Page 403 - Design for Six Sigma for Service (Six SIGMA Operational Methods)

Design and Improvement of Service Processes—Process Management 363

The key objective of lean operation is to eliminate all process wastes and
maximize process efficiency. The key elements of lean operation include
the following items:
• Waste elimination in process
• Pull-based production system
• One piece flow
• Value stream mapping
• Setup time reduction
• Work cells
Now we discuss these key elements in detail.

10.5.1 Waste Elimination in Process

In observing the mass production, Tachii Ohno (Ohno 1990, Liker 2004), an
engineering genius of Toyota and the pioneer of the Toyota production
system, identified the following seven wastes in production systems:
1. Overproduction: Producing too much, too early
2. Waiting: Workers waiting for machines or parts
3. Unnecessary transport: Unnecessary transporting of moving parts
4. Overprocessing: Unnecessary processing steps
5. Excessive inventory: Semifinished parts between operations and
excessive inventory of finished products
6. Unnecessary movement: Unnecessary worker movements
7. Defects: Parts need rework or are scrap
These seven wastes are called muda, a Japanese term for missed oppor-
tunities or slack. These items are considered waste because in the eyes of
customers, these activities do not add desired values to the products.

In lean operation principles, the seven wastes can be identified mostly by
the value stream mapping method. The waste caused by overproduction can
be reduced or eliminated by a pull-based production system. The waste
caused by excessive inventory, waiting, and unnecessary transport can be
greatly reduced by one-piece flow and work cells (cellular manufacturing).
It is often necessary to use a setup time reduction technique to make one-
piece flow possible. One-piece flow and work cells also make defect
detection easier. Besides lean operation principles, other techniques, such as
ergonomics, poke yoke (foolproof), and statistical process control should
also be applied to reduce the waste caused by defects and unnecessary
movements.