## 2 Practical Problem Identification
### Production Planning and Control System  
Before embarking on the comprehensive scheduling project, the SME operated on a hierarchical two-tier planning structure. At the most fundamental level, the aggregate production planning (APP) module manages demand across a yearlong time horizon. This purpose may be accomplished via the use of component families, rather than just end products. At this level, only common items with the greatest wait times, such as metal castings, may be purchased or ordered. The master production schedule (MPS) module augments the highest level by constructing a plan with a three-month time horizon in mind. Additionally, this module manages demand in the context of end-product families rather than component families. In a nutshell, the inputs are demand predictions and executed orders, while the output is the master manufacturing schedule. The schedule's applicability is determined by a first-level rough-cut capacity check, which is conducted manually by the planner, who compares the schedule's resource capacity requirements to a rough estimate of available machine pool capacity. Monthly revisions are made to the timetable to account for unforeseen occurrences that occurred during that time period. Mid-term planning is the second planning stage, which employs a hybrid MRP- periodic batch control (PBC) technique. Although the PBC approach is geared toward cellular manufacturing rather than functional layouts [17], the SME makes use of fundamental concepts such as planning periods and backward planning to achieve a higher level of visibility than myopic standalone MRP implementations provide. The MPS data are utilized to determine component and material needs and generate the requisite manufacturing orders. The final product requirements will be decomposed into component requirements and allocated to certain times and machine pools through a BOM explosion. The period is seven days long, and allocation starts with the lock assembly in the last period and progresses backward until the first day of the first period, which often includes the casting process. The ordering strategy is not lot-to-lot as it is with standard PBC, but economic production quantity (EPQ) states that a specific number of extra components must be produced in order to fully benefit from extended setup periods and build safety stocks. Weekly revisions are made to the final plan based on comments from the detailed scheduling module, which will be covered later. The procedure makes use of predetermined, set lead periods that are, in essence, equal to the planning period. Apart from the production plan, the MRP-PBC module produces an order backlog, including fresh and delayed production orders. Typically, the backlog is accompanied by a report detailing the capacity status of all work centers in the machine pools, allowing the planner to undertake a rough-cut capacity check on a second level. Due to the fact that this is not an automated process, the planner must release orders from the backlog to the shop floor while taking into consideration overcrowded machines, the period duration, and late orders. Production orders are issued based on the unification of the bill of materials and routings [18]. This approach was created in order to minimize the computing effort required to execute the MRP-PBC. Simultaneously, this technique resulted in the creation of stock-keeping units (SKUs) and single-phase routings for each BOM component, a proliferation that was somewhat mitigated by the introduction of phantom SKUs, or SKUs for which inventory was not maintained. Due to inconsistencies between the production planning and controlling (PPC) and ERP systems, phantom SKUs were subsequently abandoned, resulting in the issue of production orders for all components and impeding inventory control. From a planning standpoint, the primary disadvantage of this strategy is the massive volume of orders that pass through the shop floor at any one time, severely impairing the planner's planning and monitoring capabilities.