Creating a value stream map

What is a value stream map?

The method comes from lean management and was made known by Mike Rother and John Shook (“Learning to See”). It draws the path of a product family from raw material to customer: each process as a box, each inventory in between as a triangle, and on top the information flow from order to work order. In Taktane the information flow is blue: electronic as a zigzag, manual as a straight arrow, each labelled with content and rhythm (“Forecast · monthly”).

Below the drawing is the timeline: waiting times in inventories on top, processing times below. Their ratio — the value-added ratio — is below 5 % in many plants. That is exactly what the analysis makes visible.

When does it pay off?

• Delivery times are much longer than the pure processing time.
• Large inventories sit between processes and nobody knows exactly why.
• Before investing in a new machine: is it really the bottleneck?
• When several departments work on one product and blame each other for delays.

In six steps

1. 1

   Choose a product family

   Products that largely go through the same processes. One map for everything at once becomes unreadable.

2. 2

   Determine customer demand and takt time

   How much does the customer need per day? Takt time = available time ÷ customer demand. It is the yardstick for every process.

3. 3

   Record the processes on site

   Measure at the workstation, don't estimate at the desk: cycle time, changeover time, OEE, number of operators, shifts. The data sheet helps.

4. 4

   Count inventories

   What lies between the processes, in pieces. Inventory and daily demand give the waiting time.

5. 5

   Calculate lead time and value-added ratio

   The sum of waiting and processing times is the lead time. The share of processing time in it is the value-added ratio.

6. 6

   Design the future state

   Along the eight questions by Rother and Shook: where can it flow, where does it need a supermarket, which process sets the pace? This becomes an action plan.

The key figures

• Takt time: how often the customer needs a part — the yardstick.
• Cycle time: how long a process takes for one part. Above takt time, the process is a bottleneck.
• Lead time: how long a part takes from receipt to shipping, mostly waiting time.
• Value-added ratio: processing time ÷ lead time.
• OEE: how much of the planned time a machine actually produces good parts.

Common mistakes

• Average values from the system instead of times measured on site.
• Inventories estimated instead of counted — they make up most of the lead time.
• Confusing takt time and cycle time.
• A future state without measures, owners and dates remains a nice picture.

How Taktane helps

• Every figure shows its calculation with the values used.
• A method check warns when the value stream looks good but is methodically wrong.
• Future states are separate scenarios and can be compared with the current state figure by figure.
• Presentation mode for the workshop and a printable summary afterwards.