gdt training

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.


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”


The goal of GDT is to Improve Communication !!

Why Geometric Dimensioning & Tolerancing?

The reason for the importance of this subject is –


?

- because it saves Money.


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”.


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).


“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.


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.


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.


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.


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.



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


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.


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!


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


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.


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.


True Geometric Counterpart

The theoretically perfect boundary (virtual condition or actual mating envelope) or best-fit (tangent) plane of a specified datum feature.


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.


Tolerance Zone


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.


Ø 6 +/- 1

Tolerance Zone Ø 1

Virtual Condition

What will be the Dia. of it ? Guess ?!


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


GDT → Datum :

PRIMARY

DATUM PLANE

TERTIARY

DATUM PLANE

SECONDARY

DATUM PLANE

o90º

90º

90º


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 :

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


Slot is produced at LMC (8) and centered to Gage feature (5).

Datum Shift :

Datum Plane


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) .


1.5

Datum Shift :

Datum Plane

Datum B is produced at LMC (Ø11) and offset from Datum axis by 1.5 in opposite direction.


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


Sub Datum for Glove Box on IP Substrate


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

gdt training

Documents