15.2 Scheduling in Manufacturing
In manufacturing operations, scheduling refers to the process of assigning a sequence of jobs to various machines involved in the production process. It determines the order in which tasks are executed and how resources are allocated to ensure efficient workflow.
Example: Dressing Dolls
To illustrate, consider a simplified example involving the dressing of dolls. Suppose the dressing process consists of three sequential tasks:
- putting on pants,
- putting on socks, and
- putting on shoes.
Assume there are three machines, each dedicated to one task:
- Machine 1 handles pants,
- Machine 2 handles socks, and
- Machine 3 handles shoes.
Now, consider three identical dolls—A, B, and C—that must undergo the same dressing process. Figure 15.2.1 illustrates this scenario. Since all dolls follow the same sequence of operations, determining the job sequence is relatively straightforward. However, scheduling becomes significantly more complex when products require different sequences of operations.
Example Cont: Dressing Dolls
For example, suppose doll A begins the process and takes 30 seconds on Machine 1 (pants), followed by doll B. Simultaneously, doll C starts on Machine 2 (socks), taking 20 seconds. After 20 seconds, doll C is ready for Machine 1.
At this point, a decision must be made:
- Should doll C wait until only doll A finishes on Machine 1 (resulting in a 10-second wait)?
- Or should it wait for both A and B to finish (resulting in a 50-second wait)?
As the number of jobs increases, such decisions become more critical. The complexity of scheduling in manufacturing depends on several key factors:
1. Sequence of Operations
The order in which tasks are performed can vary across jobs. In the doll example, some may follow pants → socks → shoes, while others follow socks → pants → shoes. This variability is more common in batch production systems, where different products require different operations. In contrast, mass production systems—such as a car wash where every car undergoes washing, rinsing, and drying—have standardized sequences, making scheduling simpler.
2. Number of Jobs
Batch production typically involves a variety of jobs, each produced in low volumes. Each job may differ in terms of:
- Required operations,
- Sequence of tasks,
- Processing time at each machine.
For instance, in a cake manufacturing facility, a chocolate cake and a vanilla cake may use the same machines but differ in ingredients, operation sequences, and processing times. This diversity increases setup times and waiting periods, thereby complicating scheduling and reducing productivity.
3. Number of Machines
If only one machine is available, scheduling involves assigning jobs to that single resource. However, most manufacturing systems involve multiple machines, each performing different operations. A manager must decide:
- Whether operations can be grouped and performed on a single machine, or
- Whether they must be distributed across multiple machines due to their distinct nature.
Another common scenario involves multiple jobs being processed on a set of similar machines, requiring careful coordination to optimize throughput and minimize idle time.
“18 Scheduling: Importance and Methods in Manufacturing” from Operations Management by Vikas Singla is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.
