From the DCS Webinar on Worst Case: http://mkt.3dcs.com/worst-case-tolerance-analysis-webinar
Worst Case tolerance analysis is where each individual tolerance is set to a point in its range (typically a tolerance limit) where it will result in either the maximum or minimum output at a specific measured location.
A Worst Case analysis is the only way to guarantee that an assembly of good detail parts will not be out of specification.
However, in most cases, a statistical analysis gives the results needed to make decisions and reduce manufacturing costs.
Learn how 3DCS calculates, analyzes and answers Worst Case tolerance analysis. Find out about:
-- What is Worst Case?
-- Worst Case 1D vs Worst Case 3D
-- Worst Case vs RSS
-- GeoFactor Analyzer Worst Case
-- Simple Example in 3DCS
-- Worst Case User DLL
-- Larger Example in 3DCS
-- Q&A
Clutches and brkesSelect any 3 position random motion out of real world and d...
Worst Case Tolerance Analysis - What is it, why do it, and how?
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Worst Case Analysis
What, Why and How
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Agenda
• What is Worst Case?
• Worst Case 1D vs Worst Case 3D
• Worst Case vs RSS
– Which One Should You Use?
• GeoFactor Analyzer Worst Case
• Simple Example in 3DCS
• Worst Case User DLL
• Larger Example in 3DCS
• Q&A
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What is Worst Case?
Worst Case Analysis - Each individual tolerance is set to a point in its range (typically a
tolerance limit) where it will result in either the maximum or minimum output at a
specific measured location.
A Worst Case analysis is the only way to guarantee that an assembly of good detail
parts will not be out of specification.
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Worst Case 1D Example
10 ± 1 12 ± 27 ± 1
Measure Nominal = 29 mm
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Worst Case 1D Example
Worst Case Variation
at Measure: 29 ± 4 mm
11 mm 14 mm8 mm
Measure Maximum = 33 mm
9 mm 10 mm6 mm
Measure Minimum = 25 mm
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1D vs 3D Worst Case
Worst Case Range: ???
Form Tolerance
Orientation Tolerance
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1D Worst Case vs 3D Worst Case
1D Worst Case Shortcomings:
• Assumes all tolerances have a 1:1 effect on measure
• Difficult to capture angular variation
• Limited in scope, can only look at the problem in 1 dimension
3D Worst Case:
• We can capture geometric effect and angular variation!
• Doing by hand requires rigorous hand-calcs and large possibility for human error.
• Luckily, 3DCS can help!
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Example 1D vs 3D Stack
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Worst Case vs RSS
Statistical Analysis - Each component’s variation is modeled as a statistical distribution
(typically Normal by default) and these distributions combine to predict a new
distribution that describes the assembly variation, not the extreme values of that
variation.
Statistical Analysis (RSS) carries some “risk” that bad assemblies will be made from
good parts, but using inspection to spot trends and adjusting accordingly is a far
cheaper solution to designing to incredibly tight part level tolerances (as a Worst Case
analysis would recommend).
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Worst Case vs RSS 1D Example
Apply a Normal Distribution to each
tolerance for our 3 blocks as our input
0.13% at or
below Minimum
0.13% at or
above Maximum
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Worst Case vs RSS 1D Example
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GeoFactor Analyzer Worst Case
Equation based solution to quickly report a Worst Case
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Basic Model Example
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Worst Case User DLL
dcsSimuWorstCase (dcu_simu_fn.dll)
Sets all tolerances in model to a Modal distribution and leverages Monte Carlo
simulations to determine Worst Case build
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How Many Simulations?
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Advanced Model Example