Why You Should Never Do Job Shop Scheduling in Excel
Brian Hoey - June 26, 2018
Fun fact: In computer science, job shop scheduling is considered an NP-hard problem, which in this case means that the problem is complex enough that there is no known algorithm that can solve it quickly under all circumstances. If you’ve ever tried your hand at non-timed production scheduling, you can likely understand why this would be the case. As in the case of the traveling salesman problem (another NP-hard problem that famously involves finding the shortest route between a set of houses that must all be visited), non-timed production schedules generally lack an obvious linear path through the production floor, meaning that finding the option that yields the shortest product makespan is laborious at best.
In spite of the difficulty involved in optimizing non-clocked scheduling by hand, many planners continue to insist on creating these schedules with Excel spreadsheets or pen and paper. In so doing, they potentially waste many hours of labor on tasks that are still unlikely to yield optimized results. Wasted labor, however, is not the only reason that performing job shop scheduling in Excel is a losing proposition.
One of the distinct benefits of job shop production as compared to clocked production is that it implies a certain degree of inherent flexibility. Yes, that flexibility comes at a price of high complexity, but it simultaneously provides an added measure of agility when it comes to reducing makespan and tailoring machine and material usage to granular customer requirements. If planning processes become siloized, however, this flexibility becomes more harmful than helpful, as users lack the comprehensive understanding of their particular job shop operations to make informed decisions on their own.
Unfortunately for Excel devotees, planning in a spreadsheet can often result in information silos that keep mission critical information away from decisionmakers. Because spreadsheets tend not to be highly visible or well-suited to collaboration, relying on them can lead to scenarios in which the complex interrelations between machines, persons, and parts on the job shop floor becomes completely inscrutable. Rather than being able to adjust to changing requirements or stave off pending slowdowns, shorter-term decisionmakers or manual operators are left in the dark, unable to adapt.
Industry 4.0 Integration
The problems of visibility and flexibility are not, of course, isolated questions. On the contrary, a lack of visibility can also prevent job shop scheduling from being effectively integrated with other workflows in an Industry 4.0 environment. Imagine a scenario in which all of your production machinery has been successfully networked into one cohesive, interoperable system, but your production scheduling continues to be done manually in a non-digitized environment. From a technological perspective, you should be poised to take advantage of the increases in efficiency and visibility that are inherent in Industry 4.0 systems, but without a digital planning infrastructure to bring these various touchpoints on the value chain together, many of those benefits remain out of reach. Industrial internet-of-things (IIoT) devices and other smart sensors might be creating an environment for machine-to-machine communication and improved data collection, but that data will likely never reach the planning workflows that could most benefit from it.
In point of fact, there is considerable value to be gained from integrating your non-timed production scheduling into Industry 4.0 workflows. For instance, Industry 4.0 integration represents an opportunity to bring job shop scheduling into a more holistic vision of your overall value stream. Production planners can be more meaningfully tailor their schedules to crucial order and inventory management requirements, while also utilizing machine and other data in a way that adds value and staves off bottlenecks and breakdowns.
Replanning and Looking Toward the Future
Speaking of staving off breakdowns, perhaps the most important reason to avoid scheduling your job shop production in a spreadsheet revolves around one question: what happens to your plans when the unexpected arises? Maybe your factory experiences a machine breakdown. Maybe you fail to receive an important part from one of your suppliers. If your plans exist solely as an Excel file, how will you take stock of your existing resources and reimagine your production programs in a way that maintains as much value as possible? More than that, how will you create plans that are future oriented in the first place, rather than based on past demand and disruptions?
Without a robust, digitized planning infrastructure for your job shop scheduling workflow, agile, rapid replanning in the face of unforeseen circumstances remains a virtual impossibility. Due to the inherent complexity of the task, a manual replanning would often be just as time consuming as the original planning process, meaning that any disruption would immediately become magnified in scope. With a fully Industry 4.0-integrated process, on the other hand, new plans could be created and shared on the fly, freeing up planners to concentrate on building out future-oriented processes that can adapt to changing needs.