Typically a part is categorized as either a manufactured part or a purchased part with associated planning outputs. However, the manufactured/acquired split feature on the Planning Tab of the Inventory Part window allows you to define a part to be planned, based on the demand percentages to be sourced through manufacturing and purchasing. Planned receipts for the parts with such a split are calculated according to the percentages with order proposals generated for the corresponding quantities. For example, MRP planned part A could be defined as 60% manufactured using the Schedule supply type, and 40% purchased using the Requisition supply type. When MRP generates order proposals, 60% of the planned receipt quantities for any given day are converted to repetitive production schedules, and the remaining 40% of the planned receipts are converted into purchase requisitions.
It is important to be aware of lot sizing rules and rounding issues when considering the use of manufactured/acquired split percentages. When planning receipt quantities, the general rule used by MRP and master scheduling is to apply lot sizing rules before splitting the quantities into the manufacturing/purchasing percentages. For example, if MRP determines a net requirement of eight units, a lot size rule of 10 units is applied to that figure, the planned receipt quantity is rounded up to 10 units. After this lot sizing rule is applied, the 10 units are split into the 60/40 percentages — six units manufacturing and four units for purchasing respectively. If the primary supplier for this part has a minimum order quantity of five units, there would be additional rounding applied within purchasing, resulting in excess order quantities.