Capacity is one of the most important measures of resources used in production. Conventional capa... more Capacity is one of the most important measures of resources used in production. Conventional capacity measures do not include the value of the equipment in the production system and so their application can lead to erroneous operations management decisions. A new measure, the cost of unused capacity, is frequently used to characterize resource usage. In the paper two linear programming models are formulated to consider the cost of unused capacity. The objective function of one of the models incorporates the unused capacities of various machines, while increasing the contribution to profit at the same time. If the cost of unused capacity is considered in capacity planning, the idle time of valuable resources can be exploited more efficiently.
Perturbation analysis of discrete event systems is one of the most promising theories for underst... more Perturbation analysis of discrete event systems is one of the most promising theories for understanding the basic characteristics of an operating system. Here, its theoretical basis is completed with the validity range concept. The implementation in a discrete event simulation environment is intended to illustrate the logic of the algorithm. An example is presented to show how traditional simulation output results can be completed with gradient information.
Minimizing the cost of capital tied up by inventory is frequently an important management objecti... more Minimizing the cost of capital tied up by inventory is frequently an important management objective of production scheduling. The paper determines the optimal production schedule of a calendar manufacturer first with a mathematical programming model, and next with scheduling theory based sequencing rules. In both cases inventory holding cost is approximated by the interest on the cost of capital tied up by inventory. Interest is calculated with periodic and also with continuous interest calculation method providing this way a lower and an upper bound for the possible value. Based on the examination of the scheduling rules, however, it is demonstrated, that the optimal sequences of the two different methods are very rarely different in practices. The performance of the suggested methods is illustrated with the example of the calendar manufacturer.
Given demand requirements, manufacturing systems should analyze whether or not there is sufficien... more Given demand requirements, manufacturing systems should analyze whether or not there is sufficient capacity to perform the technologically-different operations. In a more flexible system, better utilization can be achieved, however, generally with higher cost. To analyze this problem, we extend traditional aggregate planning concepts to address capacity issues in flexible manufacturing systems. A 0-1 integer linear programming model is developed to help determine how to configure a manufacturing system to avoid excessive capacity over-and/or under-utilization. Also, several management priorities, such as tooling cost, machine pooling, and flexibility issues, are considered. The model is illustrated through a sample problem.
The operation of assembly lines, despite its inflexible nature, has to respond quickly to the cha... more The operation of assembly lines, despite its inflexible nature, has to respond quickly to the changing production requirements and production conditions. A possibility of increasing quick response is to speed up line configuration decisions with quick and flexible assembly line balancing planning tools. The objective of assembly line balancing (ALB) is to minimize the number of workstations or to minimize cycle time considering precedence constraints. There is generally a time/cost trade-off in assembly lines. Fewer workstations results in larger cycle time, while higher number of workstations results in lower cycle time. The objective of this paper is to show how cycle time related operations management decisions can be supported with quick solutions of ALB models in the case of a bicycle assembly process. The robustness of the optimal ALB solutions to the variation of operation times of regular and temporary workers is analyzed by discrete event simulation.
International Journal of Production Research, 1993
ABSTRACT An algorithm is presented to calculate the validity range of deterministic similarity of... more ABSTRACT An algorithm is presented to calculate the validity range of deterministic similarity of a sample path of a discrete event dynamic system when a single perturbation is introduced at the operation times. Based on the calculated range, sensitivity analysis concerning both the gradient of the throughput and some special technological feasibility of an operation schedule can be analysed. The algorithm is recommended in a manufacturing environment, when technology intensive products are produced in small lots. The implementation of the algorithm in an automated steel manufacturing process is also presented.
International Journal of Production Research, 1999
This paper presents a new approach to the loading problem in flexible manufacturing systems. It f... more This paper presents a new approach to the loading problem in flexible manufacturing systems. It focuses on the existence of alternatives routes for each part type. Also, the optimal number of copies of each tool type to be loaded into each tool magazine is directly ...
International Journal of Production Economics, 2009
ABSTRACT Minimizing the cost of capital tied up by inventory is frequently an important managemen... more ABSTRACT Minimizing the cost of capital tied up by inventory is frequently an important management objective of production scheduling. The paper determines the optimal production schedule of a single machine sequencing problem for two cases; first when the cost of capital is calculated by periodic interest calculation, and second, when the cost of capital is determined by continuously compounded interest calculation. The results are derived for common due date and for different due dates situations as well. The robustness of the suggested production schedules to the method of interest calculation is proved theoretically and demonstrated with the example of a calendar manufacturer.
ABSTRACT Operations managers need to evaluate numerous alternative uses of production capacities ... more ABSTRACT Operations managers need to evaluate numerous alternative uses of production capacities in modern manufacturing systems. To perform such a task, an aggregate capacity analysis approach is introduced based on the concept of 'operation type'. In order to avoid excessive capacity over-and/or under-utilization, a heuristic workload balancing procedure is developed, which can be applied to mixed-type manufacturing systems that encompass both single- and multi-purpose CNC machines. An iterative algorithm is presented that reschedules the set of orders which have been assigned to successive periods by a rough-cut production schedule. Using this procedure, both workload balancing and capacity utilization of the system can be improved considerably. These results are demonstrated with an example of a sample manufacturing system.
International Journal of Computer Integrated Manufacturing, 2013
ABSTRACT The objective of assembly line balancing (ALB) is the allocation of tasks to workstation... more ABSTRACT The objective of assembly line balancing (ALB) is the allocation of tasks to workstations of continuous production lines in order to minimise operating cost or other cycle time-related management criteria. As a consequence of the development of computer technology, mathematical programming models of practical-sized ALB problems can be solved by commercial optimisation software very efficiently. Therefore, the focus of research in ALB can be shifted to practice-driven model formulation and to the investigation of new areas of application. The objective of this paper is to show how cycle-time related operations management decisions can be supported with quick solution of ALB models through the case of a bicycle assembly process. Practical ALB problems related to workforce skill and to production quantity changes are presented and management implications of the results are explained.
International Journal of Production Research, 2000
Flexible manufacturing systems (FMSs) are designed to integrate the ¯ exibility of job shops and ... more Flexible manufacturing systems (FMSs) are designed to integrate the ¯ exibility of job shops and the e ciency of mass production systems. Product costing methods have to adapt to this new technological environment. On one hand, the high production overhead cost of these ...
Capacity is one of the most important measures of resources used in production. Conventional capa... more Capacity is one of the most important measures of resources used in production. Conventional capacity measures do not include the value of the equipment in the production system and so their application can lead to erroneous operations management decisions. A new measure, the cost of unused capacity, is frequently used to characterize resource usage. In the paper two linear programming models are formulated to consider the cost of unused capacity. The objective function of one of the models incorporates the unused capacities of various machines, while increasing the contribution to profit at the same time. If the cost of unused capacity is considered in capacity planning, the idle time of valuable resources can be exploited more efficiently.
Perturbation analysis of discrete event systems is one of the most promising theories for underst... more Perturbation analysis of discrete event systems is one of the most promising theories for understanding the basic characteristics of an operating system. Here, its theoretical basis is completed with the validity range concept. The implementation in a discrete event simulation environment is intended to illustrate the logic of the algorithm. An example is presented to show how traditional simulation output results can be completed with gradient information.
Minimizing the cost of capital tied up by inventory is frequently an important management objecti... more Minimizing the cost of capital tied up by inventory is frequently an important management objective of production scheduling. The paper determines the optimal production schedule of a calendar manufacturer first with a mathematical programming model, and next with scheduling theory based sequencing rules. In both cases inventory holding cost is approximated by the interest on the cost of capital tied up by inventory. Interest is calculated with periodic and also with continuous interest calculation method providing this way a lower and an upper bound for the possible value. Based on the examination of the scheduling rules, however, it is demonstrated, that the optimal sequences of the two different methods are very rarely different in practices. The performance of the suggested methods is illustrated with the example of the calendar manufacturer.
Given demand requirements, manufacturing systems should analyze whether or not there is sufficien... more Given demand requirements, manufacturing systems should analyze whether or not there is sufficient capacity to perform the technologically-different operations. In a more flexible system, better utilization can be achieved, however, generally with higher cost. To analyze this problem, we extend traditional aggregate planning concepts to address capacity issues in flexible manufacturing systems. A 0-1 integer linear programming model is developed to help determine how to configure a manufacturing system to avoid excessive capacity over-and/or under-utilization. Also, several management priorities, such as tooling cost, machine pooling, and flexibility issues, are considered. The model is illustrated through a sample problem.
The operation of assembly lines, despite its inflexible nature, has to respond quickly to the cha... more The operation of assembly lines, despite its inflexible nature, has to respond quickly to the changing production requirements and production conditions. A possibility of increasing quick response is to speed up line configuration decisions with quick and flexible assembly line balancing planning tools. The objective of assembly line balancing (ALB) is to minimize the number of workstations or to minimize cycle time considering precedence constraints. There is generally a time/cost trade-off in assembly lines. Fewer workstations results in larger cycle time, while higher number of workstations results in lower cycle time. The objective of this paper is to show how cycle time related operations management decisions can be supported with quick solutions of ALB models in the case of a bicycle assembly process. The robustness of the optimal ALB solutions to the variation of operation times of regular and temporary workers is analyzed by discrete event simulation.
International Journal of Production Research, 1993
ABSTRACT An algorithm is presented to calculate the validity range of deterministic similarity of... more ABSTRACT An algorithm is presented to calculate the validity range of deterministic similarity of a sample path of a discrete event dynamic system when a single perturbation is introduced at the operation times. Based on the calculated range, sensitivity analysis concerning both the gradient of the throughput and some special technological feasibility of an operation schedule can be analysed. The algorithm is recommended in a manufacturing environment, when technology intensive products are produced in small lots. The implementation of the algorithm in an automated steel manufacturing process is also presented.
International Journal of Production Research, 1999
This paper presents a new approach to the loading problem in flexible manufacturing systems. It f... more This paper presents a new approach to the loading problem in flexible manufacturing systems. It focuses on the existence of alternatives routes for each part type. Also, the optimal number of copies of each tool type to be loaded into each tool magazine is directly ...
International Journal of Production Economics, 2009
ABSTRACT Minimizing the cost of capital tied up by inventory is frequently an important managemen... more ABSTRACT Minimizing the cost of capital tied up by inventory is frequently an important management objective of production scheduling. The paper determines the optimal production schedule of a single machine sequencing problem for two cases; first when the cost of capital is calculated by periodic interest calculation, and second, when the cost of capital is determined by continuously compounded interest calculation. The results are derived for common due date and for different due dates situations as well. The robustness of the suggested production schedules to the method of interest calculation is proved theoretically and demonstrated with the example of a calendar manufacturer.
ABSTRACT Operations managers need to evaluate numerous alternative uses of production capacities ... more ABSTRACT Operations managers need to evaluate numerous alternative uses of production capacities in modern manufacturing systems. To perform such a task, an aggregate capacity analysis approach is introduced based on the concept of 'operation type'. In order to avoid excessive capacity over-and/or under-utilization, a heuristic workload balancing procedure is developed, which can be applied to mixed-type manufacturing systems that encompass both single- and multi-purpose CNC machines. An iterative algorithm is presented that reschedules the set of orders which have been assigned to successive periods by a rough-cut production schedule. Using this procedure, both workload balancing and capacity utilization of the system can be improved considerably. These results are demonstrated with an example of a sample manufacturing system.
International Journal of Computer Integrated Manufacturing, 2013
ABSTRACT The objective of assembly line balancing (ALB) is the allocation of tasks to workstation... more ABSTRACT The objective of assembly line balancing (ALB) is the allocation of tasks to workstations of continuous production lines in order to minimise operating cost or other cycle time-related management criteria. As a consequence of the development of computer technology, mathematical programming models of practical-sized ALB problems can be solved by commercial optimisation software very efficiently. Therefore, the focus of research in ALB can be shifted to practice-driven model formulation and to the investigation of new areas of application. The objective of this paper is to show how cycle-time related operations management decisions can be supported with quick solution of ALB models through the case of a bicycle assembly process. Practical ALB problems related to workforce skill and to production quantity changes are presented and management implications of the results are explained.
International Journal of Production Research, 2000
Flexible manufacturing systems (FMSs) are designed to integrate the ¯ exibility of job shops and ... more Flexible manufacturing systems (FMSs) are designed to integrate the ¯ exibility of job shops and the e ciency of mass production systems. Product costing methods have to adapt to this new technological environment. On one hand, the high production overhead cost of these ...
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Papers by Tamás Koltai