This posting is the final posting in my series on how I got started in TOC or more specifically, Lean, Six Sigma and the Theory of Constraints. It was a triumphant journey for me and looking back, I wouldn't change a thing.
Drum-buffer-rope was really only one part of our solution in that we also needed buffer management to help us guide the way. Drum Buffer Rope can be thought of as the planning stage of our approach and was the overall plan for how we operate the system. Buffer Management, on the other hand, was our control system that allowed us to keep a running check on how effective the system was running. When we first started our DBR effort we kept it very simple and used a white board on out work shop floor to schedule our constraint. It was so simple in that our synchronization plan was that when one job was finished at the constraint, we would then introduce another job at our gating operation. We realized that we had to protect the constraint to assure that the correct material was always ready and waiting for processing in plenty of time before the planned start date at the constraint. We achieved this by making sure that we released material in time to reach the constraint when it was needed.
When we first started our DBR/Buffer Management implementation, we applied a common rule-of-thumb which was to calculate half of the current lead time from our gating release to the estimated constraint start time. We also divided this time into 3 equal time buffer zones and color-coded them as green, which we called our safety zone; yellow, which we called our planning zone; and red, which we named our expedite zone. If our incoming part to the constraint was in the green zone, we knew everything was safe and that it should arrive at the constraint in plenty of time. If it fell into our yellow zone, we would create plans to expedite the incoming part if necessary. If it fell into our red zone, we executed our expedite plan to guarantee that it would arrive at the constraint. Were we successful with our DBR/Buffer Management implementation? What we discovered was that we had too much variability in our upstream process steps and that we had to work on stabilizing them with things like preventive maintenance, rapid response to upstream rejects and anything else that caused unplanned downtime. Because of this excessive variability we found it necessary to select a temporary, larger overall time buffer. However, once we were able to stabilize our upstream process steps, we were able to return to our original buffer calculation.
Throughout my time as General Manager of this facility we were able to use a variety of improvement tools like rapid changeover, 5S, DBR and Buffer Management, DOE’s, SPC, etc. All of these tools worked very well, but it was clear to me that if we hadn’t used them in combination with TOC, we would probably have been working on the wrong part of the process. TOC provided us with a focusing mechanism that doesn’t exist within Lean or Six Sigma. I learned this lesson the hard way, but it made me a believer back then. You might even say I was epiphanized.
My time spent at this manufacturing facility was probably my most enjoyable and rewarding position I have ever held. We were able to take this facility to performance levels it had never seen before and all because of a single book and a desire to prevent a shutdown. I became very close to my entire workforce and together we formed an unbeatable team. In just three short months, we went from losing $600 K to making $750 K! And not only did we keep the plant open and protect the jobs of all 260 people, we became the model plant for the corporation. We entertained numerous visitors from other portfolio companies all coming to see what “Kentucky” was doing. We also were asked to go to these other plants and help them turn their operations into something like ours. As for me, I left the company about 17 months later. Why did I leave you might be thinking? I received a call from my old mentor, Bob, and joined him at another company…..another turn-around opportunity. I checked back with my old company every so often just to see how things were going and unfortunately my replacement loved efficiency and utilization. About a year after I left, they ended up shutting their doors….and what a sad day that was for me.