Page 361 - Design for Six Sigma for Service (Six SIGMA Operational Methods)

Design and Improvement of Service Processes—Process Management 321

Performance measures
• Resource utilization
• Throughput capacity
• Work in process
• Cost
Decision variables
• Queuing between stations
• The production batch size of a particular part type
• The move batch size
• The sequence of products

Line Flow Shop (Production or Assembly Lines)

Line flow manufacturing consists of production or assembly lines and
transfer lines in which products move and are processed individually rather
than in a batch. Line flow systems are characteristic of many production
operations in which workstations are set up by product in a serial arrangement
and dedicated to manufacturing or assembling a single product. The idea is
to achieve a streamlined, continuous flow of material that leads to maximum
productivity. Labor and machines are highly utilized with little idle time.
Since transfer lines are sufficiently different from production or assembly
lines, they are treated separately.
Production and assembly operations that are of a line flow type are
comprised of a serial combination of two or more production, assembly, and
packaging stations typically connected by a continuous material-handling
system such as a conveyor. Nonsynchronous conveyors have become the
most popular and efficient material-handling system because they permit
parts to maintain a continuous flow while still allowing them to queue up
when necessary. Operations are often performed by hand and therefore
present a special challenge to keeping the flow as continuous as possible.
This is achieved by balancing the workload among stations, keeping each
station busy, and reducing the variability of each operation. Usually, the
more stations, the lower the cycle time, and hence the higher the throughput.
An alternative to stretching out a line into more stations to increase
throughput is to add parallel lines. At one extreme, a single line consisting
of n serial workstations may be used. The job is broken down into as many
small subtasks as possible without overproducing. At the other extreme
would be n parallel lines consisting of a single station each. The entire job
is performed on each single station line with as many lines as are needed to
meet demand. Many lines lie somewhere in between these two extremes and
consist of a mix of serial and parallel stations.