For example, you can easily change the master production schedule for an item beyond its cumulative lead time, with little effect on related material and capacity plans. For example, suppose you define the demand time fence for an item as the cumulative manufacturing lead time and the planning time fence as a user-defined time. Time fences are boundaries between different periods in the planning horizon. For example, you can easily accomplish changes to the MPS beyond the cumulative lead time while changes inside the cumulative lead time are more difficult to accomplish. For example, changes to the master production schedule can be accomplished easily beyond the cumulative lead time, while changes inside the cumulative lead time become increasingly more difficult to a point where changes should be resisted. The extend of the frozen zone is defined by the demand time fence.
Planning time fence: basically it is the period in which no changes to the plan happens automatically through MRP run. Example: it will not change the planned requirements even if you carry out MRP run if it is with in Planning time fence. The following example illustrates the basic components of a master schedule. The demand time fence (DTF) is a point in time at which master schedule review procedures and projected available balance (PAB) formulas change. 1) That point in time inside of which the forecast is no longer included in total demand and projected available inventory calculations; inside this point, only customer orders are considered.
For periods 1,2,3 before the demand time fence it is calculated as: PAB prior period PAB or on-hand balance + MPS – customer orders For periods 4,5 after the demand time fence it is calculated as: PAB prior period PAB + MPS – greater of customer orders or forecast PAB4 20 + 100 40 80 Week 1 2 3 4 5 ForeCast 40 40 40 40 40 Customer Orders 39 42 39 33 23 MPS 100 100 Projected Available Balance 40 1 59 20 80 40. 44 PRODUCTION PLANNING, MASTER SCHEDULING AND SALE Example The demand time fence is the end of week 3, the order quantity is 100, 40 are available at the beginning of the period. A master production schedule (MPS) is a plan for individual commodities to be produced in each time period such as production, staffing, inventory, etc. The MPS translates the customer demand (sales orders, PIR’s), into a build plan using planned orders in a true component scheduling environment. An example of a master production schedule for product A.