This research focuses on the effect of setup time on lot sizing. The setting is the Capacitated Lot Sizing Problem (the single-machine lot sizing problem) with nonstationary costs, demands, and setup times. A Lagrangian relaxation of the capacity constraints of CLSP allows it to be decomposed into a set of uncapacitated single product lot sizing problems. The Lagrangian dual costs are updated by subgradient optimization, and the single-item problems are solved by dynamic programming. A heuristic smoothing procedure constructs feasible solutions (production plans) which do not require overtime. The algorithm solves problems with setup time or setup cost. Problems with extremely tightly binding capacity constraints were much more difficult to solve than anticipated. Solutions without overtime could not always be found for them. The most significant results are that (1) the tightness of the capacity constraint is a good indicator of problem difficulty for problems with setup time; and (2) the algorithm solves larger problems better than smaller problems, although they are more time consuming to solve. This indicates that larger problems may be easier despite the greater computational effort they require.inventory/production: deterministic models, inventory/production: material requirements planning, programming: large scale systems

O perations management (OM) and human resources management (HRM) historically have been very separate fields. In practice, operations managers and human resource managers interact primarily on administrative issues regarding payroll and other matters. In academia, the two subjects are studied by separate communities of scholars publishing in disjoint sets of journals, drawing on mostly separate disciplinary foundations. Yet, operations and human resources are intimately related at a fundamental level. Operations are the context that often explains or moderates the effects of human resource activities such as pay, training, communications, and staffing. Human responses to OM systems often explain variations or anomalies that would otherwise be treated as randomness or error variance in traditional operations research models. In this paper, we probe the interface between operations and human resources by examining how human considerations affect classical OM results and how operational considerations affect classical HRM results. We then propose a unifying framework for identifying new research opportunities at the intersection of the two fields.

In serial production systems, storage may be provided between processes to avoid interference due to lack of synchronization. This paper investigates the behavior of lines buffered in this way and explores the distribution and quantity of work-in-process (WIP) inventory that accumulates. We study simple, generic production systems to gain insight into the behavior of more complex systems. The authors are surprised by the sometimes counterintuitive results, but are joined in this surprise by both academics and practitioners with whom the study has been discussed. Results are presented for: identical workstations with and without buffers; balanced lines in which variability of processing times differs between stations; unbalanced lines; and lines with unreliable workstations. In general, buffers between workstations increase system capacity but with sharply diminishing returns. Position as well as capacity of the buffers are important. These results are preliminary, to be confirmed and extended by further study—indeed, a primary purpose of this paper is to stimulate such study. However, even these preliminary results yield design guidelines that should be useful in industrial practice.

This paper introduces a line of research on capacity-constrained multi-stage production scheduling problems. The first section introduces the problem area as it arises from a failure of MRP systems. Then a review of the literature and an analysis of the type of problems that exist are presented in §2. Section 3 outlines linear and mixed integer-linear programming formulations. These formulations compute the required production lead times according to the demands on available capacity, thereby reducing in-process inventory compared to the usual practice in MRP. A discussion of how to use the LP version is included. However, the size of the problems in practice implies that more efficient solution techniques must be found. The final topic of this paper, Product Structure Compression, is introduced as a method to reduce the size of the problem without losing optimality.inventory/production: material requirements planning, programming: large-scale systems, programming: integer, applications

This paper concerns the modeling of low inventory lines. Currently, most models assume that processing times are independent. We consider the differences in behavior of workers in low- and high-inventory production lines. Using a laboratory experiment we show that workers speed up when they are the cause of idle time on the line. This means that processing time distributions are not independent of the size of the buffer, of the processing speed of co-workers, or of the amount of inventory in the system. We show that the direction of these effects is predictable and that the magnitude is significant. In particular, there is less idle time and higher output than would be predicted using assumptions of independence. In this experiment the effect completely canceled productivity loss due to blocking and starving. This work is important in understanding both the motivation of workers in low-inventory systems and the implications of models of manufacturing flow lines.JIT, Serial Production Lines, Independence Assumption, Job Design

No abstract

Flexible work assignment has great potential to increase productivity. When bottlenecks develop, for example, downstream operations may halt for lack of materials. A flexible worker can prevent this by moving in and increasing capacity temporarily, thereby avoiding work stoppages. In practice, it is not that simple. This paper identifies several “negative side effects” that occur in systems that rely on worker flexibility, effects that may partially or totally offset the advantages. Research has shown that performance feedback and work interruptions are factors that may explain some of these effects. Behavioral theories about those two factors lead to a series of hypotheses and two experiments. The results show that productivity loss due to these behavioral effects can be significant, in both the statistical and managerial sense of the word. Implications for the design and operation of flexible work environments are discussed, including methods for mitigating or eliminating the negative side effects, resulting in a meaningful productivity gain.

This research addresses a system of flexible worker assignments in a setting where there are more workers than machines. When organized using this system, a production line balances itself by shifting the workloads continuously and automatically in response to changes in the state of the system. The system is, in effect, buffering itself against variation by altering the work assignments on the fly. This allows the system to operate with very low levels of work-in-process inventory (WIP). In this paper, the workers (rather than machines) are the factor that limits the rate of output. We also assume that the line has a "U" shape, but many of the results do not depend on this topology. An industrial example is described. The system has some interesting and counter-intuitive properties which we demonstrate under a variety of circumstances through an exploratory approach that uses both Markovian and simulation models. Several different policies are compared under conditions of processing time uncertainty. We demonstrate that a flexible assignment system can outperform fixed assignments in a variety of circumstances. Of particular interest is the near absence of balance delay, even when the tasks cannot be divided equally among the workers.work sharing, line balancing, low WIP, on-the-fly assignment, U-shaped