Example of Allocate Gap Pools

The second part of the tolerancing procedure uses Allocate Gap Pools. In Example of Calculate Gap Pools, you calculated the gap mean and variance pools. Now, you need to specify two sets of weights, one for each pool.

In this example, the gap mean pool is 0, so it doesn't matter how you allocate it. You decide to make up the gap mean pool 50% by reducing the mean in the pad, 30% by reducing the mean in the backing, and 20% by reducing the mean in the cover.

The gap variance pool is 0.0002839, and you decide to make it up as follows:
  • 20% by reducing the variance in the piston size
  • 30% by reducing the variance in the caliper size
  • 50% by reducing the variance in the rotor size
  1. If you haven't already, perform steps 1–9 in Example of Calculate Gap Pools.
  2. Choose Six Sigma > Design for Manufacturability > Allocate Gap Pools.
  3. In Allocation weights for Gap variance pool, enter 'Var Alloc'.
  4. Click OK.

Interpret the results

As shown in the Session window output, the long-term gap Z.Bench now equals 4.5, which is the goal. More importantly, the design now has an overall yield of ~100%, compared to the original design's overall yield of 46.91%.

Note that achieving a long-term gap Z.Bench of exactly 4.5 does not always occur with a variance pool, but it should always occur with a mean pool.

The table of adjusted means and standard deviations shows what the short-term means and standard deviations must be for each element in the assembly, in order to achieve the desired long-term performance of the assembly. These values are then used to calculate the optimal tolerances for the elements in the assembly. For more information on calculations, go to Calculations for the specification limits for Calculate Gap Pools.

Tolerance Analysis: Allocate Gap Pools

Gap Specifications After Allocation of Gap Pools Nominal Value 0.126 Lower Spec 0.001 Upper Spec 0.251 Required Z.Bench(LT) 4.50 Long-Term Shift 1.50
Gap Long-Term and Short-Term Statistics Before Allocation of Gap Pools Long-Term Short-Term Mean 0.126000 0.126000 StDev 0.032 0.018 Z.LSL 3.94 7.09 Z.USL 3.94 7.09 Z.Bench 3.77 6.99
Gap Pool Statistics Mean Pool 0.0000000 Variance Pool -0.0002839
Gap Long-Term and Short-Term Statistics After Allocation of Gap Pools Long-Term Short-Term Mean 0.126000 0.126000 StDev 0.027 0.015 Z.LSL 4.65 8.36 Z.USL 4.65 8.36 Z.Bench 4.50 *
Element Means and Standard Deviations After Allocation of Gap Pools Pad 0.750 0.0047000 Backing 0.062 0.0015000 Piston 1.550 0.0016723 Cover 0.950 0.0012000 Caliper 3.700 0.0029188 Rotor 0.750 0.0125627
Overall Design Statistics After Allocation of Gap Pools Rolled Yield 100.00 DPU 0.0000374 Z.Bench 4.48

Gap Distribution After Allocation

Tolerances After Allocation

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