Production planning and control
The aim of production control is to implement the specifications of production planning in production in the best possible way and to integrate production plans into the daily production process. DIN 19226 defines production control as: “[…] a process in a system in which one or more input variables influence the output variables due to the laws of the system”. In order to continue the planning contents, it is the task of production control to transfer them to concrete work instructions and to ensure that the order is completed on time and in quality. This corresponds to task fulfillment and includes all measures necessary for production execution in order to control the material flow so that the orders pass through production without delay. Here, the availability of capacities is checked, production orders are released, production progress is monitored and, if necessary, adjustment measures are carried out in the event of target/actual deviations. In addition to order initiation, order monitoring plays a significant role in ensuring that targets are met.
The starting point for order initiation is the results of finite scheduling, which are presented in the form of rough-cut planning for the manufacturing orders. The task of order initiation is to release the concrete production orders for a specific planning period. Within the framework of detailed planning, an availability check of required resources, a machine allocation plan as well as sequence planning for optimal order processing are also carried out. One challenge of order release is the objective of minimizing lead times while maximizing capacity utilization. This means releasing production orders in such a way that capacity utilization is as high as possible and lead times are as low as possible.
Part of the availability check is the verification of the provision of materials, tools and employees for the completion of the dispatched orders. The production control tasks start with the availability check for individual workshop orders. In this context, after scheduling and releasing the workshop orders, their material and capacity feasibility is checked. The release note for detailed scheduling is only to be issued if the start date is secured by the provision of materials on the basis of lead time scheduling and capacity planning. In case of missing availability, an adjustment of the detailed scheduling or even of the production program is necessary.
Sequencing determines a concrete processing sequence of the production orders in which the operations are processed on the operating resources. Within a planning period, different production orders are available for processing at a capacity and thus generate a queue within the processing. While adhering to the required end dates, sequence planning strives for an optimal processing sequence with the help of selected criteria. Possible criteria can be fixed selection criteria, such as priority rules, or accumulation criteria in the form of minimizing setup times. The production orders in the queue are re-sorted according to their deadline urgency, marked by a priority number and thus receive the new positioning in the processing sequence. Order changes can still be made up to immediately before the order is released. The sequence planning is followed by a division of the work contents and an allocation to individual workstations. The result of sequence planning is a work distribution list, which is presented in the form of a plant-related schedule. Accordingly, production orders are assigned to individual machines or individual work steps in the machine assignment schedule. After detailed scheduling and detailed resource planning, the order is released according to different procedures or rules. The release initiates the provision of resources with all associated material, wage and confirmation slips and activates the order in production. As soon as an order has been released, the orders are executed in the specified sequence.
The core task of order monitoring is to provide feedback information on order completion during production in order to compare the actual data with the target specifications and, if necessary, to take corrective action. Due to the high level of detail of the detailed schedules, order progress monitoring is usually performed decentrally in the individual production areas. Machine and employee-related data are collected for capacity monitoring. The basis of any order progress monitoring is store floor data collection (SFDC) for monitoring both orders and capacities. Machine-processable operating data focuses on collecting and displaying order-, machine-, employee-, and material-related data. Order monitoring requires data on the start and finish dates of the operation, the time of interruption, the order quantity, number of good and scrap parts, and the resumption of interrupted operations. The results of order monitoring are forwarded to all adjacent PPS areas and are of an informal nature. In addition to order monitoring, it is also necessary to monitor the scheduled resources and to constantly control their load situation. As soon as an under- or overload of the capacity limits is detected, changes are made in detailed scheduling or sequence planning. On the material side, the reasons for delays are to be checked. If disruptions occur, they are to be adjusted to the original order specifications with the least deviation. In most cases, they are realized by building up inventory flexibility, in the form of process, product and potential reserves. However, preventive measures are to be taken to ensure production execution and to achieve the PPS targets.