Excessive Quality Inspection Doesn't Work. What matters is 〇〇.
In this article, I'm going to talk about "Excessive Quality Inspection Doesn't Work". If you're in production engineering, quality in mass production products is a concern. We should study the failure modes in FMEA in advance and introduce an inspection process somewhere in the mass production line. I will introduce some ideas.
【contents】
- Case Study of Excessive Quality Checks
- Why Excessive Quality Testing Doesn't Work
- Quality assurance methods that should be aimed for
- Quality assurance by product design
- Quality assurance by process design
- Quality assurance by process capability
Case Study of Excessive Quality Checks
We used to have a lot of customer complaints due to operational errors of our production lines.
- Product screws are loose.
- Lack of cover that is originally shipped with the product.
- Assembly dimensions of the parts are out of specification.
Thing like these...
These are NG items that can be detected in the normal mass production process. In the first place, they are abnormalities that will not occur if the operation is carried out in accordance with the predetermined rules. However, it had already been shipped to customer and we had to take some temporary countermeasures.
At first, we brought in another inspector to double check. The product's shipping box was labeled with "**** quality confirmed lot".
Initially it was just one item, but gradually, as other quality issues increased, the number of inspections to be double-checked and the text to be included in the product shipping boxes increased.
There was a single sheet of paper taped to the product shipping box, that says "Quality confirmed lot" as following.
"***** Quality confirmed lot"
"++++ Quality confirmed lot"
"------ Quality confirmed lot"
If you've read this far, you must be wondering.
The more inspection items there are, the less important each inspection becomes. Especially when it comes to human checks.
Why Excessive Quality Testing Doesn't Work
Additional inspections that are introduced after quality problem work because they are of high importance. If this level of importance is lowered, it will no longer function as an additional inspection.
In the first place, the real cause of above quality problems was originally the management of manufacturing site. This was due to poor handling of abnormalities and the failure to work according to the predetermined rules.
Demanding a number of additional inspections in such situation is not expected to be reliable. In other words, as the number of additional tests themselves increases, they stop functioning as additional tests.
Quality assurance methods that should be aimed for
Here's one idea.
Essentially, quality should be guaranteed by system. It is not an inspection.
This system is not manufacturing floor management or operator training. The systems include product design, process design, and process capability.
Quality assurance by product design
Quality assurance by product design is a design that eliminates the need for fine tuning in the production process. This is the kind of product design that makes it possible to produce a good product once the components are assembled. If products cannot be assembled without fine tuning at production process, it may not be assembled properly or its final characteristics may be out of specification, resulting in defects.
Quality assurance by process design
Quality assurance by process design is a process that can prevent process skips and automatically detect abnormal products.
For example, if the appearance of product is similar before and after the process, it is possible that the product may have skipped a process.
Automatically connecting equipment to eliminate the risk of such process skips, or introducing a system that can detect process skips at following process, can eliminate these risks from the start.
Quality assurance by process capability
Quality assurance by process capability means that the variation in the process is very low and there is a sufficient margin for specification width. In other words, it is a production process in which the product is good when assembled.
When this happens, you don't even have to inspect. Instead of guaranteeing quality with the inspection process, we guarantee quality with the process capability.
Let's go back to the beginning.
I hope you've recognized how useless the quality assurance idea is that everything should be inspected when designing products and processes. The more upstream processes such as product design and process design, the more important this idea becomes.
The only thing you can do on the manufacturing site is to do the physical work. You have to design the entire job so that this doesn't happen.
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