Page 404 - Design for Six Sigma for Service (Six SIGMA Operational Methods)

364 Chapter Ten

We will first discuss the value stream mapping method. The value stream
mapping method has two stages. The first stage is to draw a current state
map, which is a map of the current process. The second stage is to draw a
future state map, which is a value stream map of the proposed new process.
Since the drawing of the future state value stream map requires other
knowledge of lean operation, such as one-piece flow and work cells, Sec.
10.5.2 discusses current state value stream mapping, Sec. 10.5.3 discusses
one-piece flow and work cells; Sec. 10.5.4 discusses waste reduction and
future state value stream mapping, and Sec. 10.5.5 discusses other issues in
lean operation.

10.5.2 Current State Value Stream Mapping
Value stream mapping is a good method to use to chart the process and
identify and quantify the waste in a process. Value stream mapping was
developed to map and analyze the production process, especially the batch
flow shop and flow shop processes. A value stream is all the activities (both
value-added and non-value-added) required to bring a product through the
main flows.

Value stream mapping is a pencil-and-paper exercise that helps you to see
and understand the flow of material and information as the product makes
its way through the value stream. When you want to draw a value stream
map, do not use a computer; just bring a writing board, a good piece of
paper, and a stopwatch. The best way is to work backward, that is, from the
last step of the process to the first step of the process. In a production
process, the last step is usually the shipping dock; in a restaurant kitchen
process, the last step is at the point where the meal is done and the waiter is
taking it away from the customer. In a production process, the first step is
usually the receiving deck for the incoming materials; in a restaurant kitchen
process, the first step is usually the point where the customer’s order is
brought into the kitchen.

Figure 10.14 is a simplified value stream map for a production process.
Clearly, based on the definition of seven wastes, the staging, transportation,
setup, and inspection are value-added steps; casting, machining, and
assembly are value-added steps. In the figure the horizontal length of each
step is proportional to the time required to do the step. The total time
duration from the beginning of the process to the end of the process is often
called the process lead time. Clearly, in this example, the value-added time
is a small portion of the total lead time.