Tamás Koltai

A flexible costing system for flexible manufacturing systems using activity based costing

Flexible manufacturing systems (FMSs) are designed to integrate the flexibility of job shops and the efficiency 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 systems requires a special attention to overhead allocation. On the other hand, the constantly changing setup configuration and production plans require a constant recalculation of overhead allocation and an a priori estimation of the expected production cost. This paper introduces the concept of flexible costing in FMSs, and proposes a method that modifies the overhead allocation based on the results of the production plan and on the simulated performance of the process. This approach is illustrated with some numerical examples.

Application of the results of simple assembly line balancing models in practice: the case of a bicycle manufacturer

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.

Fixed cost oriented bottleneck analysis with linear programming

Despite the increasing ratio of fixed cost in the operating cost of production systems, variable cost oriented decision support methods prevail. These methods, however, have several unexploited capabilities to consider period costs as well. This paper shows how sensitivity analysis of the optimum solution of a linear programming model can provide overhead oriented information as well. The analysis is illustrated with a simple example.

Examination of the sensitivity of an operation schedule with perturbation analysis

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.

Linear programming optimization of a network for an aluminum plant: A case study

Abstract With the dawn of economical and political reforms in Hungary in the mid-1980s the aluminum industry, among others, wanted to escape the trappings of centralized planning and direction. The managers were inexperienced and unadvised regarding the path of transformation to a market economy, as well as of the OR/MS techniques that would enable them to map the activities in their operations and provide the solutions needed to make good decisions. Managers joined outside researchers in exploring opportunities in major aluminum plants. This gave rise to the present study which brought an integrated systems approach to decision making. In this paper a logistics network is developed to model the activities of a medium-sized aluminum plant. For reasons of management requirements, a linear programming optimization appeared feasible to support decision making and to explore decision alternatives by postoptimality analysis.

Analysis of the effect of learning on the throughput-time in simple assembly lines

Abstract Calculating the throughput-time of a production run, when a learning effect influences task times, is a complicated but important problem of production management. Classical assembly line balancing techniques assume a constant cycle time. However, if a learning effect is present, cycle time changes for two main reasons. First, cycle time continuously decreases as the operation time of the bottleneck station decreases due to learning. Second, the bottleneck may shift from one station to another, causing further changes in the cycle time. This paper explores the effects of an exponential learning function on the operation of simple assembly lines. An algorithm is presented to determine throughput-time, and a sample problem is provided to illustrate the required calculations. The sensitivity of the throughput-time with respect to the learning rate is also examined, and some general conclusions related to the effect of learning rate changes are presented.

Formulation of Multi-level Workforce Skill Constraints in Assembly Line Balancing Models

Abstract The objective of assembly line balancing (ALB) is to assign tasks to workstations organized to perform tasks with precedence constraints. An important element of proper assignment of tasks to workstations is the consideration of skill requirement of tasks, and skill level of workers. This paper provides a general framework to model skill requirements and skill conditions for assembly line balancing models. Three types of skill constraints are defined. Low skill constraints determine workstations for workers who are able to perform only some simple tasks. High skill constraints consider tasks which require higher than average skills of workers. Finally, exclusive skill constraints consider situations where a group of workers is specialized in a subset of tasks. The paper summarizes the mathematical description of the different skill constraints, and shows how simple assembly line balancing models can be completed with skill considerations.

Increasing Customer Satisfaction in Queuing Systems with Rapid Modelling

Companies have to increase their customers’ satisfaction to keep their competitiveness. In services, waiting has great impact on service level and customer satisfaction. Consequently, in time-based competition, one of the main objectives of service companies is to minimize customer waiting. Waiting can be defined in several ways; however, the ultimate management objective should be the maximization of customer satisfaction.

Rapid Modeling of Express Line Systems for Improving Waiting Processes

In time-based competition, one of the main management objectives in services is to decrease customers’ waiting. Accordingly, search for designs of queuing systems which reduce waiting has become a major concern of managers. A frequently used solution is the application of express lines. The operation of express line systems can be optimized based on different objective functions. The minimization of average waiting time and the reduction of the variance of waiting times are the classical objectives for operation managers. According to perception management, however, the perceived waiting times and satisfaction generated by waiting should be considered as well. To analyze the effects of different management objectives on the operation of express line systems, a numerical and a simulation model were developed. The study of a superstore shows that the rapid numerical model and the time-consuming simulation model provide the same result when the parameter values ensuring optimal operation must be determined. Consequently, in these problems, simulation can be substituted efficiently by rapid modeling.

Managerial perspectives for improving resource utilisation by applying the cost of unused capacity

For production managers, the traditional measures for evaluation resource usage are capacity utilisation and efficiency. These measures concentrate on the amount of resources used, and ignore the value of resources left idle. The concept of the cost of unused capacity developed in conjunction with activity-based costing by Cooper and Kaplan makes it possible to present information for managers about the value of idle resources as well. In this article, a continuous flow operation and a part manufacturing operation are used to illustrate the application of the cost of unused capacity in production and capacity planning-related decisions.