PLANNING AND SCHEDULING THE REPAIR SHOPS OF THE DEUTSCHE LUFTHANSA AG: A HIERARCHICAL APPROACH

To plan and schedule the repair shops for recoverable parts at Deutsche Lufthansa AC, we designed a hierarchical model consisting of two levels. The top level calculates the optimal number of parts in the system to guarantee a certain service level while minimizing the capital tied up in parts. Given this provision, the lower level schedules the repair of parts so that the service level is actually maintained. Using queuing theory, the solution gives special attention to the different hierarchical dependencies. Lufthansa has implemented the model for its repair shops of electronic parts. Their experience with the model is discussed briefly.     

COMPETITION IN REMANUFACTURING

We present a two‐period model of remanufacturing in the face of competition. In our model, an original equipment manufacturer (OEM) competes with a local remanufacturer (L) under many reverse logistics configurations for the returned items. After establishing the Nash Equilibrium in the second period sub‐game, we use numerical experiments for comparative statics. OEM wants to increase L'S remanufacturing cost. Surprisingly, while L competes in the sales market, she has incentives to reduce oem's remanufacturing cost. A social planner who wants to increase remanufacturing can give incentives to the OEM to increase the fraction available for remanufacturing, or reduce his remanufacturing costs.     

MIXED ASSEMBLY AND DISASSEMBLY OPERATIONS FOR REMANUFACTURING

In this paper we consider the problem of designing a mixed assembly‐disassembly line for remanufacturing. That is, parts from the disassembly and repair of used products can be used to build “new” products. This is a problem common to many OEM remanufacturers, such as Xerox or Kodak. We study two main configurations, under the assumption that the disassembly sequence is exactly the reverse of the assembly sequence. Under a parallel configuration, there exist two separate dedicated lines, one for assembly and one for disassembly, which are decoupled by buffers—from both disassembly operations, which have preference, as well as parts from an outside, perfectly reliable supplier. Under a mixed configuration, the same station is used for both disassembly and assembly of a specific part. The problem is studied using GI/G/c networks, as well as simulation. Due to a loss of pooling, we conclude that the parallel configuration outperforms the mixed line only when the variability of both arrivals and processing time are significantly higher for disassembly and remanufacturing than for assembly. Via a simulation, we explore the impact of having advanced yield information for the remanufacturing parts. We find that advanced yield information generally improves flow times; however, there are some instances where it lengthens flow times.     

EVALUATING THE TRADE-OFFS BETWEEN IDLING AND SHUTTING DOWN PRODUCTION LINES IN PROCESS INDUSTRIES

The costs of starting-up and shutting down production lines (and plants) in a process industry are often quite high. Therefore, when a plant's capacity significantly exceeds its forecast demand over an annual planning horizon, a manufacturer must either plan temporary production line shutdowns during the year, or plan to temporarily idle production lines without formally shutting line(s) down. The trade-offs between these two strategies can be complex. In this paper, we propose a methodology to evaluate the impact of both strategies on a plant's production costs by developing an analytical model based on the authors' experience with several process industries.     

A PAVEMENT MANAGEMENT DECISION SUPPORT SYSTEM

We present a pavement management expert system developed by the University of Wisconsin-Madison and implemented within a geographical information system for the Wisconsin Department of Transportation. The system uses pavement data regularly collected on the state's 12,000 miles of highway to assist engineers, planners, and budget analysts' management decisions about pavements to be included in 6-year improvement and 3-year maintenance programs. The system has a three-layer architecture. The lowest level suggests treatments for each of a large number of small segments of highway. The middle layer aggregates segments, suggests alternative treatments, and estimates the cost of each. The top layer prioritizes the projects and incorporates them into intermediate-range plans. The geographical information system environment enables integration of existing databases within the system using a topologically structured geographic database and specialized software.     

ROBUSTNESS OF VARIOUS PRODUCTION CONTROL POLICIES IN SEMICONDUCTOR MANUFACTURING

This paper compares several different production control policies in terms of their robustness to random disturbances such as machine failures, demand fluctuations, and system parameter changes. Simulation models based on VLSI wafer fabrication facilities are utilized to test the performance of the policies. Three different criteria, namely, the average total WIP, the average backlog, and a cost function combining these measures, are used to evaluate performance. Among the policies tested, the Two‐Boundary Control policy outperforms the others.     

TEACHING THE PRODUCTION/OPERATIONS MANAGEMENT CORE COURSE: INTEGRATING LOGISTICS PLANNING ACTIVITIES

This paper discusses the benefits of restructuring the introductory undergraduate production and operations management (pom) course to improve its pedagogical effectiveness and to better convey the importance of integrating logistics planning activities. The introduction of a dynamic integrative semester-long case study which involves students in applying pom concepts and tools through a simulation game is reported.     

MATERIAL PLANNING FOR A REMANUFACTURING FACILITY

This article describes the first fully integrated material planning system to facilitate the management of a remanufacturing facility. A number of firms are already engaged in this activity. They remanufacture automobile, truck, and other vehicle components, like starters, alternators, transmissions, and so forth. These firms take in used components, disassemble them, and assemble saleable products from the good parts they find. There is considerable uncertainty in the supply of used components, the good parts in those components, and the demand for remanufactured products. Our system is based on material requirements planning logic, something that many firms in the industry are already familiar with. Meetings with experts in the industry were used to set the parameters of the system and evaluate its approach.     

A REVIEW OF THE KANBAN PRODUCTION CONTROL RESEARCH LITERATURE

Station interdependence, blocking caused by finite buffer capacities, and periodic material handling make modeling and analysis of kanban-controlled lines challenging. Also, one must consider flows of material as well as flows of kanbans. The many models given in the literature contribute to the confusion and debate that often characterize kanban research. The only element common to all kanban systems appears to be finite buffer capacities. I describe blocking by total queue size, blocking by part type, and the single-card and twocard systems. I review the kanban literature and organize it by type of system and decision area. First, I discuss elements of system design, including setting kanban numbers, performance measures, material-handling frequencies, and container sizes. Then I cover the production control topics of sequencing and batch-sizing. I conclude with a comparison of kanban and conventional methods of production control and with suggestions for future research.     

MANAGING A FLOW LINE WITH SINGLE‐KANBAN,DUAL‐KANBAN OR CONWIP

To control the production of different parts on a single flow line, managers can choose between the Single‐kanban, Dual‐kanban, and Conwip. This paper therefore compares the three different systems. The results show that Conwip consistently produces the shortest mean customer wait time and lowest total work‐in‐process. Our results also contradict the finding of a previous study, which showed that Dual‐kanban performed better than Single‐kanban. The different findings can, however, be attributed to the use of a material transfer policy, which favors the Dual‐kanban modeled in the previous study. Our study shows that transferring replenished containers immediately to downstream stations, increasing the number of cards, and reducing the withdrawal cycle reduce the mean customer wait time significantly.     

POM TEACHING AND RESEARCH IN THE 21st CENTURY

We offer a view of operations management in the future based on a mapping of the field's history. We discuss issues raised by this view of the future that we expect will affect those who will teach and conduct research in operations management.     

A NEW PARADIGM FOR TEACHING INTRODUCTORY PRODUCTION/OPERATIONS MANAGEMENT

This paper postulates that the perception among students that operations management is a tedious, irrelevant subject is a symptom of the lack of a conceptual framework that effectively communicates the importance and relevance of the operations function in a firm. The first half of this paper discusses traditional frameworks, those most frequently found in introductory production and operations management (pom) textbooks, and several alternative approaches to teaching an introductory POM course. The discussion questions whether any of these existing frameworks is sufficient to meet the challenges faced while teaching POM in today's environment and identifies what characteristics an effective framework should possess. These characteristics include defining the scope and bounds of the field, capturing its integrative and system aspects, providing a visible depiction of the framework to aid comprehension, and promoting higher-level thinking (i.e., analysis, synthesis, and criticism) to deepen understanding. This discussion concludes that no current framework meets all of these criteria, therefore there remains a need for a more effective approach for introducing POM. The remainder of the paper describes one approach to conceptualizing the field that satisfies these criteria.     

DETERMINISTIC TIME‐VARYING DEMAND LOT‐SIZING MODELS WITH LEARNING AND FORGETTING IN SETUPS AND PRODUCTION

We study the deterministic time‐varying demand lot‐sizing problem in which learning and forgetting in setups and production are considered simultaneously. It is an extension of Chiu's work. We propose a near‐optimal forward dynamic programming algorithm and suggest the use of a good heuristic method in a situation in which the computational effort is extremely intolerable. Several important observations obtained from a two‐phase experiment verify the goodness of the proposed algorithm and the chosen heuristic method.     

AN EXPLORATORY STUDY OF PATTERNS OF PRIORITIES AND TRADE-OFFS AMONG OPERATIONS MANAGERS

A survey of 15 firms showed that agreement among operations managers on competitive priorities is related to agreement on long-run strategic trade-off decisions and not to agreement on shortrun trade-offs. Furthermore, intended short-run actions were often in conflict with stated competitive priorities. Use of management-by-objectives linked to performance appraisal was related to agreement on competitive priorities.     

LOT‐SIZING RULE AND FREEZING THE MASTER PRODUCTION SCHEDULE UNDER CAPACITY CONSTRAINT AND DETERMINISTIC DEMAND

This paper investigates the performance impact of lot‐sizing rule (LSR) selection and freezing of the master production schedule (MPS) in multi‐item single‐level systems with a single resource constraint under deterministic demand. The results of the study show that the selection of LSRS and the parameters for freezing the MPS have a significant impact on total cost, schedule instability, and the service level of the system. However, the selection of LSRS does not significantly influence the selection of the MPS freezing parameters. The basic conclusions concerning the performance of the freezing parameters under a capacity constraint agreed with previous research findings without consideration of capacity constraints.     

A SINGLE-MACHINE SCHEDULING MODEL WITH FIXED-INTERVAL DELIVERIES

We consider an environment where a production facility modeled as a single machine needs to assign delivery dates to several orders and find a feasible sequence. Tardy jobs are not allowed. The delivery dates are to be at prespecified fixed intervals. The objective is to minimize the due date penalty and the cost of earliness. We provide a dynamic programming-based solution procedure that runs in polynomial time. We develop several dominance results that reduced the computational requirement by an order of magnitude in our computational study.     

OUTPATIENT SCHEDULING IN HEALTH CARE: A REVIEW OF LITERATURE

This paper provides a comprehensive survey of research on appointment scheduling in outpatient services. Effective scheduling systems have the goal of matching demand with capacity so that resources are better utilized and patient waiting times are minimized. Our goal is to present general problem formulation and modeling considerations, and to provide taxonomy of methodologies used in previous literature. Current literature fails to develop generally applicable guidelines to design appointment systems, as most studies have suggested highly situation‐specific solutions. We identify future research directions that provide opportunities to expand existing knowledge and close the gap between theory and practice.