1. Introduction

Today companies compete not only on price and quality, but on their ability to reliably deliver products on time. A good operational production schedule, therefore, influences a company’s throughput, sales, and customer satisfaction. Despite investing millions in Enterprise Resource Planning (ERP) and Manufacturing Execution Systems (MES), many companies find these systems inadequate for detailed production scheduling, leading them to rely on manual methods such as Excel and planning boards. Meanwhile, industry trends towards reduced inventory, shorter lead times, increased product customization, SKU proliferation, and flexible manufacturing make production scheduling more complicated. Creating a feasible plan requires the simultaneous consideration of materials, labor, equipment, and demand. The complexity of scheduling is too taxing for manual planning methods or optimizer/solver-based approaches, which deliver diminishing value as manufacturing speed and agility increase to meet market requirements.

At the core of effective factory scheduling is the concept of an actionable schedule. An actionable schedule is one that fully accounts for the detailed constraints and operating rules in the system and can therefore be executed in the factory by the production staff. One common problem with many scheduling solutions is that they overlook one or more detailed constraints, making them impractical to implement on the factory floor. A non-actionable schedule requires the operators to step in and override the planned schedule to accommodate the actual constraints of the system.  At this point the schedule is no longer being followed and local decisions are being made that affect system KPIs in ways that are not visible to operators and stakeholders throughout the supply chain. In a more volatile world with increased production and supply chain complexity, higher product mix, shorter order lead times and smaller batch sizes, it is essential to have the ability to rapidly create feasible schedules that are executable on the factory floor. Manufacturing is becoming more agile and automated to support this dynamic flow of product to the market, based on actual demand and therefore the ability to create an actionable schedule in near-real time is becoming a requirement and no longer just an option.

The fundamental differences between various scheduling approaches can be illustrated with a simple example which highlights the core distinctions at a fundamental level. As production processes become more complex, requiring more agility, the differences in results between the scheduling systems become even more profound and impactful on the factory floor. This example will illustrate the clear advantages of the Simulation Event-Based approach to support the manufacturing and market demand requirements that exist today.

2. Factory Detailed Scheduling Approaches

The three most common approaches in use today to solve the operational scheduling problem include: 1) manual methods using planning boards or spreadsheets, 2) Resource Calendar-Based models, and 3) Simulation Event-Based models.

2.1 Manual Methods

The most common method in use today for operational factory scheduling is the manual method, typically augmented with spreadsheets or planning boards. This process is labor intensive, requiring multiple people to only focus on the generation of schedules and related files. These employees have tribal knowledge of the business rules and experience, if they leave the company, the rest of the organization will be left in the dark about how planning is performed. The use of manual scheduling is typically not a company’s first choice but is often the result of a failure to succeed with automated scheduling systems.

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