Industrial Quality Management Acceptance Testing

Next Week Important Review for Final Exam Please remember to attend

Acceptance Testing Receive Material Inspect it Accept / Reject based on inspection Not the best way Government & Military may require it It may be a temporary step to solve a problem Tends to Accept very good material & reject very bad material Does not work so well with medium quality material

Example 1 Given: defect rate for acceptance is not to exceed 5% A box has 95 good switches and 5 bad switches (should be accepted) What is the probability of inspecting 20 of the switches & accepting the group? 2 cases & they are:____ P(no defects) = (0.95)20 (0.3585) P(1 defect) = (0.05)(0.95)19 = 0.01887 There are 20 ways to do this 20(0.01887) = 0.3774 P(accept) = 0.3585 + 0.3774 = 0.7359 26.41% probability of rejecting good material

OR Rule vs. AND rule If we can use the word “AND” to describe our case: Multiply probabilities If we can use the word “OR” to describe our case: Add probabilities Go back to the last slide to see this

Example 2 Given: defect rate for acceptance is not to exceed 5% A box has 97 good switches and 3 bad switches (should be accepted) What is the probability of inspecting 20 of the switches & rejecting the group? 2 cases & they are:____ Please work your solution:

Example 3 Given: defect rate for acceptance is not to exceed 5% A box has 90 good switches and 10 bad switches (should be rejected) What is the probability of inspecting 20 of the switches & rejecting the group? 2 cases & they are:____ Please work your solution:

Example 4 Given: defect rate for acceptance is not to exceed 5% A box has 190 good switches and 10 bad switches (should be accepted) What is the probability of inspecting 40 of the switches & rejecting the group? 3 cases & they are:____ How many ways are there to get 2 defects? C40,2 = 40!/(2! x 38!) Please work your solution:

Poisson Probability Curve n is number of samples inspected c is the maximum number of defective allowed p is the proportion of defective items in the group Pa is the probability of accepting the group Example: From a group of 200 items with p = 0.05, c=7 What is the probability of accepting this group?

MIL STD 105D

MIL STD 105D Example Levels of Inspection Find your group size I Relaxed II Normal III Tightened Find your group size How many must you inspect? What is your level of quality? Get the acceptance / rejection criteria Given: Batch of 500 resistors Bad resistors are not to exceed 4% Normal Inspection How many resistors will you inspect? How many defective resistors are allowed before you must reject?

MIL STD 105D Example What happens if you tighten the inspection? What happens if you loosen the inspection? What happens if you can accept a defect rate of 6.5% with normal inspection? What happens if you can only accept a defect rate of 2.5% with normal inspection?