Quality control terms and glossary
- Defects and Defectives
- Defects per Hundred Units
- Double Sampling Plan
- Drawing of Samples
- During Production Inspection (DPI)
- Random Sampling
- Reduced Inspection
- Rejection Number
- Representative Sampling
- Resubmitted Lots or Batches
The acceptance number is the maximum number of defects or defective units in the sample that will permit acceptance lot or batch.
Acceptance Sampling is used to decide whether to accept or reject a production lot. After selecting a sampling from a production lot, we inspect the units, we count how many defects are found among this sampling and we use the result (number of defects found versus maximum number of defects allowed) to decide whether or not to accept or reject the lot.
The approval sample, also called golden sample, pre-production sample or PP-sample, is usually sent by the buyer to the third party inspection company and manufacturer. It is the product of reference and will be compared to the production samples. The production and the approval sample should be very similar. An inspection report will point out the differences.
Read more about the role of the approval sample during an inspection.
The AQL has two different definitions due to standard changes.
Acceptable 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.
Acceptance Quality Limit / ANSI/ASQC Z1.4-2003
The AQL is the quality level that is the worst tolerable process average when a continuing series of lots is submitted for acceptance sampling. The following note on the meaning of AQL was introduced with the ANSI/ASQ Z1.4-2003 revision:
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. The AQL values are defined as percent nonconforming or defects or nonconformities per hundred units.
Download the AQL table, and read more to get familiar with the AQL table:
- The conditions to use the AQL table.
- The AQL table history, definition and role.
- The relation between man-day calculation and AQL table.
A batch or lot is a collection of products, all identical in size, type, conditions and time of production.
This inspection is performed at the manufacturer's warehouse or at the forwarder's premises. The aim of this inspection is to verify your products, the quantity and the loading process.
This inspection includes:
- an inspection of the container before the loading (container condition)
- an inspection of your products (product check according to your P/O: quantity, appearance and general quality)
- an inspection of the loading process (cartons conditions, filling-up level etc)
This is an approach to sampling that is appropriate for the output of processes that deliver a continuous flow of a product. In this plan, we start inspecting 100 % of the units coming from the process. After a certain number of items that have been inspected with no defects, the plan goes to inspecting only a fraction of items. This continues until we find a nonconforming unit. At that point, the plan reverts back to 100 % inspection following the same pattern.
These are the extra expenses caused by delivering poor quality goods to customers. These expenses have two sources: internal failure costs (from defects before customers get the product) and external failure costs (costs after a customer receives the poor product or service). Defect sorting, Rework, repairs, image damage, brand damage, client confidence lost are a few examples of costs associated with poor quality.
This refers to all costs involved in the prevention of quality issues, defects, assessments of process performance, and measurement of financial consequences. Cost of quality is the cost justification of quality efforts. Cost of quality should be seen as an investment more than a cost.
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 defect - 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. You can provide your own list of Critical Defects to be inspected. Asia Quality Focus' default Critical Defect AQL is 0.
Major defect - 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. You can provide your own list of Major Defects to be inspected. Asia Quality Focus' default Major Defect AQL is 2.5.
Minor defect - 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. You can provide your own list of Minor Defects to be inspected. Asia Quality Focus' default Minor Defect AQL is 4.0.
Read more about Major, Minor and Critical defect to easily differentiate them.
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.: (Number of defectives x 100) / (number of units inspected)
This is an inspection technique in which you inspect a first lot of n1 size, which leads you either to accept or reject it. If you reject it, then we inspect a second sample of a larger lot size n2, which in turn leads to a decision to accept or reject the lot.
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
The inspection takes place when about 20% to 50% of the production has been completed. The aim is to ensure that contractual obligations regarding specifications, packaging, packing and marking are met and to check if the factory will be able to respect the production schedule. If recommendations have been given during a First-Articles Inspection (FAI), the During Production Inspection determines whether or not these corrective action plan has been successfully implemented.
The extent of nonconformance of product shall be expressed either in terms of percent defective or in terms of defects per hundred units (DHU).
This is a full evaluation of your supplier according to the ISO standards. It covers: profile of the supplier, internal organization, safety regulations, quality processes, performance, delivery terms and R&D. The audit also includes extensive worker and manager interviews in the factory worker's language.
Read about the difference between factory audit and inspection.
The Initial Production inspection is performed at the very first stage of the mass production. Asia Quality Focus Inspectors will inspect the quality of the material and components used in the production process and make sure it fits your requirements and is according to your approved sample (BAT). It also includes a visual check on the quality of packing materials and accessories. The inspector will also monitor the assembly process and check the first production run.
The First-Articles Inspection ensures that the customer's specifications are well-understood by the supplier/factory. The IPC will detect production discrepancies very early in the production processes; you will thus be able to take corrective actions sooner than later... saving time and securing your business
Inspection is the process of measuring, examining, testing, or otherwise comparing the unit of product with the requirements.
Read about the difference between inspection and factory audit.
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.
It is a document in which are listed all the details an inspector should check during an inspection. The objective is to avoid missing any of them.
Read more about how useful is the inspection checklist for an importer.
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.
Read more and get familiar with the inspection levels:
It defines all the process and steps the QC has to follow in order to perform the inspection. It includes the list of the details to check and the order specification verification.
ISO is a network of the national standards institutes of 157 countries, on the basis of one member per country, with a Central Secretariat in Geneva, Switzerland, that coordinates the system. ISO is a non-governmental organization: its members are not, as is the case in the United Nations system, delegations of national governments. Nevertheless, ISO occupies a special position between the public and private sectors. This is because, on the one hand, many of its member institutes are part of the governmental structure of their countries, or are mandated by their government. On the other hand, other members have their roots uniquely in the private sector, having been set up by national partnerships of industry associations.
ISO 9000 Standards: this is a set of quality standards developed in 1987 by the International Organization for Standardization. The three major areas of certification are as follows:
ISO 9002: covers everything except design and development.
ISO 9001: covers all the processes of a company from design and development to procurement, production, testing, installation and service.
ISO 9003: covers only inspection and testing.
The lot size is the total number of units available for random sampling. The lot size only includes packed products. Also called "inspection lot" or "inspection batch", it is a collection of units of product from which a sample is to drawn and inspected to determine conformance with the acceptance criteria.
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).
Normal inspection is what is used where there is no evidence that the quality of product being submitted is better or worse than the specified quality level.
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.
Also called Final Random Inspection (FRI), it is the most common inspection and it is performed when 100% of the goods ordered are finished, and at least 80% of the goods are packed into export cartons. Samples are selected randomly, according to sampling standards (usually AQL table) and procedures. They will be inspected according to your specifications, requirements and according to our protocols and expertise.
This inspection ensures that the production is in accordance with the specifications, purchase orders or letters of credit. It covers: product appearance (AQL), workmanship quality, size measurements, weight check, functionality assortment, accessories, labeling & logos, packaging, packing and other tests and special requirements, depending on the product and the export market.
Read about the role of the purchase order for sourcing in China more securely.
This is a standard sampling method by which random samples of units are chosen such that all combinations of these units have an equal chance of being chosen as the sample.
Reduced inspection under a sampling plan uses the same quality level as for normal inspection, but requires a smaller sample for inspection.
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.
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.
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.
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.
A lot sampling plan is a statement of the sample size or sizes to be used and the associated acceptance and rejection numbers.
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.
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.
Tightened inspection under a sampling procedure plan uses the quality level as for normal inspection, but requires more stringent acceptance criteria.
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.