Introduction to Geometric Dimensioning and Tolerancing
Hi!
To impart the basic knowledge of ‘Geometric Dimensioning and Tolerancing (GDT)’.
Develop an awareness of GDT concepts and explain how the techniques are used to understand, control, and help reduce variation in the overall (---) process.
Objective:
1. Think About• Product Requirements• Dimensional Management
2. Geometric Dimensioning & Tolerancing (GDT)• What is GDT?• Why is GDT required?• How it is different from conventional drawings,• Which Standards are used?• Definitions• Virtual Condition
Agenda:
2. Geometric Dimensioning & Tolerancing (GDT)
(Continued)
• Bonus Tolerance• Datum Symbology• Datum Referencing• Six Degrees of Freedom• Datum Shift
3. From GD&T to practical gauges
Agenda (Continued) :
Product Requirement Aesthetic ( Fit and Finish) Safety Durability & Operability Requirements (Functional) NVH and Buzz, Squeak, Rattle (Product experience)
Constraint Cost, (and Cost and Cost >>>) Manufacturing Process Capability Timeline
Product Design :
Product Design :
-24 -18 -12 -6 0
Launch
6
Eng
inee
ring
Cha
nges
pro
pose
d
Timeline
How to achieve the Requirements?
Locating and Attachment as per Functional Requirement (Fit and Finish, Assembly, Safety etc.)
Stack Up analysis to optimize tolerances.
As tolerances are functional and achieved using Stack Up – it eliminates unnecessary tighter tolerances.
Product Design :
Product Design :
Dimensional Management Process
Technical Design Review
Concept
Locating Strategy
Tolerance Analysis
FnF Requirement (Loop)
Technical Design Review & GDT Signoff
Engineering Release
Gage Concept & Design
Tooling Concept & Design
Gage R&R, Part Capability, FnF Inspection etc will continue.
Dimensional Management
1. Geometric Dimensioning & Tolerancing Datum (Locating & Attachment Strategy) Tolerances
2. Tolerance Analysis Worst case analysis Root Sum Square (RSS)
3. Qualification (Gaging)
Dimensional Management:
Geometric Dimensioning & Tolerancing
Geometric Dimensioning & Tolerancing :
What is Geometric Dimensioning & Tolerancing?
GDT is the language from Design to Manufacturing and Inspection defining how to qualify the part.
It is an international graphic engineering language formed to allow engineers - “say exactly what they mean”. The concepts, symbols and mathematical structure of GDT is used for describing the manufacturing tolerance zones to express the “Design (Functional) Intent” of parts or assemblies.
Geometric Dimensioning & Tolerancing :
The goal of GDT is to Improve Communication !!
Read
Important
Engineering language
Graphic language
Mathematical structure
“to say exactly what we mean”
about the “Design (Functional) Intent”
Geometric Dimensioning & Tolerancing :
The goal of GDT is to Improve Communication !!
Why Geometric Dimensioning & Tolerancing?
The reason for the importance of this subject is –
Geometric Dimensioning & Tolerancing :
?
- because it saves Money.
Geometric Dimensioning & Tolerancing :
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Tolerance
Mon
ey
1. Improves Communication Reduces subjective interpretation, ambiguity, assumptions and
the controversies. Same language for Designer, Manufacturer & Inspector.
2. Better Product Design Tool to express “what they mean exactly”. Functional philosophy for Tolerancing – studies product function
in the design stage for “Functional Tolerancing”.
3. Increased Production Tolerances “Bonus” or extra Manufacturing Tolerance – savings in cost. Functional approach provides larger tolerance in “Other zones”.
Geometric Dimensioning & Tolerancing :
4. Functional Performance Properly applied GD&T assures assembly, interchangeability,
and functional performance of all mating details.(Parts produced at different locations & assembled somewhere else – “outsourcing”)
5. Coordinated Datum Locations / Functional Tolerancing GDT provides a method of maintaining coordination between
functional design features, manufacturing processes & inspection practices (coordinated datum locations).
Geometric Dimensioning & Tolerancing :
“Maximizing production tolerances without sacrificing Quality and Reliability.”
GDT Standards
ASME, ANSI, JIS, ISO
We will refer the ASME Y14.5M - 1994
Geometric Dimensioning & Tolerancing → Standards :
GDT → Definitions :
Definitions
Dimension
A numeric value expressed in appropriate units of measure and used to define the size, location, geometric characteristic, or surface texture of a part or part feature.
ToleranceThe total amount a specific dimension is permitted to vary. The tolerance is the difference between the maximum and minimum limits.
GDT → Definitions :
Basic Dimension
A numerical value used to describe the theoretically exact size, profile, orientation, or location of a feature or datum target. It is the basis from which permissible variations are established (by tolerances).
Reference Dimension
A dimension, usually without tolerance, used for
information purposes only.
GDT → Definitions :
Unilateral Tolerance
A tolerance in which variation is permitted in one direction from the specified dimension.
Equal Bilateral ToleranceA tolerance in which equal variation is permitted in both directions from the specified dimension.
GDT → Definitions :
50 +0.25/- 0
25
+/-
0.2
5
Datum
A theoretically exact point, axis, or plane derived from the true geometric counterpart of a datum feature - from which the Geometric Characteristics of a part are established.
Feature
Physical portion of a part, such as a surface, pin, tab, hole, or slot.
Datum Feature
An actual feature of a part that is used to establish a datum.
GDT → Definitions :
Simulated Datum
A point, axis, or plane established by inspection equipment, such as the following simulators: a surface plate, a gage surface, or a mandrel (Datum Feature Simulator).
Feature of Size,
One cylindrical or spherical surface, or set of two opposed elements or opposed parallel surfaces associated with a size dimension.
GDT → Definitions :
GDT → Definitions :
Part
(Workpiece)
Simulated Datum
(Surface on Gage or Fixture Locator)
Datum Feature Simulator ( V Block)
V Block is used to simulateDatum which is Axis of the part
GDT → Definitions :
MWHEN THE PART WEIGHS THE MOST!
Maximum Material Condition
The condition in which a feature of size contains the maximum amount of material within the stated limits of size -- for example, minimum hole diameter or maximum shaft diameter.
GDT → Definitions :
GDT → Definitions :
L
Least Material Condition
The condition in which a feature of size contains the least amount of material within the stated limits of size -- for example, maximum hole diameter or minimum shaft diameter.
WHEN THE PART WEIGHS THE LEAST!
GDT → Definitions :
GDT → Definitions :
Regardless of Feature Size
The term used to indicate that a geometric tolerance or datum reference applies at any increment of size of the feature within its size tolerance.
*
* No longer required to indicate “regardless of feature size” (See rule #2 ASME Y14.5M-1994).
S
GDT → Definitions :
Regardless of Feature Size
Actual Locating Hole
RFS Pin
Spring
A
Actual Mating Envelope
(a) For an External Feature - A similar perfect feature counterpart of smallest size that can be circumscribed about the feature so that it just contacts the surface at the highest points.
GDT → Definitions :
Actual Mating Envelope
(b) For an Internal Feature - A similar perfect feature counterpart of largest size that can be inscribed within the feature so that it just contacts the surface at the highest points.
GDT → Definitions :
True Geometric Counterpart
The theoretically perfect boundary (virtual condition or actual mating envelope) or best-fit (tangent) plane of a specified datum feature.
GDT → Definitions :
A
Datum axis A(Axis of truegeometric counterpart)
Datum feature simulatorTrue geometriccounterpart of datum- feature A(Smallest circumscribedcylinder)
Work piece
Datum feature A
Tolerance ZoneThe zone which the tolerance value represents.
GDT → Definitions :
Tolerance Zone
GDT → Definitions :
Virtual Condition
A constant boundary generated by the collective effects of a size feature’s specified MMC or LMC material condition and the geometric tolerance for that material condition.
GDT → Virtual Condition :
Virtual Condition is the ‘Worst Case’ envelope of boundary that occurs due to the combination of tolerances.
GDT → Virtual Condition :
Ø 6 +/- 1
Tolerance Zone Ø 1
Virtual Condition
What will be the Dia. of it ? Guess ?!
GDT → Virtual Condition :
GDT → Virtual Condition :
GDT → Virtual Condition :
GDT → Virtual Condition :
GDT → Virtual Condition :
Positional tolerance referred @ MMC No Positional tolerance
@ MMC
O
Shaft
O
12.5
Virtual Condition = MMC
Rules
GDT → Rules :
Individual Feature of SizeRule #1
Where only a tolerance of size is specified, the limits of size of an individual feature prescribe the extent to which variations in its geometric form as well as size are allowed.
In other words, features of size require:
PERFECT FORM AT (MMC)
GDT → Bonus Tolerance :
Bonus Tolerance – (Consider effect of MMC)
Ø 6 +/- 1
Part Size Virtual Condition
Position
Tolerance
Bonus
Tolerance
Effective
MMC 7 8 1 0 1
6 1 1 2
LMC 5 1 2 3
= 6 + 1 = 7 (For Shaft)= MMC + Position Tolerance= 7 + 1 = 8
MMCVC
GDT → Bonus Tolerance :
Bonus Tolerance – (Consider effect of MMC)
Ø 6 +/- 1
Tolerance Zone Ø 1
Virtual Condition Ø 8
Axis Matching
Axis in Tol. Zone
Outside Tol. Zone
GDT → Symbology :
Feature Control Frame
BA0.5 MM
C MaterialModifier(Datum)
DatumFeatureSymbol
DiameterSymbol
CBA1 M
MaterialModifier
(Tolerance)
DatumReferenceFrame
SecondaryDatum
ToleranceGeometric
CharacteristicSymbol
How to ‘Read’ it?
GDT → Symbology :
CBA1 M
The Feature is at a Circular Position tolerance zone of Ø 1.0 when produced at Maximum Material Condition with respect to Datum A, B, C
Read
GDT → Datum :
Datum Referencing
Six Degrees of Freedom
GDT → Datum :
Z Axis Linear
Z Axis Rotational
X Axis Linear
Y Axis Linear
X Axis Rotational
Y Axis Rotational
Six Degrees of Freedom
GDT → Datum :
PRIMARY
DATUM PLANE
TERTIARY
DATUM PLANE
SECONDARY
DATUM PLANE
o90º
90º
90º
Six Degrees of Freedom
3 - 2 - 1
GDT → Datum :
FIRSTDATUM PLANE
PART
Fixed
PART
PART
Fixed
PARTSECONDDATUM PLANEPART
Fixed
PART
THIRDDATUM PLANE
3
21
GDT → Datum :
Datum Reference Frame
Sufficient datum features are chosen to position the part in relation to a set of ‘Three mutually Perpendicular’ planes, jointly called a datum reference frame.
The part is oriented and immobilized relative to the three mutually perpendicular planes i.e. the datum reference frame in a selected order of precedence.
Read
1. Functional Datum (Recommended)
The actual features which locate and attach a part / assembly to its next part / assembly (on functional basis).
2. Non-Functional Datum
Features used to locate a part or assembly to a Gage based on convenience not function.
GDT → Datum :
GDT → Datum :
Plane Surface Datum Features
GDT → Datum :
Plane Surface Datum Features
GDT → Datum :
Cylindrical Datum Features
GDT → Datum :
Cylindrical Datum Features
GDT → Datum :
Inclined Datum Features
GDT → Datum :
Inclined Datum Features
A0 M
B
9.8 ± 0.1
A0 M B M
C
15.8 ± 0.1
Datum Precedence :
* See Below
Effect of Datum Precedence and MMC
Datum Precedence :
True geometriccounterpart ofdatum feature AWithout Perpendicularitytolerance
Datum axis A
Datum feature B(Secondary)
Datum feature BTrue geometriccounterpart of Datum feature B(Perpendicularto datum Axis A)
Datum Precedence @ A then B
Datum Precedence :
Datum feature B(True geometriccounterpart of Datum feature B)
Datum axis A
Datum feature B(Primary)
(VC Counter part holeConsidering diametricalTolerance and perpendicularity)
True geometriccounterpart ofdatum feature A
Datum feature A(Secondary)
Datum Precedence @ B then A
T
Gage @ RFS :
A
Taper pin locates the datum irrespective of the feature size
Gage @ MMC :
A
Datum Shift :
Datum Shift :
When Gaging a Part with a datum FOS referenced at MMC
-Gage is of Fixed size (i.e. Virtual Condition)
AØ1 M
B
Ø 10 ± 1
A1 M B M
C
7 ± 1
A
Gage Size (VC) 5
Gage Size (VC) 8
Datum Shift :
Datum Plane
7 ± 1 @ Position 1 @ MMCBonus @ LMC of 8 is 3i.e. center plane can vary ± 1.5
10 ± 1 @ Position 1 @ MMCBonus @ LMC of 11 is 3i.e. center axis can vary ± 1.5
Datum Shift :
Datum B is produced at MMC (Ø9) and centered to Gage Pin (Ø8) .
Slot is produced at MMC (6) and centered to Gage feature (5).
Datum Plane
Datum Shift :
Datum Plane
Datum B is produced at MMC (Ø9) and centered to Gage Pin (Ø8) .
Slot is produced at LMC (8) and centered to Gage feature (5).
Datum Shift :
Datum Plane
Datum B is produced at MMC (Ø9) and centered to Gage Pin (Ø8) .
Slot is produced at LMC (8) and offset from Datum plane by 1.5 (i.e. Bonus Tolerance).
1.5
Datum Shift :
Datum Plane
Datum B is produced at LMC (Ø11) and centered to Gage Pin (Ø8) .
Slot is produced at LMC (8) and offset from Datum plane by 1.5 (i.e. Bonus Tolerance).
1.5
Datum Shift :
Datum Plane
Datum B is produced at LMC (Ø11) and offset from Datum axis by 1.5 in opposite direction.
Slot is produced at LMC (8) and offset from Datum plane by 1.5 (i.e. Bonus Tolerance).
1.5
1.5
Datum Shift for Slot is the Bonus tolerance of Hole.
The slot center is offset from hole center (i.e. Datum B) by 3
3.0
Datum and Sub Datum Sub Datum is important for Data Correlation (for
functions e.g. assembly, Fit and Finish) Tolerance Analysis for the Assembly.
GDT → Datum → Sub Datum:
Glove Box Datum
GDT → Datum → Sub Datum:
Sub Datum for Glove Box on IP Substrate
GDT → Datum → Sub Datum:
Thank you!
Thank you!
GDT → Symbology :
Datum Feature Symbol A AB
A1
10 X 20
A112
Datum Target Symbols
A125
A1
25
GDT → Symbology :
E
FG
J
Ø
K
Ø
H
Ø
GDT → Symbology :
As Shown on Drawing
A1
A1
120
25
POINT CONTACT
PART
Datum Target Point
Means This:
GDT → Symbology :
120
A1
A1
Means This:PART
LOCATING PIN
LINE CONTACT
Datum Target Line
As Shown on Drawing
GDT → Symbology :
Means This:
As Shown on Drawing
15
15
A1
12
DATUM BLOCK
PART
PARTIAL SURFACE CONTACT
GDT → Symbology :
GDT → Symbology :
Other Modifiers↔ Between Symbol
Ø Diameter Symbol
All-around Symbol
Basic Dimension
Datum Feature Symbol
Datum Target
A0 M
B
A B M C M0.5
A0 M B M
C