Repetitive Lots: Flow‐time Reductions Through Sequencing and Dynamic Batch Sizing

Abstract

This paper presents a new integrative concept for job sequencing, dispatching, and lot sizing. The interrelation between these procedures and their impact on flow-time performance is examined in a capacitated production environment. Gcnaally, lot-sizing decisions arc made without regard to shop conditions and do not consider their impact on job sc quenang procedures. The repetitive IOU (RL) concept (dcveloped and tested in thir papa) attempts to integrate these decision pmccsses.RL uses a number of features whch have not been considmd jointly in either the lotsizing or jobdispatching/sequencing literaturn These include operation batch sizes which vary by operation. transfer of work within the shop in quantities kss than operation batch size, and the usc of overlapped operations. A simulation modd is used to analyze flowtime characteristics in a hypothetical production system. ltaditional measures of flow-time performance arc compared 10 a set of nontraditional measures which capture the interaction between lot sizing and the sequencing procedure used. Subject Anax Phnnhg and Control, Producrlon/Opmrtloru Management, Scheddha and Sbnrrbrlon INTRODUCIIONThe repetitive lots (RL) concept introduces an alternative procedure for controlling the flow of materials through a production system. The procedure allows the benefits of small lot production normally associated with just-in-time (JIT) systems. However, RL does not require the significant reduction in setup times normally associated with the JIT approach.Procedures based on the RL concept incorporate a new type of sequencing logic which dynamically determines run lengths at each operation based on queue characteristics. These dynamic run lengths manage capacity utilization by controlling the setup frequency. Applying the concept results in significant reduction of flow time and flow-time variability.In this paper, we refer to job sequencing as the process of determining the order in which jobs are processed at a work center. The sequencing decision procedure has two basic elements. The first is queue discipline, which determines the ordering or ranking of jobs within the queue. The second element is job selection, which in traditional studies has been first in queue (FIQ). The RL job selection rule varies based on the state of the machine and its queue.The impact of job sequencing on system performance measures such as flow time and work in process is well documented by the literature Blackstone, Phillips, and Hogg [ 11 provide a comprehensive survey of procedures, evaluation criteria, and research findings. These findings view the determination of job characteristics (such as order sizes) as a process independent of the sequencing decision.

Discrete Lot Streaming In Two-Machine Flow Shops

“…From (12), (13), (14), (15) and (16), we see that x' yields a shorter critical path than x. D Case 2p I = P2 Theorem 6 If PI = p 2 , then there is an optimal solution x and sublot k such that i) k and every sublot before k is critical, i. e., Mi(x) = M(x) for 1 < i :S k; ii} every sublot after k is non-critical, i. e. , Mi(x) < M(x) for k < j :S s.…”

“…Goyal [11] finds the optimal sublot sizes in Szendrovits' model. Moily [15], Jacobs and Bragg [13], Kulonda [14] and Graves and Kostreva [12] also demonstrate reductions in production time and cost by using transfer lots. Steiner and Truscott [21] find the optimal lot streaming schedules in an open shop with equal size transfer lots and no idling on the machines.…”

The impact of delivery lot splitting on delivery reliability in a two-stage supply chain

“…This is due to the mechanism of overlapping operations: by allowing transportation of partial orders to a downstream stage in the production process, this stage can already start working on these partial orders while work proceeds at the upstream stage, thereby accelerating the progress of work through the production chain (e.g. [11], [13], [19], [25], and [40]). From Figure 1, it is indeed evident that the production order flow time F is shorter in case of the lot splitting policy.…”

Analysis of gap times in a two-stage stochastic flowshop with overlapping operations

“…This is due to the mechanism of overlapping operations: by allowing transportation of partial batches to a downstream station, this station can already start processing these partial batches while work proceeds at the upstream station, thereby accelerating the progress of work through the production facility (e.g. Graves and Kostreva 1986, Jacobs and Bragg 1988, Litchfield and Narasimhan 2000.…”