Page 358 - Design for Six Sigma for Service (Six SIGMA Operational Methods)

318 Chapter Ten

3. Maximize resource utilization
4. Minimize production costs
The performance measures of job shops and the decision variables that can
be changed in controlling a job shop include the following:

Performance measures
• Time to complete a set of jobs (rnakespan)
• Number of completed jobs that are tardy
• The average lateness of jobs that are completed
• Utilization of equipment
Decision variables
• The job selection rule
• The sequence in which jobs are processed
• The routing for a particular job if alternative routings are possible
• The resources assigned to particular jobs
• The transfer batch size
• Use of overlapped versus nonoverlapped production
• Overtime and shift policies
• Assignment of resources to workstations

Cellular Manufacturing
An alternative to a job shop is cellular manufacturing in which machines
are grouped into cells according to common processes. A manufacturing
cell is a group of machine tools and associated materials handling
equipment that is managed by a supervisory computer. Manufacturing
cells are often called group technology (GT) cells since group technology
is the basis for designing the cell. Group technology is an approach to
design based on the premise that similar things should be done similarly.
Parts having similar configurations or similar processes should be
produced by the same cell of machines. A cell is an independent group of
machines but may be connected with other cells to form a flexible manu-
facturing system.

The flow of parts within the cell resembles the streamlined flow achieved
in line flow manufacturing. This results in greater efficiencies by con-
solidating groups or families of products together and treating them,
from a work flow standpoint, as a single product. A cell is an excellent
way to achieve the “factory within a factory” concept and is becoming a
widely adopted approach to low-volume, high-mix manufacturing. A
flowchart for a typical cellular manufacturing process is illustrated in
Fig. 10.5.