# An Operator's Dilemma

May 5, 2003
Everyone who has faced a production problem with a need to solve the problem by using production data can relate to the notion of a brain teaser. The brain teasers have three parts: (1) the situation, (2) available data or other supporting information and (3) questions that various workers want answered for continual improvement. Recommended solutions follow in the next issue and on the Web at Quality Online (www.qualitymag.com).

Situation
Derek has been a machine operator for 23 years and has developed a sense of when his machine is not operating optimally. At times Derek notices that the machine makes strange noises, appears to slow down for some parts, or pauses slightly during the machining operation. Derek machines castings that are supplied by three companies and he suspects that differences among the castings have impacted the part's critical dimensions. Derek has talked to his supervisor and other operators about his suspicions, but everyone says the suppliers must be OK because the parts meet specifications.

After a particularly frustrating day, Derek decides to keep a log that records the parts that he measured, the suppliers of the parts and the measured values of the critical dimensions. To simplify the log, he plans to record the measurements from one part each hour. The only problem he has is that he doesn't know how to analyze the data to find out if the supplier's parts are different.

Available data
The data that Derek collected for two 12-hour shifts is given in the table "Machined Parts." The two critical dimensions are the heights, Height A and Height B, which are measured from the base of the part. The data values and specifications are coded in thousandths above 0.5 inches. The specification for Height A is 20 + or - 10 and the specification for Height B is 70 + or - 10.

Questions
1. When Derek asked how to analyze the data, he was told to make a process behavior chart. What can Derek learn from a process behavior chart of Height A and Height B?

2. What other method can Derek use to analyze his data?

3. Do the castings from the three suppliers differ?