Acceptance Sampling

1. Acceptance Sampling Prepared by Anthony Lizza Penn State University

2. What will be covered? • What is acceptance sampling? • How/When would you use it in your organization? • Acceptance sampling explained. • How acceptance sampling works. • An exercise. • Summary

3. What is acceptance sampling? • Acceptance Sampling • Statistical quality control technique, where a random sample is taken from a lot, and upon the results of the sample taken the lot will either be rejected or accepted.

4. What is acceptance sampling? • Accept Lot • Ready for customers • Reject Lot • Not suitable for customers • Statistical Process Control(SPC) • Sample and determine if in acceptable limits

5. What is acceptance sampling? • Purposes • Determine the quality level of an incoming shipment or, at the end production • Ensure that the quality level is within the level that has been predetermined

6. What is acceptance sampling? • Can be either 100% inspection, or a few items of a lot. • Complete inspection • Inspecting each item produced to see if each item meets the level desired • Used when defective items would be very detrimental in some way

7. Acceptance Sampling method

8. What is acceptance sampling? • Problems with 100% inspection • Very expensive • When product must be destroyed to test • Inspection must be very tedious so defective items do not slip through inspection

9. How/When would you use it? • Acceptance sampling advantages • Less handling damages • Fewer inspectors to put on payroll • 100% inspection costs are to high • 100% testing would take to long

10. How/When would you use it? • Acceptance sampling disadvantages • Risk included in chance of bad lot “acceptance” and good lot “rejection” • Sample taken provides less information than 100% inspection

11. How/When would you use it? • Between your organization and outside world • Samples taken run through “filter,” either passing or rejecting it • Also filter from suppliers to you

12. How/When you would use it? • When products in use could be damaged easily • When using new suppliers • When new products produced • When current supplier in question • Testing whole lot could be harmful

13. How/When you would use it? • Determine how many units, n, to sample from an lot • Determine maximum number of defective items, c, that can be found before the lot is rejected

14. Acceptance sampling explained • Acceptable Quality levels(AQL) • Number of defect percentage allowed in a lot which can still be considered accepted(Type I error) • Lot Tolerance Percent Defective(LTPD) • Amount of defects that will come with a lot of goods(Type II error)

15. Acceptance sampling explained • Sampling Plan • Forms after n and c values have been found • Producers risk • Risk associated with a lot of acceptable quality rejected

16. Acceptance sampling explained • Consumers risk • Receive shipment, assume good quality, actually bad quality • Alpha • Type I error(producers risk) • Beta • Type II error(consumers risk)

17. Acceptance sampling explained • N • Sample size taken for your sampling plan • C • Where rejections would occur when defects exceeded this percent

18. Acceptance sampling explained • Operating characteristics curve(OC) • A graph, displaying standards at which shipments would be accepted • First • Determine AQL, a, LTPD, b, • Take LTPD/AQL, this gives you the n(AQL)

19. Acceptance sampling explained • Reference n(AQL) in the table • C will be given as well when referencing the table • Next • N(AQL/AQL)=n-sample size • C= reject if more percent defects more • The equations can be tricky but the exercise later will help

20. How acceptance sampling works • Two classifications of acceptance plans • Attributes(“go no-go”) • Variables

21. How acceptance sampling works • Attributes(“go no-go”) • Defectives-product acceptability across range • Defects-number of defects per unit • Variable(continuous) • Usually measured by mean and standard deviation

22. How acceptance sampling works • Remember • You are not measuring the quality of the lot, but, you are to sentence the lot to either reject or accept it

23. An Exercise • Determine the • AQL, a, LTPD, B? • Reference table provided-

24. An Exercise cont. • Assume a manufacturer purchases wire from an outside vendor. The wire vendor has an accepted quality level of 1% and accepts a 5% risk of rejecting lots below this level. The manufacturer considers lots with 3% defectives to be unacceptable and assumes a 10% risk of accepting a defective lot. Develop a sample plan for the manufacturer to be followed by the inspection personnel

25. Summary • Acceptance sampling is used by organizations to determine if there process’s are running within a controlled limit and to see if they should reject or accept lots

26. Summary • There are many basic terms you need to know to be able to understand acceptance sampling • SPC, Accepts Lot, Reject Lot, Complete Inspection, AQL, LTPD, Sampling Plans, Producers Risk, Consumers Risk, Alpha, Beta, Defect, Defectives, Attributes, Variables.

27. Summary • Advantages/Disadvantages of acceptance sampling • Purpose of acceptance sampling • When to use acceptance sampling • Equations involved • Exercise • Notes pages have many beneficial hints and help better relate the material, the answer to the exercise is also located on a the notes page of the exercise.

28. Bibliography • (Foster, S.Thomas: “Managing Quality-An Integrative Approach:pgs. 263-274:copyright 2001) • “Quality Control in Furniture Manufacturing”:Internet http://www.mtc.com.my/publications/library/quality/qc40.htn

29. Bibliography • “Process Analysis”:Internet http://www.statsofinc.com/textbook/stprocan.html • “Quality Control”: Internet http://www.ms.ic.ac.uk/jeb/or/qcontrol.html