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Tolerance Analysis for Non-rotational Parts. Team: Dr. X. Han, S. Yao, C. Fei Advisor: Professor Y. Rong Sponsor: NSF & Delphi Corp. Tolerance Analysis in Production Planning. Tolerance analysis - Part of setup planning - Locating error coupled with process error

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tolerance analysis for non rotational parts

Tolerance Analysis for Non-rotational Parts

Team: Dr. X. Han, S. Yao, C. Fei

Advisor: Professor Y. Rong

Sponsor: NSF & Delphi Corp.

tolerance analysis in production planning
Tolerance Analysis in Production Planning

Tolerance analysis

- Part of setup planning

- Locating error coupled with process error

- Intra- and inter- setups

- Process verification and

quality control

- Integration in CAD/CAM

Four steps:

  • Tolerance stack-up analysis
    • Tolerance decomposition
    • Machining error analysis
  • Tolerance assignment
  • In process inspection
  • Quality control plan

In this project, the first step is studied.

tolerance stack up analysis
Tolerance Stack-up Analysis
  • Tolerance stack-up analysis is to evaluate the machining error effects in each setup on the feature tolerance specifications of the final product
  • Tolerance stack-up analysis
    • For given setup plan as DMG
    • For given machining errors in each operation
    • Evaluate the machining error accumulation through setups
  • Tolerance decomposition
    • The feature tolerances specified in product design can be decomposed into operation tolerances specified for each setup
    • The machining error in each setup can be decomposed into locating errors (loc) from machine tool and fixture, tool-fixture alignment errors and tool wear errors (tool), other deterministic (o) and random (ran) errors.

 = loc + tool + o + ran

tolerance achieved in one setup
Tolerance Achieved in One Setup
  • Tolerance decomposition model 1 :
  • Two related features are machined in one datum frame:
  • Tolerance decomposition model 2:
  • One of the features in the tolerance
  • relationship is the datum feature:
tolerance achieved in multiple setups
Tolerance Achieved in Multiple Setups
  • Tolerance Decomposition Model 3 The features in the tolerance relationship are machined in different setups

N,N’ = N, A + A,N’

N, A = ran

A,N’ = ori + ran

tolerance stackup searching algorithm
Tolerance Stackup Searching Algorithm

In order to identify the factors that influence the machining errors, two steps are needed:

  • Search the datum-feature relationships that construct the tolerance stackup chain
  • Calculate the total machining errors

Tolerance within one setup:

Tolerance stackup in multi-setup:

locating errors analysis
Locating Errors Analysis

Among the machine errors in one setup, the locating error (loc)can be calculated:

  • Six locating points(P10, P20, P30, P40, P50, P60) construct three orthogonal planes
  • A1 X + B1 Y + C1 Z + D1 = 0
  • A2 X + B2 Y + C2 Z + D2 = 0
  • A3 X + B3 Y + C3 Z + D3 = 0
  • A theoretical fixturing coordinate is expressed as
  • X0 is the position of the origin point
  • is the 33 orientation matrix
  • Actual fixturing coordinate reflects the variation caused by locator errors
  • T = T0T
  • T = (x, y, z, , , ). T comes from the given locator errors.
an case study on knuckle
An Case Study on Knuckle



Machining feature GD&T of OP10: 101 Surface A

Theoretical fixture CS: Actual fixture CS

with given locator

errors( )

The worse case caused by locator errors: 0.654

Overall machining error

Total = locating + mt + process +tool = 0.654 + 0.013 + 0.254 + 0 = 0.921 mm

mt,process and tool are given parameters.

a case study on engine block
A Case Study on Engine Block

Datum frames:X-Y-Z, XX-YY-ZZ, A-B-C, M-S-A-R


A comprehensive tolerance analysis framework is established for machining system planning and verification.

Tolerance stackup analysis has been studies for non-rotational part.

Three tolerance decomposition models are developed for intra- and inter-setup analysis.

  • An inter-setup tolerance stackup algorithm have been implemented.
  • The calculation of locating errors has been implemented.
  • The analysis is integrated in CAD/CAM

Acknowledgement: Dr. Y. Zhang and Dr. W. Hu contributed to the earlier work of the project.