Theory of Constraints Compliments Lean and DMAIC With System's Approach
A Systems Approach is perspective of a process that considers individual sub-system interdependencies in an effort to achieve total system optimization. Lean Six Sigma is the active integration of traditional DMAIC (Define, Measure, Analyze, Improve, Control) and contemporary Lean principles and tools. We have taken the integration a step further by the incorporation of TOC (Theory of Constraints) principles and improvement approach. Many people have identified these two approaches (Lean and TOC) to be incompatible, but we have chosen to combine them in a particular way to take advantage of each method's strong points.
The DMAIC Six Sigma approach is very strong as a process centered methodology and one that has great capability for identification of significant sources of variation. This traditional cause & effect discipline is combined with TOC's strength for focusing improvement activities on the operational constraint.
The recognized weakness of the stand alone TOC method is that it provides no disciplined method of improvement beyond the 'exploitation' phase which can generate significant short term process improvement. Improvement through systematic optimization methods of DMAIC is a synergistic improvement. DMAIC really benefits from TOC's focus on value-added product flow through the manufacturing (or service) process. The resulting synergy of controlling identified sources of (quality) variation, lean fundamentals, and TOC's obvious strength in producing value-added product flow is a real process improvement winner. TOC provides a logical tempering to traditional Lean adherence to 'zero' inventory everywhere in the process, and adds strength in addressing the effects of operation-to-operation interdependencies.