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Lean manufacturing benefits
extend to inventory, scheduling and production control. The
functional layout presents severe scheduling and inventory control
difficulties. Cellular layouts simplify
the underlying process and thereby simplify scheduling.
Every inter-departmental
move requires an outbound queue and an inbound queue. Such queues
tend to be quite large because it is difficult to precisely time the
completion of each operation and coordinate the subsequent move. Cellular
operations dramatically reduce material movement. This consequently
reduces the number of queues and the inventory in each queue.
 Lot
sizes tend to be larger in a functional environment. This
partly results from the complexity of scheduling. It seems easier to
schedule a small number of large lots rather than a large number of
small lots. Equipment selection also plays a role. Functional
layouts lend themselves to large-scale equipment. Such equipment
processes a wide range of products and increases the volume for a
given process. Large-scale equipment also tends to reduce direct
labor and appears to be more efficient. But large-scale equipment is
often difficult to setup. It must address a wider range of products.
Expensive, large-scale equipment requires high utilization. High
utilization requires more inventory.
Average
throughput time is directly proportional to inventory. We refer to
this relationship as Little’s Law. When inventories
shrink in a cellular environment, average throughput time shrinks
proportionately. The reduction in inventory frees up capital and
space for more worthwhile investment. The improved throughput time
improves customer response and helps stabilize the system.
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 Duplication
of equipment in cells seems to cause low utilization. Several
factors can mitigate this:
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The
wide variation in production requirements that characterizes
functional arrangements often results in lower utilization than
one would otherwise expect.
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Workcells
typically produce only a limited number of products out of the
factory’s product mix. They therefore
need smaller-scale, lower-volume equipment.
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Cellular
equipment is often simpler, and less expensive than
corresponding equipment in a functional arrangement. Therefore,
low utilization in a cell is less important.
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The
capital freed by inventory reductions usually provides more than
enough money for additional equipment. In
effect, workcells trade inventory for excess capacity. This
tradeoff is usually quite favorable.
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Cells
may share equipment and thereby reduce duplication.Certain
operations can remain centralized.
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The
designer can often build workcells around specific pieces of
large-scale, expensive equipment. Duplication
is then reserved for low-cost equipment in secondary operations.
Functional
layouts usually require the capabilities of Materials Requirements
Planning (MRP) systems. These systems are complex, expensive, and
cumbersome. A a cellular layout allows
simpler scheduling approaches such as kanban and broadcast.
Other
Lean Benefits
Material Handling
Inventory & Scheduling
Quality Benefits
Benefits for People
Customer Benefits |
