Six Sigma – – The Role of Cleaning

Achieving Six Sigma Capability Parts Washing

“Six Sigma” methodology is one of many tools that can be used to improve process efficiency.  The following several blogs are excerpted from an article written by Dale Bowden of the Cleaning Technologies Group and was published in Process Cleaning Magazine.  Mr. Bowden specifically explores the role of cleaning in meeting six sigma standards.  – FJF –

Many companies are moving towards work that requires higher cleaning standards in order to compete in today’s marketplace. The six sigma quality system is one such approach to meeting higher standards. For those that are not familiar with the six sigma methodology, it is a system that combines statistics and system analysis to reduce variables in the system.  As a result, the probability of meeting the specification is increased. Statistically speaking, six sigma is the probability that the next part produced will be within the specification. A six sigma process produces less than 3.4 defective parts per million parts produced.

Until recently, parts washers were considered a necessary evil. They contributed no perceived value to the end product and were seen as adding cost to the process. This is changing! Parts cleaning is becoming a more important and is now frequently seen as a valuable step in the manufacturing process. With many production parts, the onset of the six sigma quality system reveals that the quality and reliability of the final product is directly related to the cleanliness of the parts. For example, the particulate size and the number of particles left on transmission parts have been shown to be directly related to the number of transmission failures in automobiles. Residual oil on torque converters interferes with the laser welding, which in turn results in both diminished weld strength and increased smut and weld splatter. For a company to produce a six sigma product, each step – including cleaning – must also meet a six sigma level of quality.

Where to Start?

The first and most important step in achieving six sigma capabilities in parts cleaning is to define a quantifiable cleanliness specification. Without a measureable specification, a parts washer can not be considered six sigma. To develop the cleaning specification, it is necessary to perform a downstream Process FMEA (Failure Mode Effects analysis) to determine the effects of residual contamination. The analysis should determine what effect residual contaminants such as particles, oils or lubricants, moisture, detergent or corrosion preventatives will have on the product and process. In addition, particle size and exit temperature can be critically important. Typical cleaning specifications include: less than 1,000 micron particles for valve spools, less than 1.0 mg total organics for brake parts going to laser weld, and an exit temperature ± 15°F for gauging. It is important not to create a specification that is too tight because it will significantly increase the cost of both the capital equipment and operation costs with little return on value. By applying a six sigma statistical analysis to the cleaning results, one can determine the probability of a process to consistently fall below the upper specification limit. The next step is to begin to select parts washing equipment and do verification testing to assure that the desired cleanliness level is met.

– to be continued –