A CASE STUDY ON CERAMIC INDUSTRY OF BANGLADESH.pptx
GD&T
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Avijeet PSuryavanshi | Consultant |
www.avijeetsuryavanshi.blogspot.com
All rights reserved with respect to all dispositions.
Qualified Bachelor of Engineering in Mechanical Engineering from
Institute of Engineering and Technology, University of Agra, Agra
India, under taking Gov. of India, and MBA in Operations and
Supply chain Management from Pondicherry University,
Pondicherry India. Member of Indian Value Engineering
Society(NIMA2003) India, Writer.
Have significant understanding of Automotive, Computer Aided Design and Engineering
(CAD/CAE), Design Consulting and Product Engineering as well as managerial and analytical
skills. Therefore, have keen interest in Automotive, PLM Software Services, Engineering Services,
and Manufacturing.
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TOLRANCE
Size Geometry
Allowance for
Specific
Variation
Impossible to manufacture an exact size and
geometry
Large variation affect the functionality
Small variation affect the cost
Limits specifying the
allowed variation in
each dimension e.g.
length, width, height,
diameter etc. which are
mentioned on the
drawing.
Allow for specification
of tolerance for the
geometry of a part and
it is separate from its
size. Special symbols are
used to control different
geometric features of a
part
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The Design
What Can Go Wrong?
Limit dimensions were used to define part
Controls diametrically opposed elements only
Pin can be lobed and still meet this requirement
There is no form control for roundness
There is also no form control for straightness
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“The purpose of GD&T is to describe the engineering intent of parts and assemblies” –ASME Y14.5-2009
GD&T is covered by several standards
ASME Y14.5 -2009 Dimensioning and Tolerancing
ASME Y14.5M-1994 Dimensioning and Tolerancing
ASME Y14.5.1M-1994 Mathematical Definition of Dimensioning and Tolerancing Principles
ISO 286-1:1988 ISO system of limits and fits —Part 1: Bases of tolerances, deviations and fits
ISO 286-2:1988 ISO system of limits and fits —Part 2: Tables of standard tolerance grades and limit deviations for holes
and shafts
ISO 1101:2005 Geometrical Product Specifications (GPS) —Geometrical tolerancing—Tolerancing of form, orientation,
location and run-out
ISO 5458:1998 Geometric Product Specifications (GPS) —Geometrical tolerancing—Positional tolerancing
ISO 5459:1981 Technical drawings —Geometrical tolerancing—Datumsand datum-systems for geometrical tolerances
WHAT IS GEOMETRIC DIMENSIONING & TOLERANCING (GD&T)?
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ASME Y14.5M-2009
Developed and published by the American Society of
Mechanical Engineers (ASME)
Reaffirmed in 1999 and 2004
Replaced by ASME Y14.5M-2009
Committee members are selected from industry and
volunteer their time (not paid)
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Understanding of Datum
The datum features consist of capital letter enclosed on square
box.
Letters can be A,B,C..etc or combination of (AA, BB, CC..) except I,
O and Q.
Datum is generally place on a plane or size feature.
The datum targets are used to locate a part in datum
reference frame.
Symbolized as shown in above figure.
Lower half indicates associated datum with number.
Upper half indicates the datum target area.
Datum targets are used whenever the whole surface may introduce the uncertainties of obtaining repeatable measurements e.g
casting, forging, warped or bowed surface.
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Feature Control Frame
The position of the feature must be within .014 Diametrical
tolerance zone at maximum material condition and relative to
datum A,B and C.
FCF is attached to the side view of the surface
by using the leader line in surface.
For Axis, it is attached to below or closely
adjacent to the dimension or note patterning to
that feature.
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Material Conditions
This is when part weight will be the most
MMC for shaft is the largest allowable size
MMC for hole is the smallest allowable size
Also known as MODIFIER
Maximum Material Condition(MMC) M
Least Material Condition(LMC) L
In this case the weight of the part is least
LMC for shaft is the smallest allowable size
LMC for hole is the largest allowable size
Regardless of Feature Size (RFS)
Material Conditions are not to be considered
The Size feature (dimension) does not affect the specified geometric tolerance
It is applicable when geometric tolerance applied to axis or center plane
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Material Conditions
ASME Rule 1- Individual Feature of size (Taylor Principle)
Where only a tolerance of size is specified, the limits of size of an individual feature prescribe the extent to which
variations in its form – as well as in its size- are allowed
Limits of the Size for an individual feature will also control the allowable variation in Form of that feature
Does not apply to the parts which are not rigid
Where only tolerance of size is specified
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Material Conditions
ASME Rule 2- Apply to Axis
The regardless of feature of size concept (RFS) is implied for geometric tolerance and any datum feature of size
Where no MMC (M) or LMC (L) symbol is specified in the Feature Control Frame
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Bonus Tolerance
Bonus tolerance is an additional tolerance for a
geometric control
When the actual mating size of feature’s departs
from MMC towards LMC
An increase in the stated tolerance— equal to the
amount of the departure — is permitted. This
increase or extra tolerance is called the bonus
tolerance