Loss of productivity equates to a loss of revenue. If parts are worn or misshapen in some areas, the life of that part can drop drastically. This can cause premature failure in a car, plane, or any other type of machine that uses fasteners. A crack in the head of the part can lead to the structural integrity being compromised and the head coming off. All of these problems are solved by 100% inspection of parts at high-speeds.

Additionally, if a part is safety critical it is important to know that it is dimensionally and metallurgically correct. If it is out of specification or not hard enough the results can be catastrophic. It is not easy to tell if a part is hard enough to do its job without running the part through something such as an eddy current coil or doing destructive tests.

There are a few schools of thought about inspection. One is testing a part every few hundred pieces with very precise measurements to see if it is in specification. Instead of waiting for bad parts to be produced this allows for companies to see trends and act before tooling wears out. Usually this is done on a first article scanner and takes a few seconds – scanning the part completely and giving detailed measurements for that specific part.

While some measure of control can be gained from testing one part thoroughly, every few hundred parts, to see how out of tolerance tooling is getting it is better to test every part if possible. Splits or seams in the original material can lead to defects unrelated to tooling.

To catch those one must inspect every part. Machines such as Mectron’s Qualifier use both lasers and eddy current to test every part at high-speeds. The lasers inspect the part for any dimensional defects; while the eddy current tests the part metallurgically to ensure consistent hardness and no foreign material exists. It achieves its speed by comparing the part to a known good part and making its decision without human interaction. Since the machine can operate at over 300 parts a minute, it becomes practical and in the end profitable to inspect every part.

Taking things a step further past functionality, the look of the part is also important. This is especially true for commercial sales. If a customer sees a big scratch or small dent that doesn’t change the part enough to be thrown out dimensionally, they may think the goods are low quality. So surface inspection of every part also becomes necessary. For example, the Mectron Surface Qualifier uses a camera and takes pictures of the part as it moves and rotates to get the whole surface area. It then casts light on the part and looks for distortions of that light outside the norm to determine if a part has any cosmetic blemishes or defects. 

Source: https://www.fastenerandfixing.com/manufacturing-technology/qualified-fastener-inspection/