Page 32 - How To Implement Lean Manufacturing

Lean Manufacturing and the Toyota Pr oduction System 13

is an attempt to finish each batch before the appointed delivery time. The typical quality
system is inspection-based, is normally done by humans, and rework is not only
common it is necessary and designed into the process flow. This differs greatly from the
Lean solution, which is typically a cell, with a pull system, balanced at takt, flowing one piece
at a time, with a system of jidoka.
We will explain each of these more clearly later, but the key differences are that each
work station has the same cycle time, they are balanced, and all operations are synchro-
nized. All process steps are placed close together—in a cell, for example—so one-piece
flow is possible. There is no buildup of inventory between processing steps. This close
connection and lack of inventory allow the product to “flow.” Furthermore, all work sta-
tions are balanced, in that each station has the same cycle time. This allows synchroniza-
tion of manufacturing. Furthermore, the balanced cycle time is designed to be at takt,
which is the demand rate of the customer. Product is made at the same rate at which the
customer wishes to withdraw it, and production only occurs when the customer removes
the product. This is the “pull” concept, which is different from “push” production.
Quality is managed by the jidoka concept, which not only finds and removes any defects,
it initiates immediate root-cause corrective actions. Using the preceding reference tech-
niques, the Lean process itself, rather than any of its individual steps, is optimized, for-
going the optimization of local work stations. Many Lean facilities have very good jidoka
systems, but the TPS is second to none in the application of jidoka principles, largely due
to the way Toyota has managed, and continues to manage, their culture.

Handling Multiple Models of a Product
The handling of multiple models of a product is a uniqueness of Lean. In the typical
MassProd where we have multiple models, they are normally produced in large batches
even if they use the same production facilities. Generally, the reason for the batch oper-
ation is because when switching models, changeovers are required. The Lean solution
employs the concept of model mix leveling. Say, for example, we have three models of
our product. They are A, B, and C, all produced on the same process facilities. The model
mix is 50 percent A, and 25 percent of each B and C. We then would produce these three
models simultaneously in our cell, producing in this order ABACABACABAC. Of
course, to do this single minute exchange of dies (SMED), or quick changeovers, or
more likely its refinement, OTS (one-touch setups) must be very mature in this cell.
Surprisingly enough to those not acquainted with the TPS, this is not as difficult as it
sounds. In addition to accomplishing the leveling and knowing which model to
produce, a heijunka board is employed to schedule the leveling of the various models.
The heijunka board will accept the production kanban,
which are removed form the product when the product
is withdrawn. These kanban normally are circulated Point of Clarity Lean Manu-
directly to the pacemaker step and the replenishment facturing is a batch destruction
signal, the kanban itself goes directly to the produc- technique.
tion cell, normally bypassing planning altogether.

Pull Production Technology
Pull production is a confusing concept to many, but it is a critical aspect which makes
Lean work. It is one of the key tools used to avoid overproduction, both local overpro-
duction at a specific work station and overproduction at finished goods. Pull produc-
tion is the concept that the production process is not initiated by orders or schedules.