Framework library · Operations and resilience
Value stream mapping
A value stream map follows one product or service from the customer's request to delivery and records, for each step, how long the work takes, how long the order waits beforehand and how often the work arrives complete and accurate. The usual finding is that work happens for a few per cent of the elapsed time, so the quickest way to cut lead time is to remove the waiting, not to make the work faster.
Use it when
- Customers wait weeks for something that takes hours of work, such as a business Ethernet circuit or a new site connection.
- Several teams or companies hand work to each other and nobody owns the whole lead time.
- You are about to automate or outsource part of a process and want to know whether that part is where the time goes.
- Rework loops are suspected but have never been measured.
Avoid it when
- Most of the work happens in one step. Study that step directly; a map with one box shows nothing.
- Every order is different, such as bespoke engineering projects. Map a typical order, or plan the work as a project schedule.
- You need to find a capacity limit. A value stream map shows time and quality. Use the theory of constraints to set capacity against demand.
How to run it
Choose one product and one customer outcome
For example, "a 1 Gbit/s Ethernet circuit to a building on our fibre route, from order to handover". Different products follow different streams, so map one at a time.
Walk the stream from the end
Start at delivery and work back, asking each team what it does and what it waits for. Use real orders, not the process manual.
Record time and quality for each step
Process time is the hands-on work; wait time is how long the order queues before the step. Complete and accurate (%C&A) is the share of work that arrives needing no correction.
Read the totals
Lead time is all the waiting plus all the work. Process cycle efficiency is work as a share of lead time. Rolled %C&A, the product of every step's %C&A, is the share of orders that pass through without rework.
Draw the future state
Decide where waits can be removed, steps run in parallel or checks moved earlier. Set a target lead time and a plan to reach it.
Work through it
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Mistakes to avoid
- Mixing units, such as process time in minutes and waits in days. Put everything in hours, as the workbench does, or the efficiency figure means nothing.
- Mapping the process as designed. The map is only useful if it shows what real orders did.
- Speeding up the work when the waits are the problem. Most of the lead time usually sits in queues between teams.
- Ignoring %C&A. A step that sends back a third of its input adds its own wait time again each time it does.
Where it comes from
Developed at Toyota, where it is called a material and information flow diagram, as part of the Toyota Production System. Mike Rother and John Shook set it out as value-stream mapping in the workbook Learning to See (Lean Enterprise Institute), which received a Shingo research prize in 1999. Source.
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Further reading
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