Page 631 - Design for Six Sigma a Roadmap for Product Development

584 Chapter Sixteen

C

y = C – A – B
B
A

Figure 16.6 Assembly clearance.

C, that is, T C , ′ C and C , such that the clearance requirement is satisfied
with C p 2.00.
The centerpoint of clearance E(y) is (0.001 0.005)/2 0.003. Because
E(y) E(C) E(A) E(B), it follows that 0.0025 T c 2.0 1.0, T c
3.003. Then
A 0.001
A 0.00025
3C p 3
1.33
2
2
2
Similarly, B 0.00025. The variance of y is 2 A
C
B
2
2
2
0.00025 . For y, if C p 2, the required standard deviation for
C
clearance is
0 0.002
0.00033333
3C p 3
2
2
2
2
2
2
Because 0.0003333 is less than the current 2
0.00025 ,
A
B
there will be no feasible C and C , unless the tolerances for A and B are
changed. If we can change these tolerances, we can find feasible tolerance
for C. If we assume A B C , then
2
2
2
2
2
3 0.000333333 2
B
A
C
A

2
0.00033333
A 0.0001924
3
If C p is still 1.333 for A, B, and C, then
A B C 3C p A 3
1.333
0.0001924 0.00077