Asymptotic loss of priority scheduling policies in closed re-entrant lines: a computational study

In this paper we present an approximate but efficient analytical method to compute the asymptotic loss of buffer priority scheduling policies in closed re-entrant lines. For simple two-station closed re-entrant lines, this enables the verification of Harrison-Wein conjectures and Jin-Ou-Kumar resuts. For multi-station re-entrant lines, this provides an efficient way of comparing different buffer priority scheduling policies. We also use the method to evaluate the effect of high priority jobs in re-entrant lines

Performance analysis of manufacturing networks : surplus-based control

In the modern market, keeping high competition in brands and varieties in type of products is the way for survival of manufacturing industries. Therefore production control methods with capabilities of quick responses to rapid changes in the demand and efficient distribution of the raw material throughout the network are of importance among leading manufacturers. Nowadays, the production control problem has been widely studied and a lot of valuable approaches including queuing theory, Petri nets, dynamic programming, linear programming, hybrid systems were proposed and some of them are implemented. Though up to this moment many methods have been developed, the factory performance remains a challenging problem for further research. Motivated by this problem we study the performance of several manufacturing networks operated by surplus-based control. In the surplus-based control, decisions are made based on the demand tracking error, which is the difference between the cumulative demand and the cumulative output of the network. The studied networks are a single machine, a manufacturing line, a multi-product manufacturing line, a re-entrant machine and a re-entrant line. The performance analysis is based on the performance factors such as demand tracking errors and inventory levels. Specifically, given the presence of unknown but bounded production speed perturbations as well as demand rate fluctuations, we investigate how close the cumulative production output of a manufacturing network follows its cumulative production demand under a surplus-based control policy. The research is subdivided into theoretical analysis, simulation-based analysis and experimental analysis parts. Theoretical analysis By means of analytical tools, the relation between the production demand tracking accuracy and the inventory levels of the networks is investigated. In order to find this relation, classical tools from control theory are used. Models of production flow processes are formulated by means of difference as well as differential equations. In order to analyze their performance, optimal control theory and Lyapunov theory approaches are exploited. Simulation based analysis By means of simulation tools, the theoretical results on performance are evaluated by time-based simulation models. Thus, all theoretical results are illustrated and confirmed by computer simulation. Also two comparative studies are conducted. The first comparative study is realized in order to test the theoretical results on more accurate models, which are event-based. The results are shown to be in agreement with the theory. The second comparative study is on time-based models, where the behavior of a line, a single re-entrant machine and a re-entrant line is tested under three commonly used surplus-based production policies. The performance of each network is evaluated and the results are presented. Experimental analysis An experimental prototype is invented, designed and developed for education and research purposes. The prototype is a hardware tool that serves as a liquid-based emulator of manufacturing network processes. In its core, the liquid-based emulator consists of several electrical pumps and liquid reservoirs. The electrical pumps emulate manufacturing machine behavior, while the liquid reservoirs serve as the intermediate product storages, also called buffers. In the platform, pumps and tanks can be interconnected in a flexible manner. In that way the prototype permits an easy and intuitive way of studying manufacturing control techniques and performance of several network topologies. A detailed system description is provided. Several network configurations and experimentations are presented and discussed

Is good enough 'making do'?: An investigation of inappropriate processing in a small design and build company

Purpose: The aim was to address behaviour that led to inappropriate processing in a small design and build contracting organisation that employs direct labour. The objective was to reduce process waste and improve the value delivered to clients. This formed part of a larger knowledge transfer project (KTP) to improve performance on construction sites through the application of lean thinking. Methodology: Action research was used to identify and bring about change within the contracting organisation. The method was applied to live construction projects in the social housing sector in the greater London area. The intervention was to raise the awareness of site personnel to the importance of finishing tasks through informal discussions and visual management techniques. Findings: Raised awareness of the importance of finishing work to allow other trades to follow on unimpeded led to significant improvements in the quality and flow of work. This helped to contribute to significant savings in time and cost. Practical implications: This applied research is practical and cost effective to apply to live projects managed by small and medium sized contracting organisations. Academic implications: the observations made reveal a form of waste in construction that has not been widely recognised in the literature on Lean. Research limitations: Findings relate to a small SME with directly employed labour, therefore the findings have limited applicability. Further applied research is required to determine the generalisation of the approach/findings to organisations that subcontract their labour Originality/value: Provides a unique insight into the practical application of lean thinking tools and process improvement

APPROXIMATE ANALYSIS OF RE-ENTRANT LINES WITH BERNOULLI RELIABILITY MODELS

Re-entrant lines are widely used in many manufacturing systems, such as semiconductor, electronics, etc. However, the performance analysis of re-entrant lines is largely unexplored due to its complexity. In this thesis, we present iterative procedures to approximate the production rate of re-entrant lines with Bernoulli reliability of machines. The convergence of the algorithms, uniqueness of the solution, and structural properties, have been proved analytically. The accuracy of the procedures is investigated numerically. It is shown that the approaches developed can either provide a lower bound or a closed estimate of the system production rate. Finally, a case study of automotive ignition component line with re-entrant washing operations is introduced to illustrate the applicability of the method. The results of this study suggest a possible route for modeling and analysis of re-entrant systems

Modeling and Performance Analysis of Manufacturing Systems Using Max-Plus Algebra

In response to increased competition, manufacturing systems are becoming more complex in order to provide the flexibility and responsiveness required by the market. The increased complexity requires decision support tools that can provide insight into the effect of system changes on performance in an efficient and timely manner. Max-Plus algebra is a mathematical tool that can model manufacturing systems in linear equations similar to state-space equations used to model physical systems. These equations can be used in providing insight into the performance of systems that would otherwise require numerous time consuming simulations. This research tackles two challenges that currently hinder the applicability of the use of max-plus algebra in industry. The first problem is the difficulty of deriving the max-plus equations that model complex manufacturing systems. That challenge was overcome through developing a method for automatically generating the max-plus equations for manufacturing systems and presenting them in a form that allows analyzing and comparing any number of possible line configurations in an efficient manner; as well as giving insights into the effects of changing system parameters such as the effects of adding buffers to the system or changing buffers sizes on various system performance measures. The developed equations can also be used in the operation phase to analyze possible line improvements and line reconfigurations due to product changes. The second challenge is the absence of max-plus models for special types of manufacturing systems. For this, max-plus models were developed for the first time for modeling mixed model assembly lines (MMALs) and re-entrant manufacturing systems. The developed methods and tools are applied to case studies of actual manufacturing systems to demonstrate the effectiveness of the developed tools in providing important insight and analysis of manufacturing systems performance. While not covering all types of manufacturing systems, the models presented in this thesis represent a wide variety of systems that are structurally different and thus prove that max-plus algebra is a practical tool that can be used by engineers and managers in modeling and decision support both in the design and operation phases of manufacturing systems

Workload control in job shops with re-entrant flows:an assessment by simulation

One of the key functions of Workload Control is order release. Jobs are not released immediately onto the shop floor – they are withheld and selectively released to create a mix of jobs that keeps work-in-process within limits and meet due dates. A recent implementation of Workload Control’s release method highlighted an important issue thus far overlooked by research: How to accommodate re-entrant flows, whereby a station is visited multiple times by the same job? We present the first study to compare the performance of Workload Control both with and without re-entrant flows. Simulation results from a job shop model highlight two important aspects: (i) re-entrant flows increase variability in the work arriving at a station, leading to a direct detrimental effect on performance; (ii) re-entrant flows affect the release decision-making process since the load contribution of all visits by a job to a station has to fit within the norm. Both aspects have implications for practice and our interpretation of previous research since: (i) parameters given for work arriving may significantly differ from those realised; (ii) increased workload contributions at release mean that prior simulations may have been unstable, leading to some jobs never being released

Game Theory Analysis of Aircraft Manufacturer Innovation Strategies in the Face of Increasing Airline Fuel Costs

The air transportation system is a vital infrastructure that enables economic growth and provides significant social benefits. Future increases and volatility in crude oil prices, as well as environmental charges, are likely to increase the effective cost of fuel. We investigate the impacts of effective fuel cost increase on the US air transportation system historically and perform a game theory analysis of the impact of manufacturer competition on the introduction of new, more fuel efficient aircraft. The cost of jet fuel increased 244% between July 2004 and July 2008, providing a natural experiment to evaluate how fuel price increase affected continental US networks and fleets. It was found that non-hub airports serving small communities lost 12% of connections, compared to a system-wide average loss of 2.8%. Increased effective fuel costs will provide incentives for airlines to improve fleet fuel efficiency, reducing the environmental impacts of aviation, but may cause an uneven distribution of social and economic impacts if small communities suffer greater loss of mobility. Government action may be required to determine acceptable levels of access as the system transitions to higher fuel costs. Technology innovation may act as a long-term hedge against increasing effective fuel costs, enabling mobility to be maintained. The single aisle commercial aircraft market segment is the largest, but has the longest running product lines. We hypothesize that competition has important effects on manufacturers’ decisions to innovate that must be considered when designing policies to reduce fleet emissions. An aircraft program valuation model is developed to estimate expected payoffs to manufacturers under competitive scenarios. A game theory analysis demonstrates how the incentives to innovate may be altered by subsidies, technology forcing regulations, increased effective fuel costs, the threat of new entrants, and long-term competitive strategies. Increased competition may result in incumbent manufacturers producing re-engined aircraft while increased effective fuel costs may result in new aircraft programs. Incumbents’ optimal strategies may be to delay the entry of new single aisle aircraft until 2020-24, unless technology forcing regulations are implemented.This work was supported by the MIT/Masdar Institute of Science and Technology under grant number Mubadala Development Co. Agreement 12/1/06. The authors wish to thank PARTNER for access to the Piano-X software package and Robert M. Peterson from the Boeing Corporation for his valuable feedback on the aircraft program valuation model. Any errors are the authors’ alone

An Analysis of the Boiler and Heat Exchanger Manufacturing Industry in the US Using Porter's Five Forces Framework

As global trade expands and technological progress is being made in developing countries, manufacturers of boilers and heat exchangers in the United States (US) are facing increasing import competition while industry profitability is competed away from industry rivals, market entrants, as well as by the growing number of available choices for buyers, and by suppliers with larger clientele and differentiated products and services. The forces that influence profitability in this industry is an essential part of strategic planning for any boiler and heat exchanger manufacturer that aims to control competition risk and optimize profitability. This research aims to break down and analyze the influences that industry manufacturers, market entrants, purchasers, component and raw material suppliers, foreign imports, technological advances, government policies, industry organizations, and future trends have on the profitability of industry players. While it was found that the level of competition in the industry is moderate, rapid advances in technology, increasingly stringent government policies on emission standards and boiler and heat exchanger efficiencies, as well as growing import competition may catalyze industry competition in the near future. The use of Porter’s five forces in this analysis suggests the need to consider the significance of technology and the challenges posed by imports through increasing globalization, as these factors could substantially change and disrupt the industry by reducing barriers to entry and by raising the threat of substitutes. As a result, the boiler and heat exchanger manufacturing landscape in the US could become much more competitive, which in turn, could diminish returns for industry operators. This could also change the structure of the industry with the inception of industry players that offer differentiated products and services. The question for industry groups and policy-makers is to what extent should these five forces be influenced, since the degree of support for or of counteraction to these forces will guide the future competitiveness and marketization of the boiler and heat exchanger manufacturing industry in the US.

Firm Entry, Productivity Differentials and Turnovers in Import Substituting Markets: A study of the petrochemical industry in Colombia

This paper analyses plant entry, total factor productivity growth, average productivity level differentials and turnovers across Colombia's petrochemical industry for the 1974-1998 period. Results show that successful entrants shaped industry productivity and induced plant restructuring among incumbent plants. There is consistent plant heterogeneity across plant cohorts as well as across sub-markets within petrochemicals. Entry flows were steady increasing within plastics regardless of trade policy regimes. Survival rates are remarkably high and consistent over time in medium-size plants meaning that entrants adopted competitive post-entry strategies. Total factor productivity growth decomposition shows that the incumbent effect dominates the turnover effect. Market share reallocation among continuing plants constitutes an important source of productivity growth. Econometric results suggest that barriers to entry associated with plant technology licensing and dependence of imported raw materials deter entry while complementary market variables such as industry productivity levels, growth in housing construction, and fringe competition induce firm entry.Entry, Turnover, Total Factor Productivity, Petrochemical Industry

Aggregate modeling of manufacturing systems

In this report we will present three approaches to model manufacturing systems in an aggregate way leading to fast and effective (i.e., scalable) simulations that allow the development of simulation tools for rapid exploration of different production scenarios in a factory as well as in a whole supply chain. We will present the main ideas and show some validation studies. Fundamental references are given for more detailed studies