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# tolerance stack up analysis

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tolerance stack up analysis

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### tolerance stack up analysis

1. 1. TOLERANCE STACK UP ANALYSIS
2. 2. Introduction  Tolerance analysis : Study of individual tolerances Process of determining the cumulative variation possible between two or more features.  Tolerance stack up analysis is one part of tolerance analysis.  Analyzes and predicts the variation between the parts.  Determines the maximum possible variation between two components in an assembly.
3. 3. Merits of Tolerance Stack Up Analysis  Optimize the tolerances of parts and assemblies in a new design  Balance accuracy , precision and cost with manufacturing process  Determine the part tolerance required to satisfy a final assembly condition  Determine allowable part tolerance if assembly tolerance is known  Determine the effect changing a tolerance will have on assembly component
4. 4. Steps in Tolerance Stack Up Analysis  The Distance to be studied is identified and labeled  The positive and negative directions are identified  A tolerance stack up sketch is created  The dimensions in positive direction and negative directions are added individually  The nominal distance is found out by subtracting negative direction total from the positive direction total  The total possible variation is obtained by adding all tolerances  The maximum and minimum variations are obtained from the nominal distance and total variation values.
5. 5. Problem  For an inseparable assembly using tolerance stack up analysis find the maximum and minimum distance between the part 5 and 6 in assembly.
6. 6. Tolerance Stack Up Sketch
7. 7. Tolerance Stack Up Report
8. 8. Dimensional Chain Analysis  Dimensional Chain is a consecutive series of interrelated dimensions that contribute to the tolerance of a dimension and form a closed loop.  Two Basic tasks in tolerance design process : Dimensional Chain analysis Dimensional Chain synthesis  In Dimensional analysis component tolerance are specified and resulting assembly variation is calculated.  Dimensional Synthesis involves allocation of specified assembly tolerance between component dimension of the assembly.
9. 9. Equivalent tolerance method  All independent dimensions have same tolerance Tx1=Tx2=.........=Txn=T  Used when all independent dimensions in the analysed dimensional chain have same nominal value.  Deterministic approach formula is  Stochastic approach formula is
10. 10. Equivalent Standard tolerance grade method  All independent dimensions are assigned tolerance values from the same tolerance grade.  Value of dimension tolerance is : Txi = tolerance of ith independent dimension Xi = nominal value of ith independent dimension K =unknown tolerance grade factor Deterministic Approach: Stochastic Approach:
11. 11. Problem  Two holes are drilled in a plate. What are the required tolerances of dimensions A,B,C,D if the tolerance of the dependent dimension Z is required as not greater than 140 µm and the nominal values of the independent dimensions are A=124mm, B=56mm,C=87mm,D=25.5mm
12. 12. Solution
13. 13. Solution  Equivalent tolerance method TA=TB=TC=TD=TW Tz = 140 µm =0.75*T A +0.66*TB +0.75*TC +0.66*TD =2.82*TW TA=TB=TC=TD=TW = 50 µm  Equivalent standard tolerance grade method Tz = 140 µm =K*(0.75* A 1/3 +0.66*B 1/3+0.75*C 1/3 +0.66* D 1/3) K=12.11 TA=60 µm TB=47 µm TC=54 µm TD=35 µm
14. 14. THANK YOU