2.7. Explain the importance of tollgates in the DMAIC process.
At a tollgate, a project team presents its work to managers and “owners” of the process. In a six-sigma organization, the tollgate participants also would include the project champion, master black belts, and other black belts not working directly on the project. Tollgates are where the project is reviewed to ensure that it is on track and they provide a continuing opportunity to evaluate whether the team can successfully complete the project on schedule. Tollgates also present an opportunity to provide guidance regarding the use of specific technical tools and other information about the problem. Organization problems and other barriers to success—and strategies for dealing with them—also often are identified during tollgate reviews. Tollgates are critical to the overall problem-solving process; It is important that ...view middle of the document...
5 shift in mean (Figure 1.2(b)).
3.4 233 1 0.5 3.4 / 233 0.5 x ln 3.4 / 233 x ln 0.5 x ln 3.4 / 233 ln 0.5 6.2 years 6 years, 1 month
CHAPTER 2 THE DMAIC PROCESS 2-3 2.13. Explain why it is important to separate sources of variability into special or assignable causes and common or chance causes. Common or chance causes are due to the inherent variability in the system and cannot generally be controlled. Special or assignable causes can be discovered and removed, thus reducing the variability in the overall system. It is important to distinguish between the two types of variability, because the strategy to reduce variability depends on the source. Chance cause variability can only be removed by changing the system, while assignable cause variability can be addressed by finding and eliminating the assignable causes. 2.15. Suppose that during the analyze phase an obvious solution is discovered. Should that solution be immediately implemented and the remaining steps of DMAIC abandoned? Discuss your answer. Generally, no. The advantage of completing the rest of the DMAIC process is that the solution will be documented, tested, and it’s applicability to other parts of the business will be evaluated. An immediate implementation of an “obvious” solution may not lead to an appropriate control plan. Completing the rest of DMAIC can also lead to further refinements and improvements to the solution. 2.18. It has been estimated that safe aircraft carrier landings operate at about the 5 level. What level of ppm defective does this imply? If the operating limits are around the 5 level, and we assume the 1.5 shift in the mean customary for Six Sigma applications, then the probability of a safe landing is the area under the normal curve that is within 5 of the target mean, given that the true mean is 1.5 off of the target mean. Thus, the probability of a safe landing is 0.999767 and the corresponding ppm defective is (1 − 0.999767) 1,000,000 = 233.