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Manufacturing System Design Decomposition™
Illustrative
example
The following
example illustrates how low-level design decisions can be traced to
high-level system objectives with the help of the MSDD. Let us consider the
equipment selection for tempering steering gear racks with two different
machine concepts. Assume that each machine is equally capable of producing
parts to the desired specifications. One machine is a large draw furnace
capable of processing the aggregated demand from customer operations in the
departmental plant. This machine is a “process island.” The throughput time
is 1 ˝ hours. Its cycle time is 5 seconds. Parts flow continuously through
the machine on conveyors. The second concept uses an induction tempering
process. The machine is narrow and is a single cycle automatic machine. The
machine processes a part every 54 seconds at the same pace of its customer
assembly cell. Eleven machines would have to be purchased to have the same
capacity as the draw furnace. Figure 1 shows a sketch and additional
information of both machines.
Figure 1: Two different equipment concepts
The MSDD illustrates
the impact of the different equipment concepts relative to the
manufacturing system design. The draw furnace has a very short cycle time
and is fed by multiple upstream machines. Thus, it becomes difficult to
identify disruptions where they occur (FR-R112), which in turn may lead to
hiding disruptions (if one machine of the multiple machines at the upstream
process fails, the loss in production capacity does not require an
immediate response and may go unnoted). As a consequence, throughput time
variation reduction (DP-112) is difficult to achieve (see left arrow in
Figure 2).
The cycle time of
the draw furnace is five seconds, which makes it very hard to balance the
system (FR-T221) causing process delay (FR-T2). The size of the draw
furnace also hinders the ability to establish a material flow oriented
layout to reduce transportation delay (FR-T4). Both effects will eventually
increase throughput time (FR-113).
The cycle time of
the draw furnace is five seconds, which makes it very hard to balance the
system (FR-T221) causing process delay (FR-T2). The size of the draw
furnace also hinders the ability to establish a material flow oriented
layout to reduce transportation delay (FR-T4). Both effects will eventually
increase throughput time (FR-113), which is shown in the middle arrow of
Figure 2.
Figure 2: Impact of
the draw furnace in achieving high-level system objectives. The design of
the draw furnace (DP) makes it difficult to satisfy the marked low-level
FR’s. The arrows illustrate, which high-level system objectives are at risk
to be satisfied
The draw furnace
also has ergonomic weaknesses (right arrow in Figure 2). The cycle time of
5 seconds prevents man-machine separation (FR-D1) and the size of the
machine requires a lot of walking (FR-D23). Figure 2 summarizes the
discussed relationships. The induction-tempering machine would avoid the
stated problems. The machine could be integrated into a manufacturing cell
to achieve simplified material flow paths (FR-R112), to balance the system
(FR-T221), to reduce unnecessary walking (FR-D23), and to allow the
operator to operate multiple machines (FR-D1).
The discussed example
illustrates the importance of understanding how low-level design decisions
can affect the achievement of high-level system objectives. It also showed
how the MSDD can provide a communication platform for the system design.
Engineers working on equipment selection can determine how their decisions
will affect the layout designers and vice versa.
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