Matt Hrivnak

Kaizen: There's always another future state


“Kanban is like the milkman. Mom didn’t give the milkman a schedule. Mom didn’t use MRP. She simply put the empties on the front steps and the milkman replenished them. That is the essence of a pull system”
– Ernie Smith, Lean Event Facilitator in the Lean Enterprise Forum at the University of Tennessee

Now, this quote was passed on to me in an email about two years ago.  I don’t know if the quoted individual is correct, so if anyone knows otherwise please email me.  I have heard several similar quotes regarding Kanban and the milkman, as well as other metaphors regarding replishment systems.  Regardless, I wish that more people were aware of this reference.

I don’t know Mr. Smith, but I’m sure he’s a good man (I base that off of the fact that he’s spreading the good word of Lean Manufacturing!).  I like the way that this quote brings all readers into understanding through the use of something so natural and simplistic as a reference to one’s mother.  Surely, if your mother could participate in a Lean activity like a self replenishing pull system without even knowing it, then it must work pretty well if it never interrupted her daily schedule and provided for exactly what your family needed!  Now, I know not everyone was raised around their mother, but the simple idea helps bridge the gap between a supposed structured and rigid system imposed by managers to one of simplified flow.

Sometimes, people new to supermarkets, kanban, and pull system really have a hard time getting it.  They think that you can plug and play supermarkets filled with nice stacks of kanban cards and everything will simply work because you designated an area for it.  In regards to this quote, I’ve seen several cases where a supermarket has been setup and the operations around it just pull and make whatever the MRP is telling them to do.  Again, supervisors and managers want to make it look like things are always running at 100%.  I want nothing less than 100%! I hear that way too often.  That’s why it requires a complete effort from all within the company, but back to the quote.

A good portion of the time, a company will not have the luxury of producing only 3 or 4 types of products.  Usually, you’re looking at figures that are closer to 10, 50, 100 or even 1000’s of different products; all that need to be scheduled and made at different times, in different amounts, throughout the year.  This is where it gets interesting and you need to do some math.

You probably wouldn’t be resorting to the use of a supermarket if you could establish Continuous Flow in the first place.  So, now after you’ve relayed all of your equipment into cells based on the results from your recently done Product Family Matrix, you’re running the numbers to see what your least common denominators are.  Usually (going on basic assumptions) as you go upstream in your process you will see fewer and fewer variations of WIP that will later be transformed into an array of possible product configurations.  Well, it’d be nice to have each of these stored in a supermarket so that you could just pull what you need and then replace it, but most likely, it won’t be that smooth.

In most of the companies I’ve worked in, there have been so many product possibilities that I’ve had to go with the good old 80/20 rule and ended up with a small amount of supermarketed items that in the end will make most of my products.  The 80 stands for 80% of your total production, and the 20 stands for 20% of your total product count.  Clarifying that, it means that 80% of your production can be accounted for by 20% of your products.  A very simple example of this:  You make 5 products in your bread making cell – White, Wheat, Rye, Whole Grain, & Pumpernickel.  For every 20 that you sell, it breaks down like this:

  • White:  16 (accounts for 80% of sales)
  • Wheat:  1 (5%)
  • Rye:  1 (5%)
  • Whole Grain:  1 (5%)
  • Pumpernickel:  1 (5%)

So, in this very simple model, you’d use a pull system on White bread because you consistently require it based on customer demand.  Think of that scenario, but blown across 1000’s of products.  Instead of one item in your supermarket, how many would you have?  5? 10?  Figuring that out is simple enough, it is getting it to work that is the hard part.

MRP, Master Schedulers, Planners, etc. – they can all screw it up just by doing their job.  They have to be involved and MRP systems need to be adjusted, either through a built in function to work within such systems or manually, if no such feature exists in your current software.  It’s one thing to instruct someone to not make a product because there is already a supermarket full of it across the aisle, but it’s another thing to get them to actually practice it.  Supermarkets, kanbans, pull systems, whatever name your company uses, act independently from supervisors, planners and MRP. 

Kanban the Milkman makes the rounds, quietly moving product into empty spaces left by products used only minutes before; making and replenishing his whole way back to the most basic raw materials.  He’s good and if you just let him do his job – you’ll be all the better for it!!

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Comments (3) Posted by matt on Wednesday, April 16th, 2008


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