Scheduling is a challenging area for operations managers. Read this section, which explores scheduling steps and managerial considerations for ensuring quality products or services and optimal operations.
Scheduling is coordinating work tasks, people, materials, facilities, and equipment needed to create goods and services at a specific point in time. Scheduling is required for making goods and for providing services successfully. There are many different approaches to scheduling; some of the most common are discussed here.
Scheduling is the last step in the process that begins with strategic planning and proceeds through increasingly detailed stages. Each successive stage of the planning process builds on its preceding stage. Proper planning in the earlier stages increases the likelihood that a schedule can be created that will meet customer demand at a reasonable cost and without delays.
Scheduling can be one of the most challenging areas of operations management. As many companies have found, scheduling presents many day-to-day problems because there may be changes in customer orders, equipment breakdowns, late deliveries from suppliers, and a myriad of other disruptions. Techniques are very sophisticated mathematically because scheduling problems are often very detailed, have lots of information to consider, and have many possible solutions. Let’s focus on scheduling rules that can lead to good solutions as well as some relatively simple application techniques.
Scheduling is a complex process that involves many different steps. This section summarizes those steps before describing scheduling techniques.
Collecting the data needed for scheduling begins with orders from the customer. These orders identify which product the customer wants, special features, and the product due date, among other things. When data from order entry is combined with process data, the following information about the jobs, activities, employees, equipment, and facilities are available to prepare a schedule.
Order entry drives the scheduling process. Orders may originate with the customer, but they may also be generated by internal or company orders that are given to create inventory. For a make-to-order company, one that produces only to customer orders or that provides services, this occurs when a customer places an order. Given existing production schedules, capacity available, and the customer’s desired due date, the order can be scheduled. This order scheduling will be an estimate based on capacity requirements to produce the customer’s order. Producing the order will require further scheduling of the individual parts and components for a product or the employees and facilities for a service.
In a make-to-stock company, one that produces for inventory and meets customer orders from inventory, production orders are entered by the company based on the inventory level of each item in stock and the expected future demand of that item. In general, a make-to-stock company has a somewhat easier job of scheduling because it has some control over which products will be made. However, unlike a make-to-order company, which must produce whatever is demanded by the customers, the make-to-stock company will have excess inventory if it produces something that customers do not want. This increases costs and may lead to discounting in order to increase sales of an item.
In an MRP environment, the MRP system will generate planned order releases based on the master schedule. This is another form of order entry—in this case, for individual parts or subassemblies.
Orders Released for Production
The planning process involves a continual movement from strategic plans for the distant future toward more detailed plans for the less-distant future. As time frames diminish, plans become more precise and detailed until each order is released for production. At that point, the schedule is implemented.
Scheduling addresses the very near future because it is the last step in production planning. Plans are made to schedule a particular job, activity, or employee, but those plans are not converted into a detailed schedule until the last possible moment. The earlier planning stages determine the level of resources needed to meet the production plan. Scheduling allocates those resources.
When working with such minute details, such as individual machines, parts, or employees, it is always possible that changes will occur. An employee may become ill or quit, a machine may break down, or the raw materials for a part may not arrive on time. Because of these possibilities, scheduling must usually wait until the existing conditions are known with relative certainty. Even then, last minute changes must often be made, which is what makes scheduling so challenging.
As time passes and the scheduled starting time for a job or order is reached, that job or order is released for production. That step starts the job on its way through the processing operations. The final scheduling steps are the sequencing of activities, jobs, or parts in the order they should flow through processing, and then the dispatching of those jobs. Dispatching is the assignment of priorities and the selection of jobs for processing at a work center or facility. For example, a customer order for a made-to-order product must be sequenced with other orders. When the time comes for work to begin on that order, it will be dispatched at the first work center according to its priority at that time.
Scheduling is an attempt to allocate scarce resources efficiently. Machine time may be a scarce resource that is allocated to different jobs, employee time is allocated to different activities, and facilities are scheduled for a given activity at a particular time period. In all of these scheduling tasks, different criteria may be used when deciding which of several schedules will work best. Those criteria may relate to the amount of time equipment may sit idle, the importance of a certain order or a certain customer, or the level at which a resource is utilized.
The task of scheduling can be quite complex; what appears to be an optimal schedule from one viewpoint may be far from optimal from another. For example, a certain schedule may utilize one machine very efficiently, but may mean idle time for machines further along in the processing operations. Another schedule might mean that an important customer’s order will not be delivered on time. These six criteria may be used when evaluating possible schedules:
- Provides the good or service when the customer wants it
- Length of time it takes to produce that good or service (flow time), which includes both processing and waiting time
- Level of work-in-process (WIP) inventories
- Amount of time equipment is idle
- Amount of time employees are idle
- Overall costs
The relative importance of each factor depends on the product or service being produced, a company’s particular industry, and, especially, the organization’s competitive strategy. Different production processes will also incur different problems, and certain criteria will, therefore, be more important. It may be impossible to satisfy all of the six criteria listed above at one time. Instead, management must choose among the various trade-offs (Table 3.1).
|Due dates, routings, material requirements, flexibility of due dates|
|Expected duration, required activities that precede this activity, desired time for completion|
|Availability, capability, efficiency, wage rates|
|Machine or work center capacities and capabilities, cost of operation, availability|
|Capacities, possible uses, cost of use, availability|
When determining which criteria to use, a company must carefully consider its corporate objectives, competitive strategy, and capabilities. The company’s scheduling decisions will have a great impact on facility design, the type of equipment used, and the workforce requirements. Each of these will, in turn, influence its competitiveness in terms of cost, speed, and delivery reliability.
Note. Adapted from “Scheduling,” by M. Vonderembse & G. White, 2013, Operations Management, Chapter 12. Copyright 2013 by Bridgepoint Education, Inc.
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Data collection is one of the steps in the scheduling process. However, data collection can be a whole project where the PERT method can be applied in a manufacturing company that produces vehicles. While using the PERT method, the major activities will include getting information regarding the type of customers, their preferences, the quantity needed, and the time within which the vehicles are required. The events that will take place include assessing the facilities, equipment, employees, and knowledge available to carry out the outline activities and ensuring they are scheduled towards the project’s accomplishment. The optimistic time, the pessimistic time, and the most likely time should also be calculated and run in the (O+4M+P)/6 equation.