Craig H. said:
Systems Thinker:
I agree with what Greg just said. It really does not matter what we call it. Except so that we can use a name to describe a tool.
Ok, the lean process map, then. It seems to me that, at least in the case in the second link you so kindly provided, that the whole key here (and with Kaizen, too, if memory serves) is production scheduling, right? (Or not right?). This allows a reduction in WIP and finished goods inventory.
We have a situation where it seems like our production schedule is constantly changing. Being a raw materials supplier to raw materials suppliers, we feel any "whiplash effect" changes in scheduling all the way to the consumer, which can be several steps. Further, we have some customers who call and try to move shipments from next week to this Wednesday (this is Tuesday morning). I have actually had a customer tell me that if we instituted Just In Time, we could handle changes like this. I wanted to reply with something about Just Poor Planning, but I digress.
My questions are these: With a somewhat fluid scheduling stuation, how can we eliminate inventory and maintain current servicing levels? Is there any way to do this? How should I approach it?
Thanks for the input!!!
Craig
Interesting question! One of the Lean guidelines is to schedule only one point in the value stream. This is contrary to orthodox push production scheduling which attempts to schedule and control all the points in the production system with powerful computers and software. In a Lean value stream, the point at which we schedule is called the pacemaker. The pacemaker process determines the speed at which the value stream will operate and regulates production through the value stream - increase its speed, you produce more product, slow it down and you produce less. (incidentally, the concept of pacemaker finds its equivalent in the "drum" of TOC's drum-buffer-rope production scheduling and control methodology, another reason why Lean and TOC are closely aligned).
How do you create a pacemaker process? By dedicating equipment into a cell or line to run a specific product or product family in continuous flow one piece at a time. In companies which produce only one product, that's relatively easy to do; in companies which produce multiple products (mixed model environments), its more complex.
The rule is that you must pull materials from upstream shared resources into the pacemaker, but out of the pacemaker you must flow downstream to the customer.
We will schedule the pacemaker by levelling the volume and mix of products that flow through it and then flow the output into a finished goods supermarket where it is held for customers.
There are several ways you can deal with changes in customer demand. One is to buffer your finished goods supermarket to handle the variability in demand. The supermarket contains an inventory buffer which you can calculate empirically by analyzing your demand variability. You can also vary the output of the pacemaker cell by varying the number of operators in it. For example, if demand for a day is down, we let the pacemaker run slower. If demand begins to exceed what we can produce, even with the help of the buffered supermarket, we may have to add equipment, operators or even another shift.
In short, the question has no simple answer because to implement the approach above you will have to change your system of production from push to pull with JIT flow. As part of that conversion, you will create a pacemaker process which you will then schedule to regulate the value stream. It will mean suspending the common notion of using more powerful computers and software to address scheduling issues in a push environment.
A good rule to follow is that the smaller we can make lead time, the less chaos in the system. Remember, as variation approaches 0, batch size can equal 1.
Hope this helps,
systems_thinker
