Impact of operation flexibility and dispatching rules on the performance of a flexible manufacturing system

Operation flexibility is one of the eight common types of flexibility that exist in flexible manufacturing systems. Dispatching rules are commonly used in loading the machines. This paper studies the effects of different levels of operation flexibility and various dispatching rules on the performance of a flexible manufacturing system. The system performance considered is mean flow time. Simulation results indicate that the mean flow time cannot be always improved by increasing the level of operation flexibility. Altering the dispatching rules seems to have a more significant effect on the mean flow time performance than changing the level of operation flexibility.     

Evaluation of dispatching rules for cellular manufacturing

In this paper, the effects of various dispatching rules on the operation and performance of cellular manufacturing systems (CMS) are evaluated. When the study of a CMS considers the automated material handling, it is crucial to reduce the gridlock probability (i.e., the probability of an unsuccessful load transfer attempt occurring in the interface point between the intercell and intracell handling system). Preventing an unsuccessful load transfer is critical for the operation of the entire system as a blockage between the automated guided vehicle (AGV) and the overloaded cell results in a total system shutdown. The gridlock probability is influenced by the dispatching rule used to schedule the load transfers in the system. Therefore, in order to reduce this probability it is necessary to use a dispatching rule that will decrease the number of waiting loads in the transfer spurs. The main objective of the paper presented herein is to identify a dispatching rule that maintains the system operational at all times. A group of dispatching rules, including the first come first served (FCFS), shortest imminent operation (SI), longest imminent operation (LI), most remaining operations (MRO), shortest processing time (SPT), shortest remaining process time (SR), and a newly developed rule proposed by the authors, loads with the minimum number of processing first (MNP), are tested and evaluated with respect to whether the capacity of the transfer spurs of the cells is exceeded. This paper presents a simulation model of a cellular manufacturing system, which is used to further explore the effects of the dispatching rules on the system performance. The results show superior performance of the newly proposed MNP rule.     

Analysis of the number of automated guided vehicles required in flexible manufacturing systems

In this paper we examine some of the general principles and analysis methods that are used to design an automated material handling system. The paper focuses on one type of automated handling system that seems especially suitable for automation in discrete-product manufacturing. These types of automated handling systems are called automated guided vehicle systems. These systems are most applicable for the automation of low-and medium-volume handling situations, where the routeing of materials is more individualised. For guided vehicles, a new quantitative method for analysing these systems is developed in the paper. Examples are presented to demonstrate the method.     

Efficient dispatching rules for dynamic job shop scheduling

This study attempts to provide efficient dispatching rules for dynamic job shop scheduling by combining different dispatching rules. A dispatching rule is used to select the next job to be processed from a set of jobs awaiting service. A job shop will be treated as dynamic, when conditions such as continuously arriving new jobs and deviations from current schedule need to be accommodated, and a job shop should be treated as an integrated part of a manufacturing system. The discussion includes a simulation technique which uses ARENA 4.0. software to simulate the dynamic model of a job shop under various rules and performance measures . Results of the simulation show that, for most of the performance measures, combined rules perform well. In this study, the combined rules MWKR_FIFO and TWKR_SPT do well under most conditions.     

Production-flow-value-based job dispatching method for semiconductor manufacturing

In a wafer manufacturing system, the value added to a particular product at a station may differ significantly from that added to a different product at the same station. If an enterprise concentrates mainly on generating profits, throughput becomes a poor performance measurement for a manufacturing system. Job dispatching rules based on maximum throughput no longer guarantee maximizing profit. Hence, profitability would be a good alternative measurement. The main purpose of this study is to develop a production-flow-value-based job dispatching rule (PFV) by the theory of constraints (TOC) for wafer fabrication. This study derives a TOC cost estimation method and a profitability estimate of a WIP-wafer lot. Jobs are then prioritized based on their profitability. Thus the PFV job dispatching rule is developed. For comparison, two job dispatching rules, MCR and MBS, are also arbitrarily selected to perform simulations. The simulation results reveal that the proposed PFV maximizes the production flow value, while MCR and MBS do not.     

Management of product variety in cellular manufacturing systems

In today’s markets, non-uniform, customized products complicate the manufacturing processes significantly. In this paper, we propose a cellular manufacturing system design model to manage product variety by integrating with the technology selection decision. The proposed model determines the product families and machine groups while deciding the technology of each cell individually. Hedging against changing market dynamics leads us to the use of flexible machining systems and dedicated manufacturing systems at the same facility. In order to integrate the market characteristics in our model, we proposed a new cost function. Further, we modified a well known similarity measure in order to handle the operational capability of the available technology. In the paper, our hybrid technology approach is presented via a multi-objective mathematical model. A filtered-beam based local search heuristic is proposed to solve the problem efficiently. We compare the proposed approach with a dedicated technology model and showed that the improvement with the proposed hybrid technology approach is greater than 100% in unstable markets requiring high product varieties, regardless of the volumes of the products.     

Applying simulated annealing to cellular manufacturing system design

Cell formation and cellular layout design are the two main steps in designing a cellular manufacturing system (CMS). In this paper, we will present an integrated methodology based on a new concept of similarity coefficients and the use of simulated annealing (SA) as an optimization tool. In comparison with the previous works, the proposed methodology takes into account relevant production data, such as alternative process routings and the production volumes of parts. The SA-based optimization tool is parallel in nature and, hence, can reduce the computation time significantly, so it is capable of handling large-scale problems. Finally, the SA-based procedure is compared with a genetic algorithm (GA) based procedure and it will be shown that the SA-based algorithm can be as effective as a GA-based algorithm, but with less computational time and effort.     

Design of cellular manufacturing systems using objective functional clustering algorithms

Cellular manufacturing (CM) has emerged as an alternative to conventional batch-type manufacturing owing to the former's capability of reducing set-up times, in-process inventories and throughput times. It provides the basis for implementation of just-in-time (JIT) and flexible manufacturing systems (FMS). The machine-part group formation is an important issue in the design of CMSs. This paper presents objective functional clustering algorithms for cell formation problems in the design of cellular manufacturing systems. A deterministic objective functional algorithm (hard clustering) and a fuzzy objective functional algorithm (fuzzy clustering) are used to form the part families and machine cells simultaneously. A collection of data sets from open literature is used to test these algorithms. A software package has been developed to verify the implementation.     

New dispatching rules for scheduling in a job shop — An experimental study

We present two new dispatching rules for scheduling in a job shop. These rules combine the process-time and work-content in the queue for the next operation on a job, by making use of additive and alternative approaches. An extensive and rigorous simulation study has been carried out to evaluate the performance of the proposed dispatching rules compared with those by the SPT rule, the WINQ rule, a random rule based on the SPT and WINQ rules, and the best existing rule. The important aspects of the results of the experimental investigation are also discussed in detail.     

A neural network for dispatching rule selection in a job shop

This paper investigates an intelligent system that selects dispatching rules to apply locally for each machine in a job shop. Randomly generated problems are scheduled using optimal permutations of three different dispatching rules on five machines. A neural network is then trained to associate between a statistical characterization of the job mix in each of these problems, with the best combination of dispatching rules to use. Once trained, the neural network is able to recommend for new problems a dispatching rule to use on each machine. Two networks are trained separately for minimizing makespan and the mean flowtime in the job shop. Test results show that the combinations of dispatching rules suggested by the trained networks produce better results, for both objectives, than the alternative of using a single rule common to all machines.     

Allocating new parts to existing part families in cellular manufacturing systems

The problem of allocating new parts to existing part families in cellular manufacturing systems is addressed in this paper. A part-family identification model is proposed to develop a part-allocation scheme based on the tooling requirements of the parts and the tooling available on the machine tools. Using this scheme, new parts may be allocated to appropriate families based on their tooling requirements. The approach suggested in this paper is demonstrated using real data from an industrial setting.     

A virtual testbed for the life-cycle design of automated manufacturing facilities

A large-scale automated manufacturing facility employs various types of automated machines and equipment including material handling and material processing systems. It typically involves extremely complicated operations to achieve the desired performance with less or no manual labour. Design of such a complete system requires a series of difficult design and implementation tasks. This paper describes a virtual testbed to support the life-cycle design of large-scale automated manufacturing facilities such as the postal mail process facility and gear manufacturing factory. The architecture of the virtual testbed is based on the extended real-time control system. The virtual environment provides the design engineer with a unique way of considering all functions of life-cycle system support in the process of facility design. Two examples are given to illustrate the effectiveness and extent of the virtual design system.     

A tradeoff analysis between process plan selection and cell formation in cellular manufacturing

In this paper, an algorithm to evaluate the tradeoff between conflicting objectives in process plan selection and cell formation is developed. Consideration of the minimisation of intercell material movement in cellular manufacturing is necessary but not in itself sufficient to produce a system for which the total work content is minimised. Solving the process plan selection and the cell formation problem for all possible alternative process plans is a time-consuming task, and therefore not economically justifiable. The algorithm is illustrated through the use of a sample problem that shows how it is possible to create a cell using the algorithm presented in this paper.     

Dispatching, routing, and scheduling of two automated guided vehicles in a flexible manufacturing system

This article presents a new approach for planning the dispatching, conflict-free routing, and scheduling of automated guided vehicles in a flexible manufacturing system. The problem is solved optimally in an integrated manner, contrary to the traditional approach in which the problem is decomposed in three steps that are solved sequentially. The algorithm is based on dynamic programming and is solved on a rolling time horizon. Three dominance criteria are used to limit the size of the state space. The method finds the transportation plan minimizing the makespan (the completion time for all the tasks). Various results are discussed. A heuristic version of the algorithm is also proposed for an extension of the method to many vehicles.     

On modeling the design of cellular manufacturing systems

A new optimization model is discussed for the design of cellular manufacturing systems. It is based on an integer programming formulation that updates some other models by eliminating redundant machine assignment and cost coefficients dependent on cell configuration. To reduce computational burdens, a simplified integer programming model and a decomposition algorithm are proposed. Several computer solutions were performed to evaluate the performance of the new model. The computational results are discussed.     

Modelling and simulation analysis of process alternatives in the cellular manufacturing of axially symmetric parts

This paper highlights the issues of multi-stage process planning within facilities of definite processing capabilities, under the consideration of multiple choices of process routings. The process alternative based on operation concentration, accomplished by integrating burnishing into machining operations, is compared to a process with operation differentiation, assuming part finishing in separate grinding operations. A modelling approach to manufacturing knowledge representation, an average linkage clustering procedure of defined machine capability patterns and a set of validation criteria are proposed to enable the cellular decomposition of the facilities and optimum part flow allocation. Simulation investigations of alternative process flows have been performed using stochastic type models and data sets derived from industrial practice. The investigations show the distinct prevalence of the design solutions with operation concentration in terms of assumed performance measures. The results of this work indicate the practical usability of the developed modelling framework applied to exploring the total operational issues of cellular flexible manufacturing systems (FMSs).     

单元制造技术及其实施方法

随着生产的发展和市场的变化,出现了基于过程重构的单元制造技术,分析了单元制造在中国发展的潜力及其研究现状,并结合CMIS工程的实践,提出了单元制造技术的实施方案。     

基于单向环形方式的制造单元布局方法

考虑机器具体规格对各对位置距离的影响,将输入、输出点看成和机器一样的节点,同时考虑每个产品的首尾工序和需要到外单元加工的产品与输入、输出点的物流关系,构建了一个设施—产品关系矩阵.在此基础上构建一个面向随机需求并考虑机器具体规格的模型,并提出一种基于局部搜索的多种群蚁群算法,解决了单元制造系统中带有同型机的单向环形设施布局问题.实验分析结果表明,提出的方法是可行且有效的.     

复杂机械产品生产单元的组织改造

企业的精益化改造是企业成功信息化的关键因素,而生产系统组织的精益化是最根本的问题。以人为本的机械产品精益组织的特点是细胞化、自管理及团队协作。相应的设计改造过程是一个长期持续的改进过程。从设计原理、步骤到设计结果举例,结合国内航空实践,详细描述生产系统组织改造的方法,具有现实意义。