Product Inspection Explained: Pre-Production, In-Line and Pre-Shipment Checks

Inspection is not a formality carried out after production ends; it is a tool for catching quality issues at different stages. Done at the right time and in the right way, it removes most surprises before shipment. This article looks briefly at the three main inspection timings, the sampling method used in practice, the content of a good report and how to deal with defects.

When should an inspection take place?

In practice, inspections happen at three main points:

• Pre-production inspection: checks raw materials and components, the production plan and starting samples. It catches a run that has begun with the wrong materials within the first days.
• In-line inspection: takes place while production is at a certain stage; it exposes workmanship errors and systematic problems before the run is complete.
• Pre-shipment inspection: is carried out after production and packing are finished, before loading. For most buyers it is the last line of defence.

Which point suits you depends on the risk of the product, the production timeline and how long you have worked with the supplier. On a first order with a new supplier, pre-production and pre-shipment inspections should both be considered. In a steady, repeating relationship, an in-line inspection earns its place by showing the source of a problem earlier.

AQL and sampling

An inspection does not examine every single unit; instead it draws a sample based on an acceptable quality limit (AQL). In practice the common reference is an international sampling table such as ISO 2859-1. The inspector reads the number of units to check from the table, based on lot size and the chosen inspection level.

A concrete example: for a lot between 3,201 and 10,000 units, the normal general level draws a sample of 200 units. At AQL 2.5 the typical acceptance number for that sample is 10; if the defect count reaches 11 the lot is rejected. The AQL value varies by product and defect class: critical safety defects call for very tight limits, while products where some cosmetic flaws are tolerable allow looser ones. The numbers change, but the method stays the same: lot size, sampling level, AQL and acceptance number should all be written down before the inspection.

The inspection plan should also cover:

• Definitions of defect classes: critical, major and minor
• The rule that samples are selected at random
• Location, date and identity of the inspector
• Who makes the accept or reject decision

Who carries out the inspection matters as much as the result. A supplier's own quality team gives useful feedback, but an independent inspection adds a neutral basis to the accept decision. On first orders and on higher-value shipments, a third-party inspector or a party you nominate yourself is usually the better choice.

What an inspection report must contain

A good inspection report should support your decision on whether to ship. It must stand on its own and be understandable without extra explanation.

What a report needs:

• Supplier, lot, date and shipment reference details
• The sampling plan: lot size, sample size, AQL and acceptance number
• The number, class and photo documentation of defects found
• Results for packing, labelling, functional checks and appearance
• Overall verdict: accept, conditional accept or reject, plus the inspector's sign-off

Photos and measurements must be concrete. A statement that things look acceptable is not enough on its own; it should be clear which measurement was taken where and which unit was weighed.

Handling defects

Defects are usually grouped into three classes: critical, affecting safety or legal conformity; major, preventing use or sale; and minor, acceptable cosmetic issues. Which class is governed by which AQL should be defined in the contract or on the order form.

After a rejection there are three basic options: repair the defects and re-inspect, accept with a discount, or cancel the order. The choice depends on the nature of the defect and your urgency; whatever the outcome, record it in writing with photos. If the same defect appears a second time, request corrective action: cause, actions to take, responsible person and deadline.

Conclusion

Inspection costs money, but correcting a wrong shipment, returning it or recalling a faulty product from the market usually costs far more. As your product, volumes and acceptance criteria become clear, you can state your inspection requirements as well when you send your request through the Request a Quote page.