Page 252 - Orlicky's Material Requirements Planning

CHAPTER 12 Master Production Schedule 231

FIGURE 12-3

A resource requirements profile.

Resource: Total Fabrication

Capacity
Service Parts

Interplant Interplant
Product C Product C
Product C Lot #2 Product C Lot #4
Lot #1 Lot #3 Product C
Lot #5
Product B Lot #1
Product B Lot #2

Product A Lot #1 Product A Lot #2 Product A
Lot #3

Simulating the effect of alternative MPSs is part of the selection/decision process. If
the load generated by a proposed MPS is unsatisfactory (because of significant overload
or underload in one or more periods), the schedule is changed usually on a trial-and-
error basis, and the procedure is repeated. Note that in a business with a line of simple
products made to and shipped from stock, planned-order schedules of a time-phased
order-point system may be used to represent the schedule of factory requirements. The
latter would be converted into an MPS through use of the firm planned-order technique,
which also would be used to modify the schedule. This is diagrammed in Figure 12-4 at
the end of the next section.
In the absence of such a procedure, the MRP system, of course, will process any
MPS, and load will be calculated subsequently. The load report (assuming it is based on
both open and planned orders) then serves as a resource requirements profile, but if it
proves unsatisfactory, the MPS would have to be changed and reprocessed—an unwieldy
and costly procedure. Thanks to the availability of load profiles, a large number of poten-
tial MPSs can be tried for fit in a very short time.
Selecting a feasible MPS is the final step in this process. This ensures that the sched-
ule roughly fits capacity constraints. Further capacity adjustments will be made subse-
quently in the course of short-range capacity requirements planning (see Chapter 13),
when overtime, work transfer, subcontracting, and so on will compensate for the fluctu-
ation of load from period to period. In the typical manufacturing business, the MPS
decided on by management corresponds to some specific rate, or level, of production
(e.g., 60 machines a month, 80 vehicles a day) to which all activities then are geared.
The purpose of resource requirements planning is twofold, as indicated earlier. Over
the short horizon, it is to keep load within the bounds of available capacity. Over the long