Transfer Batch cannot and many Times should not be Equal to the Process Batch:

Lot size is significant variable, which plays important role in inventory make-up and throughput. OPT advocates two lot sizes (instead of one, as in traditional system). These are transfer-batch and process batch. From part of the viewpoint, lot size is the transfer batch size. Though, from resource point of view, lot size is procedure batch size.

Example

Imagine a part requires three operations: drilling, milling, and inspection. The processing time for specific part and for one process-batch of l00 parts is as follows :

Process Batch is Greater than Transfer Batch

While process-batch is same as transfer-batch, the situation is same as in first Figure. Thus, while milling of 100 items is absolute, they are transferred to drilling and so forth. The entire time is 100 hours. if the transfer batch is smaller than process-batch (which is 100), a smaller batch (such as 44 parts, after getting processed on milling, transferred from milling to drilling after every 20 hours; and 57 parts, later on getting processed on drilling, transferred to inspection later than every 20 hours of drilling for this batch) can be transferred; next operation on the process-sheet. The situation can be one like shown in Figure. In the modified scenario, there shall be a substantial reduction in total idle time of machines and overall enhance in the throughput-time. Additionally, there shall be marked reduction in inventory pile- up and operating expense. Therefore, one process-batch (which is 100 in above example) needs one set-up on machines. Although, in every process-batch, there may be more than one transfer to next machines. As depicted above, the smaller transfer-batch (than process-batch) enhances the throughput, decrease inventory pile-up, reduces operating cost and decrease the total busy time of the resources.