Principles of Sequencing and Scheduling, 2nd Edition

12Lot Streaming Procedures for the Flow Shop

12.1 Introduction

Lot streaming is the process of splitting a job into sublots so that its operations can be overlapped. We can think of lot streaming as a special type of lot splitting. The term lot splitting refers to breaking a given lot size into smaller sublots during production. The lot size itself is a predetermined quantity, typically set by the customer or by planning processes that precede scheduling. The opportunity to split lots arises in the short term – in the implementation of a detailed schedule – and two cases are worth distinguishing. The more common case involves interrupting a job, performing other kinds of work, and later returning to finish the interrupted job. We refer to this phenomenon as preemption, which is motivated by a desire to implement appropriate priorities in a situation where two or more jobs compete for limited resources.

The second case involves overlapping operations for a given job. Before an entire job is complete on a particular machine, some portion of the job is moved ahead to a downstream operation. We refer to this case as lot streaming, which is motivated by a desire to move a job through several work stations as quickly as possible. Lot streaming is distinct from preemption because it deals with a particular job: Rather than give priority to another job, the objective is to expedite the current job. Expediting by preemption can cause cascading instability, so it is often considered ...