Available data
Ivan brought the actual data as well as the charts to the meeting with Yvonne. The data his team collected are in the table, “Flatness Values for Product RS66: Before and After Process Changes.” Data were collected on the first three units that were produced each time the product was manufactured. The dates of the manufacturing runs are in the table.
Answers to April Brain Teaser
In his position as supplier quality manager for a company that sells and distributes dental equipment, Raoul noticed an increase in complaints from his dental customers about the swivel angle on lighting fixtures. To follow up on the situation, he decided to ask for data from the manufacturers of these fixtures. One supplier sent data very quickly and Raoul wants to analyze the data correctly to understand the situation.
Q: After observing that all data values did meet the requirement of a maximum of 270 degrees, Raoul was concerned that the data looked “too good.” How can these data help him respond to his customers? What additional data should he request?A: On an individuals and moving range chart of the initial data provided, Raoul noticed that the data values he received showed a predictable process with an average of 268.47 degrees and natural process limits of 267.93 to 269.02. He noticed that the data were in a column called “Average” and decided to request the individual data values used to compute the average.
Q: The data that Raoul received were averages of the two production lines. He decided to request the individual values from each production line to see if this could help explain why the customers were complaining. These data appear in the table, “Swivel Angle Data for Lines 1 and 2.” The data in this table appear in the April Brain Teasers.A: When Raoul received the additional data for each production line, it appeared that the values for Line 1 were always lower than the values for Line 2. Because these are two different production lines, he set up two separate individuals and moving range charts to analyze the data. He discovered that the swivel angle from both production lines was predictable but at different averages and with different amounts of variation. See the charts, “Swivel Angle for Production Line 1” and “Swivel Angle for Production Line 2.”
Q: What analyses can Raoul do with these additional data to understand why his customers are complaining?A: Along with the process behavior charts for each production line showing predictable behavior, Raoul can do capability analyses to determine how each line performs relative to the maximum specification of 270 degrees. Production Line 1 has a Cpk of 2.084 while Production Line 2 has a Cpk of 0.121. Production Line 1 does have a larger amount of variation, but the average is low enough so that all of the angles meet the specification. Production Line 2 has an average value that is almost on the specification limit of 270 degrees. This accounts for the Cpk value that is near zero. The results for Line 2 are shown in the chart, “Capability Analysis for Production Line 2.”
Q: In his position, what actions can Raoul take to deal with the complaints?A: He can show the supplier the results of his analyses of the data they provided along with the complaints from the dental customers. Because Production Line 1 meets the specifications and has a Cpk of 2, the first challenge for the supplier is to operate Production Line 2 at a lower average angle to meet the specification. The second, and less pressing, challenge is to reduce the variation of Line 1 to that of Line 2.
