Page 250 - Orlicky's Material Requirements Planning

CHAPTER 12 Master Production Schedule 229

4. Simulating the effect of alternative MPSs
5. Selecting a realistic schedule that makes the best use of (existing or planned)
resources
Defining the resources to be considered is a management function. Resources range
from engineering personnel to cash to capital equipment and plant square footage. In the
discussion that follows, only one such resource, productive capacity, will be referenced. For
purposes of resource requirements planning, productive capacity may be subdivided
into individual capacity resources or groups. For example, the entire machine shop may
be defined as a resource, and the impact of a given MPS then is measured in terms of total
load on the shop. Or the shop may be defined as two or more resources by function, such
as heavy casting machining, miscellaneous machining, and sheet-metal operations.
Individual departments or groups of departments may constitute measured resources. A
still finer breakdown would identify work centers or even individual machines. A single
critical machine legitimately may be identified as a resource under this approach.
Resource requirements planning, however, is intended for relatively large group-
ings because its purpose is not to determine the exact load on an individual resource but
rather to evaluate the overall impact of a given MPS. Resource requirements planning is
conducted on a macro level using rough approximations of load, and a precise fit is not
sought. The important thing is to be able to develop the alternative loads quickly so that
several different MPSs may be tried out.
Computing load profiles for individual products is based on the simple proposition
that each (quantity of) product in the MPS generates measurable load and that the same
procedures that are used to arrive at a machine load report can be used to compute a
product load profile. A given load profile consists, for instance, of the standard hours of
fabrication required, by period, to produce one unit of product measured against what-
ever fabrication resource is selected.
The load profile for a given product may be thought of as a load report for a simu-
lated product lot of one computed on a relative time scale. In Figure 12-2, the end of peri-
FIGURE 12-2
Product X
A product load Resource: Heavy Presses
profile for a single
Standard Hours
resource.

1 2 3 4 5 6 7 8 9 10
Periods
Product Lot
Due Date