What happens when your inspected products reach a customer who complains about performance issues? Does this mean that the quality inspection wasn’t done properly? Maybe not, because QC inspectors check products against pre-defined specifications and it’s not their job to validate if a product design will likely cause problems.
A product reaches customers and doesn’t perform as expected after inspections
Let’s set the scene with an example to illustrate this point. And we will take a silly example, to avoid any resemblance to a real case.
You are selling an e-bike. It undergoes quality inspections during production and passes.
It is exported from China and finally gets to customers.
Some customers complain that, after a few weeks of use, the brakes stop operating. It is disappointing and highly unsafe.
So, did the quality inspector make a mistake?
Testing to specification versus reliability testing
To understand why the e-bikes could go through a quality inspection and still fail to perform in some cases, we need to consider the difference between quality inspections and reliability testing.
Quality inspections
Quality inspectors will, typically in the supplier’s factory, check production against any specifications the customer gives to them. The goal is to ensure that the product reaches specifications and that there are no defects.
They will answer questions such as:
- Is it the right frame, and are the critical dimensions OK?
- Does the welding look up to spec?
- Is it the right battery, with the right parameters (perhaps there is time to do a full discharge and a partial recharge during the inspection)
- Is the product aesthetically correct (color, etc)?
- When the bike is ridden for a few meters, or perhaps a few hundred meters if space allows, are there any issues?
- Are there defects such as imperfections, scratches, etc?
An inspection will often take just 1 or 2 man-days of work and provide a snapshot of the state of the products that are ready to be exported.
Reliability testing
Reliability testing is commonly done in a testing laboratory and, obviously, completing those lab tests by real usage is desirable.
It includes a battery of tests that aim to evaluate how well the product performs under specified conditions over time, and noting when and why it fails (if it does fail at all).
The test results demonstrate how reliable the product will be in the field and warn of possible weak points. They also help you to make a judgement about whether they will reach your expected lifetime (such as a warranty period) when used in the field by customers.
Tests may include:
- Fatigue and abuse testing
- Stress testing (extreme conditions)
- Vibration and shock testing
- Endurance testing
- Power cycling (for electrical/electronic products)
Reliability testing takes days and often weeks.
That’s how the issue of brake pads that get “consumed” excessively fast might be caught. A design review (including checking the bill of materials) would also be likely to catch that issue.
Side note: we are trying to simplify the discussion here. For an e-bike, some safety testing (see ISO 4210 for example) is part of compliance requirements. And in this case there is quite a bit of overlap between that safety testing and compliance testing.
Could the inspector have done more?
Let’s look at what the inspector would do when inspecting the e-bikes.
They go to the factory and have a set list of specifications in hand to check. (Note: there is usually a focus on what requirements are most important, so the inspector doesn’t take days and days checking everything. The customer usually doesn’t want to pay more than 1 or 2 days of work in this case.)
They check dimensions, aesthetics, if there are any defects, and they do a simple ride test that includes hitting the brakes.
The e-bike passes. The inspection confirms that the bike ‘works’ in a short and simple test. It says nothing about the bike’s ability to resist certain stresses over a certain length of time.
Now, some customers do have a concern about stresses over the product’s lifetime, and in some cases some “fatigue testing” or even some “abuse testing” can be performed. It is a rough and un-scientific approach to doing an accelerated reliability test, but it is better than nothing.
Unfortunately, on a product as complex as an e-bike, many aspects could be “fatigue tested”, and just that can take days of work. I’d usually suggest focusing on safety functions first, but that’s not always the main source of concern for customers.
How about the issues in the field?
If the inspector checks that the e-bike can be ridden and its brakes work, does this guarantee that e-bikes can withstand use in the field? No.
To give assurance that the product can withstand different use cases, it would have to go through reliability testing where different situations which validate that the e-bike’s design will not lead to early failure.
Conclusion: Square pegs for round holes
In this example case, the e-bike probably needs to go through reliability testing and compliance testing first, and then quality inspections before it is shipped.
Just doing an inspection is a great idea, but they’re not meant for assessing a product’s reliability or durability over time, they only give a snapshot of if the products coming out of the factory reach specifications.
If you have questions about a case like this or quality inspections, let us know. We’re here to help you across Asia and beyond.
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