A review of quantitative approaches in just-in-time manufacturing

The objectives of this survey are four-fold: (1) to describe the principle of just-in-time production, (2) to provide an overview of the problems and research issues in scheduling, lot sizing and determining the number of kanbans, (3) to describe prior studies which use quantitative approaches to study JIT production and its variant systems including simulation, stochastic process, and mathematical programming, and (4) to identify fertile opportunities for further research in the quantitative analysis of JIT production.     

A comment on: A note on the EOQ-JIT relationship

In a recently published note in this journal the need for independent control of the production rate (R) and production time (L) was established in order to adapt the economic production quantity (EPQ) model in JIT settings. In this comment we aim to improve the relevance of EPQ in a JIT environment. We focus on two issues, namely, modelling the production rate as a decision variable and also deriving an expession for the optimal number of batches (n* ) for the raw materials and/or subcomponents needed.     

JIT purchasing: attribute classification and literature review

To find critical JIT purchasing attributes for manufacturing industry, 56 refereed articles are reviewed. These articles are categorized as conceptual, case and empirical studies. Thirty-four attributes are thus identified. An input-output model is developed to classify these attributes. The inputs to JIT purchasing environment consists of buyer, supplier and joint buyer-supplier actions with 13, six and six attributes, respectively. The interaction between these attributes leads to the JIT purchasing environment. Output of this environment consists of nine attributes. By using the frequency of citation of an attribute as a measure of its importance, consensus is found among conceptual and case studies regarding those attributes of JIT purchasing considered critical. However, many of these attributes have not been investigated empirically, while others have not been rigorously examined. Common supplier evaluation criteria are identified. Benefits and problems with JIT purchasing implementation are discussed. Analysis suggests the need for comprehensive and statistically rigorous empirical studies.     

An investigation into the use of OPT production scheduling

The paper is a case study describing the experience of a single company which uses OPT software for production scheduling. The company produces a range of over 500 different items. Optimized Production Technology (OPT) is a proprietary computer software. Although the OPT software requires a similar database to MRP systems and addresses the same problems, OPT is a finite scheduler, unlike MRP which assumes (unrealistically) infinite capacity. The paper defines the underlying terminology and explains the major features of the algorithm underpinning the software. Details of the scheduling frequency, scheduling routine and reports are described. Practical implications observed are the necessity of short process routes and a multi-skilled workforce (somewhat like the case of JIT cells). Benefits of using the system are discussed.     

A note on an economic production quantity model and just-in-time production

In this paper an economic production quantity (EPQ) model in which the production rate is variable is studied. An analysis is presented of the impact of a variable production rate on the optimal production quantity and the total relevant cost. It is observed that this EPQ production and inventory system, in which the production rate is close to the demand rate, possesses many characteristics that are similar to a just-in-time (JIT) production system. It is shown that the normal prerequisites and benefits of JIT production can be identified from an analysis of such an EPQ system.     

A chance-constraints linear programming model on the economic evaluation of flexible manufacturing systems

The implementation of flexible manufacturing systems (FMSs) normally entails a large initial investment under a long-term, uncertain environment. Many effects of installing a FMS will be due to improvement in throughput efficiency, quality, flexibility and the opportunity costs. However, most economic evaluations of FMSs assume the problem is deterministic, such that they fail to model accurately and capture the nature of FMSs. This paper uses stochastic variables to capture the.nature of a FMS under given resource limitations and leads to a multistage chance-constraints linear programming (LP) formulation. Finally, in order to incorporate the uncertainty of capital investment, the interest rate as a function of time is considered over the whole planning horizon and the decision model is extended under continuous and variable discounting.     

Production planning and control in automated manufacturing systems

Automated manufacturing systems (AMSs) have the potential for providing a high level of manufacturing performance. Owing to the high cost of capital investment, a high utilization level of AMSs with the help of suitable production planning and control (PPC) is feature of AMSs. Realizing the potential of PPC in AMSs, an attempt has been made to review the available techniques/methods for solving the problems of production planning, control and scheduling in AMSs. The need for further research on PPC of AMSs is brought to the fore along with future research directions.     

Some implementation experiences with just-in-time manufacturing

A case study on the implementation of a just-in-time (JIT) production system by a Canadian manufacturer in the heavy machinery industry is presented. Many hurdles and difficulties were encountered during implementation and the way in which these problems were resolved is reported. While the successful implementation of a JIT system depends on a host of technical and human factors, this study suggests that the people involvement factor is the most crucial. It is seen that the key elements to securing people involvement are institution leadership, company-wide education and training and mutual understanding, trust and respect among employees. The moral of this study is that without employee involvement nothing will happen and no result will be achieved.     

KBSS: a knowledge-based job-shop scheduling system*

Abstract. A knowledge based job-shop scheduling system (KBSS), which employs artificial intelligence techniques to solve general job-shop problems, is presented. The system consists of two main components: a knowledge base (KBSS model) and a control mechanism. The KBSS model has a three-level architecture which captures, in frames, knowledge about the job-shop domain and the characteristics of individual job-shop problems. The control mechanism consists of two modules: the primary scheduler (PS) and the heuristic scheduler (HS). PS is a rule-based scheduler built around a time-transcending heuristic which attempts to minimize the makespan and meet the due dates. If PS fails to meet the due dates then HS applies a combination of A* and beam search techniques in the space of alternative solutions and returns the best alternative it finds. The emphasis on due dates is a distinctive feature of KBSS. Experience with evaluating the presented scheduling system is reported and discussed.     

A methodology for industrial studies of productivity performance

This article describes a methodology for measuring productivity and competitiveness in industry. The methodology is developed mainly for the mechanical industry (including shipyards, offshore and electromechanical companies). Two different approaches are described—one is based on a self-audit using a questionnaire answered by the industry itself, the second, using a more complete audit, is based on expert teams analysing the company. The productivity is described by indicators given points on a scale from 1 to 7 (1—far behind international competitors, 7—(best practice’).     

Job sequencing to minimize tool changeovers in flexible manufacturing systems

The combination of group technology and heuristic is used to schedule jobs on a machine equipped with an automatic tool changer (ATC). The problem is prominent in flexible manufacturing systems where the efficiency in operation is, in part, obtained by use of ATC. The procedure presented here is efficient and does not require complex mathematics.     

Building a short-term production planning system for flexible manufacturing systems: an integration viewpoint

From the viewpoint of integration, the production objective of flexible manufacturing systems (FMS) should follow results of MRP/CRP. Thus, the planning goal of short-term production planning (STPP) is to satisfy quantity and due date requirements determined by MRP/CRP. The STPP of FMS should cover part type selection, production ratio, process selection, process ratio, resource allocation, machine grouping, routing mix and loading problems.

A STPP system is built to solve the STPP problem of an FMS having multiple machine types, each with multiple m.'ichinc units. This system adopts a variable-period flexible planning approach, using part mix and process selection flexibilities to solve STPP problems. It also provides flexibilities in its operations sequence and in the machine routing to the dynamic operation planning system.     

Hierarchical control of semi-automated production systems

An integrated control model of a hierarchical production system is presented where the output can be measured only at preset control points as it is impossible or costly to measure it continuously. Three levels are considered—company, section, production unit—each level faces stochastic optimization problems. Each unit produces a given target amount by a given due date (common to all units) and has several possible speeds, which are subject to disturbances. On the unit level, at each control point, decision-making centres on determining both the next control point and the speed to proceed with up to that point. The section level is faced with problems of either reallocating resources among the section's units or reassigning the remaining target amounts among the units so that the faster one will help the slower one. The company level is faced with similar problems, i.e. reallocating resources or reassigning target amounts among the sections. Two different cases are considered: (1) cost parameters are not taken into account, i.e. there are two conflicting objectives, namely to maximize the probability of completing the production on the due date and to minimize the number of control points, but the first objective is dominant; (2) the objective is to maximize the expected net profit. Various optimization problems at each level are presented. Examples from steel, construction and mining industries are given.     

Time aggregation in production control and scheduling: towards efficient decision-support systems

A software system is developed for efficient optimal scheduling and production control in process industries modelled by production departments separated by buffers in serial or recycled paths. The new concept of time aggregation presented is easily implementable allowing a very fast solution of the optimal control of buffer levels. This optimal control problem is a large scale singular one (due to the chosen cost function) conveniently solved by a special technique of hierarchical calculus:'the iterative solution of a sequence of nonsin-gular problems converging to the singular one. Numerical results applied to a pulp and paper mill show that the new algorithm is substantially faster than the one previously used. This fact allowed the development of a complete software platform, presented in the paper, composed of several modules: modelling of industrial complex, (re)configuration, simulation, optimization, user interface—aiming at the realization of a decision support system for interactive use by daily operators and in instruction activities.     

Performance measurement systems and time-based manufacturing

Today's production environment is often undermined by control mechanisms that were designed for another era. Specifically, most organizations control manufacturing wholly or in part using cost-based performance measurement systems. Depending upon the firm's objectives and key manufacturing task(s), too much attention upon cost considerations can have devastating effects upon overall performance. This paper discusses this issue in the context of corporations that increasingly find themselves competing for business on the dimension of time. A case study is presented to illustrate how time-based companies can be adversely affected by an overemphasis upon cost.     

Reducing delivery times for OKP products

The management of the manufacture of ‘one-of-a-kind’ products (OKP) is a neglected field in production management. The key to an improvement in productivity and profitability in this field appears to depend mainly on a reduction in the delivery times for products, which in turn requires a reduction in material throughput times, and in design and production planning lead times. This paper looks at some of the ways which can be used to reduce OKP delivery times.     

Simulating alternative organizational structures of production systems

Changes in international competition lead to changes of the requirements on production enterprises. The introduction of new production technologies does not seem to be exclusively an adequate reaction to the increasing problems. Therefore tools of computer-integrated production (CIM) and new organizational concepts have to be conceived. Because these organizational and technical means are linked on the one hand with severe changes in the production system and, on the other hand, with rather higher economic risks in their realization, the effects have to be estimated in advance in the planning stage. Consideration of dynamical system behaviour plays an important part because the main goal is the improvement of order processing. This paper presents a simulation program, which can be used during the design phase of the organizational structure of production systems as a powerful tool for predicting the effects of new computer-aided tools and structures.     

A step-by-step guide to the identification of an appropriate computer-aided production management system

The increasing dissatisfaction of users with their Computer-aided production management (CAPM) systems has been widely reported. This dissatisfaction led the UK's Science and Engineering Research Council to initiate a major study to improve CAPM systems use. The research results presented here form part of the overall initiative and focus on the development of a set of guiding principles for companies seeking to implement appropriate CAPM systems. The research team have identified three key elements that must be considered when implementing a CAPM system. First, that CAPM implementation can be eased if the overall manufacturing-system is first simplified. Second, we recognize that even then most companies will still require a computerized solution thus any methodology must include a software specification. Third, the overall performance of the system may be enhanced by changes to the infrastructure that supports the software. In attempting to meet these requirements the research team developed a four-stage methodology. The first two stages of the methodology deal primarily with the strategic context for CAPM, i.e. the simplification. The last two stages develop a software specification and present guidelines for the development of appropriate infrastructure configurations.     

Production planning and control within a CIM environment: some current developments and requirements for the future

Abstract. This paper considers the integration problems associated with incorporating production planning and control (PP&C) systems within CIM; these problems are typically not differentiated from functionally related problems, and have in the past received relatively little attention. The on-going emergence of a number of standards relevant to manufacturing software systems provides an opportunity to assess the current situation with regard to proprietary PP&C systems and to suggest ways forward towards ‘seamless’ integration of PP&C within the CIM environment. The problems arising from conventional integration approaches are briefly described, and the concept of a simplifying ‘integration platform’ is introduced; the three-schema information architecture is presented as part of this ‘integration simplification’ approach. Current and developing PP&C systems are assessed against a number of information system integration criteria, and the results of a small survey of proprietary packages are presented. The paper concludes that information must be regarded as an enterprise-wide asset, rather than belonging to individual software applications, and that the adoption of relevant standards will enable seamless integration within a three-schema architecture. An increasing number of proprietary packages are adopting standards and methodologies which ease the integration problem significantly.