Surfaces
32/38
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals o f Mod ern Manufac tur ing 3/e
Surface Changes by Thermal Energy
Metallurgical changes (recrystallization, grainsize changes, phase changes at surface)
Redeposited or resolidified material (e.g.,welding or casting)
Heat-affected zone in welding (includes someof the metallurgical changes listed above)
Hardness changes
7/22/2019 Dimensions, Tolerances, And Surfaces
33/38
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals o f Mod ern Manufac tur ing 3/e
Surface Changes by Chemical Energy
Intergranular attackChemical contamination
Absorption of certain elements such as H and
Cl in metal surfaceCorrosion, pitting, and etching
Dissolving of microconstituents
Alloy depletion and resulting hardness changes
7/22/2019 Dimensions, Tolerances, And Surfaces
34/38
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals o f Mod ern Manufac tur ing 3/e
Surface Changes by Electrical Energy
Changes in conductivity and/or magnetismCraters resulting from short circuits duringcertain electrical processing techniques suchas arc welding
7/22/2019 Dimensions, Tolerances, And Surfaces
35/38
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals o f Mod ern Manufac tur ing 3/e
Dimensions, Tolerances, and Surfaces
1. Dimensions, Tolerances, and Related Attributes
2. Surfaces
3. Effect of Manufacturing Processes
7/22/2019 Dimensions, Tolerances, And Surfaces
36/38
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals o f Mod ern Manufac tur ing 3/e
Tolerances and Manufacturing Processes
Some manufacturing processes are inherentlymore accurate than others
Examples:
Most machining processes are quiteaccurate, capable of tolerances = 0.05 mm( 0.002 in.) or better
Sand castings are generally inaccurate, and
tolerances of 10 to 20 times those used formachined parts must be specified
7/22/2019 Dimensions, Tolerances, And Surfaces
37/38
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals o f Mod ern Manufac tur ing 3/e
Surfaces and Manufacturing Processes
Some processes are inherently capable ofproducing better surfaces than others
In general, processing cost increases withimprovement in surface finish because
additional operations and more time areusually required to obtain increasingly bettersurfaces
Processes noted for providing superiorfinishes include honing, lapping, polishing,and superfinishing
7/22/2019 Dimensions, Tolerances, And Surfaces
38/38
Thats All for Today
2007 J h Wil & S I M P G F d t l fM d M f t i 3/