Quality control (QC)
Quality control encompasses the inspection, testing, and measurement activities that verify products conform to specifications. Unlike quality assurance, which prevents defects through systems, QC is reactive: detecting nonconformances after they occur. QC catches problems, provides data for improvement, and ensures only conforming products reach customers.
Examples
Incoming inspection: QC inspects received materials against specifications before releasing them to production. Dimensional checks, material verification, and visual inspection identify defects before materials enter manufacturing.
In-process inspection: QC checkpoints throughout manufacturing verify that work-in-process meets requirements at each stage. Catching defects early prevents adding value to defective products.
Final inspection: Before shipment, QC performs final verification that finished products meet all specifications. Functional testing, visual inspection, and documentation review confirm readiness for delivery.
Definition
QC methods include visual inspection, dimensional measurement, functional testing, material analysis, and statistical sampling. The appropriate method depends on the characteristic being verified, risk level, and practical constraints.
Sampling plans determine how many units to inspect and acceptance criteria. One hundred percent inspection catches the most defects but is expensive and sometimes impractical. Statistical sampling provides reasonable confidence at lower cost but accepts some probability of passing nonconforming lots.
QC data drives quality improvement by revealing defect patterns, process trends, and supplier performance. Analyzing QC data identifies where problems originate and whether corrective actions are effective.
QC responsibilities may be shared between suppliers and buyers. Suppliers perform QC before shipment. Buyers may perform incoming QC, accept based on supplier certification, or use skip-lot programs for proven suppliers. The appropriate approach depends on supplier reliability and defect consequences.
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