Operations and Supply Chain Management The Core

MATERIAL REQUIREMENTS PLANNING chapter 9 269
The Aggregate Plan and the Master Production Schedule for Mattresses
exhibit 9.3
Aggregate Production
Plan for Mattresses
Month 1 2
Mattress production 900 950
Master Production
Schedule for
Mattress Models
Model 327
Model 538
Model 749
Week
1 2 3 4 5
200
100 100
100
400
150
6 7 8
200
200
100
100
200
∙ Be visible to all levels of management.
∙ Objectively trade off manufacturing, marketing, and engineering conflicts.
∙ Identify and communicate all problems.
The upper portion of Exhibit 9.3 shows an aggregate plan for the total number of mattresses
planned per month, without regard for mattress type. The lower portion shows a
master production schedule specifying the exact type of mattress and the quantity planned
for production by week. In month 1, for example, a total of 900 mattresses are scheduled:
600 Model 327s, 200 Model 538s, and 100 Model 749s. The next level down (not shown)
would be the MRP program that develops detailed schedules showing when cotton batting,
springs, and hardwood are needed to make the mattresses.
To again summarize the planning sequence, the aggregate operations plan, discussed in
Chapter 8, specifies product groups. It does not specify exact items. The next level down
in the planning process is the master production schedule (MPS). The MPS is the timephased
plan specifying how many end items the firm plans to build, and when. For example,
the aggregate plan for a furniture company may specify the total volume of mattresses
it plans to produce over the next month or next quarter. The MPS goes the next step down
and identifies the exact size mattresses and their qualities and styles. All of the mattresses
sold by the company would be specified by the MPS. The MPS also states period by period
(usually weekly) how many of these mattress types are needed, and when.
Still further down the disaggregation process is the MRP program, which calculates and
schedules all raw materials, parts, and supplies needed to make the mattress specified by
the MPS.
Time Fences
The question of flexibility within a master production schedule depends on several factors:
production lead time, commitment of parts and components to a specific end item,
the relationship between the customer and vendor, the amount of excess capacity, and the
reluctance or willingness of management to make changes.
The purpose of time fences is to maintain a reasonably controlled flow through the
production system. Unless some operating rules are established and adhered to, the system
could be chaotic and filled with overdue orders and constant expediting.
Exhibit 9.4 shows an example of a master production schedule time fence. Management
defines time fences as periods of time having some specified level of opportunity for the
customer to make changes. (The customer may be the firm’s own marketing department,