Continuous Improvement and Problem Solving
Six Sigma utilizes the DMAIC methodology for continuous improvement of existing processes. The acronym “DMAIC” stands for Define, Measure, Analyze, Improve, and Control. The DMAIC process is a structured, data-based approach that guides teams through the definition of the problem, identification of root causes of variation, determination of solutions or improvements, implementation of those solutions, and, finally, maintenance, or control, of those improvements.
The goal of the DMAIC approach is to take a process from its current level (baseline) to a new, desired, target. Many excellent problem solving and process improvement tools are found in the DMAIC “tool kit”. These include many varieties of process maps, value stream mapping, team decision-making tools, work standardization, mistake-proofing (Poke-Yoke), as well as a large variety of statistical tools for analyzing variation and determining whether observed variation is simply sampling variation or whether it is likely due to some real phenomenon. The statistical tools include descriptive graphical displays, such as histograms, Pareto charts, multiple boxplots, mosaic plots, scatterplots, control charts, variability charts, surface and contour plots. They also include inferential methods, such as confidence intervals, ANOVA, contingency tables, regression, measurement systems analysis (gage R&R), design of experiments, and response surface methodology.
The improvements made to the process are measured via Key Performance Indicators (KPI); these are tied to characteristics of the process that are critical to quality (CTQ) for the customer. KPIs may be measured characteristics of parts or materials, they may be Defects Per Million Opportunity (DPMO), perhaps rolled throughput yield (RTY) for some applications, or some other measure that the DMAIC project team finds critical to the process. Financial KPI measurements may also be used in addition to process KPI values. Careful identification and monitoring of KPIs is critical to the success of the project.
Although the DMAIC methodology applies to both manufacturing and transactional (non-manufacturing) processes, the tools and emphases differ to some extent. Training materials for Blackbelts and Greenbelts often differ based on whether the intended application is manufacturing or transactional processes.
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