Six Sigma seeks to improve the quality output of processes by identifying and removing the causes of defects (errors) and minimizing variability in manufacturing and business processes. It uses a set of quality management methods, mainly empirical, statistical methods, and creates a special infrastructure of people within the organization ("Champions", "Black Belts", "Green Belts", "Yellow Belts", etc.) who are experts in these methods. Each Six Sigma project carried out within an organization follows a defined sequence of steps and has quantified value targets, like increase productivity, increase efficiency, reduce pollution, reduce cost, increase customer satisfaction, increase profits and become more competitive. Sigma is the designation for the standard deviation, and a process capability of six standard deviations equals 3,4 defect per million opportunities. That is an ambitious goal! It requires continuous improvement and focus on understanding variation to gain control of production.
Six Sigma projects follow a project methodology inspired by Deming's Plan-Do-Check-Act Cycle. It includes 5 phases and bear the acronym DMAIC. DMAIC is used for projects aimed at improving an existing business process.
- Define the system, the voice of the customer and their requirements, and the project goals, specifically.
- Measure key aspects of the current process and collect relevant data; calculate the 'as-is' Process Capability.
- Analyse the data to investigate and verify cause-and-effect relationships. Determine what the relationships are, and attempt to ensure that all factors have been considered. Seek out root cause of the defect under investigation.
- Improve or optimize the current process based upon data analysis using techniques such as design of experiments (DOE), Components of variation (CoV), poka yoke or mistake proofing, and standard work to create a new, future state process. Set up pilot runs to establish process capability.
- Control the future state process to ensure that any deviations from the target are corrected before they result in defects. Implement control systems such as statistical process control - SPC, production boards, visual workplaces, and continuously monitor the process.