Value stream maps
A value stream map draws the whole journey, the work, the waits and the information, on one page, with a timeline underneath.
About 6 minutes to read.
Key idea
A value stream map is a picture of how a product or service really flows, drawn by walking the process rather than reading the procedure. Each step shows who does it and how long the work takes. Between the steps sit the piles of waiting work. Along the bottom runs a timeline that alternates waiting time and working time.
Adding up the timeline gives two numbers that tell the story: the total lead time, and the value-added time within it. Their ratio is the process cycle efficiency. Ratios of a few per cent are common in offices, which sounds alarming but is really an invitation: there is a great deal of waiting to remove.
Takt time completes the picture. It is the available working time divided by customer demand, the pace at which the process must finish one item to keep up. A step whose work time is longer than takt is a bottleneck in waiting.
Example: a furniture maker
Six weeks for nine hours
A small upholstery workshop builds sofas to order. Walking the process with a stopwatch, the team finds about nine hours of real work per sofa, framing, springing, covering and finishing, spread across six weeks of lead time. Frames wait two weeks for fabric, because fabric is ordered only after the frame is built.
Ordering fabric when the customer pays, and building frames in the order fabric arrives, takes the lead time down to three weeks in this example. The map made the obvious visible, which is often all a map needs to do.