Ronald G. Askin

Cell formation in group technology: review, evaluation and directions for future research

Abstract This paper discusses and reviews a fundamental issue in cellular manufacturing—cell formation. This problem is of strategic and operational importance in that it affects the fundamental structure and the overall layout of a cellular manufacturing system. We first provide a comprehensive mathematical formulation of the cell formation problem and then propose a methodology-based classification of prior research. This classification is used in reviewing the most recent literature on the cell formation problem. Based on a comparison and critical evaluation, we highlight the shortcomings of current approaches and also outline directions for future research.

Scheduling flexible flow lines with sequence-dependent setup times

Abstract This paper examines scheduling in flexible flow lines with sequence-dependent setup times to minimize makespan. This type of manufacturing environment is found in industries such as printed circuit board and automobile manufacture. An integer program that incorporates these aspects of the problem is formulated and discussed. Because of the difficulty in solving the IP directly, several heuristics are developed, based on greedy methods, flow line methods, the Insertion Heuristic for the Traveling Salesman Problem and the Random Keys Genetic Algorithm. Problem data is generated in order to evaluate the heuristics. The characteristics are chosen to reflect those used by previous researchers. A lower bound has been created in order to evaluate the heuristics, and is itself evaluated. An application of the Random Keys Genetic Algorithm is found to be very effective for the problems examined. Conclusions are then drawn and areas for future research are identified.

A graph partitioning procedure for machine assignment and cell formation in group technology

SUMMARY This paper proposes a mathematical model and solution procedure for the group technology configuration problem—the grouping of individual machines into cells and the routing of components to machines within cells. Costs of inventory, machine depreciation, machine setup and material handling are first incorporated into a mathematical programming formulation. The formulation is then divided into two subproblems to facilitate solution. A heuristic graph partitioning procedure is then proposed for each subproblem. The first subproblem assigns components to specific machines. The second subproblem groups machines into cells. An approach for determining economic batch sizes in this environment is also included. Examples are included and the flexibility of the approach to various environments is discussed.

Comparing scheduling rules for flexible flow lines

Abstract This paper explores scheduling flexible flow lines with sequence-dependent setup times. Three major types of heuristics are explored. Insertion heuristics (based on insertion heuristics for the traveling salesman problem) attempt to simultaneously equalize workload on all processors at a stage, and minimize total or single-stage flowtimes. Johnsons algorithm for two-stage flow shops and its heuristic extensions to m-machine flow shops are modified for parallel processors and the flexible flow-line environment. A set of naive greedy heuristics is investigated for comparison purposes. The performance of the heuristics is compared on a set of test problems. Results indicate the range of conditions under which each method performs well.

A Hamiltonian path approach to reordering the part-machine matrix for cellular manufacturing

The formation of machine and part groups is a central issue in the design of cellular manufacturing systems. The part-machine incidence matrix has formed the basis of several techniques for cell formation. In this paper, we propose formulating machine and part ordering as a Hamiltonian Path Problem. Similarity coefficients are used to form a distance measure for machines and parts. The resulting solutions are shown to be better than those obtained from binary clustering on a set of test problems.

Forming effective worker teams with multi-functional skill requirements

Throughout much of the past century, manufacturing efficiencies were gained by constructing systems from independently designed and optimized tasks. Recent theories and practice have extolled the virtues of team-based practices that rely on human flexibility and empowerment to improve integrated system performance. The formation of teams requires consideration of innate tendencies and interpersonal skills as well as technical skills. In this project we develop and test mathematical models for formation of effective human teams. Team membership is selected to ensure sufficient breadth and depth of technical skills. In addition, measures of worker conative tendencies are used along with empirical results on desirable team mix to form maximally effective teams. A mathematical programming formulation for the team selection problem is presented. A heuristic solution is proposed and evaluated.

A parallel station heuristic for the mixed-model production line balancing problem

Demand for customized products and proliferation of optimal features have increased the need for flexible assembly systems that are capable of simultaneously producing multiple versions of similar products. Serial assembly systems have traditionally been used for the production of a single product type, and more recently for mixed model production. In this paper, a nonlinear integer program is proposed as a model for the production line balancing problem (PLBP). This problem entails the assignment of tasks to stages in a serial production line. The model allows mixed-model production and the use of identical parallel workstations at each stage of the serial production system. The objective function trades off idle workstation time with duplication of task-dependent equipment/ tooling cost. A heuristic is developed to create parallel workstations and assign tasks. Station utilization is also explicitly considered by using a threshold variable for target (acceptable) levels. The procedure is illustrated wit...

A methodology for designing flexible cellular manufacturing systems

Cell formation in cellular manufacturing deals with the identification of machines that can be grouped to create manufacturing cells and the identification of part families to be processed within each cell. Dynamic and random variations in part demands can negatively impact cell performance by creating unstable machine utilizations. The purpose of this paper is to introduce and illustrate an interactive cell formation method that can be used to design ‘flexible’ cells. Flexibility in this context refers to routing flexibility (i.e., the ability for the cellular system to process parts within multiple cells) and demand flexibility (i.e., the ability of the cell system to respond quickly to changes in part demand and part mix). Through an experimental analysis using multiple data sets, we also validate the procedure and provide guidelines for parameter settings depending upon the type of flexibility of interest to the user. Finally, trade-offs and interdependences between alternative types of flexibility in the context of cellular systems are illustrated.

Project selection, scheduling and resource allocation with time dependent returns

In this paper we formulate and analyze the joint problem of project selection and task scheduling. We study the situation where a manager has many alternative projects to pursue such as developing new product platforms or technologies, incremental product upgrades, or continuing education of human resources. Project return is assumed to be a known function of project completion time. Resources are limited and renewable. The objective is to maximize present worth of profit. A general mathematical formulation that can address several versions of the problem is presented. An implicit enumeration procedure is then developed and tested to provide good solutions based on project ordering and a prioritization rule for resource allocation. The algorithm uses an imbedded module for solving the resource-constrained project scheduling problem at each stage. The importance of integrating the impact of resource constraints into the selection of projects is demonstrated.

Forming effective worker teams for cellular manufacturing

Cellular manufacturing has been extensively adopted as a measure to reduce cycle time, increase productivity, and improve product quality. The past research in cellular manufacturing has focused on the methodology for identification of machine groups, part families, and determination of processing routes. The relocation of existing workers into cells and their training for a team-oriented, cellular manufacturing environment have largely been ignored. In this research, a mixed integer, goal programming model is formulated for guiding the worker assignment and training process to create worker teams with high team synergy and individual job fitness meeting cell requirements for technical and administrative skills. The model integrates psychological, organizational, and technical factors. Several solution methods including greedy heuristic, filtered beam search, and simulated annealing techniques are developed and tested. It appears that heuristics such as beam search are capable of obtaining good solutions with reasonable computational effort.