Master Production Schedule
The aggregate production plan, as presented in Chapter 15, specifies product groups. It does not specify exact items. The next level down in the planning process after the development of the aggregate plan is the master production schedule. The master production schedule (MPS) is the time-phased plan specifying how many and when the firm plans to build each specific end item. 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 then goes to the next step down in the process and identifies the specific models and sizes of the mattresses. All the mattresses sold by the company would be pecified by the MPS. The PS also states period by period (which is usually weekly) how many and when each of these mattress types is n eded.Still further down the disaggregation process i the MRP program. which calculates the requirements and schedules for all of the raw materials, parts. and supplies needed to make each of the different mattresses that are identified in the MPS.
The question of flexibility within an MPS depends on several factors. including production lead time, the commitment of parts and components to a specific end item. the relationship Second-tier
between the customer and supplier. the amount of excess capacity, and the reluctance or willingness of management to make changes. Exhibit 17.4 shows an example of a master production schedule time fence. Management defines time fences as periods of time, with each period having some specified level of opportunity for the customer to make changes. (The customer may be the firm's own marketing department, which may be considering product promotions, broadening variety, etc.) Note in the exhibit that for the next eight weeks the MPS for this particular firm is frozen. Each firm has its own time fences and operating rules. Under these rules. fro-en could be defined as anything from absolutely no changes in one firm to only the most minor of changes in another. Moderately firm may allow changes in specific products within a product group. so long as parts are available. Flexible may allow almost any variations in products, with the provision that capacity remains about the same and that there are no long lead-time items involved. 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. With the trend towards reducing lead times and increasing product choices. companies are continuously trying to reduce the time period within which the MPS is frozen without wreaking havoc on the factory floor. This allows firms to react more quickly to changes in customer demand. To accomplish this, the overall quantity of products within a product group or family is typically frozen while the mix of products. within the group or family. in terms of specific models. remains flexible up until the last minute,