2019

STATISTICS ROUNDTABLE

Go With the Flow

Simple flow diagrams can help expose, explain process problems

by Lynne B. Hare

Years ago, while on my way to conduct a statistical process control (SPC) short course at a local ASQ meeting, I was stopped by a man who told me he had attended my short course the previous year and had gotten a lot out of it.

"Tell me," he said. "How come the people in your company don’t do what you say?"

"I don’t know," I said. "I have a wife, three children, two dogs and a cat. None of them do what I say. Why should the people in my company be any different?"

"Very funny," he said, obviously meaning the opposite. "I’m the director of manufacturing for XYZ Co., and I’m getting ready to pull the plug on purchasing from your subsidiary company because of lousy quality. What are you going to do about it?" He said that loudly with his index finger beating a rapid staccato on my chest.

Well, he was a little guy, and I thought I could take him, but that didn’t seem like the right business move. So I told him that I knew the subsidiary’s president and I would contact and inform him of the issue. "I’ll give you two months," he said, and he walked away.

Finding the source

That was on a Friday. The following Monday, I called the subsidiary’s president. He scolded me for teaching the course. When he calmed down, he admitted he was aware of the customer dissatisfaction and that something must be done—the customer accounted for one-third of his business. How soon could I be at the manufacturing site?

A few days later, I was there. In the meantime, the plant management had reorganized the manufacturing staff into teams, each with a focus on an individual operation unit. After the usual plant tour and meeting with the plant manager and staff, I began discussions with individual teams, starting with the first operation unit.

The unit consisted of an "extraction phase" during which key ingredients of the finished product were extracted from raw materials through a process involving counter-current flow of the raw materials and a powerful acid. With odors and noise, it wasn’t a cheerful place to work. The only thing missing was a sign saying, "Abandon all hope, ye who enter here."

Six unfortunate souls ran this first operation unit. The quality of their output influenced the success of all subsequent unit operations and, ultimately, the quality of the finished product. Business success, therefore, hinged to a large extent on their success at taming this first-phase beast.

We retreated to a conference room where I asked about process control mechanisms. Each team member had a different tale to tell. Each instituted controls his or her own way. Arguments broke out about which gage, wheel or zapper should be used to control which aspect of the first phase output. "Good," I thought. "No place to go but up." I did my best to stifle the din and encourage a focus on improvement.

My opening gambit was to ask each of the six team members to separately draw a process flow diagram. How many of you think I got six different flow diagrams? In fact, I got seven: One person wasn’t sure, so she drew two.

Clearly, the flow diagram exercise underscored the fact there had been no common understanding of the process; therefore, there could be no process control, no variation reduction opportunity and no path to improvement.

If used properly, the flow diagram can be the first link in a long chain to improvement. In the case just described, we called in the engineering manager and worked toward a common process understanding, and we developed improved process control procedures and appropriate action rules for out-of-control events.

With this approach carrying through the remaining operations units of the manufacturing process, the subsidiary company went from the worst to the best supplier in six months, thanks to diligent management and staff.

Flowing together

When I’m blessed with an audience on the topic of quality improvement, I often start with the flow diagram in Figure 1. It draws a few chuckles, and we move from there to talk about some important aspects of flow diagrams.

Figure 1

Unlike the flow diagram of Figure 1, yours should have a clear beginning and end. It also should be obvious what is flowing. I’d reserve greater formality for engineering and software development. For our purposes, a simple selection of symbols will do.

In Figure 1, there are only rectangles and diamonds. In most quality improvement cases, it doesn’t need to get more complicated than that. And hand-drawn diagrams are just fine. The flow diagram should be a working document and a communication device.

I never saw the manufacturing director for XYZ Co. again. My guess is he was happy with the long-term results, but he probably wouldn’t be amused by my coffee break flow diagram.


Lynne B. Hare is a statistical consultant. He holds a doctorate in statistics from Rutgers University in New Brunswick, NJ. He is past chairman of the ASQ Statistics Division, and is a fellow of ASQ and the American Statistical Association.


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