100% Inspection

A 100% inspection is exactly what it sounds like. It is a check on every single piece of work. The inspection can be done on both physical products on the shop floor, or information in an office setting.

Most 100% inspections originate from a few main sources:

• Government regulations. Some agencies require 100% inspections.
• Products requiring perfection. This is usually safety related or to protect the perception of the product as high-grade.
• Demanding customers. Some customers have enough clout to drive action by a company. This may be explicit, such as a major customer demanding a 100% inspection. Or, it may be initiated by the company to preserve the relationship in the face of quality problems.
• Known quality issues. In this case, the extensive inspection is an admission that there are quality problems that the leadership team is unable (or unwilling) to address.

The primary purpose of a 100% inspection is to avoid shipping any bad products. An alternative to a 100 percent inspection is a sampling plan, in which the inspection gives an indication of an overall quality level.

In a sampling plan, the results of the sample are used to make decisions about what to do with entire product runs rather than to act as a safety net to capture problems. With a sampling plan, the decision is generally driven by an acceptable quality level, the threshold set for how many bad items are allowed. This is not an acceptable option where customers demand zero failures.

Problems with 100% Inspections

While a 100% inspection does find more issues than a sampling plan, there are some problems. The first is that a 100% inspection is generally an indicator that quality is poor. If it is left in place permanently, it also suggests that the company is not focused heavily on continuous improvement, as presumably, an issue that warrants the resources of a 100% inspection should also warrant some problem-solving resources.

The resources a 100% inspection consumes is the second problem. Complete inspections tend to be very wasteful.

The final problem is that full inspections generate overconfidence. When people operate with a safety net, they may not worry as much about quality, as they know the product will be getting a final look. 100% inspections can undermine quality in a company, rather than build it up.

Deming and Inspections

Deming’s 3^rd point is “Cease dependence on inspection to achieve quality.”

He recognized that inspections are wasteful and a crutch and are actually a sign of poor quality.

The bottom line is that if you have good quality, you don’t need inspections.

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Be careful about errors in the inspection process. An inspection is not infallible. Every product can obviously be good or bad, and every inspection can result in a pass or fail. Taken together, this gives four possible combinations, two of which represent incorrect outcomes.

• Good Product Passes: This is the desired outcome.
• Bad Product Fails: While not desired, this is an outcome that is correct.
• Good Product Fails: Known as a false positive or a type-I error or an alpha error, the test flags a product it shouldn’t. This costs money, as good products are scrapped. Think of this as crying wolf, albeit unintentionally. This error is also known as producer’s risk.
• Bad Product Passes: In production environments, this is the worse of the two failure types. A false negative or type-II error or a beta error, means the test fails to catch a problem. This is also known as consumer’s risk.

Even if you are unable to completely remove a 100% inspection, you should at least try to reduce as many checks as possible. This streamlines the inspection process, saving cost.

Make sure to convey to the production team what will be checked in ‘final’, though. They need to know that the safety net for their process is gone.

Take a close look at your inspections. Pay special attention to the reasons for the inspection and whether they should be permanent (i.e. regulatory) or if there is the potential to eliminate the need for the inspections.

Once you understand what you are checking, test the effectiveness of your inspections. Over an extended period of time, randomly check inspected units. To prevent the Hawthorne Effect from creeping in, only check items that were signed off on prior to the secondary inspectors showing up. This keeps the primary inspectors from adjusting their process based upon the check. The goal here is to highlight the shortcomings of inspecting quality into a process.

Armed with this information, work to get rid of inspections. The best way to eliminate them is to understand the problems that are being identified. Make sure you have an inspection log and are compiling data about the defects. With that information, you can do two things.

The first is the best option. Build quality into the process where the error is occurring and eliminate the need for the inspection.

The second is to move the inspection closer to the point of origin. When the inspection is conducted at the end of a process, it has the unoriginal name of end-of-line inspection.

Source inspections are done much closer to where the error actually occurred, often with the inspection even being done by the person who did the work.

Inspections can also be done at the next downstream process, which serves to get a second set of eyes on an item. This is sometimes called a subsequent inspection. With the check being done so close to the work, the inspector can still show the operator the problem for immediate action.

In both of these last two inspection types, the operator gets the advantage of seeing the conditions that caused the error, often while the issue is still present. End-of-line inspections tend to give limited feedback that arrives too late to do a thorough investigation.