Have you been involved in discussions regarding the reasons for product nonconformance? Invariably fingers are pointed at surface cleanliness as the culprit.

The cleaning process people will swear that the process was working well and was not the cause for nonconformance. Perhaps they present records indicating quality control monitoring of the solvent, pH monitoring of the bath, or to a prearranged change-out schedule.

Do you identify with this scenario? If so, let us consider what is missing. It is obvious that in this situation no surface cleanliness verification is being done. Monitoring the process in the manner mentioned above, while important, has its limitations. It is therefore important to monitor the product’s surface cleanliness.

Factors That Contribute to Inadequate Cleaning
The cleaning process people are going by their belief that the process was not exhibiting any abnormalities. Other folks blame surface cleanliness because there is no verification that the process is working well.

Even though the cleaning process variables are under control, there are several factors that can contribute to inadequate cleaning of parts.

First, the number of parts put through the cleaning process in a given period may vary.

Second, parts may have varying degrees of contamination from time to time.

Third, the type of contamination (soil) on the parts may be different, and the cleaning process may not be effective in removing this type of soil.

These changes can be related to a change in the product mix or to changing in processes by outside suppliers. It stands to reason that to truly control cleaning process, cleanliness monitoring must be an integral part of the cleaning process.

The Benefits of Verification
The benefits of cleanliness monitoring include being able to establish an acceptable level of cleanliness; optimize the cleaning process by varying cleaning process parameters; maintain ongoing control of the cleaning process despite factors that contribute to inadequate cleaning; and ensure product quality.

Nonproductive Costs to Consider
What are the costs one should look at if no cleanliness monitoring or verification is done? First, consider the value-added costs associated with nonconforming parts if problems are discovered downstream instead of at the source (i.e., the cleaning process).

In one case, a customer returned 3,000 parts for poor cleanliness. The vendor was not using any cleanliness monitoring or verification system. Instead, he was relying on control of cleaning process parameters. By using a cleanliness monitoring system, the vendor was able to test all of the parts and find approximately 30 parts that were not clean. These parts were re-cleaned and the whole shipment was returned to customer with full confidence that the parts were clean.

The cost associated with shipping the parts back and forth, unpacking them for inspection, and repackaging them for shipping — not to mention lack of customer satisfaction — by far outweighed the cost of cleanliness monitoring.

In this case there were no subsequent operations, so the cost of re-cleaning was minimal. When subsequent, value-added operations are performed on parts, it becomes even more critical to assure that the cleaning process is in control.

Other costs that should also be considered are those associated with time spent arguing about the source of any nonconformance encountered when surface cleanliness is not verified. These costs are nonproductive and can be minimized or eliminated by verifying cleanliness.

Cleaning cost is directly proportional to the level of cleanliness. The higher the cleanliness level, the higher the cost of achieving that level. Hence, costs associated with overcleaning parts are nonproductive costs. Similarly, the level of nonconformance is indirectly proportional to cleanliness level, i.e., the lower the cleanliness level, the higher the nonconformance due to surface cleanliness.

Costs associated with nonconformance due to poor cleanliness are also nonproductive costs.

The total cost of cleaning should include the cost of cleaning and the cost of nonconformance. It is this cost that we should strive to minimize (optimize). Without the use of a cleanliness monitoring or verification system, it is very difficult, if not impossible, to define and maintain an optimum level of cleanliness.