In the last post we left off after covering the two pillars of the TPS House: JIT and Jidoka.
Here is the basic TPS House once again:
Just as the twin pillars of JIT and Jidoka are there to support the roof (Goal: highest quality, lowest cost and shortest lead time), the “hows” in the TPS floor are there to support JIT and Jidoka. And the placement of these three “hows” indicate which pillar they are there to support.
On the far left is “Heijunka”. This is usually translated as “leveling”. This “how” is used to support the JIT pillar by leveling/smoothing the process flow. And this leveling/smoothing is there to improve the flow (time) for both the process owner (production) and the process user (customer). But doesn’t “takt time” level the flow? Yes but only for a given product with a given, but changeable, customer demand. “Heijunka” means leveling production of a mix of products that may or may not have the same customer demand or “takt time”.
The tools used to implement Heijunka range from the very simple to the very complex.
One of the simplest applications of Heijunka is grouping your various products/services into families that have similar processes and process components. Then you can create separate “Value Streams” for each process family which minimizes process complexity and changeover requirements within a given Value Stream. This usually assumes dedicated installed capacity for each Value Stream.
If you want or need to share installed capacity with several Value Streams or product/service types, then Heijunka can rapidly increase in complexity. For high mix/low volume mixed model production in a shared capacity system, be prepared to tackle some serious math and statistics.
Heijunka is one of the electable “hows”. But I highly recommend early adoption of the process family/Value Stream approach. Immediate benefits in flow management are usually achieved. The adoption of a “Heijunka Box”, mixed model flow line should probably wait until the turmoil resulting from the JIT/Jidoka interactions have reached a very manageable level.
“Standardized Work” is located right in the middle of the two pillars and supports both. On the JIT side, standardized work acts in conjunction with Heijunka to smooth the flow. If you continuously vary the way the work is done, the flow will likely vary also – sometimes dramatically. And that leads us to how it supports Jidoka. Reproducibility is key to minimizing process stoppages with Jidoka. Standardized work helps assure reproducibility in product flow. It reduces the uncertainty that always makes problem solving difficult. If the work method is the problem, you want that method to be reproducible. You can then identify it as the problem, then change the standardized work method to fix the problem and thus improve.
Standardized work is a must “how” – unless, of course, you just like the bizarre world of “fire-fighting” (and, unfortunately, many people earn a good living doing just that). Here’s Ohno again:
“Standardized work at Toyota is a framework for kaizen improvements. We start by adopting some kind – any kind – of work standards for a job. Then we tackle one improvement after another, trial and error.”
And so now we come to “Kaizen”, probably the most powerful and also the most misapplied “how” in the entire TPS House. This is a very, very, very wide ranging topic and for the purposes of this discussion I will confine my comments to how “Kaizen” fits within the basic TPS House framework. I can’t think of a better way to start (and end) than to quote Masaaki Imai (Founder, Kaizen Institute) on his reflections of Ohno’s career:
“His lifelong pursuit was to make a smooth and undisturbed flow as a foundation of all good operations. He believed that wherever and whenever the flow is disrupted, there is an opportunity to do kaizen.”
That is why “Kaizen” is directly beneath the Jidoka pillar in the TPS House. Kaizen is the key to making Jidoka work. And making Jidoka work is the key to creating continuous flow. And continuous flow is the key to reaching the Goal in the roof of the TPS House: Highest quality, lowest cost and shortest lead time. To Ohno this was not a trivial pursuit – according to Imai, it was his lifelong pursuit. Here is Ohno one more time:
“Kaizen is about changing the way things are. If you assume that things are all right the way they are, you can’t do kaizen. So change something!”
I believe these two quotes epitomize the difference between Lean/TPS and other approaches to “continuous improvement” and/or production process optimization. MRP, MRP II, ERP, APO, etc., etc., etc. try to manage around flow disruptions instead of eliminating flow disruptions. Factory Physics emphasizes the management of inventory, capacity and time buffers to manage variability rather than reducing the need for buffers by reducing the variability by improving flow. Six-sigma is tacked on to Lean in order to reduce variability while not realizing that reducing waste reduces variability on its own, by improving flow – no fancy statistics needed. (Don’t get me wrong – I have no aversion to statistical analysis. DOE is one of the most powerful tools I have ever used in my career. I just think the marriage of six-sigma and Lean is more of a political rather than a practical strategy).
Which brings us to the foundation of the TPS House – “Stability”. Together, “Heijunka”, “Standardized Work” and “Kaizen” create the “Stability” needed for the foundation of the TPS House by ensuring that the JIT/Jidoka interaction works.
And that is “how” Lean works.
But remember that the “how” is there to generate the “what”. Always remember the “what”! That should be the ultimate focus in all our efforts. Too many people get caught up in the “hows” (toolbox anyone?) and forget (or never knew) the “what”. Here is the “what” once again (but not for the last time). While reading this, please reflect on “how” JIT, Jidoka, heijunka, standard work and kaizen are key to achieving this underlying principle (this, of course, assumes that my explanations above allow someone to do this – I hope):
Thus the underlying principle behind TPS/Lean is the systemic creation of the shortest possible lead time for the continuous flow of materials and information in order to generate the highest quality and lowest cost.
To sum up, please note that the very first quantifier in that principle is “lead time”. “Time” is the key to successful Lean. Yes, Lean means eliminating waste, but only eliminate the waste that affects lead time. That’s what Lean is all about. That is what the “hows” should be focused on. That’s what the “just-in-time” pillar is all about. Art Byrne (of Wiremold fame) put it very well in his book The Lean Turnaround:
“Think of Lean as a time-based growth strategy. The steps you take to improve your value-adding processes will automatically reduce the amount of time it takes you to do everything.”
I will be discussing the crucial role of “Time” in much greater detail in future posts.
One last thought before I end this post. Everything I have outlined in these three posts is valid for any process system – not just manufacturing. Anywhere you have processes giving you an output, the TPS/Lean system will work to improve that output. In economic theory “production” does not mean “manufacturing” (although manufacturing does belong in the economic group comprising production). Production simply means the “creation of value”. Thus:
The Toyota Production System = The Toyota Value Creation System