2. As each new set of data is used and new limits are calculated, how does the robot arm extension length behave?
3. What would Melinda have noticed if the limits on the process behavior chart had not been recalculated each time there was new data 4. What are the consequences of continually recalculating limits as new data are collected?
Q: What is the behavior of the returns and repair processes for hard drives?
A: Both the number of parts returned and the percentage that could not be repaired were unpredictable. For the number of parts returned, the first five weeks showed a wide, zigzag behavior with the last eight weeks of the quarter showing a predictable process with an average of 139.6 and natural process limits of 121 to 158. The repair time was predictable at an average of 51.2 minutes with natural process limits of 16 to 86. Both the number of new parts used in the returns and the percent of returned parts OK were predictable. The number of new parts used averaged 72 with natural process limits of 36 to 108 while the percentage of returned parts OK averaged 6.3 with an upper natural process limit of 14. See the charts, "Number of Parts Returned" and "Time to Identify and Repair Failure."
Q: How does understanding process behavior help Juan to evaluate possible ways to reduce costs?
A: Process behavior is key to making management decisions because of the critical difference between predictable and unpredictable processes. An unpredictable process has exceptional behavior that might distort the costs at one or more time periods. Identifying and eliminating the causes of exceptional behavior can lead to opportunities to reduce costs. Predictable processes are essentially locked into a behavior that may be detrimental to reducing costs. In such cases, a fundamental change will be necessary if costs are to be reduced. For example, the time to find and make a repair to a faulty part is currently predictable. Finding faster ways to identify the failure and make the repair could lower labor costs, but this would require a fundamental change in the way the failures are identified and fixed.
Q: Based on the data available, what might Juan work on first to reduce costs?
A: Reduction of time to identify and repair the units, as well as the number of new parts used, are two areas for investigation and both of these processes are predictable. Reducing the time and the number of new parts used could reduce costs in this department.
Q: What additional data and analyses could help Juan take actions to reduce costs in his department?
A: Juan could step out of the current box and compare the costs of the current approach for handling returned parts with the costs associated with a certain amount of improvement in the time and use of new parts. For example, if the time to identify and repair the faulty parts could be cut in half and the number of new parts used also cut in half, what would be the reduction in costs? Also, Juan might compare the current costs with a completely different approach such as always sending a new part in return for a faulty one-do not repair the faulty part. His department would still need to determine the failure for feedback to production in order to work on eliminating the faulty parts in the future.
Dr. Sophronia Ward is a continual improvement specialist and Six Sigma Senior Master Black Belt and coach. Brain teasers are now incorporated in the new training programs, Six Sigma Training for Champions, Black Belts and Green Belts, offered by Dr. Ward and her associates at Pinnacle Partners Inc. For more information, call (865) 482-1362 or visit www.pinnaclepartnersinc.com.