Now that we have covered the “what” of Lean, I will begin to flesh out the “how”. But as we go through this exercise we must keep the “what” that was outlined in the last post firmly in our mind:
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.
Many think that the “how” is what is generally referred to as the “Lean Toolbox”. Actually many seem to think this magic box also contains the “what”. But these “many” would be wrong. Lean is much more substantive and nuanced than these views portray. That is why the “why” (why Lean works) is seldom understood.
Let’s go back to the TPS House:
We have covered the roof of the house, “Goal: Highest quality, lowest cost, and shortest lead time”, and part of the JIT pillar, continuous flow – the “what”. Everything else in the “TPS House” comprises the “hows” to create flow, reduce lead time, increase quality and reduce cost. Some are elective but most are “must do”.
At this point it may be educational to compare this original “basic” TPS house to the many versions that came after this one. Google “TPS House” and look at the multitude of images that are presented. As you scroll through the various depictions you will find every buzz word that has ever been invented for Lean in one or the other houses. That is indicative of the confusion that exists in Lean today. But we will be using the basic house depicted above. There are relatively few terms but each is key to understanding TPS and thus to understanding Lean. Even the placement of the various terms is significant.
One other quick note before we continue on. We are now discussing TPS – the Toyota Production System. This is not the same as the “Toyota Way” which formally came about in 2001, many decades after TPS was well established within Toyota. While the two pillars of the TPS House are “JIT and Jidoka”, the two pillars of The Toyota Way are “Continuous Improvement and Respect for People”.
The Toyota Way is a broader approach to the Toyota management culture and TPS is embedded within that structure. In fact, “Respect for People” may be the most powerful aspect of the entire Toyota culture and was present early on at Toyota, well before “The Toyota Way” was officially launched. The Toyota Production Control Department published a paper in 1977 titled “Toyota production system and Kanban system Materialization of just-in-time and respect-for-human system”. (I have been told that “respect for humanity” is a better translation from the Japanese language than “respect for people”). It was this emphasis on employee involvement that drew me into the JIT/TPS world several decades ago.
But for now let us concentrate on TPS. Without fully understanding TPS, “Respect for People” can lead to unintended frustration for a whole lot of those people.
The two pillars of the TPS House, Just-In-Time (JIT) and Jidoka, are must “hows”. They are true pillars and without these, TPS cannot achieve the “Goal” outlined in the roof. JIT establishes flow and Jidoka makes visible any interruption of flow and/or visibly stops flow when the quality of that flow is jeopardized. Together they make flow (or lack thereof) visible. Together they establish lead time and make time visible. Together they make quality (or lack thereof) visible. Together they make cost visible. JIT creates the flow; and Jidoka interrupts the flow to make the waste that is preventing continuous flow visible.
JIT contains two other components (other than “continuous flow” itself) which regulates the flow: “takt time” and “pull system”. “Takt time” sets the rate of flow and prevents over and under production. This also determines the installed capacity needed to achieve the correct level of flow. The “pull system” is what creates the “just” in just-in-time. JIT means having the right part in the right place in the right quantity at the right time.
In a “pull system” the product/service flows downstream, while the information that specifies which product to pull, flows upstream. The “pull system” places the focus on the demand side (the customer) rather than the supply side (everybody else). Its nemesis the “push system”, which pushes both product and information downstream, focuses on the supply side and leaves it to “hope” that the demand side is satisfied.
Although both “takt” and “pull” are must “hows” in creating flow, they are also critical visual signals when flow is impaired and thus also become critical aspects of Jidoka itself. Any deviations from the target “takt time” is an easily measurable and very visible indicator of flow problems. The “pull system” is by definition a binary (yes/no) process in that the desired component is present or it is not. If it is not present the process stops (i.e., very visible).
Of course the first component in the Jidoka pillar is “Stop and notify of abnormalities”. This means the abnormality, no matter what it is, must be addressed now. This may mean a temporary countermeasure but a permanent fix is expected very soon. Also, TPS incorporates a “zero defect” policy. You do not pass defects to the next process and you do not accept defects from the previous process – Period! “Stop and notify” is an absolute must “how”.
The second component of Jidoka is “Separate human and machine work”. There is no reason for a human being to be present when a machine is doing work – that is a waste of potential human work. Let the worker do work on several machines. Design all machine processes to stop on their own and signal when there is an abnormality (poka-yoke) – do not force a human to waste their time waiting and watching for that abnormality to occur (respect for human). Whether or not this “how” is an elective or must “how” very much depends on the type of process system you have in place.
Jidoka is probably the least understood and least appreciated component of TPS (and thus Lean) but probably one of the most important. To most people Jidoka represents what must be avoided at all cost – a process stoppage (Horrors!). But the real horror is what you get in the end as the result of not stopping a faulty process – defects, rework, low productivity, frustration, missed deadlines, etc. and, most importantly, lost customers. To quote Ohno:
“A production line that does not stop is either a perfect line or a line with big problems. When… the flow does not stop, it means that problems are not surfacing. This is bad. … [T]here is no reason to fear a line stop.”
Even though there should be no fear, the JIT/Jidoka relationship can create temporary turmoil for a system with marginal processes. But that turmoil is what identifies the waste that must be removed to reduce lead time, increase quality and reduce cost. “Takt” and especially “pull” can become very difficult to master until the JIT/Jidoka relationship is reasonably stabilized – until flow is reasonably stabilized.
I will have much more to say about the twin pillars of “JIT” and “Jidoka” in the near future. I just wanted to get the interrelationships between the two and with the roof laid out in a general context. In the next post I will cover the “hows” in the floor and foundation of the TPS House.