Quality Inspection Guide for Sourcing from China

1. The Four Inspection Stages

Professional quality control follows a four-stage approach throughout the manufacturing lifecycle. Each stage serves a distinct purpose and should be specified in your purchase agreement.

1.1 IQC — Incoming Quality Control

IQC is performed on raw materials and components before they enter the production line. It ensures that the base materials meet your specifications. This is especially important when your supplier sources sub-materials from third parties.

• Typical checks: Material composition, dimensions, surface finish, hardness, packaging condition
• When to use: First order with a new supplier, critical safety components, or when material quality affects downstream processes
• Sampling: Typically MIL-STD-1916 or AQL 1.0–2.5 for materials

1.2 IPQC — In-Process Quality Control

IPQC monitors production quality at defined checkpoints during manufacturing. It catches defects early, preventing waste of materials and labor on already-defective parts.

• Typical checks: First article inspection (FAI), dimensional checks every 50–100 units, process parameter verification (temperature, pressure, cycle time), visual inspection at each operation
• When to use: Long production runs, complex assemblies, high-value manufacturing, new production lines
• Key tool: Control charts (SPC — Statistical Process Control) for critical dimensions

1.3 FQC — Final Quality Control

FQC is performed on finished goods before packaging. It verifies that the final product meets all specified requirements in appearance, fit, function, and safety.

• Typical checks: Dimensional verification against drawing, functional testing (if applicable), visual inspection per AQL standard, weight/size consistency, packaging integrity
• When to use: Every shipment, without exception
• Sampling: Based on AQL tables (see below)

1.4 OQC — Outgoing Quality Control

OQC verifies the quality of packaged goods ready for shipment, focusing on packaging quality, labeling accuracy, and quantity verification. It is the final check before the goods leave the factory.

• Typical checks: Carton condition, labeling accuracy (barcodes, shipping marks, regulatory markings), quantity count, loading inspection for full-container shipments
• When to use: Every shipment
• Sampling: Often 100% inspection for labeling, statistical for carton condition

2. AQL (Acceptable Quality Limit) Sampling

AQL is the most widely used sampling standard in China manufacturing. It is defined in ANSI/ASQ Z1.4-2008 (which is equivalent to MIL-STD-1916 and ISO 2859-1). AQL specifies the maximum number of defective units allowed in a sample for the lot to pass inspection.

Standard AQL Levels

AQL Sampling Table (Single Normal Inspection, Level II)

Ac = Accept (max defects allowed to pass); Re = Reject (defects ≥ Re means lot rejected). ↓ = Use next higher sample size code.

3. Defect Classification System

Every inspection standard requires clear classification of defects. For China sourcing, the widely accepted classification is:

• Critical Defect: Renders the product unsafe or illegal to sell (e.g., lead above RoHS limits, sharp edges, electrical fire risk). Action: Lot automatically rejected. Report to authorities if required.
• Major Defect: Product will not function as intended, fails to meet essential specifications, or has obvious appearance issues that affect saleability. Action: Reject lot if number exceeds AQL limit. Options: sort 100%, negotiate discount, return for rework.
• Minor Defect: Does not affect functionality but deviates from specifications (e.g., slight color variation within tolerance, minor scratch). Action: Accept or negotiate allowance per AQL limit.

4. Third-Party Inspection Companies

For most foreign buyers, using a third-party inspection company is the most reliable way to ensure quality. These companies provide independent, professional inspectors who follow international standards.

How to Choose an Inspection Company

1. Check accreditation: Ensure the inspection company is ISO/IEC 17020 accredited for inspection and ISO/IEC 17025 accredited for laboratory testing.
2. Industry experience: Some companies excel in specific sectors. For electronics, Intertek and TÜV are strong. For hardlines and textiles, SGS and BV are market leaders.
3. Local presence: An inspector based in the same province as your supplier can often be arranged at a lower cost and with shorter notice.
4. Language: Most major companies provide English-language reports as standard. Check if you need bilingual reporting.
5. Booking timeline: Book at least 3–5 working days in advance. Urgent inspections (next-day) typically incur a 50% surcharge.

5. Setting Up Your Inspection Protocol

1. Define specifications clearly in writing: Engineering drawings, material specs, color tolerance (Pantone numbers), packaging requirements — all must be documented before production begins.
2. Include inspection clauses in your purchase order: Specify AQL levels, which stages are inspected, who pays (usually buyer), and what happens on rejection (rework at supplier cost, sorting, or cancellation).
3. Use a checklist: Provide the inspection company with a checklist custom to your product. Include dimension callouts, visual standards, and functional test criteria.
4. Review and act on reports within 48 hours: Rejected lots should trigger immediate communication with your supplier to arrange corrective actions.