In a process flow optimization or value stream mapping project, the organization is seeking the ideal process steps that will maximize the efficiency of its resources. By identifying waste and methods to increase output, the end result becomes a guiding reflection. Team members that bear the burden of the constraint can be motivated quite effectively by this process. However, when the evaluation crosses multiple organizations, it presents the challenge of motivating the non-constraint or non-bottleneck team.
I was manually refilling my portable PUR 30 Cup Dispenser with my kitchen faucet the other day before leaving to run some errands. It is the slow drip version that, once filled, takes about 4-minutes to pass through the filter slowly. When the batching tub was full, I sought out other things I needed to do before I left, because I could not add any more water at that moment. I strived to time it right, so I went to the washer and transferred my laundry to the dryer. Maybe 100 seconds. I then unloaded the dishwasher for about another 100 seconds, thinking that my timing would be perfect and the batch tub would be close to empty. However, I was wrong. The tub was empty. The bottleneck of this morning's routine had stalled and I was in a delay to run my errands. I understand it was not a big delay, but I had allowed the buffer to get to zero water. So the bottleneck, the PUR, stopped producing due to a non–bottleneck unit which was me. But wait... most academics indicate that improving the capacity of a non-bottleneck unit creates no value. As I sat there, filling up the empty batching tub, I realized that improving the non-bottleneck has value and it is somewhere between zero and a lot.
Most leaders in any production process have read The Goal by Eliyahu Goldratt (March 31, 1947 – June 11, 2011). Either given out in a training module or recommended by a lean-thinking consultant, the book is a staple allowing leaders to relate to their own production processes. Within this book, Goldratt ventures you into the production journey of the UniCo Manufacturing and introduces the reader to the framework of the Theory of Constraints. I have read this book many times and highly recommend it to leaders starting their careers in management. I also agree with the concept that an underlying goal in any production process is to increase effectiveness there is a heightened focus on the bottleneck. But I want to reflect on the non-bottleneck unit or the unit(s) that either feed or consumer material of bottleneck. I want to reflect on "me" not filling the PUR in time. These are the production units where any improvement in capacity is worth something between nothing and a lot. These are the production units that create disruptions outside of the responsibilities of the team members on the bottleneck.
The Theory of Constraints is a methodology for identifying the most important limiting factor (i.e., constraint) that stands in the way of achieving a goal and then systematically improving that constraint until it is no longer the limiting factor. In manufacturing, the constraint is often referred to as a bottleneck. - Leanproduction.com
Imagine a bottleneck operating unit between two other production units. There is a working inventory in front of the operating unit that balances the ability to have continuous production of the bottleneck. Too much work-in-process (WIP) and we are gambling on unfavorable losses that could surface from this constraint buffer. Consider losses like expired inventories or too much cash tied up in products not sold. Consider the possibility that rejecting material could be higher because the team just elects to run a different incoming source. On the outlet side of the bottleneck, we are balancing the downstream capacities to ensure that we are shipping on time to the next processing step or the customer. The downstream unit could create a log jam and create no areas to place WIP. All material above the optimum WIPs is overproduction.
Within the overall production system, there will always be an individual step or steps limiting the overall throughput – the bottleneck, constraining the overall system performance. Increasing WIP arbitrarily will not overcome the limiting effects of the bottleneck. - Projectionproduction.org
In the Theory of Constraints, it is routinely quoted to say that there is no value in increasing the capacity of a non-bottleneck unit for the betterment of the system. Google it, and you will see things like it is a "mirage" or "it is of zero value." What is typically not addressed is the real world's version of parallel and series processes and the variability of the process and flows caused by the non-bottleneck. Preventing a 1-hour delay from occurring on a non-bottleneck unit might increase the OEE or capacity of a non-bottleneck unit, but is there value? The classic response is, “There is no value. Any additional increase in capacity is a figment of the imagination.” But what if you had a 24-hour long delay. “Well, that’s different.”
Sometimes, non-bottlenecks can become bottlenecks owing to variability in OEE factors. - Tina Jacobs, Throughput.world.org
The difference is that the buffer has been compromised and the bottleneck has been impacted. We should incentivize improvements within the non-bottleneck teams by increasing their effectiveness and capacity before they become the bottleneck unit. The benefit this creates is the prevention of the buffer from being depleted. The trick is to seek out the right amount of increased capacity. The additional capacity of the non-bottleneck does not increase the capacity of the non-bottleneck. Instead, it does increase the utilization of the bottleneck.
Too many people dwell on the academic equation and not the reality that this isn’t what happens in the real world. When the academic equation comes up, incentivizing the improvement of the non-bottleneck team becomes challenging. They hear that there is no value in increasing their operating unit's capacity and it becomes a demoralizing motivation. The message should change to the value of preventing disruptions of the bottleneck and less of a focus on capacity. Non-bottleneck units impact the bottleneck due to inserting variability within the process as a whole. Running and quantifying projects with this value as the theme is critical.
To monitor for this, organizations can evaluate the process and flows that impact the bottleneck. Idle time in the form of delays on the bottleneck and flow in the form of the variability of the bottleneck’s speed can become influenced by non-bottleneck units. The incentive for the non-bottleneck unit is to evaluate the idle time they impacted the bottleneck unit. It is generally captured as a delay, but sometimes in tight batch operations, it might show up in the OEE Speed Loss calculation. This approach is atypical because the non-bottleneck team accepts being measured by a performance indicator typically measured in another production area.
The reason is that speeding up the bottleneck adds capacity to the system, while speeding up a non-bottleneck does not. However, speeding up a non-bottleneck does have a beneficial effect, especially in systems with variability, because faster non-bottlenecks are better able to feed the bottleneck. - Wallace J. Hopp
The next time someone says, there is no value in improving the capacity of a non-bottleneck unit remember that they are wrong and the answer is somewhere between zero and a lot. The motivation for these non-bottleneck team members is to improve capacity to a point where there is no increase in WIP and there is no impact on the bottleneck.
Additional resources:
Bottleneck-Oriented Order Release with Shifting Bottlenecks: An Assessment by Simulation by Prof. Matthias Thürer, Jinan University and Prof. Mark Stevenson, Lancaster University
A study on the factors causing bottleneck problems in the manufacturing industry using principal component analysis by S.O. Ongbail, S.A. Afolalu, S.A. Oyedepo, A.K. Aworinde, and M.A. Fajobi