Realistic Cleaning Specifications
Posted: Friday, March 21, 2008
by Aaron Dexter
Midbrook, Inc.
With parts cleaning technology and ability on the rise, manufacturers are eager to make use of the advanced capabilities that cleaners are offering. They design cleaning specifications for their products that are more stringent and demanding than ever. The logic behind the tightening of cleaning specifications is sound on the surface. If the specifications are tighter, the parts will be cleaner, and the end product will run smoother than ever before. However, this is not how it always works out. A cleaning specification can be too tight- and move into the realm of unrealistic. An unrealistic specification can never be adequately met, and time, resources, and money will be wasted trying to reach it. The unrealistic specification becomes a burden for all involved in the project, but thankfully, it can be avoided with proper planning.
Part material is a major factor in how clean a part can be. Some materials will naturally produce particles, and if the specification does not take this into account it will be tough to meet the specification. For instance, cast aluminum is a popular material for parts in the automotive industry. Due to a variety of factors that occur during the production process and because of the nature of cast aluminum, the parts will continue to generate particles once they have been produced. These small aluminum particles are impossible to eliminate. If a specification calls for these particles to be eliminated, it will be virtually impossible to properly meet it.
The type of contaminants on the part is important. In some cases, a company may want to limit the size of a particle on the part, but neglect to determine if they want to limit all types of particles or just certain ones. A part may fail if a big enough particle of metal is not removed, but it may be unaffected if an even larger particle of another material is present. Before creating the specification, the manufacturer must know which types of particles will be present on their part and how they will affect the performance of the part. If 250 micron metal parts will make the machine fail, then that should be included in the specification. However, if on the same part, a 250 micron piece of silicone or another material will not cause the part to fail, then the manufacturer needs to make sure that the specification states that no metal particles of over 250 microns can be present, as opposed to no particles at all of over 250 microns. It may seem logical to eliminate all particles over that size, but different materials react differently and it may be unnecessarily wasteful and time-consuming to focus on eliminating all the particles if they are irrelevant to the performance of the part.
This leads to testing the part for its known failure mode. Before any specification is finalized, the part needs to be tested until failure. It is common sense that an automotive part does not need to be as clean as a surgical tool. If they did need to be that clean, then the parts would never be able to function in the real world. A specification should not be set just inside the failure mode, a certain amount of cushioning and wiggle room is acceptable. However, designers need to keep in mind the diminishing returns of cleanliness past a certain point. The cost of increasing cleanliness is not linear but rather it is exponential. If the part performs admirably with 1mg contaminant per part with no particles greater than 120 microns, there is no plausible reason to require a cleaning specification that requires less than .2mg contaminant with no particles greater than 50 microns. While the part would be very clean at that standard, the increased cost with no real benefit to performance makes it wasteful.
Finally, the cleaning specification must look at the process and setting of the cleaning. Parts are often tested in a laboratory, under lab conditions. The result is highly accurate testing, but it is not repeatable under factory conditions usually. The laboratory test is vital to the design of the specification and should not be ignored- but keep in mind real world conditions when implementing the results. In a factory setting, the parts cleaning machine will not be as well maintained as the one used for testing. It will be subject to the workers, who will not perform maintenance as regularly or thoroughly as the laboratory will. The general air conditions of the plant will also be much dirtier than the lab where the part was originally tested. When designing the specification, these unavoidable facts must be taken into account. If a specification can only be met in the sterile conditions of the laboratory, it is of no practical value in the production process. The specification, if implemented before being refined for the true production process, will be a sticking point in production and result in inefficiency.
Manufacturers that have their parts tested by an experienced parts cleaning laboratory can avoid many of the pitfalls that are along the road to creating a cleaning specification. By using a laboratory with a wealth of experience, the manufacturer can draw upon the cleaner's experience with similar parts and specifications. They can work together to craft a specification that addresses the key issues affecting the part and is practical in the production phase. The co-operation between the two will result in a better, more efficient cleaning process and the best possible quality part.
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