A few years back, I wrote an article related to dimensional control about the limitations of asking inspectors to write the exact values they find when checking measurements of items like garments and precision mechanical pieces. First, the numbers you can read in a report are not necessarily the reality, and I cited many ways this happens: Use of measurement instruments that are not calibrated (poor accuracy) or that lack precision Inadvertent human errors (misreading the instrument, … [Read more...]
What Is the Confidence Level when Working with AQL Tables?
A reader wrote to me and asked the following question about sampling plans by attributes: What is the "Confidence Level" when using the AQL Tables? How can we determine what the confidence levels are, and are there formulas we can use? That's a valid question. When playing with statistics, one often mentions a confidence interval. For example, "90% of the time, the value will be between 34.5 and 66.0". In theory, I guess one could do the same with the values in the AQL tables. There is a … [Read more...]
A Simple AQL Calculator To Prepare Your Product Inspections
One of our developers prepared this simple AQL calculator for Sofeast. You can use it instead of reading the AQL tables to quickly produce your sample size and permissible defect number. … [Read more...]
When To Do a Random AQL Inspection vs. Check 100% of the Goods
First, let me get one thing out of the way: not all batches need to be checked. If a manufacturer has great systems and processes, and if they have a history of complying with your quality standard, there is usually no reason to send quality inspectors to their facility. Similarly, if you can easily return the whole batch and it can be reworked quickly, you probably don't want to spend resources on checking whether they did as promised. Now, let's assume you do want confirmation of … [Read more...]
QC Basics: What is a Quality Inspection? Context, Tools & Template
This article answers the question: 'What is a quality inspection?' and explores when they typically take place (before, during, and after production). We will cover the types of inspections most widely used by buyers in international trade. They should be performed by 3rd party QC providers (appointed by the buyer), or by the buyer's own inspectors, if you buy from China, Vietnam, India, or another low-cost country. … [Read more...]
3 Common Ways Factories Try to Cheat Inspectors/Auditors
Every day in China, in Vietnam, in Bangladesh, and in India, thousands of inspectors and auditors take a bus or a car to a factory. And, in some of those factories, managers are plotting how to cheat those unwelcome visitors. Let's look at 3 very common ways this is done, so you are warned and ready to avoid unscrupulous suppliers like this... … [Read more...]
Some Problems Can’t Be Detected During Apparel QC Inspections
A few years ago, I wrote about the limits of random quality inspections. My focus in that article was on the random elements, on human mistakes, and on the tricks that manufacturers can play. Today I'd like to write about issues that simply can't be detected during inspections, even if 100% of the goods are checked and inspectors do a perfect job. I will write about a product line that I know well: apparel. … [Read more...]
Why Improving Quality Leads to Lower Manufacturing Costs
I am tired of repeating certain things over and over when I am in Chinese factories. One of them is this: If you work on improving quality, you will cut your costs at the same time if you follow the right approach. This is nothing new. As Deming wrote: Management in some companies in Japan observed in 1948 and 1949 that improvement of quality begets naturally and inevitably improvement of productivity. So, how can better quality lead to lower costs? What is the "right approach"? I listed 6 … [Read more...]
The Different Sampling Plans Contained in the ISO 2859 Series
The vast majority of inspectors follow the ISO 2859-1 standard. But about ISO 2859-2, -3, and so on? The relationship between these parts is explained in ISO 2859-10:2006 (introduction to the ISO 2859 series of standards for sampling for inspection by attributes): ⎯ Part 1: Sampling schemes indexed by acceptance quality limit (AQL) for lot-by-lot inspection ⎯ Part 2: Sampling plans indexed by limiting quality (LQ) for isolated lot inspection ⎯ Part 3: Skip-lot sampling procedures ⎯ … [Read more...]
Why the AQL tables are not in favor of the buyer
This is the third and last video about the ANSI tables (also known as “AQL tables”). As I explained in the last video, these sampling schemes were designed for very stable relationships, where the manufacturer keeps making the same products and keeps shipping them regularly (e.g. twice a month) to the same customer. As a consequence, the assumption is that quality is under control. And an inspection is used to catch the big accidents. What it means is that the statistics are way, way … [Read more...]