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G D & T - OverviewNatarajan R
Director
EGS Computers India Private Limitedwww.egs.co.in * www.egsindia.com
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
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
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
Dimensional Management
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...
Dimensional Management
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
Dimensional Management
● 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
Setting BuildObjectives
Define VectorLoop and
ContributorCharacterisitics
Calculate MeanValue of BO
Determine methodof Analysis
Calculate Variationof BO
Optimize forRobustness
End
Tolerance Analysis Process
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.
Starting PointFinish Point
+
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.
Starting PointFinish Point
+
D1
D2 D3
Example Assembly
• Equal Bilateral Tolerancing
Vector Loop Equation
0..321 =+++− OBDDD
321.. DDDOB −−=
Start
Setting BuildObjectives
Define VectorLoop and
ContributorCharacterisitics
Calculate MeanValue of BO
Determine methodof Analysis
Calculate Variationof BO
Optimize forRobustness
End
Tolerance Analysis Process
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
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