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Chasing due dates? There is a better way.

Article Excerpt
EXECUTIVE SUMMARY

One reason it's difficult to meet due dates is that they are often set badly, with managers relying on simplistic scheduling methods that do not account for the current workload. The availability of reasonably priced and easy-to-use finite scheduling software can be a boon to managers who can use it to create due dates that account for the dynamic nature of production.

Why chase due dates? Because they're important. Customers expect delivery as promised. This is truer now than ever before as more manufacturers lean out their production processes and shift to just-in-time processes.

One reason it's often difficult for organizations to meet due dates lies with the dates themselves. Sometimes they are set badly or agreed to unwisely, which offers little hope of meeting them. Often there is no real basis for setting reasonable due dates--managers simply rely on rules of thumb (like eight times the standard hours for doing the complete job) that offer no consideration of the current or projected workload in the shop. Sometimes unexpected problems develop in the shop--machines break down, mw materials arrive late, jobs get lost, or extra workload consumes time on critical machines. Sometimes new jobs show up with earlier due dates or old jobs get assigned new due dates because of customer requirements.

Beyond the problem of badly set due dates is the issue of naive management and scheduling of resources. The approach used in many firms is to release jobs to the floor well in advance of the due date with the notion that the jobs will flow through work centers in sufficient time to meet the due date. Each work center manages jobs independently using one of several well-known rules to prioritize jobs through the center, the most common of which is first-in-first-out. The underlying idea behind this behavior is that each new job will have a later due date than jobs already in the system. This may not be the case:

A customer may request a job earlier than others or the job may require a greater number of operations.

Recognizing this possibility, some work centers prioritize jobs for a given day or week based on the due date of each job. While this is often better than the FIFO approach, it ignores the amount of time each subsequent work center might need to perform required work. For example, a center supervisor would place the job that has a due date 10 days from today behind a job that has a due date five days away But it could be that the job due in 10 days requires four more operations, each of which takes two days, while the job due in five days is at its final stage of work and could be completed in two days. In this case, the better choice would be to start the job due in 10 days ahead of the job due in five.

Often, there is little recognition of the workload in other work centers, which can lead to a situation in which a lathe work center supervisor would process a job scheduled for a mill operation--a work center that is already loaded and running behind--ahead of jobs that could move an idle work center.

The above situation depicts a dynamic job shop situation in which jobs are received and are worked through a sequence of operations to completion and shipment. While the jobs are being worked, new jobs arrive. Due dates are set for the new jobs and they too enter into the various work centers and compete for resources. We assume that meeting due dates is important and that some prioritization rules are used in each work center, but the problem often associated with relying on prioritization in the work center is that the work center supervisor generally does not have the big picture.

The big picture would include a view of not only all the operations required for any specific job but also the operations and due dates for every job in the shop. It would have a view of not only what has been done on each of these jobs but also what remains to be done, as well as a view of the flows of all jobs to each work center.

An approach that provides and uses a big-picture tactic is finite scheduling. Finite scheduling enables a firm to process jobs in a way that best meets due dates and most effectively uses resources. Not long ago, this approach wasn't feasible, but because of greatly increased computing capabilities, firms of...

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