- 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
- 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? 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
- 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-
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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