Page 456 - Design for Six Sigma for Service (Six SIGMA Operational Methods)

414 Chapter Twelve

• Throughput
• Inventory
• Operational expenses
In a manufacturing plant circumstance, Goldratt and Cox think that these
measures are more relevant in moneymaking than frequently used performance
measures such as machine efficiency, equipment utilization, and downtime.

In The Goal, the following basic concepts of the theory of constraints are
outlined (Goldratt and Cox 1986):
• Bottleneck resources are “resources whose capacity is equal to or less
than the demand placed upon it. A non-bottleneck is any resource whose
capacity is greater than the demand placed on it.” If a resource presents
itself as a bottleneck, then things must be done to lighten the load. Some
of the appropriate steps might be to off-load material to relieve a bot-
tleneck or to work only on the parts in the bottleneck that are needed now.
Beware of lost production at a bottleneck due to poor quality or rejects.
• Balanced plants are perhaps not a good thing. Do not balance capacity
with demand, but “balance the flow of product through the plant with
demand from the market.” The plant may be capable of generating
inventories and goods at record levels, but this may jam up the plant’s
system. The idea is to make the flow through the bottleneck equal to
market demand. One can do more with less by just producing what the
market requires at the time. It is possible that the existing plant has more
than enough resources to do any job, but the flow must be controlled.
• Dependent events and statistical fluctuations are important. A sub-
sequent event depends on the one prior to it. The story of Herbie and
the local scout pack describes how the slowest member of a group
restrains the pace of the group (Fig. 12.1). Similarly, a bottleneck
restrains the entire throughput.

Figure 12.1 The Slowest Member of a Team Sets the Speed for the Whole Team