Rules of Job Sequencing in Production

One of the ultimate goals in manufacturing is to ensure that all customer demands are produced on time for the lowest cost possible. As most resources in a production facility have limited capacity, it is common to have multiple jobs in the queue, waiting to be worked on by those resources.

One of the challenges faced in the creation of the schedule is determining the order in which jobs are to be worked on. Job sequencing rules exist to assign priority to each job to determine which jobs should be done first. This process addresses potential scheduling issues that may lead to a lack of efficiency.

Deciding on the order of jobs can be a real challenge for schedulers as you must coordinate variables such as material availability, resource capacity, upstream and downstream operations, and the need date - to name a few examples. 

When a sub-optimal schedule is created, you may inadvertently create a ‘waiting line’ in front of slower machines, thereby increasing the number of WIP items and inventory holding costs.

Job Sequencing Rules have been created to help manufacturers and schedulers create optimized production schedules. Your production schedule sets the course for your business performance. An optimized production schedule will ensure that jobs and orders are completed within the timeframe they are given.

Job Sequencing Rules

There are many Job Sequencing Rules that can be used. Here are some of them:

• Earliest Due Date - A common job sequencing technique is to prioritize jobs that have the earliest need date. This can also be referred to as ‘Due Date Assignment’ and it places a high priority on processing jobs with early dues dates in an effort to complete all jobs on time. This technique allows you to measure job shop quality performance through the number of late jobs, average tardiness across late jobs, and average tardiness among all jobs. Although the goal of this technique is to ensure that all jobs are completed before their due date, there can be some inefficiencies in the schedule due to frequent changeovers.
• Longest Processing Time - The longest processing time methods assigns highest priority to jobs with the longest processing time. When scheduling longer jobs at the beginning of the schedule, the schedulers can reduce a large amount of much more time consuming jobs at the end of the job schedule. This form of job sequencing is extremely beneficial to manufacturers as it ensures that long jobs have time to complete before they are needed. This job sequencing technique relies on knowing the processing length for each operation to determine which jobs actually take the longest.
• Shortest Processing Time - Another common method of job sequencing that is based on completion time is the shortest processing time method. This method assigns highest priority to jobs with the shortest processing time. Similar to the longest processing time job sequencing method, this requires a time estimation for each operation of the job. The shortest processing time can effectively reduce the average flow time and minimize the mean waiting time for jobs.
• First-Come, First Serve - The first-come, first-served sequencing method processes orders in the order of their arrival at their production facility or resource. The arrival time is a key component and factor within the job sequencing rule, which is what separates it from methods such as longest processing time and shortest processing time. This method is commonly used in production facilities as it is extremely easy to implement and there is no estimation required for the processing time length.
• Least Setup Hours - This rule is often used in cases where setup or changeover time is incurred when changing from one type of material, dye, or other attribute to another. This is also referred to as ‘sequence-dependent setup time’. This rule will create a schedule where there is the least amount of setup hours required, which is usually achieved by grouping jobs with like attributes together.

The above examples represent only a few of the many job sequencing rules that can be used. Applying these different rules to your production schedule will give you different outputs in which some may be more effective in meeting your business’s goals than others. 

Although these rules may seem simple in isolation, scheduling hundreds of jobs simultaneously requires a lot of information such as the job’s due date, routing, standard setup, processing, whether alternative machines can be used to do the work, the current status of the job, and much more.

We feed it the facts we know, and it automatically proposes an optimized schedule that allows us to meet those dates. It’s something we tried, but never could do manually.

DICK MARX, MATERIALS MANAGER, KNAPHEIDE TRUCK EQUIPMENT

Manual scheduling using spreadsheets can be extremely time-consuming and prone to error. This is why softwares such as PlanetTogether’s Advanced Planning and Scheduling (APS) system are becoming prevalent among manufacturing operations. PlanetTogether allows you to automatically create an optimized schedule based on the job sequencing rules you prefer. 

In PlanetTogether, Optimize Rules are used in conjunction with Release Rules to define scheduling preferences and determine the best sequence of operations. This software also provides users with the flexibility of creating the schedule by using weighted factors and key performance indicators of interest.

Advanced Planning and Scheduling (APS) Software

Advanced Planning and Scheduling Softwares have become a must for modern-day manufacturing operations as customer demand for increased product assortment, fast delivery, and downward cost pressures become prevalent. These systems help planners save time while providing greater agility in updating ever-changing priorities, production schedules, and inventory plans. APS Systems can be quickly integrated with an ERP/MRP software to fill the gaps where these systems lack planning and scheduling flexibility, accuracy, and efficiency.

With PlanetTogether APS you can:

• Create optimized schedules that balance production efficiency and delivery performance
• Maximize throughput on bottleneck resources to increase revenue
• Synchronize supply with demand to reduce inventories
• Provide company-wide visibility to resource capacity
• Enable scenario data-driven decision making

The implementation of an Advanced Planning and Scheduling (APS) Software will take your manufacturing operations to the next level of production efficiency by taking advantage of the operational data you already possess in your ERP system. APS is a step in the right direction of efficiency and lean manufacturing production enhancement. Try out a free trial or demo!