Mapping the value stream
The first step in mapping the value stream is determining the product family. You can read in the previous blog how to do this.
Next up is mapping the current state. The current state is the process as it works today. You take your pen and paper and go to the gemba. On the right you can see the icons you can use to map the value stream. When you map the value stream you time and measure everything you need. When you start mapping the value stream you start with the customer. Make sure you map both the material and the information flow into the value stream.
Next up is mapping the future state. This is the value stream of the future. Where can you cut down waste and add more value.
Last, but not least is the plan to go from current state to future state.
How do you know when the next process box starts?
The next process box start whenever the work is transferred from one work station, team or machine to the next. It can at times also be wise to define a new processes box when wait times within a process box need to be made more explicit than is the case by measuring lead time.
Looking at process boxes this way helps to spot information flows. Whenever there is a transfer, information needs to be transferred as well. It also helps in spotting wastes, like defects and inventories.
Going to the gemba is an important tool in getting the process boxes right.
What differences are there between plotting the future state and the current state?
Below you can see a table with a step by step comparison for mapping the current state and the future state. In the future state you will look to replace push with pull. Sometimes pull is not instantly possible. In these cases it can help to use FIFO, supermarkets and kanbans.
You will also look at leveling cycle times and to bring the cycle times closer to the Takt time. You can do this by using kaizen and kata to train your front line people how to improve. One incredibly helpful tool is 5S. IT is important to use all the 5S’s and not just the one about sorting and cleaning.
What kind of data do you need?
You need quite a lot of data. You can see a line below the value stream (picture on the left). This line contains the following data:
- Cycle time: the actual time spent working on bringing a product to the next process box
- Lead time: The time it takes a process box to bring the product to the next process box
In the data box you usually have:
- Change over time: Time needed to change from producing one product family to producing another product family
- Number of operators
- Available work time every shift in seconds
- Uptime of machines
In the inventory box you usually put in the number of pieces in the inventory. You will also put in the number of days the inventory will be there before it starts moving again.
If you want to know more, please read the book ‘Learning to See’ by Mike Rother and John Shook. It is the best book our there on this subject and I still enjoy it immensely.