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M.K. Chaw la An optimum level of cleanliness is the one that minimizes the total cost . Even-tually one can arrive at a cleanliness level where the savings in the failure/non-conformance costs will not be offset by incremental cost of achieving cleanliness beyond th e optimum level. A small range around the optimum level of cleanliness can b e established as the "Acceptable Level" of cleanliness. 7. DEFINING ACCEPTABLE ("OPTIMUM") LEVEL OF CLEANLINESS It is expected that the non-conformance levels will increase as the level of cleanliness decreases or vice versa. It is important to understand the relationship between the level of cleanliness and non-conformance rate in order to establish the "acceptable level of cleanliness". For example, if the failure/non-conformance rate is too high due to the surface cleanliness level, then the surface cleanliness level will have to be improved i n order to reduce the failure rate. On the other hand, no failures or a very low failure rate due to the surface cleanliness level im-plies that the surface may be "over-cleaned." It may be desirable to optimize the cleaning process by comparing the cost of failures/non-conformance with the cost of cleaning the surface. Generally, in-creasing the level of surface cleanliness will result in increased cleaning cost. An increased level of cleanliness should lower the rate of non-conformance, which, in turn, reduces the non-conformance cost. As long as the reduction in non-conformance cost more than offsets the increased cost of cleaning, it would be cost effective to increase the achieved level of surface cleanliness. When the de-crease in non-conformance cost fails to offset the increase in the cleaning cost, then an optimum or "acceptable" level of cleanliness has been achieved. To establish the optimum level of surface cleanliness, two approaches are out-lined here. One approach utilizes the success of the subsequent operation that de-pends on surface cleanliness level. The other approach is to start monitoring the cleanliness levels achieved and corresponding level of failure/non-conformance rate. Once an acceptable level of cleanliness is established using one of the two approaches, cleaning process can be monitored in production to assure ongoing product quality. 7.1. Controlled experiment This approach requires that the measure of success be defined for the subsequent operation that depends on surface cleanliness. For example, if the parts are to be bonded, then the adhesion strength of the bond will be the measure of success. If the parts are to be coated after cleaning, then the adhesion strength of the coating should be correlated to surface cleanliness. The acceptable level of surface cleanliness is the one that results in the desired level of bond/adhesion strength. One simple approach is to start monitoring and recording the cleanliness level of each part. A statistically significant sample must be monitored to assure valid
DOI link for M.K. Chaw la An optimum level of cleanliness is the one that minimizes the total cost . Even-tually one can arrive at a cleanliness level where the savings in the failure/non-conformance costs will not be offset by incremental cost of achieving cleanliness beyond th e optimum level. A small range around the optimum level of cleanliness can b e established as the "Acceptable Level" of cleanliness. 7. DEFINING ACCEPTABLE ("OPTIMUM") LEVEL OF CLEANLINESS It is expected that the non-conformance levels will increase as the level of cleanliness decreases or vice versa. It is important to understand the relationship between the level of cleanliness and non-conformance rate in order to establish the "acceptable level of cleanliness". For example, if the failure/non-conformance rate is too high due to the surface cleanliness level, then the surface cleanliness level will have to be improved i n order to reduce the failure rate. On the other hand, no failures or a very low failure rate due to the surface cleanliness level im-plies that the surface may be "over-cleaned." It may be desirable to optimize the cleaning process by comparing the cost of failures/non-conformance with the cost of cleaning the surface. Generally, in-creasing the level of surface cleanliness will result in increased cleaning cost. An increased level of cleanliness should lower the rate of non-conformance, which, in turn, reduces the non-conformance cost. As long as the reduction in non-conformance cost more than offsets the increased cost of cleaning, it would be cost effective to increase the achieved level of surface cleanliness. When the de-crease in non-conformance cost fails to offset the increase in the cleaning cost, then an optimum or "acceptable" level of cleanliness has been achieved. To establish the optimum level of surface cleanliness, two approaches are out-lined here. One approach utilizes the success of the subsequent operation that de-pends on surface cleanliness level. The other approach is to start monitoring the cleanliness levels achieved and corresponding level of failure/non-conformance rate. Once an acceptable level of cleanliness is established using one of the two approaches, cleaning process can be monitored in production to assure ongoing product quality. 7.1. Controlled experiment This approach requires that the measure of success be defined for the subsequent operation that depends on surface cleanliness. For example, if the parts are to be bonded, then the adhesion strength of the bond will be the measure of success. If the parts are to be coated after cleaning, then the adhesion strength of the coating should be correlated to surface cleanliness. The acceptable level of surface cleanliness is the one that results in the desired level of bond/adhesion strength. One simple approach is to start monitoring and recording the cleanliness level of each part. A statistically significant sample must be monitored to assure valid
M.K. Chaw la An optimum level of cleanliness is the one that minimizes the total cost . Even-tually one can arrive at a cleanliness level where the savings in the failure/non-conformance costs will not be offset by incremental cost of achieving cleanliness beyond th e optimum level. A small range around the optimum level of cleanliness can b e established as the "Acceptable Level" of cleanliness. 7. DEFINING ACCEPTABLE ("OPTIMUM") LEVEL OF CLEANLINESS It is expected that the non-conformance levels will increase as the level of cleanliness decreases or vice versa. It is important to understand the relationship between the level of cleanliness and non-conformance rate in order to establish the "acceptable level of cleanliness". For example, if the failure/non-conformance rate is too high due to the surface cleanliness level, then the surface cleanliness level will have to be improved i n order to reduce the failure rate. On the other hand, no failures or a very low failure rate due to the surface cleanliness level im-plies that the surface may be "over-cleaned." It may be desirable to optimize the cleaning process by comparing the cost of failures/non-conformance with the cost of cleaning the surface. Generally, in-creasing the level of surface cleanliness will result in increased cleaning cost. An increased level of cleanliness should lower the rate of non-conformance, which, in turn, reduces the non-conformance cost. As long as the reduction in non-conformance cost more than offsets the increased cost of cleaning, it would be cost effective to increase the achieved level of surface cleanliness. When the de-crease in non-conformance cost fails to offset the increase in the cleaning cost, then an optimum or "acceptable" level of cleanliness has been achieved. To establish the optimum level of surface cleanliness, two approaches are out-lined here. One approach utilizes the success of the subsequent operation that de-pends on surface cleanliness level. The other approach is to start monitoring the cleanliness levels achieved and corresponding level of failure/non-conformance rate. Once an acceptable level of cleanliness is established using one of the two approaches, cleaning process can be monitored in production to assure ongoing product quality. 7.1. Controlled experiment This approach requires that the measure of success be defined for the subsequent operation that depends on surface cleanliness. For example, if the parts are to be bonded, then the adhesion strength of the bond will be the measure of success. If the parts are to be coated after cleaning, then the adhesion strength of the coating should be correlated to surface cleanliness. The acceptable level of surface cleanliness is the one that results in the desired level of bond/adhesion strength. One simple approach is to start monitoring and recording the cleanliness level of each part. A statistically significant sample must be monitored to assure valid
ABSTRACT
Once a cleanliness monitoring method has been selected, it can be used to establish the cleanliness level achieved by current cleaning process ("Benchmark"). The production can then be monitored to assure that benchmark cleanliness level is being achieved. In addition, the product can be followed through the manufacturing process to assure that no problems occur downstream as a result of inadequate surface cleanliness. The level of non-conformance related to the level of
cleanliness achieved should be monitored. The cost associated with a given level of cleanliness and the cost of non-conformance associated with that given level of surface cleanliness should be combined to determine the "total cost". Changes should be made to the cleaning process to minimize the "total cost", i.e. optimize the "total cost". The level of cleanliness associated with the "optimum total cost" should be considered the optimum or "acceptable" level of cleanliness.
