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Prepared by Anthony Lizza Penn State University

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1 Prepared by Anthony Lizza Penn State University
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 You will be informed with the general knowledge to better understand and implement acceptance sampling into your organization.

3 What is 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. In general, acceptance sampling is an approach to test the conformance of the products you have produced. You can either test a few items or every item in the lot. (LOT)-is the entire batch, group of items produced.

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 (LOT)-entire batch, group of items produced.

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 Remember your main purpose is to sentence the lot basically to life or death. You will reject or accept it but not measure the quality of the product.

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 Certain situations will tend to favor different sampling methods.

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 Acceptance sampling is very favorable when weighing out the advantages and disadvantages associated with complete inspection. However, certain situations favor different approaches as stated earlier.

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 The how and when slides will begin to show you and give you a respect towards the different approaches, not only to show you how and when to implement, but also why you should.

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 The disadvantages show shy acceptance sampling could be bad. You may be confused right now about what method to implement. You must choose which one would fit proportionately with your organizations procedures.

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 Filter is a way of preventing defects from being issued to customers, and defects coming to you from suppliers.

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 These are a few situations in which your organization would find it worthy of using the acceptance sampling approach.

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 Now you will begin to understand the variables and there meaning when doing the equating during the acceptance sampling process.

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) These are more terms you need to know when equating, Type I and II errors are explained in the next couple slides.

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 More basically producers risk is the chance of the suppliers shipment being rejected by the organization when the shipment is good. Consumers risk is the risk involved when sending products to consumers and assume the lot to be good, but it’s not.

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
Sample size taken for your sampling plan C Where rejections would occur when defects exceeded this percent N is the number of products sampled. C is where you would reject a lot if percentage of defects surpassed it. OC is the graph showing the point where the lot would be accepted to.

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 How to begin equating.

20 How acceptance sampling works
Two classifications of acceptance plans Attributes(“go no-go”) Variables Acceptance Plans- attributes 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 Difference between defect and defectiveness in attributes. Definitions of attributes and variables.

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 NOT MEASURING QUALITY, REJECTING OR ACCEPTING A LOT DEPENDING ON CERTAIN CIRCUMSTANCES.

23 An Exercise Determine the AQL, a, LTPD, B? Reference table provided- c
LTPD/ AQL nAQL 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 Remember the equations from earlier. Answer and method: LTPD/AQL=.03/.01=3 - these numbers were provided in the problem, the vendor has a 1% acceptable quality level and the manufacturer considers 3% defectives unacceptable. N(AQL)=3.286 – you have to find the number closest rounded to three fro the previous equation. C=6, from table N(AQL)= 3.286/.01= 328.6, 329-round up This means that you would take a random sample of 329 units for the specific lot and reject it if more than 6 units were defective.

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 :copyright 2001) “Quality Control in Furniture Manufacturing”:Internet

29 Bibliography “Process Analysis”:Internet “Quality Control”: Internet

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