Acceptance Sampling Prepared by Anthony Lizza Penn State University What will be covered?



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Acceptance Sampling

  • Prepared by
  • Anthony Lizza
  • Penn State University

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

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.

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

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

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

Acceptance Sampling method

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

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

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

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

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

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

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)

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

Acceptance sampling explained

  • Consumers risk
  • Alpha
    • Type I error(producers risk)
  • Beta
    • Type II error(consumers risk)

Acceptance sampling explained

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

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)

Acceptance sampling explained

  • Reference n(AQL) in 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

How acceptance sampling works

  • Two classifications of acceptance plans
    • Attributes(“go no-go”)
    • Variables

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

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

An Exercise

  • Determine the
    • AQL, a, LTPD, B?
    • Reference table provided-
  • c
  • LTPD/ AQL
  • nAQL
  • c
  • LTPD/ AQL
  • nAQL
  • 0
  • 44.890
  • .052
  • 5
  • 3.549
  • 2.613
  • 1
  • 10.946
  • .0355
  • 6
  • 3.206
  • 3.286
  • 2
  • 6.509
  • .0818
  • 7
  • 2.957
  • 3.981
  • 3
  • 4.890
  • 1.366
  • 8
  • 2.768
  • 4.695
  • 4
  • 4.057
  • 1.970
  • 9
  • 2.618
  • 5.426

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

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

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.

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.

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

Bibliography

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


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