How can planners of job shops create realistic production schedules

    September 27, 2023

    Scheduling production in a job shop, or generally in a high-mix low-volume manufacturing company is a Herculean task for planners. The one constant element in the scheduling is the constant change of the schedule. Instead of planners being in the position of processing the jobs in an orderly manner, they are firefighters, because a new unexpected situation in production constantly arises that puts the process and the schedule in jeopardy. 
    Why is that, why can't you set up an orderly schedule for production in an HMLV manufacturing company? Where to start to steer production into orderly, controlled channels? Elmar Karlowitsch wrote an exceptional book "Automatic Finite Scheduling" about HMLV production scheduling and here are his bits of advice:

    Many individual manufacturers do not schedule their jobs at all or only inadequately, e.g. with Excel, although the result of the planning is decisive for success. Here, it is not due to the inertia of the planners or managers to deal insufficiently with scheduling, but simply the complexity that scheduling in an HMLV production environment entails.

    Being aware of the special challenges and characteristics that imply HMLV production scheduling is the first step to better understanding and dealing with scheduling challenges. The second step is to choose the right action to take. The third step is to find a suitable tool that can effectively support the planner.

    Inaccuracy in data input

    As the degree of customization is very high while the respective volumes are small, the estimation of runtimes is difficult and a recurring but necessary task. As there are usually few empirical values based on experience, one has to "live" with imprecise estimates. The inaccuracy inherent in the data input is then inevitably transferred to the scheduling output. In other words: an optimum should not and cannot be aimed at with HMLV scheduling as the entire set of very imprecise input data does not allow for a precise optimum at all. The evaluation of past data is helpful, but additionally bringing in the individual experience of the production planner is even more essential. In general, generating planning data is a process of continuous improvement.

    No upfront calculable demand

    As the scheduling environment of HMLV shops is not stable at all but very dynamic, the demand is barely calculable upfront as it is mostly customer-order driven. Furthermore, the constant unforeseeable incidents force the schedule to be constantly revised. With HMLV scheduling, it is therefore very important to be able to react quickly and flexibly to the constant changes in the environment.

    The main premise of scheduling is on-time delivery

    As mentioned before, in HMLV shops, scheduling is mainly order-focused. This means that on-time delivery and an increase in throughput are the highest prioritized scheduling targets. Even if it is often difficult to convey, resource utilization plays a subordinate role, and idle times of resources in certain time windows even can be intended.

    Many individual routings

    As routings in HMLV environments can be all individual, it is difficult for the planner to gain visibility. In other words: getting visibility of shop floor activities is the key to successful job shop scheduling.

    Importance of a combination of skilled workers and machine

    In a make-to-order company, the shop floor workers' capacity is a limiting factor, as well as the machine capacities, and must be considered in scheduling. The normal case to schedule a job shop operation is to find the best available combination of a needed machine and a worker that has the skill to operate it.

    Lack of shop floor progress information

    The dynamic environment of an HMLV manufacturer must be reflected in the strategy of execution. In this regard, it is essential to authorize the shop floor to make short-run decisions. Hence, the schedule should always function as a guideline including a productive range of making decentral decisions. The progress of the shop floor must also be integrated into the schedule regularly as the dynamic progress of one job has a significant impact on the entire schedule and all other jobs. It follows that the planning accuracy differs in the schedule: due to the importance of the shop floor progress information, the accuracy and feedback of these data have a higher value than data for the rest of the schedule.

    Integrating scheduling into existing corporate planning

    HMLV businesses mostly are small businesses. Hence, the average budget available for implementing and operating consistent scheduling is limited. In addition, most of these companies do not have an established software network system or only use an ERP system rudimentary. As companies usually have great growth potential, the aim must be to integrate HMLV scheduling into the existing corporate planning. In this regard, an Application Programming Interface (API) is a necessary tool to easily realize the matter of interfacing. So APIs are the basis to rationalize data flow and ensure higher process efficiency.

    Advice from a scheduling expert

    "First of all, it starts with one crucial decision: Change things in a structured and sustainable way and have the willingness to invest time and money in doing so. Secondly, it is essential to realize that you are not trying to find the Holy Grail." The citation source is Elmar Karlowitsch, Co-Owner of NETRONIC, a company that owns just plan it, a production scheduling software for HMLV manufacturing. In his book "Automatic Finite Scheduling - A practical guide to master production scheduling if you are a high-mix low-volume manufacturer, he summarizes his insights for successful HMLV production scheduling. Controlling and managing a high-mix low-volume business is a Herkules task for sure, but he experienced that automatic finite scheduling is the way out of the dilemma. If you no longer want to constantly fight new trouble spots in scheduling like a firefighter but want to move to orderly, realistic production scheduling in an HMLV environment, I recommend reading his book  :-) 


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