Page 233 - Orlicky's Material Requirements Planning

212 PART 3 Managing with the MRP System

FIGURE 11-9 Mechanical Power
Common Stick Shift Automatic Steering Steering
Completed
modularization. A13 C41 D12 L40 Z75

F28 P24 S36 B88 B62

E10 G53

R38 T65

tangled. Either such combinations must be forecast (and form separate modules), or the
items in question can be assigned to more than one grouping in the modularizing
process. For example, item D14 (Figure 11-6) could be duplicated in both the stick-shift
and mechanical steering modules (Figure 11-9), ensuring that it would never be under-
planned. Such duplicating is particularly indicated for inexpensive items of this sort, in
preference to separate forecasting or redesign.

Options Within Options
The option-combination items just discussed represent one type of complication from the
modularization point of view. Another one is options within options. The tractor used in
our example can have four-wheel or three-wheel construction, and an option in the latter
is a single or double front wheel. This is an option within an option, and it calls for estab-
lishing three modules, that is:
1. Items common to the three-wheel-construction option
2. Items unique to the single-wheel suboption
3. Items unique to the double-wheel suboption
The proper treatment of optional product features is overplanning, that is, forecast-
ing and safety stock. This means that a suboption will have to be even more overplanned
than an option. For example, the following sets of items might be scheduled when 300
tractors are to be produced:

Basic tractors (common items): 300
Option
Four-wheel construction: 100
Three-wheel construction: 275
Suboption
Single front wheel: 200
Double front wheel: 125
Note that the option is overplanned by 75 sets of components, but when the subop-
tion is taken into account, the overplanning amounts to 125 sets (100 200 125 425).