Line balancing in a just-in-time production environment: balancing multiple U-lines

The introduction of multiple, independent production lines has helped many firms to increase their production flexibility, provide for redundancy when equipment breaks down, reduce idle time and labor costs, and achieve many other benefits. This paper introduces and formalizes the multiple U-line balancing problem. Optimal solution methodologies are provided for Type I (minimize the number of stations for a given cycle time), Type II (minimize the cycle time for a given number of stations), and cost-minimization line-balancing problems. A branch-and-bound algorithm is also developed for the situation in which equipment requirements are dependent on the line configuration and the task assignment to stations. Computational results indicate that the greatest benefit of exploiting multiple lines occurs for smaller cycle-time problems that require higher output.     

Cyclic scheduling in synchronous production lines

In this paper we address the scheduling problem in unpaced synchronous mixed-model production lines operated under a cyclic scheduling policy. We first discuss operations of a production line with the synchronous transfer of parts. We then present an integer programming formulation of the problem. The problem, however, is W-hard, and for its exact solution we propose an implicit enumeration scheme. We discuss a property of the scheduling problem which allows us to effectively solve large size instances of the problem. We also present an approximate solution procedure with very good avenge performance. Useful managerial insights are obtained as we search for ways to improve the performance of synchronous lines. The relaxation of one of our original assumptions in the scheduling problem formulation results in an easy problem whose solution generates the absolute best in throughput performance configuration of the production line. Implementation of this solution, however, requires increasing the number of buffers in the line. We suggest other performance improvement ways to better balance the tradeoff between throughput and average Work-In-Progress (WIP) inventory in the line.     

Flow-line scheduling problem with controllable processing times

In this paper we address the simultaneous scheduling and optimal-processing-times selection problem in a multi-product deterministic flow line operated under a cyclic scheduling approach. The selection of processing times plays an important role in achieving the desired production rate with the least possible operating cost. We first formulate the important subproblem of optimal-processing-times selection for different objectives, when the sequence of jobs is fixed, and then develop an efficient solution procedure for it. The fast solution of the fixed sequence problem is necessary for the development of efficient approximate solution procedures for the simultaneous scheduling and optimal-processing-times problem. A computational study on the effectiveness of the proposed solution procedure is presented. For the solution of the simultaneous scheduling and optimal-processing-times problem we suggest an iterative solution procedure, and report our computational experience with this procedure. For the solution of large problems we present a genetic algorithm. The effectiveness of the algorithm is demonstrated through computational results and by evaluating the performance of the obtained solutions against lower bounds that we developed for the problem.     

A mathematical programming model for global plant location problems: Analysis and insights

In this paper, we study the design of global facility networks. We present a mixed integer programming model that captures essential design trade-offs for such networks and explicitly incorporates government subsidies, trade tariffs and taxation issues. The resulting formulation can be solved for reasonable size problems with commercially available mathematical programming software. Focusing on special cases of the problem enables us to provide useful insights on preferable international facility networks for various environments. We demonstrate the pervasive, and often dominating, effects of subsidized financing, tariffs, regional trade rules and taxation in shaping the manufacturing and distribution network of global firms.     

Dynamic pricing for multiple class deterministic demand fulfillment

We consider how a firm should allocate inventory to multiple customer classes that differ based on the price they pay and their willingness to incur delay in fulfillment of their demand. The problem is set in a deterministic demand, economic-order-quantity-like environment with holding, backorder, lost demand and setup costs. The firm either fulfills demand or offers a price discount to induce the demand to wait for fulfillment from the next reorder. We determine the optimal policy and discuss how changes in various parameters affect profitability, customer service, and operational measures such as order frequency and base stock levels. We compare the results to a policy that only rations inventory without dynamic discounting and to a policy that only provides discounts. Through the comparison, we observe that dynamic pricing can be seen as a combination of a pricing mechanism which determines demand and an allocation mechanism that differentiates between customer classes, serving each ones needs. We show that if lower-value customers are distinguished by accepting reduced service, it is possible that both high and low-value customer classes see better levels of service under the optimal policy than under a discounting only policy. In addition we demonstrate the applicability of the results to a stochastic version of the problem.     

A min—sum—max resource allocation problem

In this paper we describe a class of resource allocation problems with a min-sum-max objective function. We first discuss practical applications of the problem. We then present a result on the computational complexity of the problem. We propose an implicit enumeration procedure for solving the general case of the problem, and report on our computational experience with the solution procedure.     

Competition, Learning and Investment in New Technology

Efforts to describe the evolution of production costs must simultaneously include the impact of investment in new technologies as well as experience-based learning. In this paper we formulate a dynamic model of technological investments, which includes the impacts of learning curve effects, investment levels in new technologies with uncertain timing, and competitive responses. Our results highlight the interaction of investment and output rate decisions in monopolistic and duopolistic situations, and illuminate the impact of the planning horizon length on such decisions. The model results elaborate upon how the attractiveness of new technologies is related to the firm's ability to learn using its existing technology, how competition can increase or decrease the market size for new technologies, and how investment levels are driven in opposite directions by considering longer horizons on one hand and the competitive response on the other.     

A simulated annealing procedure for single row layout problems in flexible manufacturing systems

In this paper we address a layout problem in flexible manufacturing systems (FMSs). A layout type that has been extensively implemented in FMSs is the single row machine layout. In such a configuration machines are arranged along a straight track with a material handling device moving jobs from one machine to another. The single row layout problem (SRLP) deals with the optimal arrangement of the machines for the above configuration. We propose a simulated annealing (SA) heuristic for the solution of SRLP. Extensive computational results, and ways to improve the performance of the SA algorithm through parameter fine-tuning procedures, are reported.     

Frequency and characteristics of post-transfusion hepatitis in Greece with emphasis on hepatitis C: comparing second- and third-generation assays

In order to evaluate the role of hepatitis C virus (HCV) in post-transfusion hepatitis (PTH) in Greece we prospectively followed 143 transfusion recipients, receiving 790 units of blood and/or products from 789 donors, between October 1989 and December 1991. The mean number of units transfused per patient was 5.52. PTH was observed in 18 patients (12.59%). One patient (0.70%) developed hepatitis B, in four (2.80%) hepatitis could be attributed to CMV infection, 10 (6.99%) developed hepatitis C and three (2.10%) showed only raised alanine aminotransferase (ALT) levels. The risk of PTH per 1000 units transfused was 22.8. The patient who developed hepatitis B (PTH-B) was transfused with four units, one of which was positive for anti-HBc and anti-HBe. Seven of the 10 patients (70%) who developed hepatitis C (PTH-C) were transfused with at least one unit seropositive in the anti-HCV screening with 2nd-generation tests (ELISA-2 and RIBA-2), whereas 9/10 of PTH-C cases (90%) were transfused with at least one unit positive in 3rd-generation assays. Of the three patients who showed only ALT elevation, none was transfused with anti-HCV seropositive blood, although one of them was transfused with at least one unit with elevated ALT levels. We conclude that: (1) the incidence of PTH in Greece remains high, (2) screening of all donations for anti-HCV with an ELISA-2 does not exclude transmission of HCV and (3) ELISA-3 and RIBA-3 seem to be more sensitive in blood donor screening and in detecting seroconversions than ELISA-2 and RIBA-2.