Specify information about the elements for Calculate Gap Pools

Six Sigma > Design for Manufacturability > Calculate Gap Pools > Options > Elements

Enter the nominal and specification limits for each element, element complexities, diametrical correction factors, and shift and drift factors.

Complexity
Enter a column that contains the complexities for the elements in the assembly. These are the numbers of times that the elements appear in the assembly. The default value is 1.
Lower spec
Enter a column that contains the initial lower specifications for each element in the assembly. If you do not enter initial lower specifications, Minitab uses, for each element, (the initial nominal – (4.6505 * initial long-term standard deviation)).
Upper spec
Enter a column that contains the initial upper specifications for each element in the assembly. If you do not enter initial upper specifications, Minitab uses, for each element, (the initial nominal + (4.6505 * initial long-term standard deviation)). Minitab uses the initial upper specifications to calculate the initial Z-values and PPMs for the elements.
Nominal spec
Enter a column that contains the initial nominal specifications for each element in the assembly. If you do not enter initial nominal specifications, Minitab uses the initial element means.
Note

After you allocate the mean gap pool, the new element means become the new nominal specifications. Minitab uses the initial nominal specifications to calculate the initial default upper and lower specification limits.

Diametrical correction factors
Enter a column that contains the diametrical correction factors for the elements in the assembly. If you do not enter diametrical correction factors, Minitab uses the default value of 1 for each element.
Mean shift factors
Enter a column that contains the shift factors for the elements in the assembly. If you do not enter shift factors, Minitab defines the shift factors such that each element shifts 1.5 standard deviations toward the nearest gap specification.
Variation expansion factors
Enter a column that contains the drift factors for the elements in the assembly. These are the ratios between the long-term and short-term standard deviations for each element. If you do not enter drift factors, Minitab uses the default value of 1.8.
Long-term Z values
Enter a constant or a column that contains values between −7 and 7 to represent the desired long-term Z.Bench for each element in the assembly. These values define the number of standard deviations to use for calculating the upper and lower specs for each element. Minitab uses these values both before allocation (if initial upper and lower specs are not entered) and after allocation. For example, for a Z-value of 4.5 (the default), Minitab defines the specifications as follows:
  • Upper specification is nominal + (4.645 * long-term standard deviation)
  • Lower specification is nominal – (4.645 * long-term standard deviation)
Note

Setting the specifications at ± 4.645 standard deviations results in a Z.Bench of 4.5 for each element, or an approximately 3.4 PPM defective rate.

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