Value Stream Mapping Math

The lead-time ladder process ‘branch’

Here’s some often overlooked and misunderstood value-stream mapping math.

The lead time ladder has two levels or “rungs.” The bottom rung is the process or processing rung on which the relevant process time is dropped down. This is usually pretty straightforward... unless there is a split or branch in the material, service, or knowledge flow within the value stream.

For example, after a fabrication process, the material may flow 35 percent of the time to a coating process and then to an assembly process, while 65 percent of the time the coating process is skipped altogether. The value-stream map essentially reflects a process time for a hybrid (or weighted average) product or service, in such a situation. Accordingly, the process times for these branches must be apportioned by the split percentage, as illustrated in the figure below.

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Comments

Branch is a new stream

With different operations, don't we have a different value stream? which would then have different demand (e.g. TAKT time) and operator loading and different playbook(s) and...and...and...

By merging the streams, we are in danger of not recognizing the variety needed and designing necessary flexibility to accomodate the variety. By manipulating the math to merge streams, we muddy the view of the process. When our streams get muddy and many, our process starts to look like a puddle. My preference is to view clean, clear streams and not muddy puddles.