# Beyond Kanban: POLCA-Constrained Scheduling for Job Shops
## 4 Industrial Case: Aerospace Manufacturing Firm
### The Proposed Methodology
#### 4.2.1 POLCA Implementation  
The existing POLCA system is implemented as a fully digital hybrid push-pull control mechanism that, unlike in the Basic Case, constructs loops between pairs of cells rather than between individual workcenters. In the industrial case, workcenters are grouped into cells based on location and type; consequently, it is possible for consecutive jobs within aproduction cycle to be executed on different workcenters that belong to the same cell. This digital POLCA system retains its pull characteristics by requiring virtual POLCA cards to authorize work-in-process (WIP) movements between cells, thereby strictly limiting the WIP for each part number and ensuring that no cell becomes overloaded. At the same time, it incorporates push elements via order release dates provided by the ERP system, which dictate when a job is eligible to enter the production process. For each workcenter, key parameters such as annual working hours and target throughput times are determined, from which a standard WIP level is derived to represent the average processing duration. The standard WIP for a cell is then obtained by aggregating the standard WIP levels of its constituent workcenters. Production cycles are defined by a predetermined sequence of cell crossings, and for each cell a workload quantum is calculated based on the cumulative processing times of tasks performed within that cell. The quantum for a POLCA loop is determined by summing the workload quanta for each pair of consecutive cells. In this digital framework, virtual POLCA cards are managed without any physical representation; instead, each part number digitally subtracts from the available WIP level associated with the cell and its corresponding loop, thereby establishing the total number of virtual POLCA cards available. A traffic-light visual tool is employed to monitor and highlight overload conditions within each loop by comparing the standard WIP level with the post-authorization WIP--which accounts for additional work already in process. The system generates an authorization list for each cell, indicating the sequence of jobs awaiting permission to commence processing. Authorization dates and the dispatching policy are derived from the start times computed by the existing commercial scheduler. Under normal operating conditions, the system adheres to the pre-established schedule; however, if an anomaly is detected, the production controller for each cell can intervene without exceeding the loop WIP norm. In the subsequent shift, a new schedule is generated, and operations resume accordingly.  
Developing an accurate model required substantial data engineering effort. The dynamic data sets extracted from the ERP were subjected to rigorous cleansing. These datasets enabled the precise encoding of POLCA logic within a multi-objective constraint programming (CP) formulation designed to minimize total tardiness and lead times.  
Embedding the optimizer into the shop-floor decision-support process demanded careful change management. A set of post-run analytics and aggregated dashboards was made available to clarify how POLCA and capacity constraints influenced each scheduling decision, significantly improving user acceptance and trust.