Monday, August 17, 2009

Data Tells a Story, but are You Reading the Whole Story?

spc_chart Eighteen years ago I learned an important lesson about the intersection of data and people. The data alone rarely tells the whole story.

The engineering manager was preparing his weekly report for the staff meeting. He asked me, the intern, to investigate a SPC (Statistical Process Control) chart gone wild and summarize my findings. The chart graphed several “critical” dimensional characteristics of a headlight reflector for one of the highest selling vehicles at the time. This was a simple task.

Injection molding is a complex process, so the machines were instrumented with several sensors to monitor and record important process parameters. I strolled down to the production floor control room and pulled up the historical data from the data acquisition system for the previous week. I saw a dramatic change in several readings which were consistent with the dimensional hiccup on the SPC chart. Based on the readings and my knowledge of the injection molding process, I could predict which process settings were probably changed by the technician.

Ahh, the Story is developing.

I went out to the machine where the parts were being made and checked the Process Deviation log to verify my predictions and see if the technicians documented any changes. For the most part they did, and I was correct in my analysis of which process settings were changed. I also verified the gage at the quality check station was calibrated and working properly; it was.

I summarized my findings in a report based on data I collected in the control room, the shop floor, the quality check area, and the SPC chart. Unfortunately, I was missing one source of data from my findings... the technician who made the changes.

When the manager’s weekly report came out with a small reference to the Dimensional problem, the 2nd shift technician was upset because he felt like he was being unfairly criticized for deviating from the standard approved process and for causing the problem. He left a “See me” note on my chair.

And now the rest of the Story

The technician “kindly” explained to me that the reason for the dimensional problem was that the mold, which is normally water cooled, developed a crack in the steel that caused water to pour out of the mold (bad). Normally the mold would be taken to the tool room to get repaired, but the part it was making was for one of the highest selling cars and the other duplicate mold was already in the tool room for routine maintenance.

In order to keep the mold cool and maintain a safe work environment (no water all over the floor and machine), they ran compressed air through the water lines. This required numerous changes to the machine settings to keep the dimensions in the functionally acceptable range. The dimensional variation was much different from normal, but was still acceptable for assembly and to the customer.

Now regardless of whether or not it is consistent with best practice to run the mold in the non-standard condition, it was obvious the technician was doing his best to work in the interest of the company. Unfortunately, by neglecting to check with the person responsible for making the process changes, my report left the impression the technician was just not doing what he was supposed to do – something others might assume to be evidence of bad intent, laziness, or some other negative trait. This could have been avoided by applying the following advice:

“In order to understand why somebody does something, you’ll find the answer faster if you look for what’s right about their behavior, rather than what’s wrong.”

Craig Henderson

The above quote was taken from the presentation Nobody Likes Bad Change by Craig Henderson. This is a philosophy that has guided my work since that day - long ago.

No comments:

Post a Comment