Showing papers in "International Journal of Production Research in 1997"

Cellular manufacturing at 46 user plants : implementation experiences and performance improvements

Abstract: Despite the increasing popularity of cellular manufacturing, by now a firmly entrenched approach to factory work organization, the number of large-scale systematic studies aimed at investigating issues surrounding implementation is still relatively sparse. This paper reports on a survey study of plants involved with cellular manufacturing. A target population of high-probability users received mail questionnaires designed to collect responses related to characteristics of industry cells and the firms that have implemented them (a companion paper, based on the same survey data, describes procedures and issues in cell design). Forty-six plants supplied detailed data on 126 of their cells, including reasons for establishing them, types of operations performed in the cells, problems faced and lessons learned during implementation, and achieved performance improvements. This study provides confirming evidence that manufacturing cells, which may house a large variety and many combinations of processes, can prov...

A comparison of production-line control mechanisms

Abstract: We study the performance of the kanban, minimal blocking, basestock, CONWIP, and hybrid kanban-CONWIP control policies in a four-machine tandem production line making parts for an automobile assembly line. Cases with both constant and changing demand rates are studied. The main performance measures are the service level and the amount of work-in-progress. We also consider other performance measures such as variability amplification along the line. The results are obtained by extensive simulations. We find that the best parameter choices for the hybrid policy decrease inventories by 10% to 20% over the best kanban policy while maintaining the same service levels. The inventory difference grows as the demands on service level increase. The performance of basestock and CONWIP policies falls between those of the kanban and hybrid policies. The CONWIP and hybrid policies also give significantly better response to changes in the demand rate.

Rescheduling job shops under random disruptions

Abstract: In this work, an algorithm for rescheduling the affected operations in a job shop is presented and its performance, with respect to measures of efficiency and stability, is compared with that of Total Rescheduling and Right-Shift Rescheduling. Algorithms for all three methods are implemented in a rescheduling program which, based on keyed-in disruption information, produces three new schedules and outputs their related performance measures. A designed factorial experiment is performed on benchmark scheduling problems to study the effect of different rescheduling methods as well as various problem characteristics and disruption scenarios on the performance of the new schedules. The results demonstrate that the Affected Operations Algorithm overcomes the disadvantages associated with other rescheduling methods.

Order review and release strategies ina job shop environment: A review and a classification

Abstract: In many job shop environments production orders arrive continuously at the production system over time. If an 'order review and release'(ORR) technique is applied, the arrival itself does not necessarily involve the release of a job to the shop floor; in fact, the ORR activities determine which jobs have to be selectively dispatched to theshop floor and when job releaseis to takeplace, so as to improve job shop management and performances. This paper introduces a review and a classification framework of the main research work carried out to date. We have considered eight main dimensions that describe the fundamental principles, characteristics and logic of existing order review and release techniques. The classification of selected models from the specialised literature by means of the proposed framework provides a better understanding for the practitioners and, on the other hand, aims to indicate to researchers the most promising research paths.

Total quality management in the supply chain : what is its impact on performance?

Abstract: Recent empirical studies of quality management have led to mixed findings regarding a significant positive relationship with performance. By combining nonlinear (DEA) and linear (regression) analyses, we demonstrate that TQM practices are related to performance. We establish this relationshp using objective (not self-reported) quality performance data. We believe that this is the first study to use objective quality data collected by a third party. Our findings should encourage manufacturers to continue promoting TQM practices throughout the supply chain; certain practices do lead to better performance.

Production scheduling/rescheduling in flexible manufacturing

Abstract: Scheduling of production in flexible manufacturing systems (FMSs) has been extensively researched over the past years and it continues to attract the interests of both academic researchers and practitioners. The generation of new and modified production schedules is becoming a necessity in today's complex manufacturing environment. Genetic algorithms are used in this paper to obtain an initial schedule. Uncertainties in the production environment and modelling limitations inevitably result in deviations from the generated schedules. This makes rescheduling or reactive scheduling essential. Four different types of uncertainties that normally cause discrepancies between the actual output and the planned output are considered in this paper. These include unforeseen machine breakdowns, increased order priority, rush orders arrival and order cancellations. In this paper, the current status of the shop is considered while rescheduling. The proposed algorithms revise only those operations that must be reschedule...

A neural network approach for the analysis of control chart patterns

Abstract: Control chart pattern recognition is an important aspect of statistical process control (SPC). The presence of unnatural patterns indicates that a process is affected by assignable causes, and corrective actions should be taken. This paper describes two types of pattern recognizers based on different neural network architectures: a multilayer perceptron trained by back-propagation and a modular neural network. The pattern recognizers were developed to take the advantage of the fact that a particular unnatural pattern is often associated with a set of assignable causes. Identification of unnatural patterns can greatly narrow the set of possible causes that must be investigated, and thus the diagnostic search could be reduced in length. The performances of the proposed pattern recognizers were evaluated through Monte Carlo simulations on the basis of appropriate performance measures. An extensive evaluation indicates that the proposed pattern recognizers could recognize multiple unnatural patterns for which...

Optimal disassembly of complex products

Abstract: This paper presents a method for determining the optimum disassembly sequence for selective disassembly of discarded complex products. This methodology has been developed within the framework of the increasing need for formulation of a theory on selective disassembly and the various purposes of it. The objective of the optimization is maximizing the economic performance of the disassembly process within given technical and environmental constraints. It is demonstrated that the method, that is based on graphs, can be used to generate optimum sequences according to various objectives in a straightforward way. Also a ranking of the most favourable alternative sequence is possible. This is important to the inclusion of other criteria in the model and in adaptation of the disassembly system to fluctuating parameters like material yields and constraints. Contrary to earlier work on generation of disassembly sequences, in selective disassembly all possible incomplete disassembly sequences are included. This cons...

Job shop scheduling with a genetic algorithm and machine learning

Abstract: Dynamic job shop scheduling has been proven to be an intractable problem for analytical procedures. Recent advances in computing technology, especially in artificial intelligence, have alleviated this problem by intelligently restricting the search space considered, thus opening the possibility of obtaining better results. Researchers have used various techniques that were developed under the general rubric of artificial intelligence to solve job shop scheduling problems. The most common of these have been expert systems, genetic algorithms and machine learning. Of these, we identify machine learning and genetic algorithms to be promising for scheduling applications in a job shop. In this paper, we propose to combine complementarily the strengths of genetic algorithms and induced decision trees, a machine learning technique, to develop a job shop scheduling system. Empirical results, using machine learning for releasing jobs into the shop floor and a genetic algorithm to dispatch jobs at each machine, are...

Feature-based control chart pattern recognition

Abstract: This paper describes a new approach for the recognition of control chart patterns (CCPs). The approach uses features extracted from a CCP instead of the unprocessed CCP data or its statistical properties for the recognition task. These features represent the shape of the CCP explicitly. The approach has two main steps: (1) extraction of features and (2) recognition of patterns. A set of CCP feature extraction procedures are described in the paper. The extracted features are recognized using heuristics, induction and neural network techniques. The paper presents the results of analysing several hundred control chart patterns and gives a comparison with those reported in previous work.

Evaluating the end-of-life value of a product andimproving it by redesign

Abstract: As society progresses towards ecological maturity, the issue of reducing the environmental burden imposed by worn-out products becomes increasingly prominent. For a given product, the design stage is the best one at which this issue should be tackled. An algorithmic approach to this design-for-recycling problem is presented, based on a new algorithm for quantitative evaluation of the end-of-life value of a product. Given this algorithm, routines for identifying weak spots in the design, as well as for suggesting possible solutions, are built. In a CAD environment that can verify design against specification, automation of the optimization for recycling is thus possible in a way concurrent with other optimization considerations.

An evaluation of capacity planning techniques in a remanufacturing environment

Abstract: Remanufacturing is a growing segment of the manufacturing industry, aided by environmental greening initiatives. There is scant literature on how to manage operations in this emerging industry segment. In this study, an important component of the manufacturing planning and control function, capacity planning is analysed. It is shown that the remanufacturing environments characteristics are sufficiently different from the traditional new product manufacturing environments that production planning and control techniques need to be different. New capacity planning techniques are developed and implemented along with some standard capacity planning techniques in a remanufacturing environment. The results show that the new techniques, developed for the remanufacturing environment are significantly better than the standard techniques, which had been developed for the traditional new product manufacturing environment.

Improving the product mix heuristic in the theory of constraints

Abstract: The product mix heuristic is the component in the theory of constraints (TOC) which develops a master production schedule (MPS) to maximize system throughput. Prior research identified certain conditions where the TOC product mix heuristic does not identify the optimal solution. This paper revises the TOC product mix heuristic to identify the optimal product mix under conditions where the original TOC heuristic failed. The revised heuristic continues to be relatively easy for managers to understand and use when developing a MPS.

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

Abstract: 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...

Dynamic scheduling selection of dispatching rules for manufacturing system

Abstract: The scheduling strategy proposed is based on a dynamic selection of certain pre-determined dispatching rules. A new selection is carried out each time a machine becomes available, depending on: (1) primary and secondary performance objectives, (2) operating conditions, (3) an analysis of the system state, which aims at detecting particular symptoms from the numerical values taken by state variables. This selection method is improved through the optimization of the numerical thresholds used in the detection of symptoms. A simple heuristic dispatching strategy, called 'shift from standard rules' (SFSR), has been designed based on this dynamic selection approach. It is compared to SPT, SIx, COVERT, CEXSPT, and CR/SPT on a job shop problem, already used in other research works. The results indicate significant improvements on the mean tardiness and the conditional mean tardiness. Moreover, this new approach allows several performance criteria, such as the mean flowtime and the mean tardiness, to be taken into...

Product structure complexity and scheduling of operations in recoverable manufacturing

Abstract: Recoverable manufacturing is becoming an increasingly important alternative to firms as they develop environmentally sound strategies aimed at minimizing waste and resources. Remanufacturing helps minimize costs and conserve resources through methods such as extending product life cycles via refurbishments and technical upgrades which require the use of only a fraction of the resources and energy associated with a new product. In this study the impact of product structure complexity on other managerial operating decisions is examined in a remanufacturing environment. It is shown that in the remanufacturing environment, with its greater inherent uncertainty, product structure complexity significantly affects the choice of scheduling policies used. Recommendations as to the scheduling policy to use for a dominant product structure in a given environment are made.

Joint optimization of lot-sizes, safety stocks and safety lead times in an MRP system

Abstract: This paper reports on a simulation study of an MRP system affected by stochastic demand and stochastic lead times. Experiments are conducted to assess the impact of three data sets: the amount of lead time variability, the amount of demand variability, and the influence of the stockout cost/inventory holding cost ratio. Lot-sizes, safety stocks and lead times are optimized using simulated annealing. The effects of either using safety stocks or safety lead times are compared to each other with the purpose of finding the best method for protection against uncertainties in lead time and demand.

On the equivalence of operational performance measurement and multiple attribute decision making

Abstract: Measurement of operational performance and decision making under multiple attributes are shown to be essentially the same process. A recent operational performance measurement (OPM) procedure called OCRA (operational competitiveness rating) and a multiple attribute decision making (MADM) method called TOPSIS (technique for order preference by similarity to ideal solution) are shown to produce ratings that are identical up to a linear transformation. Further investigations into OPM and MADM lead to their equivalence. The equivalence of the two methods can open up new research and application possibilities in both productivity analysis and MADM. Reviews of both the non-parametric approach that leads to the OC RA procedure and the TOPSIS method are provided, new perspectives on these methods are introduced and examples offered.

Short-termism and the appraisal of AMT capital projects inthe US and UK

Abstract: Over the past two decades, the traditional investment appraisal criteria and techniques used in the evaluation of advanced manufacturing technology (AMT) have come under increasing scrutiny. Several reasons have been put forward concerning the perceived inadequacy of these traditional approaches. Included among these reasons are the myopic(short-term) focus of the criteria, the difficulty in quantifying benefits associated with AMT, and the treatment of project risk. An empirical study, summarized in this paper, was completed to determine if practitioners have taken the advice of experts and academics. This international study surveyed financial directors and senior executives in the UK and US on several factual and perceptual questions. The results show that the sophisticated investment appraisal techniques, such as discounted cash flow, are perceived to be unsuitable for evaluating AMT projects, and what is preferred by management is a basic financial appraisal method, such as Payback, possibly linked t...

Surface interrogation and machining strip evaluation for 5-axis CNC die and mold machining

Abstract: This research is focused on the investigation of robust surface interrogation tools which can support the planning and programming of 5-axis die/mold surface machining. Surface curvature information is evaluated to determine optimal tool orientation for 5-axis machining. A method for calculating machining strip width is proposed for 5-axis cutter path generation. This paper is focused on the development of computational geometry techniques and their application to design, analysis, and manufacturing automation. The proposed planning and programming methodology consists of three phases: (1) surface interrogation; (2) machining strip width evaluation; and (3) optimum tool orientation for 5-axis machining. This proposed research can be used to improve the quality of 5-axis die/mold machining.

Multi-period international facilities location: An algorithm and application

Abstract: In today's markets, customers want to buy the best quality products at the lowest prices, regardless of where they are produced. Hence, most companies can no longer afford to operate in a single domestic market. To penetrate global markets and obtain their benefits, companies are under tremendous pressure to be competitive and to reduce their production costs. Establishing foreign manufacturing facilities has therefore been taking place rapidly and is further enhanced by trade agreements such as NAFTA. Even though there has been much written on facilities location, in general the literature on international facilities location is rather limited. This paper surveys the available literature and provides an efficient branch and bound procedure for solving the uncapacitated multi-period international facilities location problem. This branch and bound procedure is applied to a case study and tested for its efficiency. The solutions and computation times are compared with those obtained using LINDO. This extens...

Experiences of US- and foreign-owned firms : A new perspective on ISO 9000 implementation.

Abstract: Responses from over 500 companies relating to their experiences with ISO 9000 implementation are presented. Companies were categorized according to ownership: US-owned (Type U) and foreign-owned (Type F) manufacturing firms. The results reveal the importance and the dual role of documentation as a critical factor necessary to obtain ISO 9000 registration: (1) as the critical element requiring the highest level of effort in the registration process;and (2)as one of the key potential barriers to successful implementation. Increasing market share is the highest rated reason for achieving ISO 9000 registration. ISO 9000 registered companies expect a high degree of improvement in product design , process design , product quality , communication , and supplier relations. The findings also reveal that there is no significant difference between the two firm ownership types for all variables tested, indicating that the ISO 9000 standards appear universal in applicability.

Representation and selection of assembly sequences in computer-aided assembly process planning

Abstract: In order to determine the best sequence to be used for the assembly of a product, all the feasible sequences should first be identified and then they should be evaluated in order to select the best one. However, since there usually exists a large number of feasible sequences, an efficient and compact representation method is necessary. A representation method called the Assembly Sequence Graph is presented in this paper, which offers a useful tool to the engineers in the industry in order to conveniently represent all the feasible assembly sequences, and then to evaluate them using qualitative and quantitative criteria. An example has been provided to illustrate the proposed approach.

Application of simulated annealing to a linear model forthe formulation of machine cells ingroup technology

Abstract: The central issue in group technology is the cell formation problem, which involves the grouping of parts into families and machines into cells, so that parts with similar manufacturing (and design) attributes are identified and processed by dedicated cells of machines. In the present work, the cell formation problem is modelled as a linear integer programming problem with the objective of minimizing the number of intercellular moves subject to cell-size constraints and taking into account the machine operation sequence of each part. An interesting feature of the proposed formulation is that there is no need of specifying a priori the number of cells to be used, which is automatically adjusted within the solution procedure. A very efficient random search heuristic algorithm, based on the simulated annealing method, is adopted for its solution. The heuristic is tested on a number of problems and its performance is evaluated. Subsequently, a straight forward model is presented to identify the families of pa...

Preprocessing for static and dynamic facility layout problems

Abstract: Most facility layout problems have departments with unequal areas and have significant rearrangement costs. This paper describes a model and improved algorithm which simultaneously handles these parameters. An existing algorithm solves the dynamic facilities layout problem while permitting the departments to have unequal areas. One part of the algorithm solves a mixed integer programming problem to find the desired block diagram layout. This large, complex problem could only be solved optimally for small problems. Therefore a preprocessing method was developed to prespecify certain obvious department pair orientations, which had previously required binary variables. The method uses estimated location, department sizes, and flow costs to determine the probable variable values. Then, a revised branch and bound strategy solves for the less obvious department pair orientations. Test results show a significant cost reduction on a variety of previously published problems, and feasible solutions to previously un...

Optimal selection of process parameters for turning operations in a CAPP system

Abstract: The importance of optimization of process parameters is increasingly felt in the wake of the adoption of expensive NC technologies into the shop-floor. In this context, the present paper reports the development of an optimization module for determining process parameters for turning operations as part of a PC-based generative C flexibility in the model formulation is highlighted. Following this, improved mathematical models are formulated by modifying the tolerance and workpiece rigidity constraints for multipass turning operations. The formulated models are solved by the combination of geometric and linear programming techniques. APP system. The need for an optimization approach that permits

An uncertainty importance measure of activities in PERT networks

Abstract: In a PE RT network, the importance of each activity needs to be assessed in order to identify those that warrant more attention from the project management. For this purpose, two measures are frequently used: criticality index; and uncertainty importance measure. While the former is used to identify which activity's expected duration to decrease in order to decrease the expected project completion time, the latter can be used to identify those that deserve more attention in reducing the magnitude of the uncertainty (variability) in the project completion time ( T ). This paper defines an uncertainty-importance measure of an activity, or of a pair of activities, and develops a method for evaluating the defined measure under the assumption that the durations of activities are independently and symmetrically distributed. The method utilizes Taguchi tolerance design technique with modifications. First, PE RT networks are classified into two types: Type A with a dominantly longer path than the others, and Type...

A post-industrial paradigm: To integrate and automate manufacturing

Abstract: The research team conducted in-depth, on-site interviews with executives from four companies to understand how these organizations cope with automation and integration. The authors contend that management's approach to automation and integration, which was developed in the industrial stage, may not be successful as firms enter a post-industrial environment characterized by global competition, rapid market change, shorter product life cycles, and advances in manufacturing and information technology. In the industrial stage, managers tend to select the 'best' method to automate specific tasks, creating islands of automation. Once these automation efforts are working, they are integrated by linking these islands with automated material handling capabilities and appropriate paperwork flows. This approach often leads to a less than optimal automation effort and results in manufacturing systems which are not capable of responding quickly or effectively to rapidly changing customer needs. Firms operating in the ...

Design for agile assembly: An operational perspective

Abstract: The concept of agile manufacturing is driven by the need to quickly respond to the changing customer requirements. Agile manufacturing demands a manufacturing system to be able to produce efficiently a large variety of products and be reconfigurable to accommodate changes in the product mix and product designs. The manufacturing system reconfigurability and product variety are critical in agile manufacturing. The concept of agility has an impact on design of assemblies. To implement agile manufacturing, methodologies of design for agile manufacturing are needed. Design for agile assembly is accomplished by considering operational issues of assembly systems at the early product design stage. In this paper, three rules applicable to the design of products for agile assembly from an operational perspective are proposed. These rules are intended to support the design of products to meet the requirements of agile manufacturing. Illustrative examples are provided to demonstrate the potential of the design rules...