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G D & T - OverviewNatarajan R

Director

EGS Computers India Private Limitedwww.egs.co.in * www.egsindia.com

http://www.egs.co.in/

Agenda

• Introduction to GD & T• DimXpert for GD & T• G D & T by examples• Benefits of G D & T

What is GD & T?

• GD&T is a Universal Language for communicating engineering design specifications

• Includes all symbols, definitions, mathematical formulae and application rules necessary to convey specifications

• Conveys nominal dimensions and tolerances for a part• Independent of Country and native language• Approved by ASME, ANSI and DoD• Language that designers use to translate design

requirements into measurable specifications

What is GD&T?

• Way of communicating dimensional and tolerance requirements

• Allowable imperfection• GD&T practices are governed by

standards manuals

ASME Y14.5M-2004

ASME Y14.41-2003

What is GD&T?

• ANSI -– Y14.5M-2004: Application of

GD&T– Y14.41-2003: Display of GD&T

in 3D• ISO -

– ISO 1101: Application of GD&T – ISO 16792: Display of GD&T in

3D

ASME

ISO

What is GD&T?

Geometric TolerancingPlus/Minus Tolerancing

Why use GD & T?

• It is important for the designer, manufacturer and inspector to understand part dimensions in the same manner

• GD & T principles result in time and cost savings• Ensures adherence to quality criteria• Reduces part rejection, mis-interpretation of drawings,

reworking, inter-departmental crossfire and art-to-part transformation time

• Avoids assembly mis-match, failures and quality problems

• Variation is inherent in nature– Nothing real is perfect!

• CAD doesn’t manufacture components– Actual Manufacturing Processes do!

Why use GD & T?

“Thousands of Hyundai's, Nissans and BMWs are targets of recalls --- Nissan announced the recall of about 116,000 Sentras because of a sensor problem.” ASSOCIATED PRESS,

•Improving productivity by reducing wasteful costs is imperative in today’s increasingly tough, competitive environment - ultimately affecting a company’s survival and its bottom line.

•Need for a holistic integrated systems solution to the COPQ problem.

The Truth - Cost of Poor Quality (COPQ) Design Quality Progress Magazine

Why use GD & T?

Why use GD & T?

GD & T and Tolerance Analysis target and solve these assembly build quality issues to reduce/eliminate COPQ

Upfront Information Saves Money

• GD & T and Tolerance Analysis during the part design phase permits optimization of the part from both functional and manufacturing perspectives before any tools are cut.

$Design Production

PRODUCT LIFE CYCLE

DFSSEnables!

COST BENEFIT

Cost of poor qualityEnd result:• No surprises• Higher Quality

Parts• Lower Cost• Material Flexibility

Design Methodolgoy with GD & T and Tolerance Analysis

• Evaluate different design conceptsLocating schemesAssembly methods

• Evaluate manufacturing processes• Re-assign Tolerances

Loosen if possible,Tighten if required

• Cost Savings Opportunities

Cost is Directly Related to Tolerances

SPECIAL EQUIPMENT

HIGH ACCURACY BORING

GENERAL BORING

DRILLING

0.0 0.1 0.2 0.3 0.4 0.5

10

15

20

25

30

Rel

ativ

e C

ost

mm

SOURCE: British Std. BSI PD-6470

*

*

How does GD&T Work?

Four simple steps:• Identify part surfaces to serve as origins and provide

specific rules to establish starting point and direction for measurements

• Convey nominal (ideal) dimensions and orientations from origins to other surfaces

• Establish boundaries and / or tolerance zones for specific attributes of each surface along with specific rules for conformance

• Allow dynamic interaction between tolerances (simulating actual assembly possibilities) where appropriate to maximize tolerances

14

Features of Size - Four Fundamental Levels of Control

Level 1:Controls size and circularity (for cylinders and spheres) at each cross section only

Level 2:Adds overall form control

Level 3:Adds Orientation control

Level 4:Adds location control

Each higher-level tolerance adds a degree of constraint demanded by feature’s functional requirement

All lower-level controls remain in effect

Single feature can be subject to many tolerances simultaneously

15

Example

16

Resultant Interpretation

17

With GD&T

18

Explanation

19

Geometric Characteristic Symbols

20

Modifier Symbols

How can GD&T make a difference?

G D & T Simplified

Gear Box Cover Design

G D & T – Reflecting Fit, Form & Functional Requirements

Gripper Assembly

Gripper Assembly – Exploded View

Gripper Holder Drawing

Gripper Holder – Completeness of GD & T

How to develop GD & T schemes? DimXpert Example

• Intelligent, automated dimensioning and tolerancing of 3D models

• Visual feedback on dimensional completeness

• Automatically displays in 2D drawing

• Integrated with Tolerance Analysis

GD & T Scheme for Hydraulic Actuator Flange

Complete 3D GD & T Annotation

Completeness of GD & T

GD & T Drawing

Dimensional Functionality: Schemes

• Geometric and Plus-minus dimension and tolerance schemes

Geometric Plus-Minus

Dimensional FunctionalityShow Tolerance Status

• Show Tolerance Status– Informs user when the

dimension and tolerance scheme is complete

– Each face is colored based on its status:• Green = Fully constrained• Yellow = Under constrained• Red = Over constrained• Native color = Not Recognized

by DimXpert

Before

After

Benefits of G D & T

• Maximizes Tolerances thereby reducing per part cost

• Ensures unambiguous translation of designs into measurable specification

• Eliminates re-work and ensures assembly all the time

• Reduces product development cycle time

Thank You !

Tolerance Stack Up Analysis - Overview

Agenda

• Introduction to Tolerance Stacks• Why Tolerance Stacks?• Tolerance Analysis – Step by Step Process• Review by Example• Benefits of Tolerance Stack Up Analysis

What is a Tolerance Stack ?

A method of mathematically predicting the resultant effect of piece part and subassembly tolerances along with assembly process and fixturing variation on a particular build objective of the assembly.

What is Tolerance Stack-up Analysis?

Worst-case analysis– Assumes dimensions vary within the entire range of their tolerance

zones and that the accumulation of tolerances will experience all possible variations

Gmin = L1 + L2 + L3 + L4… + Ln

= L1 + L2 + L3 + L4

= 152.75 + (-60.75) + (-42) + (-50.5) = -0.5 Interference

Performing worst-case analysis using a tolerance graph and hand calculation to determine the smallest permissible gap (G)

What is Tolerance Stack-up Analysis?

Worst-case tolerance analysis is dependent on how parts are actually assembled in real life

It is incorrect to think max worst case is when the parts are at their largest and min worst case is when they are at their smallest

PartNominal Assembly Worst-case

MaximumWorst-case Minimum

● Also referred to as dimensional control, dimensional variation management or dimensional engineering

● A process by which the design, fabrication, and inspection of a product are systematically defined and monitored to meet predetermined dimensional quality goals.

● An engineering process that is combined with a set of tools that make it possible to understand and design for variation.

● Aim is to improve first-time quality, performance, service life, and associated costs.

Dimensional Management

A typical Dimensional Management system consists of the following tools● Simultaneous or Concurrent Engineering Teams● Written Goals and Objectives● Design for Manufacturability and Assembly (DFMA)● Geometric Dimensioning and Tolerancing (GD&T)● Key Characteristics (KCC/KPC)● Statistical Process Control (SPC)● Variation Measurement and Reduction● Variation Simulation Tolerance Analysis


Historic Build-Test-Fix Method

Concept Model Design (CAD)

Default andCarry overTolerances

Manufacturing

Analysis (FEA)

Customer

Fire Fighting&

TroubleShooting

Iterative Loop

B-T-F Process

COPQWarrantyReworkRetoolECO'sOvertimeLost TimeEtc...


Concept Model

Define Performance Requirement

Design (CAD) & Analysis (FEA)

Functional Datum Structure Logic

Manufacturing Process Capability

3-D Variation Modeling

Design Evaluation, Optimization & Validation

ManufacturingSatisfied Customer

Evaluate Geometric sensitivity

Evaluate and Optimize Assembly Process

Functional Gauging & Fixturing

Key Characteristics SPC

Quality Process Manual

MaintenanceSmooth Launch

New PD Process


● Analyze and optimize dimensional variability within an assembly system

● Establish piece part tolerances ● Reduce product costs by increasing tolerances● Identify key tolerance contributors● Reduce product cycle time and improve quality● Determine if existing design and tooling will meet the

build objective requirements (CTQs)

Why Perform Tolerance Analysis?

Tolerance: Engineering specifications that are put in place to define or control the extreme limits of variation from nominal geometry. Defined based on product functionVariation: The deviation of a geometric feature property from its nominal. A property of the manufacturing process

Tolerance Vs Variation

Start

Setting BuildObjectives

Define VectorLoop and

ContributorCharacterisitics

Calculate MeanValue of BO

Determine methodof Analysis

Calculate Variationof BO

Optimize forRobustness

End

Tolerance Analysis Process

● Early in the design process● Customer Focus - perceptions of quality● Benchmarking, Focus Group Meetings● Representation from all internal groups● Formal buy off - signatures

Setting Build Objectives

● Key measurable characteristics of a product or process whose performance standards or specification limits must be met in order to satisfy the customer

● They align improvement or design efforts with customer requirements.

CTQ's – Critical To Quality Characteristics

● Fit● Finish● Function

Types of Build Objectives

• Component Mating• 100% Assemblability• Hole/Pin interface• Clearance/Interference Pin

Diameter

Hole Diameter

Fit Objective

• Aesthetics• Gap• Flush• Centering• Consistency• Consumer Products

Speaker grille over flush to the door substrate

Door Substrate

Speaker Grille

Finish Objective

• Assembly Function• Range of Motion• Locks• Latches• Alignments• Guides

Latch Engagement

Latch

Functional Objective

XYZ Inc. - Build Objectives, Product XXX• Competition

- Benchmarking- Competitive Assess.- QFD- VOC

• Quality• Warranty• Costs

- Scrap- Down Time- Bottlenecks- Lost

Customers

Qualify Quantify

Function

Fit

Finish

Build Objectives

Start








End


Tolerance Loops (Vector Loops)

• A systematic method of approaching a tolerance stack, and selecting the contributing tolerances.

• A tolerance loop allows for the evaluation of not only the stack variation, but also the stack nominal value.

10 ± 0.02D1

4 ± 0.015D2

3 ± 0.01D3

B.O.

Starting PointFinish Point

+

• Establish start and finish points on each side of the objective.• Travel from the start point to the finish point in the shortest

route, this direction will be called +.

Tolerance Loops

10 ± 0.02

4 ± 0.015 3 ± 0.01 B.O.


+

D1

D2 D3

B.O. = D1 – D2 – D3

• Go around the tolerance circuit in the opposite direction from previous step, taking the most direct route.

• Add signs to the nominal values according to their direction.

Tolerance Loops

Tolerance Loops - Steps

D1 (-)

D2 (+) D3 (+) B.O. (+)

Loop Start Surface

• Start at one side of the objective surface• Subtract each dimension that moves to left while adding each

dimension that moves to right until the starting objective surface has been reached

10 ± 0.02

4 ± 0.015 3 ± 0.01 B.O.


+

D1

D2 D3

Example Assembly

• Equal Bilateral Tolerancing

Vector Loop Equation

0..321 =+++− OBDDD

321.. DDDOB −−=

Start








End


Worst Case Analysis

Worst case stacks simply sum all the tolerances in the assembly in a linear direction and predicts the maximum variation expected for a particular build objective.

Worst Case Analysis Formula

Build Objective Variation = T1 + T2 + T3 + T4 +…..+ Tn

- Ti are the tolerance contributorsaffecting a particular build objective

- Ti are assumed equal bilateral tolerances - n is the number tolerances in the stack

Worst Case Analysis

• Ignores tolerance distribution types • Assumes all tolerances at their extreme limits• Guarantees 100% assembleability• Drives tight piece part tolerances / higher costs• Restrict to critical mechanical interfaces

X = 3 ± 0.045 or as a range = 2.955 to 3.045.

NominalDimensions

Tolerances

+

+10 0.020

-4 0.015

-3 0.010

+3 0.045

D1:

D2:

D3:

Worst Case Example

• Sum the Nominal Values• Sum the Tolerances

Worst Case Example - Mean

321.. DDDOB µµµµ −−=

33410.. =−−=OBµ

Worst Case Example - Variation

3 ± 0.045

Nominal Dimensions

± Tolerance

+

-0.820 0.008

+0.810 0.008

+0.090 0.006

-0.065 0.008

+0.015 0.030

Example

One Dimensional Loop Calculation

Flange Gap Study in Sheet Metal

Tolerance Stacks – Assembly Study

Mechanism – Elevator Gear Train

M O T O R WO R M G E A R T IP M O V E M E NTSpecification: L SL= 0.0000, Nominal= 0.0000, USL= 0.1500Control L imits: L CL =-0.0023, Mean= 0.0506, UCL = 0.1652

%Out of spec.= 0.9200, Cp= 0.8958, Cpk= 0.8740, Mean Shift= 0.0506

1 1 0 . 0

9 9 . 0

8 8 . 0

7 7 . 0

6 6 . 0

5 5 . 0

4 4 . 0

3 3 . 0

2 2 . 0

1 1 . 0

0 . 0

90.0

0

10.0

0

90.00%: 10.00%: GEAR 1 BA S E

Distr. Type: Gamma 5000S ample S ize:

95.0% Conf. Int. in Est. S ample Est. Low. CI Upp. CI (99.7%)

Mean: 0 .0 4 9 7 0 .0 5 1 5 Min.: 0 .0 0 0 4 -0 .0 0 2 3

S td Dev: 0 .0 3 1 6 0 .0 3 2 8 Max.: 0 .3 1 3 9 0 .1 6 5 2

Cp: 0 .8 7 8 3 0 .9 1 3 4 %<LS L: 0 .0 0 0 0 0 .0 0 0 0

Cpk: 0 .8 5 4 5 0 .8 9 3 4 %>US L: 0 .9 2 0 0 0 .9 2 0 0

%OutS : 0 .6 6 0 0 1 .1 8 0 0 %OutS : 0 .9 2 0 0 0 .9 2 0 0

ppm OutS : 6 6 0 0 1 1 8 0 0 ppm OutS : 9 2 0 0 9 2 0 0

Freq

uency

-0.0

313

-0.0

098

0.0

118

0.0

334

0.0

550

0.0

765

0.0

981

0.1

197

0.141

3 0.1

628

0.1

844

0.2

060

0.2

276

0.2

491

0.2

707

0.2

923

0.3

139033

6699133166199232266299332365399432465499

NOMINAL− 3 σ + 3 σ

USLLSL

Measurement Summary Bar Chart for WOR M GEAR TIP MOVEMENTMOTOR WOR M GEAR TIP MOVEMENT

0.3455

0.3075

0.2696

0.2317

0.1937

0.1558

0.1179

0.0799

0.0420

0.0041

-0.0339

Simulation Number

Mea

sure

men

t

50 100 150 200 250 300 350 400 450 500

LSL

USL

LCL

UCL

Mean

Mean: 0.0506 Nominal: 0.0000 Mean Shift: 0.0506 %<LSL: 0.0000 ppm OutS: 9200LCL: -0.0023 LSL: 0.0000 Std Dev: 0.0322 %>USL: 0.9200 Cp: 0.8958UCL: 0.1652 USL: 0.1500 Range: 0.1674 %OutS: 0.9200 Cpk: 0.8740

Tolerance Stack-Up Analysis

Problem Definition – Specifying Build Objective

Specifying the Vector Loop

Incorporating G D & T in Stack Up Calculations

Node Tree Definition for Vector Loop

Roll Up Calculations

Sensitivity Report for Tolerances affecting Assembly Build Objective

Predicting PPM

Summary of Features

• Maximum/minimum tolerance stack-up

• Identifies key contributors• Graphically displays result• Reduces prototyping and

testing for assembly fit• Leverages DimXpert• Eliminates error-prone hand

calculations• Enables fast tolerance

optimization

Summary of Benefits

• Eliminates ambiguity in Drawing Generation

• Confirms to Standards• Eliminates re-work• Selective Tolerancing

controls Cost• Eliminates Rejection• Reduces per-piece cost• Helps understand and

correct process deviations• Increases profitability

Thank You

egsindia - solidworks sales & technical · pdf filewhat is gd&t? • way of...

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