Dimitris Mourtzis

Digital manufacturing: History, perspectives, and outlook

Abstract Digital manufacturing has been considered, over the last decade, as a highly promising set of technologies for reducing product development times and cost as well as for addressing the need for customization, increased product quality, and faster response to the market. This paper describes the evolution of information technology systems in manufacturing, outlining their characteristics and the challenges to be addressed in the future. Together with the digital manufacturing and factory concepts, the technologies considered in this paper include computer-aided design, engineering, process planning and manufacturing, product data and life-cycle management, simulation and virtual reality, automation, process control, shopfloor scheduling, decision support, decision making, manufacturing resource planning, enterprise resource planning, logistics, supply chain management, and e-commerce systems. These technologies are discussed in the context of the digital factory and manufacturing concepts.

DESYMA: assessing flexibility for the lifecycle of manufacturing systems

The objective of this work is to describe a method of assessing the flexibility of a manufacturing system, in an uncertain market environment, under lifecycle considerations. The flexibility of a manufacturing system is determined by statistical analysis of the discounted cash flow (DCF) estimates of the manufacturing systems lifecycle cost, over a time horizon and for a large variety of market scenarios. The systems lifecycle cost is calculated at a minimum level with the help of a specially developed algorithm. The method is used in a test case for investing in a production system, using real-life data derived from the automotive industry.

Refinery short-term scheduling with tank farm, inventory and distillation management: An integrated simulation-based approach

This work addresses primarily the scheduling of a refinery importing various types of crude oil. The refinery operation discussed in this paper involves the unloading of crude oil to storage tanks, the transfer and blending from storage tanks to charging tanks and crude oil distillation units, and the arrangement of the temperature cut-points for each distillation unit. The paper describes a simulation-based approach to the refinery operation, which is modelled as a pooling problem. The proposed approach uses a random-search formulation, which allows for controlling search depth, breadth and solution quality, as well as computational effort. An implementation of the proposed approach is presented in a real case scenario.

Quantifying the flexibility of a manufacturing system by applying the transfer function

This paper discusses a method of estimating the flexibility of a manufacturing system. The proposed approach is motivated by the dynamic behaviour analogy between a mechanical and a manufacturing system. The main hypothesis is that the flexibility of a manufacturing system can be calculated in the same manner as the damping factor of a mechanical system. In order for the validity of the proposed method to be tested and discussed, a set of experiments has been designed and executed, initially for a simple production system. An industrial production system has also been studied using the same approach. The results prove that this method can be used for the estimation of a manufacturing systems flexibility.

Chaos Theory in Production Scheduling

Abstract In this paper the concept of chaos in manufacturing systems is briefly introduced and tools used in the characterization of a chaotic system are discussed. The scheduling of a simple manufacturing system, with the help of commonly used assignment rules, has been simulated first. The results have been studied with the help of phase portraits. Some conclusions have been drawn and a new method for scheduling is proposed. The method is tested against conventional rules and the results are evaluated and discussed.

Oscillator analogy for modelling the manufacturing systems dynamics

The purpose of this paper is to present an approach of modelling and analysis of the dynamic behaviour of manufacturing systems. The manufacturing system is considered to be responding to an excitation, namely a demand that varies over time, by producing a number of parts over time. This resembles a mechanical system that displaces its mass responding to a varying input force. Based on this analogy, this paper establishes a manufacturing systems modelling method. A system identification technique is used for deriving inertia, damping and stiffness from the manufacturing systems response to different excitations. Based on these attributes, the response of a manufacturing system to any given input can be estimated. Furthermore, a definition for assessing manufacturing flexibility, based on this approach, is being discussed.

An integrated system for managing ship repair operations

The global competition pressure drives manufacturing companies to be lean, virtual and global. However many manufacturing companies, such as ship repair yards, are handicapped in marketing competition owing to their complex and uncertain manufacturing environment, resulting in problems related to scheduling, control and capacity planning of their manufacturing operations. The approach discussed in this paper is designed to support the management of a ship repair yard by integrating in an open and flexible system a number of critical business functions with production planning, scheduling and control. This approach is implemented in a software system fully developed in Java and designed by using UML. The proposed software system operates at a ship repair yard in a pilot mode, concurrently with the existing working practice. With the use of the new concept for production planning activities, the managers of the shipyard are assisted to produce overall schedules in a more efficient way in order to allocate work in the various departments.

A simulation-based hybrid backwards scheduling framework for manufacturing systems

This paper presents a hybrid backwards-scheduling method, referred to as HBS, which mainly addresses discrete manufacturing environments. It operates under the framework of hierarchical finite capacity shop-floor modelling and discrete event simulation. HBS applies a set of transformation relations in order to convert a finite capacity forwards scheduling method (FS) that can employ different assignment policies to their backward counterparts. These policies include both single criterion conventional dispatching rules, as well as an adjustable multiple-criteria decision making technique that can take into consideration a number of different conflicting criteria, such as flowtime, tardiness and manufacturing cost. Performance of the HBS method was studied through a set of simulation experiments in a typical textile industry and was evaluated through a number of relevant performance indicators.

Flexibility evaluation: A toolbox approach

Flexibility is an important aspect of modern manufacturing systems. Although a systems capability to monitor, predict and improve flexibility has long been considered as a major competitive advantage, the development of methods and algorithms for the measurement of manufacturing flexibility remains an open issue both from an academic and an industrial point of view. The purpose of this work is to propose a holistic approach for short, mid- and long-term flexibility performance measuring and monitoring in industrial practice. In the core of the suggested approach stands a flexibility evaluation toolbox, which can be utilised for real-life industrial cases.

Dispatching policy for manufacturing jobs and time-delay plots

In the present paper, the concepts of chaos and nonlinear dynamics are briefly introduced and the tools used in the characterization of a chaotic or nonlinear system are discussed for studying the performance of dispatching policies in manufacturing systems. The scheduling of a simple manufacturing system with the help of common assignment rules has been simulated first. The results are studied and analysed with the help of time-delay plots. Some conclusions are drawn and, based on them, a new method of scheduling is proposed. The method is tested against conventional rules and the results are evaluated and discussed, specifically by addressing practical and generalization issues.