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| Steps to 6 sigma quality | |
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The steps on the path to Six Sigma quality
1. Measurement
Six Sigma quality means attaining a business-wide standard of making fewer than 3.4 mistakes per million opportu-nities to make a mistake. This quality standard includes design, manufacturing, marketing, administration, service, support-all facets of the business. Everyone has the same quality goal and essentially the same method to reach it. While the application to engine design and manufacturing is obvious, the goal of Six Sigma performance-and most of the same tools-also apply to the softer, more administrative processes as well.
After the improvement project has been clearly defined and bounded, the first element in the process of quality im-provement is the measurement of performance. Effective measurement demands taking a statistical view of all proc-esses and all problems. This reliance on data and logic is crucial to the pursuit of Six Sigma quality.
The next step is knowing what to measure. The determination of sigma level is essentially based on counting defects, so we must measure the frequency of defects.
Mistakes or defects in a manufacturing process tend to be relatively easy to define-simply
a failure to meet a specifi-cation. To broaden the application to other processes and to further improve
manufacturing, a new definition is help-ful: a defect is any failure to meet a customer
satisfaction
requirement, and the customer is always the next person in the process.
In this beginning phase, you would select the critical-to-quality characteristics you plan to improve. These would be based on an analysis of your customer's requirements-(usually using a tool like Quality Function Deployment.)
After you clearly define your performance standards and validate your measurement system (with gage reliability and repeatability studies), you would then be able to determine short-term and long-term process capability and actual process performance (Cp and Cpk).
2. Analysis
The second step is to define performance objectives and identify the sources of process variation. As a business, we have set Six Sigma performance of all processes within five years as our objective. This must be translated into spe-cific objectives in each operation and process.
To identify sources of variation, after counting the defects we must determine when, where and how they occur. Many tools can be used to identify the causes of the variation that creates defects. These include tools that many people have seen before (process mapping, Pareto charts, fishbone diagrams, histograms, scatter diagrams, run charts) and some that may be new (affinity diagrams, box-and-whisker diagrams, multivariate analysis, hypothesis testing).
3. Improvement
This phase involves screening for potential causes of variation and discovering interrelationships between them. (The tool commonly used in this phase is Design of Experiment or DOE.) Understanding these complex interrelationships then allows the setting of individual process tolerances that interact to produce the desired result.
4. Control
In the Control Phase, the process of validating the measurement system and evaluating capability is repeated to in-sure that improvement occurred. Steps are then taken to control the improved processes. (Some examples of tools used in this phase are statistical process control, mistake proofing and internal quality audits.)
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