Civil Engineering Reference
In-Depth Information
which makes it easier to transport on conveyor belts. The product can also be equipped
with handholds (permanent or temporary) to simplify manual lifting.
Product design is also important because, by virtue of the design features, certain
manufacturing processes will become necessary. The process equipment may be
available in only one part of the plant, and a transportation need is then created. It may be
possible to move the process equipment, so that it is practical for the manufacture of a
specific product. However, there is usually a mix of products, and expensive process
machinery must be used for many different products. Such issues are then important for
the design and layout of a manufacturing facility.
The purpose of just-in-time (JIT) manufacturing is to structure the transportation
activities. According to this philosophy, smaller quantities of parts are delivered to a
manufacturing plant and then distributed to workstations, just in time for processing and
assembly. The JIT philosophy has an interesting effect in that the need for storage of
parts and products is reduced. Therefore, the manufacturing plant can be made smaller,
and the cost of buying the land is also reduced (in Japan the cost of land is very high,
which favors JIT).
10.8
MATERIALS HANDLING DEVICES
Table 10.9 presents a list of materials handling devices. There are many possible usages
of materials handling devices in receiving, at workstations, and between workstations,
testing, packaging, and warehousing. The usage depends entirely on the application and
the task at hand. We cannot suggest any fixed formula; it depends on the creativity of the
designer. Several of the aids are illustrated in Figure 10.7. Some devices are used for
horizontal transportation in the plant and some of them for vertical transportation. From
the ergonomics points of view it is particularly important to minimize vertical
transportation, particularly if manual lifting is involved. “Don't put it on the floor, so you
won't have to pick it up again.”
It is difficult to avoid horizontal transportation in the plant, although one can try to
minimize the transportation distance by optimizing the layout of the facilities. For
horizontal transportation, conveyors have generic applicability and can be used for all the
different manufacturing stages, including storage in the warehouse. Carts and carousels
are also fairly generic, and can be used at several sequential processes. A cart can be used
as a moveable workstation that is passed down the line. It can be designed so that an
operator can work conveniently at the cart.
Horizontal transportation is continuous and connects the different manufacturing
functions. Vertical transportation is mostly local and discrete, and does not connect the
different systems. An interesting maxim for the design of a plant would be “Minimize the
vertical movement.” This can be done, for example, by removing the top and the bottom
shelves in storage. For JIT, with its minimal requirement for storage, this is not an
unrealistic scenario.
Three of the vertical devices listed in Table 10.9 are automatic: self-leveling tables,
gravity feed conveyors, and overhead balancers. These devices are particularly interesting
because they do not require any action by the worker.
