Acceptance Sampling by Variables - Compare

User-Defined Plans - Average Outgoing Quality (AOQ)

  

The average outgoing quality level represents the relationship between the quality of the incoming material and the quality of the outgoing material, assuming that rejected lots will be 100% inspected and all defective items will be replaced or reworked.

As the defect level of the incoming parts increases, the inherent quality of the accepted lots decreases; however, the number of rejected lots also increases. The sorting of the bad parts (100% inspection and removal) helps the outgoing quality level, but at a high cost. The maximum possible defect level, an important characteristic of the sampling plan, is the average outgoing quality limit (AOQL).

Example Output

Compare User Defined Plan(s)

 

 

 Sample     Critical   Defectives  Probability  Probability

Size(n)  Distance(k)  Per Million    Accepting    Rejecting    AOQ     ATI

    100      3.44914          100        0.854        0.146   83.0   612.3

    100      3.44914          600        0.224        0.776  130.8  2815.1

 

    150      3.44914          100        0.899        0.101   86.1   500.1

    150      3.44914          600        0.172        0.828   98.8  3007.3

 

    200      3.44914          100        0.928        0.072   87.6   444.7

    200      3.44914          600        0.135        0.865   76.3  3142.0

 

 

Sample     Critical     Maximum         At Defectives

  Size  Distance(k)  StDev(MSD)   AOQL    Per Million

   100      3.44914   0.0027533  145.6          369.7

   150      3.44914   0.0027533  138.5          288.9

   200      3.44914   0.0027533  136.7          256.4

 

Z.LSL = (mean - lower spec)/standard deviation

Z.USL = (upper spec - mean)/standard deviation

Accept lot if standard deviation ≤ MSD, Z.LSL ≥ k and Z.USL ≥ k; otherwise reject.

Interpretation

For the camera data, when the average incoming quality level is 100 defectives per million, the average outgoing quality is 83.0, 86.1, and 87.6 defectives per million, when the sample sizes are 100, 150, and 200 and the critical distance is 3.44914. When the average incoming quality level is 600 defectives per million, the average outgoing quality is 130.8, 98.8, and 76.3 defectives per million, when the sample sizes are 100, 150, and 200 and the critical distance is 3.44914.

Keeping the critical distance at 3.44914:

·    When the sample size is 100, the AOQL is 145.6 defectives per million.

·    When the sample size is 150, the AOQL is 138.5 defectives per million.

·    When the sample size is 200, the AOQL is 136.7 defectives per million.

As the sample size decreases, the number of rejected lots with all defects removed also decreases, so the quality gets worse. This results in a higher average outgoing quality limit.