Step 1 – Define
The Define phase is about coming up with a focused problem statement and a supporting measure of success or failure.
The deliverable for the Define phase is a team charter like the one below:
Step 2 – Measure
The Measure phase is about documenting the current process and assessing baseline performance. Some of the important tools in this phase include trend charts, basic Pareto charts, process flowcharts, Gage R&R, and process capability measurement (sigma level, also referred to as process sigma).
Depending on the project scope, the team might hold off on the process flowchart and Gage R&R activities until primary focus areas are identified further into the project. In some cases, a macro flowchart is useful in providing all team members with an initial, high-level view of the process –
Oftentimes the Measure phase provides early clues that will direct team toward top problem areas and solutions, as shown in the following trend and Pareto charts for our outdoor furniture company example –
In the case of our furniture manufacturing company example, the project team also performs a Gage R & R study on a known critical measurement (screw torque) that affects a cracking condition on one of its chair lines – this will come in handy later in the project. The initial GR&R results show that the screw torque measurement method introduces far too much variation –
Using a graphical technique learned in Gage R & R training, the team finds that the first operator in the study is recording consistently higher readings than the other two operators –
Finally, after correcting operator #1’s measurement technique and updating the measurement procedure, the team conducts a follow-up Gage R & R study with much-improved results –
Finally, the baseline sigma level for the overall defect rate is estimated using a sigma conversion chart, providing a relative indicator of how close the current process is to delivering zero defects. A Six Sigma process has a sigma level of six, and for all practical purposes is considered a defect-free process over the long run, provided that adequate controls are in place to maintain capability. In the example above, an overall defect rate of 2.6% reflects a sigma level of 2.1.
Step 3 – Analyze
The Analyze phase in DMAIC isolates the top causes behind the metric or CTQ that the team is tackling. In most cases there will be no more than three causes that must be controlled in order to achieve success – if too many causes are identified, then the team has either not isolated the primary causes or the project goal is too ambitious to achieve success with a single project. There are always exceptions, but speed and results are key ingredients to building Six Sigma momentum inside an organization, and projects should be sized to assure team success and project closure inside reasonable time limits.
The Analyze phase deploys a number of tools for collecting team input and conducting objective experiments to identify or confirm top causes.
Not all tools are used on all projects.
In our outdoor furniture manufacturing example, the team must understand the reasons behind two of the biggest Pareto items discovered in the Measure phase: (1) returns on the “AD Chairs” product line and (2) returns on Direct-Ship products. A detailed analysis via product tear-downs produces the following sub-Pareto charts, which bring the team closer the the primary causes that are driving high customer return rates –
There is still a great deal of additional work for the team as they proceed down the path to their primary causes in this case, but the sub-Pareto charts noted above will further narrow the team’s focus to (1) cracked back-slats, (2) shipping damage, and (3) missing hardware.
Step 4 – Improve
The Improve phase focuses on fully understanding the top causes identified in the Analyze phase, with the intent of either controlling or eliminating those causes.
Step 5- Control
DMAIC’s Control phase is about sustaining the changes made in the Improve phase. The best controls are those that require no monitoring (irreversible product or process design changes).
But oftentimes there are process settings, procedures, etc., requiring that employees follow specific requirements in daily operations – these items are typically documented in a control plan. In cases like this the Six Sigma team should do everything possible to error-proof the process, and should then add the appropriate checks and balances to the quality system for the long run.