Value Stream Mapping for High Mix
Tips for creating mixed model value streams for a complex environment with high variability of demand, mix, and/or customization
The Lean methods described on this page are a countermeasure to
variability -
variability of customer demand, and variability of a large
number of potential deliverables.
It is a common misconception (or attempted excuse?) to believe that "lean won't work here because we don't have a customer like Toyota that feeds us a steady flow of predictable demand", or "lean won't work here because we have too many offerings that are too customized and routed through a spaghetti maze of unpredictable and ever-changing processes".
The truth is that there are lean techniques that can radically improve the quality, cost, and speed of delivery for ANY mix of ANY product or service. A few of those techniques are introduced here.
Tip: If your company has a large number of offerings with high variability of demand, you will probably benefit greatly from hiring a seasoned Lean consultant - who should have mastery of an entire bag of lean solutions to common and not-so-common challenges.
The single most important lean technique for dealing with high variability is to segment your products into the right product families, and then to manage the total demand for the entire product family.
Follow the step-by-step instructions on the Help worksheet of the Product Family Matrix template, which comes with the Value Stream Mapping bundle of templates, which will walk you through how to:
- Segment all of your products into rough product families
- Refine each product family:
- To identify any offerings that take so much more time to produce that they might need to be either moved to another product family or be scheduled using special techniques
- To determine resource requirements (for equipment or any other potentially-constrained resource)
Dedication
The more that you can commit resources to be dedicated to one (and only one) product family - the less confusion and variability you will have.
Dedicated equipment is not a requirement for lean methods - but it sure makes things a whole lot easier whenever it is possible.
Get creative. It is not uncommon to be very worthwhile to trade the speed of an expensive shared machine for the flexibility and availability of a smaller dedicated machine, or even manual processing.
Mix Logic Flowchart
In the top "information" section of your value stream map, it is often a
good idea to provide a hyperlink to a
flowchart containing yes or no logic
paths to guide your Scheduler for what to do in any circumstance.
For example: What to do if there there more orders than you can produce in one day? When to work overtime? When to bring in cross-trained staff? When to pull from inventory? When to level the volume?
What to do if there are fewer orders than the planned production level? When to replenish inventory? When to assign workers to other assignments? What assignments? Maintenance, 5S, cross-training, continuous improvement...? Do we have pre-established Standard Work Instructions pre-established that divide the work load between different numbers of workers?
What to do if the mix of orders is outside of system tolerances? When to limit the quantity per interval for an usually-time-intensive product? When to stick to your guns and keep labor constant - building products in a load leveling sequence? When to build ahead to a supermarket and/or a FIFO Lane?
Mix Logic Chart requirements:
- All decisions are yes or no (no maybe, usually, or sometimes)
- Every branch ends in a specific action to be taken (reflecting the pre-meditated responses of the best minds in your company)
- Every possible circumstance is covered (if a new one arises - update the chart)
A
Swing and a Miss
If every member of your team is not VERY familiar with the lean concept
of Pitch,
then your lean
effort does not have any chance of hitting one out of the park.
Yes, pitch is THAT important in a high variability lean environment.
Your Systems2win Value Stream Mapping PowerTool automatically calculates Pitch, making it infinitely easier for your people to really "get it".
Know your pacemaker
One of the key lean principles to radically simplify any complex environment is to schedule only one point in the value stream.
Use your pacemaker (and only your pacemaker) to determine the Takt Time, Pitch, Pitch Batch Size, and EPEx for the overall value stream. (Tip: Your Systems2win Value Stream Map auto-calculates all of these - making it so much easier for your people to really "get it".)
Every Part Every Interval
Although your Systems2win value stream map will automatically answer the
question:
"What is the EPEx for the pacemaker?"
(which then serves as EPEx for the entire value stream)...
it is even wiser to use what-if scenarios to answer the even
more powerful question:
"What Change Over times are needed for our
target EPEx?"
And then use SMED setup reduction methods to do what it takes to meet your strategic objectives.
Queue Time for a Shared Process
How to handle Queue Time for a shared process?
If a process is shared by more than one value stream - a lot of people get confused.
Some people (incorrectly) try to change the Takt Time for the shared process.
The definition of Takt Time =
How often completed units NEED to come out the end of the pipe - as established by customer demand
Or more precisely... "Customer demand for THIS product family."
So a shared process might serve many different product families, each with their own takt time.That shared process needs to churn out each of those product families at the varying paces required for each product family.
So from a value stream mapping perspective, the takt time for THIS product family is still the same for any shared process or non-shared process.Now if you are the operator for the shared process, you need to know YOUR takt time, which would be calculated from the COMBINED demand for all value streams served.
And if you think about it, those value streams might be so different from each other that there might be no common unit of measure that makes any sense - which is why it is not uncommon for a shared process to measure its takt time in terms of some generic unit of measure, such as weight, or linear feet, or dollar value...
It would serve no purpose other than confusion to include on each value stream map that generic unit of measure with that "out-of-the-blue" takt time (which is constantly changing every time that the demand for ANY product family changes. Talk about non-value add activity... trying to keep each value stream map in sync with those rapid changes...)
So the takt time for a shared process on a value stream map is treated just like any other non-shared process.
So what needs to vary in order to accurately depict a real-life lead time for a shared process?
The Standard WIP Inventory in the queue feeding the shared process.
It is sometimes helpful to think of it this way...
Your inventory is standing in line to get theatre tickets -
waiting in line along with a whole queue of other people also waiting for the same ticket person to serve them.So there are two ways to handle it on your value stream map:
(and overriding Takt Time is not one of them)
1) Rather than just your own product family's Standard WIP - enter an estimate of the typical Standard WIP for ALL product families served by the shared process.
2) Don't even bother trying to estimate Standard WIP. Instead, (in the Queue Time Override field) just enter an estimate of how long your inventory usually waits.
Suggested Reading
Creating Mixed Model Value Streams, by Kevin Duggan