I’ve Always Wanted To Know:
What is quality control? How can items leave the factory defective?
Quality control is the process where manufacturers verify that an product conforms to the expected standards and functionality. Almost all factories and manufacturers have some form of quality control but why is it you still receive defective merchandise? Do the quality control employees and systems fail? Is quality control a lie? Is there some other secret to why it always seems like if there is a bad one you’ll end up with it?
So what types of quality control are there?
Let’s start by looking at how quality control is done in a manufacturing environment.
Raw Material Sample Testing: The raw material used to create the basic components may be tested per batch that comes into the factory to determine it is the right make-up and consistency as ordered.
Sub-Component Random Sampling: The components which make up a final device are randomly tested to verify they perform and are physically as requested. One out of every 100 or one unit per batch may be randomly sampled to determine this. The number and frequency of the random sampling is controlled by the manufacturer.
Sub-Component Full Testing: All of the components which make up a final device are tested to verify they perform and are physically as requested. This testing may be complete or may just check certain aspects of the sub-components.
Final Product Partial Random Testing: The final assembled product is randomly tested to verify that certain known possible manufacturing faults are not present. These faults are usually known to the manufacturer and may be visual inspections or certain electrical or performance tests.
Final Product Full Random Testing: The final product are randomly tested to verify they perform and are physically as requested. One out of every 100 or one unit per batch may be randomly sampled to determine this. The number and frequency of the random sampling is controlled by the manufacturer.
Final Product Full Testing: The final device are all tested to verify it performs and are physically as requested. This testing will be complete and verify the product conforms to all specifications.
Your final product can go through multiple of these steps and combinations of these steps depending on the product being manufactured. For example in a spark plug factory the spark plugs may be regularly tested with low voltage and once per hour a sample of each batch at high voltage with the plug being split open to verify internal construction (a more accurate but time intensive and destructive test.) In a medical instruments factory a kidney dialysis machine will have all components thoroughly tested on each and every machine produced.
Why the difference? Simple: If your low cost spark plug malfunctions the manufacturer is willing to accept the returns/faults to keep the price low. If your kidney dialysis machine malfunctions then someone may die and the resulting law suit would cost the company more then the intensive quality control testing.
The percent of defects acceptable (no one is perfect) for a product will vary as each company and manufacturer sets a standard they are willing to accept and quality control test to meet or exceed that standard. Time is money so the longer they spend testing the more expensive a product will be. It’s a tricky balance that depending on the application sometimes leads to “better 1 out of 1000 be defective than all 1000 cost 10% more.”
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