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Just-in-time (JIT) scheduling is a strategy designed to minimize the quantity of manufacturing work in progress (WIP) and inventories of raw materials and finished goods. Just-in-time scheduling is one aspect of the general principle of just-in-time production. The primary goal of JIT production is to minimize the time between receiving supplies and delivering the finished product to the end customer. Although JIT production was conceived as a standalone methodology (about 50 years ago by the Toyota Motor Corporation), today it is typically considered one aspect of lean manufacturing.
Just-in-time scheduling is the means by which a manufacturer ensures, on a day-to-day basis, that each order is produced with just enough time to achieve on-time delivery. This same objective characterizes just-in-time planning, but the time horizon for JIT planning is weeks or months. Just-in-time scheduling enables a manufacturer to adjust to last-minute changes, which may arise due to work order modifications, time overruns, material availability issues, and other factors. JIT scheduling is designed to avoid late deliveries on the one hand, and a backlog of materials, WIP and finished goods on the other.
By reducing backlogs and inventories, just-in-time scheduling helps companies reduce waste from expired or damaged materials. Manufacturers also cut costs associated with warehousing inventory or stockpiling materials along a production line. With just-in-time scheduling, production cycles can also be optimized so that companies enjoy greater productivity from their manufacturing facilities.
As with other planning and scheduling tasks in manufacturing, the execution of just-in-time scheduling has evolved from a paper-based operation, to an application of general spreadsheet programs, to interactive software systems designed specifically for planning and scheduling. Today, advanced planning and scheduling (APS) systems manage the complexities of manufacturing schedules. APS systems accomplish just-in-time scheduling with powerful tools that account for the many factors that affect the production schedule:
Advanced scheduling software performs complex operations to determine optimal just-in-time production scheduling. These include:
Order-based multi-constraint scheduling—Schedulers can create order-based schedules and apply a ranking or weighting to prioritize the orders. The just-in-time scheduling system creates schedules based on availability of resources, additional constraints and materials required for the order. Schedules can take into account different operation run speeds on different resources, apply sequence-dependent changeover times based on operation attributes, and allow overlaps and slack time between operations.
Advanced constraint modeling—Just-in-time scheduling software models advanced resource constraints, such as rules about concurrent usage, limits on time between operations, and by how much an operation time can be extended.
Advanced material handling—This capability enables the scheduler to implement custom rules about how materials are consumed. When allocating materials, a just-in-time scheduling system filters and ranks data to account for quality-related or customer-specific material usage constraints.
Advanced schedule optimization—Schedulers can define additional schedule optimization rules to address issues like minimization of changeover times, preferred sequencing and campaigning. Composite rules may also be built with the software’s workflow tool.
Assembly process visualization—A just-in-time scheduling system enables users to visualize the assembly process from raw materials through finished goods and sales orders. A graphical view of material dependencies and plots of stock levels over time allow users to see where shortages will occur. The user can choose to keep them as a constraint or ignore them.
Interactive schedule viewing—Just-in-time scheduling systems may be designed to allow staff members to interact with the schedule while preventing them from saving any changes they make. Such viewers enable:
Development environment—Advanced scheduling software allows database schema and constraint model to be altered as required, including adding tables and fields. This means that production schedulers can create custom scheduling rues to solve specific scheduling problems, or they can create custom data manipulation tools for use with the workflow engine.
By employing advanced scheduling software to implement a just-in-time scheduling strategy, manufacturers are able to create realistic just-in-time schedules that account for a high number of complex production variables. As a result, the schedule can be created in a way that optimizes productivity.
Successful implementation of just-in-time scheduling requires close coordination with the supply chain, so the degree of success is dependent on the reliability of supply chain partners. A sudden surge in orders is more challenging to accommodate with the reduced inventories of JIT scheduling. Just-in-time scheduling also may leave a company vulnerable to manufacturing interruptions in the event of natural disasters and other disruptions. Advanced scheduling software builds in contingencies so that each manufacturer can determine the level of risk to be tolerated.