Hello, I'm Ray Sheen.
Your Value String Maps are also characterized
by the Value Stream Data Box that is associated with each step.
Let's take a closer look.
A data box is just that,
a set of boxes on your value stream map that encloses the data.
Every step will have a data box located just below the step.
Each data box contains the measurable data that is associated with that step.
Now to make it easy to read the map, every data box on a map
will have the same list of data in the same sequence in the box.
Which data items are listed change from map to map, but
the data items are consistent within a Value Stream Map.
Now normally, they will have at least one time-based data element
such as total time or value-added time.
Normally, there will be at least one resource-based element
such as the number of people or units of equipment in that step.
And normally,
there will be at least one quality based element such as first pass yield.
In my experience,
most data boxes will actually have three to eight data elements.
Your business may have a standard data box format.
And if so, use it.
If not, work with the organizations black belts to
decide what are the appropriate elements for your process.
Again, try to have time, resource, and quality elements in your data box.
Another data recording approach found on many Value Stream Maps is the time ladder.
The time ladder shows the allocation of all process time into one of two
categories, either it's value added time or non-value added time.
There are no other choices.
The value added time is the time spent in the process when the operator or
equipment is actively working on the process item in a way that adds customer
value to that item.
Everything else is none value added.
That means if the non-value added time includes all the time spent by items in
a batch that are waiting their turn.
It includes time when the item is sitting waiting to be worked on like on night
time or on weekends.
It includes when someone is working with that item but
their activity is not value added.
Things like moving the item from station to station or correcting an error.
When determining the values to use in the time ladder, use the average value for
the items that you're measuring, not the worse case or the best case.
Time ladder is normally shown below the data boxes on the value stream map.
The ladder is drawn as a set of horizontal lines with the lower ranks are the values
added time for each step and centered under the data boxes for that step.
And the upper ranks are the non-value added time between the steps.
So let's look at how all these come together.
As you can see, I'm showing four steps on a Value Stream Map.
Under each of these steps is the data box and below that data box is a time ladder.
When you look at the data boxes, they each have the same format.
The first element is the step name, second element is the total time for
that step, third item is the value-added time for the step,
fourth item is the batch size, fifth item is the first pass yield for that step,
and the sixth item is the number of people involved in doing the work at that step.
Notice that the first two steps, setup and cleaning, have no value-added time.
There's no customer value-added activity going on at that step.
Now that doesn't mean that you don't do the step.
It just means that the step does not increase the value of the item.
The next two steps have very low value-added time
as compared to the total time.
The reason for that is the batch size.
While one item is being etched for two minutes, the other 49 are sitting idle.
We can see this time playing out on the time ladder.
Since the first two steps have no value added time,
all of the step time is on the upper rung of the ladder.
In the next two steps,
the value added time for one unit is in the lower rung of the ladder.
And the rest of the time is on the upper non-value added run of the ladder.
So this is showing the amount of value added time for
one item to go through the process.
Caution, not only is it important to have the same element in each data box but
make sure that everyone who collects the data is using the same definitions of
the data elements.
Now that means the same units and measure the same way.
If possible when collecting data try to measure a number of items through a step
and use the average.
If you just follow one item, it is likely that item will be treated special and
you won't get a good picture of what is actually happening in the process.
In many organizations today, some aspect of a step may be recorded
in an information management system such as an ERP or a CRM system.
When that happens, you have a time stamp for that step.
And you can then look at historical records and
determine the average amount of time for an item to go through the process.
I recently worked with an organization where we didn't have a timestamp for
their system for every step.
But we did have a timestamp for about half of them.
We could then create a pretty accurate time ladder.
We just had to determine how to allocate the time across several steps
that occurred between two timestamps.
When some black bets and green belts think of data,
they only think of six sigma statistics.
But lean analysis is also heavily dependent upon collecting and
analyzing data.