The main aim of Six Sigma is to reduce defects in process and costs associated with it. There are 2 models used for this purpose DMAIC(for improving the process) and DMADV(for designing process).
Define the process improvement goals that are consistent with
customer demands and enterprise strategy.
Measure the current process and collect relevant data for future
comparison.
Analyze to verify relationship and causality of factors.
Determine what the relationship is, and attempt to ensure that all factors
have been considered.
Improve or optimize the process based upon the analysis using
techniques like Design of Experiments.
Control to ensure that any variances are corrected before they
result in defects. Set up pilot runs to establish process capability,
transition to production and thereafter continuously measure the process and
institute control mechanisms.
Define the goals of the design activity that are consistent with
customer demands and enterprise strategy.
Measure and identify CTQs (critical to qualities), product
capabilities, production process capability, and risk assessments.
Analyze to develop and design alternatives, create high-level
design and evaluate design capability to select the best design.
Design details, optimize the design, and plan for design
verification. This phase may require simulations.
Verify the design, set up pilot runs, implement production
process and handover to process owners.