What is the advantage of the pull
system? How difficult is it to implement a pull system in a plant
set up for a push system? How does Goldratt’s theory of constraints
relate to lean and JIT process systems and the pull system? The 10
guidelines of the theory are detailed on pp. 188–190 of the text.
Include examples to support your analysis.
the 10 Guidelines of the Theroy :
1. Flows rather than capacities should
be balanced throughout the shop. The objec-tive is to move material
quickly and smoothly through the production system, not to balance
capacities or utilization of equipment or human resources. 2.
Fluctuations in a tightly connected, sequence-dependent system add
to each other rather than averaging out. 3. Utilization of a
non-bottleneck is determined by other constraints in the sys-tern,
such as bottlenecks. Non-bottleneck resources do not restrict the
amount of output that a production system can create. Thus, these
resources should be managed to support the operation those
resources (i.e., the bottle- neck resource at a higher rate of
output than the bottleneck resource does put. Clearly, operating, a
nonfat to increase the output produced by the entire production
system. 4. Utilizing a workstation (producing when material is not
yet ,leetled) is not the same as activation. Traditionally,
managers have not made a distinction between “using” a resource and
“activating” it. However, according to the theory of constraints, a
resource is considered utilized only if it is helping the entire
system create more output. if a machine is independently producing
more output than the rest of the system, the time the machine is
operated to produce outputs over and above what the overall system
is pro-ducing is considered activation, not utilization. 5. An hour
lost at a bottleneck is an hour lost for the whole shop. Since the
bottleneck resource limits the amount of output the entire system
can create, time when this resource is not producing output is a
loss to the entire system that cannot be made up. Lost time at a
bottleneck resource can result because of downtime for maintenance
or because the resource for work. For example, if a hair stylist is
idle for an hour becaus weansostcustom-ersarvecl arrive, this hour
of lost haircuts cannot be made up, even if twice as many customers
as usual arrive in the neytpielo 6. An hour saved at a
nonbottieneck is a mirage. Since nonbottlenecks have plenty of
capacity and do net limit the o production system, sav-ing time at
these resources does not in- crueapcuttcAatllike)utout. The
implication for managers is that time-saving improvements-ceotto
the ‘system should be directed at bottleneck resources. 7.
Bottlenecks govern shop throughput and work-in–process
inventories. 8. The transfer batch need not be the same size as the
process batch. The size of the process batch is the size of the
batch produced each time a ob is run. Often, this size is
determined by trading off various costs, as is done with the
economic order quantity (E0Q) model discussed in Chapter 7, Supp.
B. On the other hand, the size of the of the batch transfer batch
is the size of parts moved from one work center to another work
center. Clearly, parts can be moved • smaller batches than the
process batch. Indeed, consider-able reductions in batch flow times
can often be obtained by using a transfer batch that is smaller
than the process batch. For example, assume that a manufacturer
produces a part in batches of 10. This part requires three
oper-ations, each performed on a different machine. The operation
time is 5 min-utes per part per operation. Figure 5.4a demonstrates
the effect on flow time when a process batch of 10 units is reduced
to a transfer batch of one unit. Specifically, in Figure 5.4a the
transfer batch is the same size as the process batch, and a flow
time of 150 minutes results. In Figure 5.4b, the one-unit transfer
batch reduces flow time to 60 minutes. The reason for long flow
time with a large transfer batch is that in anypbraotcceh, the
first part must always wait for all the other parts to complete
their processing before it is started on the batch has to wait 45
next machine. In Figinuerepa5rtAsa. ,wthheefirst part in the * the
n the transfer batch is reduced to one unit, the parts in batch do
to wait for the other parts in the minutes for the other ni not
have process batch. 9. The size of the process batch should be
variable, not fixed. Because the eco-nomics of different resources
can vary, the process batch does not need to be the same size at
all stages of production. For example, consider an item that is
produced on an injection molding machine and then visits a trimming
department. Because the time and cost to set up injection molding
equip-ment are likely to be very different from the time and cost
to set up the trim-ming equipment, there is no reason why the batch
size should be the same at each of these stages. Thus, batch size
at each stage should be determined by the specific economics of
that stage. 10. A shop schedule should be set by examining all the
shop constraints simulta-neously. Traditionally, schedules are
determined sequentially. First, the batch size is determined. Next,
lead times are calculated and priorities set. Finally, schedules
are adjusted on the basis of capacity constraints. The theory of
constraints advocates