Intercell Flow Research Articles

A cut-tree-based approach for clustering machine cells in the bidirectional linear flow layout

This paper considers the joint cell clustering-layout problem where machine cells are to be located along the popular bidirectional linear material flow layout. The joint problem seeks to minimize the actual intercell flow cost instead of the typical measure that minimizes the number of intercell movements when the layout problem is excluded from the clustering process. Owing to the computational difficulty, a three-phase approach is proposed using the cut-tree-network model to solve this joint problem. The cell clustering and layout problem is transformed into a multi-terminal network flow model. A cut tree is constructed and partitioned into a number of subgraphs via the selected primary path. Each subgraph is a clustered cell and their locations are assigned to the layout sequence by comparing the cut capacities. Thus, the proposed approach concurrently determines the machine cells and their relative sequences in the bidirectional linear flow layout. Computational procedures are illustrated and additional experiments, with data adapted from the literature, are performed to demonstrate the viability of the approach.

An efficient heuristic for the design of cellular manufacturing systems with multiple identical machines

In practice, in a manufacturing system, there are multiple machines of some machine types to meet the capacity requirements. Therefore, this factor should be taken into consideration in the design of cellular manufacturing systems (CMS). On one hand, this is a constraint to be satisfied for the cell formation problem, on the other hand, appropriate assignments of identical machines to different cells will reducte and simplify intercell flows. Thus, we should make use of this advantage in cell formation. The problem is that we do not know the specific machine within the identical machines that are to be used for the processing of an operation, and so it is difficult to assign operations to a specific machine within the group of identical machines. By using the information of operation sequences for each part type, we present a graphical model that can describe the part families with respect to the machine types of multiple machines. Thus, the identical machines can be assigned into different cells based on the part families without involving complex computation. With the model developed here, a merging-and-breaking heuristic is proposed to solve concurrently both the traditional cell formation problem and the assignments of the identical machines to different cells. Three examples are taken to show the power and application of the approach.

A concurrent approach to cell formation and assignment of identical machines in group technology

In designing a cellular manufacturing system, an important way to reduce and simplify intercell flows is to identify shared machines and duplicate them to some cells. However, the shared machines may not be properly identified by the existing cell formation methods. Thus, some unnecessary machine duplication may be made in the sense of capacity requirement and capital investment. In fact, for practical applications, the number of machines of a machine type should be determined by the capacity requirement of the parts to be produced in the system, and should be the constraint for the cell formation problem. Therefore, multiple identical machines should be appropriately assigned into different cells in designing a cellular manufacturing system. To overcome this drawback of the existing methods, in this paper a network model is developed for the design of a cellular manufacturing system. In the model, the machine type which has only one machine is represented by a simple node. The machine type which has two or more machines is represented by a complex node. Thus, this model can describe multiple machines of the same type. Based on this model, a new approach is presented. By the proposed approach, the cell formation problem and the proper assignment of identical machines are solved concurrently. Therefore, the proposed approach provides a more effective solution than the existing methods.

Locating [formula omitted] points of flexible manufacturing cells with the consideration of within-cell and inter-cell flow distance

The locations of cell I O points are critical to the inter-cell flow efficiency. Traditional I O point locating methods often focus on minimizing inter-cell flow distance. However, an inter-cell movement incurs not only inter-cell flow distance but also within-cell flow distance. I O point locating methods that neglect within-cell flow distance will not be able to produce optimal I O points. The negligence also causes the lack of considering the effects of within-cell facility layouts on the locations of I O points in traditional methods. The purpose of this paper is to develop an I O point locating method without the aforementioned shortcomings of traditional methods.

Implementing Intrawell, Intercell Flow into Finite-Difference Ground-Water Flow Model

The U.S. Geological Survey, finite-difference flow model (MODFLOW) is the most commonly applied numerical code in ground-water hydrology. This flow model is frequently used in the design of pump-and-treat systems for aquifer remediation. In this paper we modified the MODFLOW well package to improve on the approximation of multilayer well effects when simulating vertical wells that penetrate several layers and adjacent cell effects when simulating horizontal wells. This was done by simulating flow through a well as flow through a closed conduit pipe, to incorporate flow between adjacent model cells that contain the well. Thus, water exchange between adjacent layers or cells containing the same well as dependent on the flow within the well and flow outside the well of the adjacent cells containing the well. Examples are presented involving ground-water extraction to demonstrate the applicability of the approach to simulate horizontal and vertical wells. It was proposed that the shape of the capture zone of pumping was closer to that of a pear than that of an ellipsoid.

An algorithm for the cell formation and the machine selection problems in the design of a cellular manufacturing system

In this paper, we consider the cell formation and the machine selection problems for the design of a new cellular manufacturing system. The objective is to solve these problems in an acceptable time while considering machine capacity, alternative routeing and constraints on cell size. We propose a heuristic algorithm which consists of two main resolution phases. The first phase forms a configuration of independent cells using a cell aggregation procedure. The second phase considers the introduction of intercell flow to eliminate the machines that are under-utilized. An illustrative numerical example and computational experience are conducted.

Genetically assisted optimization of cell layout and material flow path skeleton

A continuous plane manufacturing cell layout and intercell flow path skeleton problem formulation involving rectilinear distances between cell input/output stations is mapped to a genetic search space. Certain properties of such a search space are exploited to design a very efficient method for reduction of a mixed-integer programming problem formulation to an iterative sequence of linear programming problems. This paper reports theoretical and computational insights for efficiently finding good solutions for the above problem formulation, taking advantage of the solution structure and the search stage. The scores of the objective function on a set of test cases indicate better solutions than those previously reported in the literature. The empirical results based on multiple runs also suggest that the method generates final results that are not dependent on the quality of the initial solution; hence the solution search seems to be more global than many of the previous approaches.

Genetically assisted optimization of cell layout and material flow path skeleton

A continuous plane manufacturing cell layout and intercell flow path skeleton problem formulation involving rectilinear distances between cell input/output stations is mapped to a genetic search space. Certain properties of such a search space are exploited to design a very efficient method for reduction of a mixed-integer programming problem formulation to an iterative sequence of linear programming problems. This paper reports theoretical and computational insights for efficiently finding good solutions for the above problem formulation, taking advantage of the solution structure and the search stage. The scores of the objective function on a set of test cases indicate better solutions than those previously reported in the literature. The empirical results based on multiple runs also suggest that the method generates final results that are not dependent on the quality of the initial solution; hence the solution search seems to be more global than many of the previous approaches.

Manufacturing cell formation by state-space search

This paper addresses the problem of grouping machines in order to design cellular manufacturing cells, with an objective to minimize inter-cell flow. This problem is related to one of the major aims of group technology (GT): to decompose the manufacturing system into manufacturing cells that are as independent as possible. This problem is NP-hard. Thus, nonheuristic methods cannot address problems of typical industrial dimensions because they would require exorbitant amounts of computing time, while fast heuristic methods may suffer from poor solution quality. We present a branch-and-bound state-space search algorithm that attempts to overcome both these deficiencies. One of the major strengths of this algorithm is its efficient branching and search strategy. In addition, the algorithm employs the fast Inter-Cell Traffic Minimization Method to provide good upper bounds, and computes lower bounds based on a relaxation of merging.

Reducing flow between manufacturing cells: a sensitivity analysis

Abstract We evaluate the sensitivity of cellular manufacturing performance to a reduction in intercell flow. Results from our simulation experiment indicate that the performance of cellular shops operating with lower run time variability, smaller batch sizes, longer setup times and larger reductions in setup times due to dedication, has a greater sensitivity to a reduction of intercell flow. In these scenarios, it would be easier to justify an investment in additional machines or specialized tooling required to reduce the level of intercell flow.

Cell formation: the need for an integrated solution of the subproblems

Abstract Cellular manufacturing is a viable option in many manufacturing systems. There are various subproblems in the design of a cellular manufacturing system. These are machine group and part family formation, machine duplication, intracell layout and intercell layout. The only comprehensive design strategy that attempts to address all of these is production flow analysis. However, this technique is a sequential strategy where the subproblems mentioned above are assumed nested within each other and are solved in a forward pass with no feedback. This is a satisfactory approach only in cases where the part families are relatively disjoint and machine groups are formed without constraints on machine duplication to eliminate intercell flow. The presence of bottleneck machines and parts renders the problem considerably more complex, as the subproblems influence each other substantially. This paper presents an integrated framework for solving these subproblems by generating a limited set of feasible alternative solutions.

Optimization analysis of flexible cellular manufacturing: Route selection and determining the optimal production conditions for ordered products

This paper describes a procedure for optimizing the route selection and production conditions considering alternate process plans in a cellular manufacturing environment. The type of production is mainly production-to-order which deals with the unexpected products resulting from changing environmental conditions. Flexible cellular manufacturing can be viewed as a complete unification of both flexible manufacturing process and flexible production management. The integrated problem for designing flexible cellular manufacturing associated with determining the optimal values of the machining speeds, overtime, and intercell flow is formulated as a Nonlinear Mixed Integer Programming (NMIP) problem in order to minimize the total incremental production cost. This is achieved by introducing marginal cost analysis into the NMIP, to obtain optimal machining speed, overtime, intercell flow, and routing. The application of this procedure offers greater flexibility to take advantage of cellular manufacturing due to optimum use of resources. A solution procedure for this problem was developed and a numerical example is included.

Virtual manufacturing cells: exploiting layout design and intercell flows for the machine sharing problem

Existing approaches to cell formation concentrate on machine grouping and part family formation. Since their input data usually do not consider flow directions and volumes, they neglect layout and handling strategies that can simplify the machine sharing problem. Hence, these approaches fail to relate the intracell and intercell layout decisions to the machine grouping and sharing decisions. This paper introduces a new approach for cell formation which integrates machine grouping and layout design, neglecting part family formation. The concepts of a hybrid cellular layout and virtual manufacturing cells are related. It is shown that a combination of overlapping GT cells, functional layout and handling reduces the need for machine duplication among cells. This approach questions the traditional emphasis on machine duplication to create independent cells that is suggested by the standard machine-part matrix clustering methods. The steps in the method are demonstrated by using two illustrative examples obtai...

Design of Cellular Manufacturing Systems

This paper describes a method for layout design of a Cellular Manufacturing System (CMS) that would allow simultaneously, the grouping of machines unique to a part family into cells and those shared by several cells to be located together in functional sections. Using an illustrative example, this integration of the flexibility of a functional layout, the reduced handling gained from cell formation and allowance of limited intercell flows among adjacent cells is described. Thereby, the traditional strategy of simultaneous formation of part families and distribution of machines into independent cells which creates machine distribution and unbalanced utilization problems is avoided. This is justified by an analysis of the complex interactions between the critical subproblems in cell formation—machine grouping, part family formation, distribution and utilization of shared machines, intracell layout, intercell (or shop) layout and material handling. This approach represents a new direction in cell formation where, by allowing the handling function to limit the extent of machine duplication between adjacent cells, a new graph theoretic structure for simultaneous machine grouping and layout design was developed and validated.

Manufacturing system cell formation and evaluation using a new inter-cell flow reduction heuristic

The initial stage in the implementation of cellular manufacturing involves the determination of part families and machine cell (PF/MC). We developed a new heuristic for PF/MC formation that provides a variety of PF/MC alternatives. In addition, we developed a simulation model of a group technology (GT) system using the new heuristic and compared this to that of a traditional process layout (TPL) system. We used performance criteria such as: machine utilization, queue length, flow time, etc. The simulation experiment included a TPL shop, an original GT shop, and an alternative GT shop, each with different part demand distributions.

Countering the negative impact of intercell flow in cellular manufacturing

AbstractAlthough there are numerous studies that address the problems of optimal machine grouping and part family classification for cellular manufacturing, little research has been reported that studies the conditions where cellular manufacturing is appropriate. Flynn (1984) was one of the first to address this issue through a simulation modeling study, and although she did not specifically control for the effect of intercell flow, i.e., the proportion of operations that must be completed for a part outside its assigned cell, the models developed in this study resulted in large amounts of intercell flow. More recently, Morris and Tersine (1990) also addressed the desirability of cellular manufacturing under select manufacturing environments, but their models assumed that no intercell flow was present. In practice, some intercell flow will typically occur after a large‐scale conversion unless many additional machines are purchased to allow each cell to process the complete set of tasks for all parts in a family. In our study, we seek to fill the gaps between the prior simulation studies of cellular manufacturing system performance. We do this by 1) illustrating the negative impact of low to medium intercell flow levels when operating in a wide range of cellular manufacturing environments, and 2) indicating how changes in other operating factors caused by the conversion of a job shop to cellular manufacturing may counter the negative impact of intercell flow. Indeed, we show that many conditions exist where cellular manufacturing can achieve better system performance than a traditional job shop. However, our experiments also point out, like the previous studies, that a conversion to cellular manufacturing can easily degrade system performance—unless other environmental factors are simultaneously changed to counter the negative impact of intercell flow and other problems caused by conversion to cellular manufacturing.Simulation experiments were designed to accomplish these two objectives. We tested the effect of independent variables including intercell flow level, setup time, run time variability, batch size, material handling time, the reduction of setup time made possible by conversion to cellular manufacturing, and product‐mix stability. We found that a conversion to cellular manufacturing is a good alternative to job shop manufacturing when the conversion results in much lower run time variability or in a great reduction in setup times, or when small batch sizes are deemed necessary by management. Further, we found that, in many cases, the performance of cellular manufacturing as measured by mean flow time or work‐in‐ process inventory is better than that of a job shop when the conversion to cellular manufacturing results in a low level of intercell flow—even when other operating factors do not improve after the conversion. This notion substantiates the objective of many cell formation techniques to minimize the level of intercell flow. Finally, we showed that the effect of product‐mix variation is most detrimental to system performance when operating in a cellular manufacturing mode.

Accounting for intracell flow in models with emphasis on water table recharge and stream‐aquifer interaction: 1. Problems and concepts

Intracell flow is important in modeling cells that contain both sources and sinks. Special attention is needed if recharge through the water table is a source. One method of modeling multiple sources and sinks is to determine the net recharge per cell. For example, for a model cell containing both a sink and recharge through the water table, the amount of recharge should be reduced by the ratio of the area of influence of the sink within the cell to the area of the cell. The reduction is the intercepted portion of the recharge. In a multilayer model this amount is further reduced by a proportion factor, which is a function of the depth of the flow lines from the water table boundary to the internal sink. A gaining section of a stream is a typical sink. The aquifer contribution to a gaining stream can be conceptualized as having two parts; the first part is the intercepted lateral flow from the water table and the second is the flow across the streambed due to differences in head between the water level in the stream and the aquifer below. The amount intercepted is a function of the geometry of the cell, but the amount due to difference in head across the stream bed is largely independent of cell geometry. A discharging well can intercept recharge through the water table within a model cell. The net recharge to the cell would be reduced in proportion to the area of influence of the well within the cell. The area of influence generally changes with time. Thus the amount of intercepted recharge and net recharge may not be constant with time. During periods when the well is not discharging there will be no intercepted recharge even though the area of influence from previous pumping may still exist. The reduction of net recharge per cell due to internal interception of flow will result in a model‐calculated mass balance less than the prototype. Additionally the “effective transmissivity” along the intercell flow paths may be altered when flow paths are occupied by intercepted recharge.

Cell Development and Merger in an Illinois Thunderstorm Observed by Doppler Radar

A reflectivity and triple-Doppler radar study of the development of several cells and their successive union within a nonsevere thunderstorm is presented. Two characteristic separations were found between the newly formed cells and the parent thunderstorm, with the closer cells forming in response to the collapse of an active cell and the more distant cells forming in a previously existing storm-modified area characterized by mesoscale convergence and rain cooled air. The manner in which these cells evolved appeared to be partially related to differences in the environment in which they formed. As suggested by Peterson, the cells that formed closer to the main storm resembled the “weakly evolving” cells of Foote and Frank. The updraft of the “weakly evolving” cell analyzed here merged with the updraft in a cell in the main storm as one cell was decreasing in intensity and the other was increasing. Later in the life cycle of the storm, two cells which initially formed further away from the main storm appeared more like classical “strongly evolving” cells. While the vertical air velocity analyses of these cells were incomplete, a trend towards the maintenance of a discrete cell updraft was noted. The ways in which the reflectivity cores of these two cells became merged with the main storm differed. In one case the development of a new cell between two existing cells produced the merger, in the second case differential cell motion played an important role. Additionally, periods of significant intercell flow at 4 km coincided with the times when the midlevel reflectivity bond linking the cell cores showed a rapid intensification. It is proposed that the intercell flow is a result of radial outflow observed at heights above the maximum updraft level in the actively growing echoes. The strengthening of the reflectivity bridge may have been the result of both particle transfer and environmental modification brought about by this radial outflow.