Summary of the six-sigma IMPROVE stage

The Improve phase focuses on developing ideas to remove root causes of variation, testing and standardizing those solutions. This involves:

• identify ways to remove causes of variation;
• verify critical Inputs;
• discover relationships between variables;
• establish operating tolerances which are the upper and lower specification limits (the engineering or customer requirement) of a process for judging acceptability of a particular characteristic, and if strictly followed will result in defect-free products or services;
• optimize critical Inputs or reconfigure the relevant process.

Key questions:

• Once we know for sure which inputs most affect our outputs, how do we control them?
• How many trials do we need to run to find and confirm the optimal setting/procedure of these key inputs?
• Who should the old process be improved and what is the new process?
• How much have Defects Per Millions Opportunities (DPMO) decreased?

The most applicable tools at this phase are:

• Process Mapping - this tool helps to represent the new process subsequent to the improvements.
• Process Capability Analysis (CPK) - in order to test the capability of process after improvement actions have been implemented to ensure we have obtained a real improvement in preventing defects.
• DOE (Design of Experiment) - This is a planned set of tests to define the optimum settings to obtain the desired output and validate improvements.