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What is ANSI/ASQ Z1.4-2003?
ANSI/ASQ Z1.4-2003 is the non-Government standard on sampling procedures and tables for inspection by attributes. It replaced the military standard MIL-STD-105E which was officially cancelled in February 1995 by a Notice of Cancellation.



What is MIL-STD-105?
MIL-STD-105 is a United States defense standard that provides procedures and tables for sampling by attributes based on Schuchard, Harry Romig, and Harold Dodge sampling inspection theories and mathematical formulas. Widely adopted outside of military procurement applications.

The last revision was MIL-STD-105E.

It was officially cancelled in February 1995 by a Notice of Cancellation with a recommendation that future acquisitions should refer to an acceptable non-Government standard on sampling procedures and tables for inspection by attributes, such as ANSI/ASQC Z1.4-1993



Is MIL-STD-105E still used?
Yes, a few organizations still retain legacy systems based on MIL-STD-105 but it is no longer in use by the military. It was officially cancelled in February 1995 by a Notice of Cancellation with a recommendation that future acquisitions should refer to an acceptable non-Government standard on sampling procedures and tables for inspection by attributes, such as ANSI/ASQ Z1.4-2003



What is the difference between MIL-STD-105E and ANSI/ASQ Z1.4-2003?
ANSI/ASQ Z1.4-2003 is nearly identical to MIL-STD-105E. There are no changes in the tables of sampling plans. ANSI/ASQ Z1.4-2003 makes the use of the limit numbers for switching to reduced optional. In addition, ANSI/ASQ Z1.4-2003 contains additional OC curves called scheme OC curves that describe the protection provided by the switching procedure during periods of constant quality.

Numerous changes where also made to the explanatory text but which do not affect any procedures.



What is the difference between ANSI/ASQC Z1.4 1993 and ANSI/ASQ Z1.4-2003?
In December 2003 the ASQ (American Society for Quality) released the ANSI/ASQ Z1.4-2003 standard. This is a revision to the ANSI/ASQC Z1.4-1993 standard.

The name of the standard was changed to drop the "C" to reflect the 1997 name change of American Society for Quality Control to the current American Society for Quality. The definition of AQL has been changed from Acceptable Quality Level to Acceptance Quality Limit .

The Discontinuation of Inspection rule has been changed from 10 consecutive lots or batches on tightened inspection to 5 consecutive lots or batches not accepted on tightened inspection.

The notes in this revision specify that the numbers and tables remain the same as the MIL-STD-105E except for the changes to the footnotes.

ANSI/ASQ Z1.4-2003 makes the use of the limit numbers for switching to reduced optional. In addition, ANSI/ASQ Z1.4-2003 contains additional OC curves called scheme OC curves that describe the protection provided by the switching procedure during periods of constant quality.

Numerous changes where also made to the explanatory text but which do not affect any procedures.



What is an Acceptance Number?
The acceptance number is the maximum number of defects or defective units in the sample that will permit acceptance lot or batch.



What is an Acceptance Quality Level (MIL-STD-105E, ISO 2859-1 (1999))?
The acceptable level (AQL) is defined as the maximum percent defective (or the maximum number of defects per hundred units) that, for purpose of sampling inspection, can be considered satisfactory as a process average. The sampling plans most frequently used by the department of Defense are based on the AQL.



What is an Acceptance Quality Limit (ANSI/ASQ Z1.4-2003)?
The AQL is the quality limit that is the worst tolerable process average when a continuing series of lots is submitted for acceptance sampling.

The concept of AQL only applies when an acceptance sampling scheme with rules for switching between normal, tightened and reduced inspection and discontinuance of sampling inspection is used. These rules are designed to encourage suppliers to have process averages consistently better than the AQL. If suppliers fail to do so, there is a high probability of being switched from normal inspection to tightened inspection where lot acceptance becomes more difficult. Once on tightened inspection, unless corrective action is taken to improve product quality, it is very likely that the rule requiring discontinuance of sampling inspection will be invoked.

Although individual lots with quality as bad as the AQL can be accepted with fairly high probability, the designation of an AQL does not suggest that this is necessarily a desirable quality level. The AQL is a parameter of the sampling scheme and should not be confused with a process average which describes the operating level of a manufacturing process. It is expected that the product quality level will be less than the AQL to avoid excessive non accepted lots.



What are Defects and Defectives?
A defect is any nonconformance of the unit of product with the specified requirements. A defective is a unit of product which contains one or more defects. Failure to meet requirements with respect to quality characteristics are usually described in terms of defects or defectives.

Critical - A critical defect is on that judgment and experience indicate is likely to:

  • result in hazardous or unsafe conditions for individuals using, maintaining, or depending upon the products; or
  • prevent performance of the tactical function of a major end item. A critical defective is a unit of product that contains one or more critical defects.

Major - A major defect is one, other than critical, that is likely to result in failure, or to reduce materially the usability of the unit of product for its intended purpose. A major defective is a unit of product that contains one or more major defects.

Minor - A minor defect is one that is not likely to reduce materially the usability of the unit of product for its intended purpose, or is a departure from established standards having little bearing on the effective use or operation of the unit of product. A Minor defective is a unit of product that contains one or more defects.



What is a Double Sampling Plan?
A double sampling plan involves sampling inspection in which the inspection of the first sample to a decision to accept, to reject or to take a second sample. The inspection of a second sample, when required, lead to a decision to accept or reject.



What does “Drawing of Samples” mean?
Basic to sampling inspection is the assurance that the sample selected from a quantity of units represents the quality of that quantity of units. Hence, the procedure used to select units from a lot must be such that it assures a sample free of bias.



What is “Expression of Nonconformance”?
The extent of nonconformance of product shall be expressed either in terms of percent defective or in terms of defects per hundred units (DHU).



What does “Defects per Hundred Units” mean?
The number of defects per hundred units of any given quantity units of product is one hundred times the number of defects contained therein (one or more defects being possible in any unit of product) divided by the total number of units of product, i.e.:

Defects per hundred units = number of defectives x 100 ÷ number of units inspected .



What is “Inspection”?
Inspection is the process of measuring, examining, testing, or otherwise comparing the unit of product with the requirements.



What is “Inspection by Attribute”?
Inspection by attributes is inspection where by either the unit of product is classified simply as defective or non-defective, or the number of defects in the unit of product is counted, with respect to a given requirement or set of requirements.



What are the Inspection Levels?
The standards provides for three general inspection levels and four special inspection levels. These seven levels permit the user to balance the cost of inspection against the amount of protection required.



What does “Lot or Batch” mean?
The term lot or batch shall mean "inspection lot" or "inspection batch" i.e., a collection of units of product from which a sample is to drawn and inspected to determine conformance with the acceptance criteria, any may differ from a collection of units designated as a lot or batch for other purposes (e.g., production, shipment, etc.).



What does the term “Nonconformance” mean?
Nonconformance may be defined as the failure of a unit of product to conform to specified requirements for any stated quality characteristic. The extent of nonconformance of product to the required quality characteristics shall be expressed either in terms of percent defective or in terms of defects per hundred units (DHU).



What is “Normal Inspection”?
Normal inspection is that which is used where there is no evidence that the quality of product being submitted is better or poorer than the specified quality level.



What does “Percent Defective” mean?
The percent defective of any given quantity of units of product is one hundred times the number of defective units of product contained therein divided by the total number of units of product, i.e.: Percent defective = number of defectives x100 / number of units inspected



What is a “Reduced Inspection”?
Reduced inspection under a sampling plan uses the same quality level as for normal inspection, but requires a smaller sample for inspection.



What is the “Rejection Number”?
The rejection number is the minimum number of defects or defective units in the sample that will cause rejection of the lot represented by the sample.



What is “Representative Sampling”?
When appropriate, the number of units in the sample shall be selected in proportion to the size of sub-lots or sub-batches, or parts or the lot or batch, identified by some rational criterion. When representative sampling is used, the units from each part of the lot or batch shall be selected at random.



What are “Resubmitted Lots or Batches”?
Lots or batches found unacceptable shall be resubmitted for re-inspection only after all units are re-examined or retested and all defective units are removed or defects corrected. The responsible authority shall determine whether normal or tightened inspection shall be used and whether re-inspection shall include all types or classes of defects or only the particular types or classes of defects which caused initial rejection.



What is a “Sample”?
A sample consists of one or more units of product drawn from a lot or batch, the units of the sample being selected at random without regard to their quality. The number of product in the sample is the sample size.



What are “Sampling Plans”?
A lot sampling plan is a statement of the sample size or sizes to be used and the associated acceptance and rejection numbers.



What is a “Single Sample Plan”?
A single sampling plan is a type of sampling plan by which the results of a single sample from an inspection lot are conclusive in determining acceptability. The number of sample units inspected shall be equal to the sample size given by the plan.



What does “Severity of Inspection” mean?
The severity of inspection concerns the total amount, kind and extent of inspection specified by the quality assurance provisions established for the unit of product, or as dictated by quality history.



What does “Unit of Production” mean?
The unit of product is the thing inspected in order to determine its classification as defective or non-defective or to count the number of defects. It may be a single article, a pair, a set, a length, an area, an operation, a volume, a component of an end product, or the end product itself. The unit of product may or may not be the same as the unit of purchase, supply, production, or shipment.



What is “Tightened Inspection”?
Tightened inspection under a sampling procedure plan uses the quality level as for normal inspection, but requires more stringent acceptance criteria.



What is “Discontinuation of Inspection Rule”?
For ANSI/ASQ Z1.4-2003 and ISO 2859-1. If the cumulative number of lots not accepted in a sequence of consecutive lots on original tightened inspection reaches 5, the acceptance procedures of this part of ISO 2859 shall not be resumed until action has been taken by the supplier to improve the quality of the submitted product or service, and the responsible authority has agreed that this action is likely to be effective. Tightened inspection shall then be used.

For MIL-STD-105E, In the event that 10 consecutive lots or batches remain on tightened inspection (or such other number as may be designated by the responsible authority) inspection should be discontinued pending action to improve the quality of submitted material.

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