Inspections are vital to ensuring the quality of components that make up thousands of products. Yet, 100% inspection eats up significant time and cost without even guaranteeing 100% compliance.
This is why manufacturers and customers alike rely on a sampling plan in quality control, and for good reasons.
Visual inspections are done to detect a variety of surface finish issues in metal parts, from corrosion and contamination to cracks and surface irregularities. But given the large quantities that many manufacturers work with, it is impractical to look at 100% of the parts in every lot. And for manufacturers that routinely produce lots consisting of 100,000 parts or more, inspecting such a large lot means it is easy to make an error.
Even with a range of very precise tools available, it is impossible to examine every tiny segment of a part’s surface.
Experience has shown us that inspecting a small portion of a lot is not only faster and more cost effective. It also allows us to pay closer attention to the inspection process.
In a sampling plan, a relatively small number of pieces from the lot are inspected to determine if the entire lot will be accepted or rejected based on the number of defective pieces in the sample. With every piece in the sample being more carefully inspected, the likelihood of errors or of simply missing something is reduced. It also provides statistically valid results, with high confidence that if the sample is defect-free, the entire lot will meet the customer’s requirements.
The number of pieces to be inspected and the acceptable number of defects are usually based on published Acceptable Quality Level (AQL) and index values. The higher the AQL, the fewer number of parts that will be inspected.
Our process includes QC sampling at various stages: at raw material receiving, at designated steps during production, as well as at the end. This enables us to be sure that quality is tightly controlled throughout the process.
With a statistically valid QC sampling plan, a smaller number of pieces can be inspected more carefully. This gives customers a high level of confidence that if the sample is acceptable, the entire lot is acceptable.
Whatever your preferred sampling plan may be, it is important to include this information in your specifications and RFQs. That way, your manufacturing partner can provide a more accurate and timely quote that includes an inspection process.