Production Inspection 101: Ensuring Quality Control

Production inspection helps ensure quality control by detecting defects and providing data and feedback on each stage of manufacturing. This article walks through the four main types of production inspection, the cost of performing inspection, and quality control strategies.

What Types of Production Inspection Should be Conducted?

Pre-Production Inspection (PPI)

Before production begins or at the very start, you’ll need to ensure everything is ready for a production run, particularly the raw materials, component, and the factory’s setup.

Initial Production Check (IPC)

This is conducted when 1% to 20% of the order is completed. The very first units off the line (often called First Article Inspection) is inspected to verify that the factory’s process is producing a product that matches the Golden Sample (the approved prototype) and to catch setup errors early.

During Production Inspection (DPI)

DPI is done between 20% to 80% production completion, when an inspector goes to the factory to check if the finished or half-finished products meet expectations. Inspectors also need to review the production line to ensure the supplier is following the agreed-upon process.

This kind of inspection is to ensure quality remains consistent and that the factory is on track to meet the shipping deadline. It is the best time to catch systemic issues that might have developed after the initial start, and so they be fixed before the whole batch is finished.

Pre-Shipment Inspection (PSI)

This is done at 100% production completion, before the goods leave the factory. This is considered the most critical and mandatory inspection for every order that acts as the “last line of defense” before paying the final invoice.

You need to check the finished products, packaging, shipping cartons, labelling, etc. You can even do simulated “wear and tear” to ensure products survive the transit process. It uses statistical sampling (AQL) to decide if the entire batch should be accepted or rejected.

Who Should Perform Production Inspection?

Manufacturers

It is the industry standard for every manufacturer to have an internal Quality Control (QC) department. They perform inspections at every stage of production to minimize returned products.

From our experience, quality control is typically done by the manufacturers as they have more context of design than a 3rd-party inspector. An outside inspector needs the same level of knowledge as the designer to make “judgment calls” for some grey areas, which requires a massive transfer of information. Manufacturers naturally possess deeper context than 3rd-party inspectors because they designed the tooling, sourced the specific raw materials, and understands the intent behind every curve or bolt.

3rd party inspectors

Independent inspectors are regarded as not “grading their own work” by following objective standards like a checklist of specs and Golden Samples to minimize “judgement calls”.

In the real world, there is always a hybrid method for quality control – manufacturer self-check for daily internal QC once trust is established, and a 3rd party does final pre-shipment inspection.

How Much Does Production Inspection Cost?

When manufacturers conduct QC on their own, it is a standard part of the manufacturing “package.” You don’t see a separate line item for it because the factory includes the labor cost of their internal inspectors in the price of the goods.

While some may assume 3rd-party inspections are cheap, a professional, bilingual, and ethical inspection is a specialized service. Budgeting roughly $300 per day is the safest market standard for quality results.

The costs of production inspection are generally calculated by “man-days” (one inspector working for one day). While an average inspector’s base labor might be around $20/hour, a well-trained, bi-lingual inspector’s cost might be much higher, with total service cost typically being around $300 per day.

What Affects Inspection Cost

Complexity

• Simple products: For pre-production inspection, if you don’t have a lot of raw materials, it could just be a day. For product inspection, a visual check on basic goods is fast and usually stays within the one-day range.
• Complex products: The number of parts and assemblies all drive up the complexity. If the inspector has to perform technical tests, check intricate parts, or use specialized tools for complex parts such as electronics products, the time required increases, raising the cost.

Sample size

The pre-shipment inspection is often the most expensive because it is the most thorough, which requires at least one day. If you want a high percentage of your order tested (e.g., checking 100% of the goods versus a random sample), it will require more man-days.

Your inspector may have input regarding sample size and sampling plan in accordance to your specific product, the amount of products manufactured and acceptance criteria. There are several standard sampling methods that are internationally recognized such as: ISO 2859, PPAP and ANSI/ASQ Z1.4.

Production method and phases

• Continuous production: The factory starts the machines and runs them until the entire order is finished. You usually only need one DPI visit. The inspector visits when the products are about 30-50% finished.
• Phased production: The product is made in separate steps, often with time gaps in between. This often happens with electronics products, which require multiple DPI check-ins to monitor each phase (after assembly, after testing, etc.).

Hidden costs

The final price includes more than just the person standing on the factory floor. These “hidden” costs are baked into the total $300 price:

• Travel costs: Getting the inspector to and from the factory.
• Administrative fees: Reporting, scheduling, and client communication.
• Training and Ethics: Costs associated with training inspectors and conducting “fraud/bribery audits” to ensure the inspection is honest and unbiased.

Pro Tips for Quality Control

Use Golden Samples throughout production

Reference samples (also known as “golden samples”) should be used throughout the quality control process. A golden sample should be a representative sample that is approved by the inventor to be used as a visual and functional reference to both the inventor and manufacturer to ensure consistency across production runs. It serves as a visual and physical baseline to ensure the factory is meeting your exact standards from start to finish.

At the start of production, samples are used to verify raw materials. For example, if you are manufacturing a wood or plastic product, the inspector uses a reference sample to check if the raw material has the correct grade, texture, and appearance before the assembly line starts.

The pre-shipment stage is where Golden Samples are most important. It ensures unique textures, irregular shapes, and color matching – Pantone codes can sometimes be misleading depending on the material it is applied to.

It can act as the golden standard to help mitigate the information gap when inspectors don’t have enough context of your design and tend to make incorrect judgement calls.

Build and keep good relationship with manufacturers

Manufacturers are naturally more inclined to prioritize your projects when a relationship already exists. By building that relationship early and initiating inspections as soon as possible, you create a shared understanding: you trust them, but you still need to verify and safeguard your own interests.

A strong relationship also allows the inspection process to evolve. Instead of a static Pass/Fail test, the relationship enables a feedback loop that helps you refine the process and scale safely.

Visit the Factory

Visiting the factory in person is strongly recommended especially during the first production run.

Sharing a meal with factory managers moves the relationship from just an order number to personal, which helps you stand out among their hundreds of distant clients, reducing their hesitation of manufacturing your product and leading to better production speeds and more attention to detail.

Besides, simply showing up in person allows you to negotiate better payment terms and lower minimum order quantities that wouldn’t be possible over email.

By being on the factory floor, you can also learn exactly where the pain points are in the production line.

FAQs

Do inspectors need to be trained engineers? Can an inspector perform complex “engineering-level” tests?

Inspectors are not typically degreed engineers. They are highly trained specialists with deep experience in their specific product areas. They are trained to “think like an engineer” by following rigorous Standard Operating Procedures (SOPs) and logical workflows to ensure every technical detail is verified.

Inspectors can perform technical tests and operate factory machinery to verify product durability or performance. As long as there is a clear pass/fail criteria and a defined procedure, an inspector can supervise and execute advanced testing to ensure your products meet global standards.

What happens if the factory doesn’t have the right testing equipment?

If a factory lacks the necessary labs or machinery for a specific test, we recommend using a Third-Party Testing Lab. Inspectors should work directly with these labs to ensure the integrity of the process.

How do I ensure consistency across different inspectors?

Consistency comes from the Pass/Fail criteria. Don’t rely on an inspector’s “gut feeling.” Instead, provide them with detailed checklists and specifications. By following these structured steps, the inspector ensures the product is made to your exact specifications every time.