GUEST POSTING: Quality Control Basics, Part 4/4: Putting It All Together
Example 1: 5,000 widgets from a new supplier
You have no information about the factory, so you should adopt the normal level (a.k.a. level II). The order quantity is comprised between 3,201 and 10,000pcs. If you open the first AQL table, you see the code letter is L. (If you forgot how to read the tables, see the article about AQL tables). And with the second AQL table you see that 200 samples have to be checked by the inspector. If you opt for the standard AQL limits (0 C. / 2.5% M. / 4.0% m.), the inspection is failed if at least one of these conditions comes true:
- One or more critical defects are found
- Eight or more major defects are found
- Eleven or more minor defects are found
When to inspect? If this is a standard product and you have flexibility with timing, a final (pre-shipment) inspection should be enough.
Example 2: 30,000 watches from unknown supplier(s)
You suspect that your supplier gave orders to several workshops to produce your goods, but he won’t tell you. And these items are rather valuable. A level-III inspection is probably the most appropriate.
If we read the AQL tables as we did above, we have to inspect 500 samples, and the maximum number of defects is: 0 critical, 18 major, 18 minor.
If a visual check on all samples and a function/accuracy check on a few pieces is enough, it probably takes two or three man-days.
When to inspect? If the supplier refuses to disclose the factory information, you have to go for a final (pre-shipment) inspection.
Example 3: Four different styles of garments from a good factory
You know that this factory’s workmanship is quite good. But you want an inspector to check all the conformity elements, and in particular the measurements. Level I should be enough. You sell these products in boutiques at a high price, so you can only accept 1.5% major defects and 4.0% minor defects (for garments, there are generally no critical defects). The fitting is quite important, especially for the brassiere and the brief, so 3 to 5 samples should be measured in each size. There are 4 different types of products, so there has to be 4 inspections:
The total number of samples to check is only 127 pieces. But this order cannot be checked in one man-day, for two reasons:
Order Qty (in pcs)
No. of samples to check
Max. No. of defects
No. of samples to measure
3 sizes x 3 pieces
3 sizes x 3 pieces
6 sizes x 5 pieces
3 sizes x 5 pieces
- There are four different inspections to carry out. For each product, the inspector has to check all the conformity elements (fabrics, colors, accessories, stitchings...). And there are four reports to prepare.
- There are 63 samples to measure, across four different products and many sizes.
When to inspect? The best is clearly during production, when the products are on the line. As the 4 products might not all be processed at exactly the same time, it might be preferable to send an inspector at different times. And if an inspection is failed, a re-inspection can probably be performed at the supplier’s charge.
Now what about you? Tell us briefly about your case in the comments section, and I’ll give you some advice.
Renaud Anjoran is the founder of Sofeast Quality Control, a third-party QC firm specializing in garments and textile in China. He also writes on the Quality Inspection blog. You can email him at firstname.lastname@example.org.
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