公差分析和尺寸链方法.ppt

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公差分析和车身尺寸链方法Tolerance Analysis & Auto-body Dimension Chain Method
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Contents
1-D Tolerance analysis
Auto-body Dimension Chain Method
Variation vs. Tolerance
Variation Simulation Methods
Advantages and Limitations of Each Method
Integration of Key Characteristic of Product & Process
Assembly Constraints
Tolerance and Solving of Dimension Chain
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Part I1-D Tolerance analysis
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Characterizing the performance of a process
Central tendency or mean:
Spread or variation
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Deviation
Variation vs. Tolerance
Variation:
• is what the process gives us,
• may be quite different from the tolerance.
Tolerance or Specification is
• the allowable level of variation,
• based on functional consideration,
• used to establish a part's conformability to design.
But the techniques for predicting variation or tolerance for an assembly is the same.
Variation Simulation
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Given individual part dimensions and their distribution, what are the assembly dimensions ?
But the method can applied more widely than mechanical assembly.
The general form is: given a function Y=f(x1, x2, …), and the distributions of xi, What is the distribution of y ?
Distribution of Tolerance
Worst Case
Statistical:
Root sum squares
Monte Carlo
Assembly Model
Explicit:
Linearized Sensitivity
Mechanistic Model
Non-linear Model
Implicit:
Variation Simulation Methods
Two things are essential in order to perform variation analysis. One is an assembly model or input-output model. The other is the distribution of variables.
Commonly UsedVariation Simulation Methods
Worst Case:
(Conway, 1948; Chase and Parkinson, 1991)
Root Sum Squares (RSS):
(Spotts, 1978, Lee and Woo, 1990)
Monte Carlo Simulation:
(Craig, 1989)
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x ± a
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x ± c
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y ±
t
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Simple Variation Simulation Example
Given component tolerances, determine the variation in the
measured dimension (the gap between the blocks and the base).
In worst case analysis, it is assumed that the contributing dimensions are always within tolerance. By making this assumption worst case limits can be found within which the measured dimension must always fall.
Worst Case Analysis