BATCH PROCESSING

11.9 BATCH PROCESSING

In typical manufacturing environments, it is quite common to encounter processes or machines that operate on a number of jobs (product units) as a group. The group size is usually a prescribed fixed number, but it may also be random. In many cases, the group of jobs becomes a permanent assembly and continues its manufacturing process as a single unit. In some cases, the converse occurs, and a group of jobs is split into the constituent individual members. In manufacturing parlance, job groups are said to be processed in batches. Examples of batch processes include painting, heat treatment, packaging, various assembly and montage operations in the auto and electronics industries, as well as a variety of operations such as sterilization, shaking, and centri- fugation in chemical and pharmaceutical facilities and many others. The Arena con- structs that support group processing functionality are the Batch and Separate modules. The Batch module supports both permanent and temporary batches. Conversely, the

Figure 11.31 Dialog spreadsheet of the Statistic module with Output statistics for estimating delay probabilities in the packaging buffer.

254 Modeling Production Lines Separate module recovers the constituent individual members of temporary groups;

permanent groups cannot be split into their constituent members. To illustrate batch processing, we modify the failure-modified packaging line of Section 11.7 by incorporating batching and separating, as shown in Figure 11.32, and refer to this system as the batch-modified packaging line model. Let product unit interarrival times in the batch-modified model be uniformly distributed between 5 and

10 seconds. Assume that Labeling Process labels batches of five units at a time, following which the units proceed separately as individual units. Assume further that batches of 10 units are packed together in Packing Process. Each batch labeling time is

25 seconds, and each batch packing time is 30 seconds. To enable batching and separating, we need to increase the buffer capacity at Packing Process to accommodate batches. For simplicity, we just set all buffer capacities to infinity, thereby eliminating blocking. However, machine failures and stoppages are retained in the batch-modified model. We are interested in the mean flow time of unit entities from their arrival at queue

Filling Process.Queue until their arrival at module Interdeparture Time. Figure 11.33 displays the dialog box of the first Batch module following the capping operation. This Batch module, called Batch 1, collects unit entities into temporary batches (Type field) of size 5 (Batch Size field). Recall that labeling is then carried out for each batch as a whole. The Rule field specifies that batches will consist of any unit entity (option Any Entity), rather than restricting batching to unit entities with the same value of a prescribed attribute (By Attribute option). Next, the Temporary option in the Type field displayed in Figure 11.33 specifies that this batch is to be split later on (as opposed to the Permanent option). Finally, the Save Criterion field is used to select

Figure 11.32 Arena model for the batch-modified packaging line system.

Modeling Production Lines 255 the set of attributes associated with each batch. For example, in the dialog box of Figure

11.33, the option Last was selected, indicating that batch attributes are inherited from the last unit entity of the batch (the one that completes the batch). Following the labeling operation, each batch enters the Separate module called Split, whose dialog box is displayed in Figure 11.34. The Split Existing Batch option in the Type field stipulates that batches are to be split back into their individual constituent members. The other Type field option, Duplicate Original, is used to create duplicates of the entity that enters this module. The option Retain Original Entity Values selected in the Member Attributes field ensures that the original attributes of all batch members will be recovered upon splitting.

After the sealing operation is completed, the units are packed at Packing Process into carton boxes in batches of 10. Package entities then enter additional modules, where they

Figure 11.33 Dialog box of the Batch module Batch 1.

Figure 11.34 Dialog box of the Separate module Split.

256 Modeling Production Lines are counted and their system flow time is tallied before being disposed of at module

Finished. The simulation Resources report for one replication of the batch-modified model is displayed in Figure 11.35. Finally, the corresponding User Specified report is displayed in Figure 11.36.