Many people have asked me how to depict the Inventory or the Cycle Times when those are in parallel on the real process.
Do they must make the sum or take the biggest?
The answer is: for Inventory you must consider the biggest, however for the Cycle Time you must do the Sum.
Please see the example on the VSM Toyota 500N center cell current state second quarter 2004.
Please note that for the first processes of VSM the cycle time considered on Lead Time (VA) was the sum of (30 sec + 2 sec + 62 sec = 94 Sec).
And for the Inventory that coming from those processes was considered the biggest one of the 4 Inventories ( 4 Days, 5 Days, 4 Days 1.5 Days) , to be represented on Lead Time as NVA.
Same considerations were taken for the VSM Future Toyota 500N center Cell Quarter 2004.
I really hope this can help you on your next projects.
Reference: The Toyota Way Fieldbook – Jeffrey K. Liker and David Meier.