This dissertation is concerned with the tail asymptotics of queueing networks with subexponential service time distributions. Our objective is to investigate the tail characteristics of key performance measures such as cycle times and waiting times on a variety of queueing models which may arise in many applications such as communication and manufacturing systems. First, we focus on a general class of closed feedforward fork and join queueing networks under the assumption that the service time distribution of at least one station is subexponential. Our goal is to derive the tail asymptotics of transient cycle times and waiting times. Furthermore, we argue that under certain conditions the asymptotic tail distributions remain the same for stationary cycle times and waiting times. Finally, we provide numerical experiments in order to understand how fast the convergence of tail probabilities of cycle times and waiting times is to their asymptotic counter parts. Next, we consider closed tandem queues with finite buffers between stations. We assume that at least one station has a subexponential service time distribution. We analyze this system under communication blocking and manufacturing blocking rules. We are interested in the tail asymptotics of transient cycle times and waiting times. Furthermore, we study under which conditions on system parameters a stationary regime exists and the transient results can be generalized to stationary counter parts. Finally, we provide numerical examples to understand the convergence behavior of the tail asymptotics of transient cycle times and waiting times. Finally, we study open tandem queueing networks with subexponential service time distributions. We assume that number of customers in front of the first station is infinite and there is infinite room for finished customers after the last station but the size of the buffer between two consecutive stations is finite. Using (max,+) linear recursions, we investigate the tail asymptotics of transient response times and waiting times under both communication blocking and manufacturing blocking schemes. We also discuss under which conditions these results can be generalized to the tail asymptotics of stationary response times and waiting times. Finally, we provide numerical examples to investigate the convergence of the tail probabilities of transient response times and waiting times to their asymptotic counter parts.

Dans le processus de fabrication en fraisage à grande vitesse ‘FGV’, l’étude de la réaction de la machine au cours de l’usinage est une tâche très délicate et importante. En effet, l’identification du comportement de la machine nécessite la modélisation de la loi de mouvement des axes et de la trajectoire réelle aux niveaux des discontinuités. Le nombre important de discontinuités engendrent une instabilité de la vitesse de déplacement des axes, ce qui implique une augmentation du temps d’usinage et un non-respect de la vitesse d’avance programmée, se traduisant par des problèmes de productivité et une sous-estimation du coût de l’usinage pour l’industriel. L’objectif de cette thèse est de développer un outil informatique qui permet de calculer la vitesse d’avance et de faire une estimation précise du temps de cycle pour n’importe quelle trajectoire générée par un logiciel de FAO. Pour ce faire, nous avons déterminé un modèle qui permet d’identifier le comportement cinématique des axes d’un centre d’usinage en FGV pour toute forme de trajectoire. À partir de la modélisation de la variation de la vitesse d’avance, nous avons déterminé le temps réel selon les trajectoires et l’erreur imposée par le bureau des méthodes. Enfin, nous utilisons ces résultats pour mettre en place une méthodologie pour l’aide au choix du diamètre de l’outil et de la stratégie d’usinage. Afin de valider les modèles et les méthodologies développés, une étude expérimentale a été réalisée sur des applications didactiques et industrielles. / In the context of high speed milling ‘‘HSM’’, the feed rate does not always reach the programmed value during the machining process which implies an increase of machining time and non-compliance with the programmed feed rate. This phenomenon leads to productivity issues and an underestimation of the cost of machining for the industry.The aim of this study is to develop a computerised tool in order to automate the determination process of the evolution of the feed rate for an imposed error and the estimation of cycle time and production cost. To begin with,a modeling approach in order to evaluate feed rate during any type of discontinuity between linear and circular contours in different combination by taking into account the specific machining tolerances.is presented. Then, the cycle time will be estimated with a maximum error of 7% between the actual and the prediction cycle time. The proposed method permits to develop a methodology to determine the optimal diameter of the tool and the optimal strategy. Finally, an industrial application was carried out in order to validate models and to determine the influence of feed rate evolution on the cycle time.

This thesis deals with the optimisation of the selected manufacturing process. The aim is to analyse the effectiveness of the selected welding and assembly lines. Another objective is to do a detailed analysis for the line with the lowest efficiency in terms of cycle time and the Overall Equipment Effectiveness and calculate the lost production time due to availability, performance and defects. The third objective is to identify possible measures leading to higher utilization of manufacturing line and to propose a possible implementation. The theoretical part is based on the literature examining the term standardization, the norms of labour intensity, the cycle time, the Total Productive Maintenance and the calculation of the Overall Equipment Effectiveness. In the practical part the profile of Car manufacturing is being presented, the analysis of secondary data to calculate the Overall Equipment Effectiveness is being done and the appropriate manufacturing line for the innovative plan is being selected. Furthermore, the analysis of secondary data regarding the effectiveness of the using time of the manufacturing line is being done, the calculation of the Overall Equipment Effectiveness and the collection of primary data is being carried out. Subsequently, the problematic spots of the manufacturing line are being found and the possible measures leading to higher efficiency of manufacturing line are being proposed.

The constant needs for the reduction of companies operational costs has transformed Inventory into a targeted source for this end by upper management. The high investment value that it represents for organizations, aside from the immediate contribution to cash flow, when it is reduced, allows inventory to be a source of strategic advantage. The objective of this study is to understand the behavior of independent variables such as production cycletime or lead-time, daily demand rate of finished product and the interval between production orders and their effects on the determination of an inventory policy. The study is performed in a manufacturing company that produces intermittent, repetitive small batches and a large variety of products. Cash flow techniques are applied to detail the production processes and respective planning. The historical data of mentioned variables refer to the period from January 2000 to February 2002. These data are used to develop the calculations of safety stock and average and maximum stock from the viewpoint of the management approach in Replenishment Point and Periodically Review. The real application of the data available from the company is studied to calculate the inventory policy. It is concluded that, in spite of the adoption of a sophisticated mechanism of production planning and a strong culture of measurements by the company, the statistical data of fundamental variables are not utilized systematically to determine the inventory policy. This fact confirms the thesis that inventory reductions, in general, are circumstantial and is not supported by fundamental techniques. / A constante necessidade de redução dos custos operacionais das empresas tem transformado o Inventário em fonte preferencial, para este fim, pela alta administração. O alto valor de investimento que ele representa para as organizações, além da contribuição imediata no fluxo de caixa, quando da sua redução, faz com que o inventário seja uma fonte de vantagem competitiva.O objetivo deste estudo é compreender o comportamento das variáveis independentes como tempo de ciclo da produção ou lead-time, taxa diária de demanda do item de produto acabado e tempo de intervalo entre ordens de produção, e os seus efeitos no cálculo de uma política de inventário.O estudo é realizado em uma empresa de manufatura de produção intermitente repetitiva em lotes de pequenas quantidades e grande variedade de produtos.Técnicas de fluxo de valor são aplicadas para detalhamento dos processos de produção e do seu respectivo planejamento. Os dados históricos das variáveis mencionadas referem-se ao período de janeiro de 2000 a fevereiro de 2002. Com estes dados, desenvolvem-se os cálculos de estoque de segurança, estoque médio e máximo,sob a óptica das abordagens de gerenciamento por Ponto de Reposição e Revisão Periódica. Analisa-se a real aplicação dos dados disponíveis na empresa, para o cálculo da política de inventário. Conclui-se que apesar de ser adotado mecanismo sofisticado de planejamento de produção e haver uma forte cultura de medições por parte da empresa, os dados estatísticos das variáveis fundamentais não são utilizados de forma sistemática para o cálculo da política de inventário. Este fato confirma a tese de que as reduções de inventário, de uma maneira geral, são circunstanciais e não sustentadas por fundamentos técnicos.

Lean production is one of the proven approaches for identifying and eliminating the activities that do not add value to the customers and delivering and provide the best possible quality service to customers. Implementation of lean is deemed to be feasible in any organization regardless of its size or industry background. For initiating lean in an organization there are many tools, techniques and approaches that are available. Value Stream Mapping (VSM) is one such tool that is touted as cost-effective and easy to be implemented. This thesis proposes to conduct Value Stream Analysis (VSA) at at e-commerce (online) department at the case company to understand their material and information flows by analyzing the current state and develop implementable solutions to improve the overall productivity of the online deliveries. The tasks to perform are: · To map the current state value stream. · To identify wastages and propose solutions to eliminate them. · To provide productivity improvement proposals. A mix of quantitative and qualitative methods were used in this study for data collection and data analysis. This project, which is designed as a longitudinal case study that pri-marily focuses on gathering accurate, real-time data related to the product family, and on drawing a visual representation of the current materials and information flow. VSM has been implemented and the data were analysed. The results obtained from this study concludes that, VSM is an appropriate technique to initiate lean ways of work in larger firms that lacks sufficient knowledge and experience on lean. In addition to it, produc-tivity improvement proposals provided in this study are considered to be key factors in initiating lean transformation in an organization from a technical point of view while, management support and acceptance of change is necessary from an organizational point of view. This thesis will be useful to researchers, professionals and others con-cerned subject to understand the significance of value stream mapping in larger e-com-merce logistic firms.

This thesis deals with the analysis of data obtained by observing and measuring workplaces of assembly lines with a focus on the efficiency of their utilization, through selected elements of industrial engineering, which the reader can get acquainted with in the theoretical part of the thesis. In this thesis the line productivity during the shifts is analyzed, an ideal line balancing condition is defined and suggestion for changing the time of line consumption norm according to the measured line cycle time is made. According to the complex analyzes of the workplaces, suggestions are concluded and an economic appreciation of these proposals is also elaborated. The author of this thesis finds the main benefit of this work in increasing of the productivity of the analyzed line in the case of implementation of solution designs.

Despite decades of automation initiatives, manual assembly still represents one of the most cost-effective approaches in scenarios with high product variety and complex geometry. It represents 50% of total production time and 20% of total production cost. Understanding human performance and its impact in the assembly line is key in order to improve the overall performance of an assembly line. Along this thesis work, by studying the deviations occurring in the line, it is aimed to understand how human workers are affected by certain functioning aspects of the assembly line. To do so, three different influence factors have been chosen, and then observed its impact in human performance: i. How past events occurring in the line affect the current action of the worker. ii. How do scheduled stops affect the current action of the worker. iii. How does theoretical cycle time affect the performance of the worker. In order to observe these influence relationships, it has been used data gathered in the shop floor from SCANIA's Manufacturing Execution System (MES). By applying methods of Knowledge Discovery in Database (KDD) data has been indexed and the analyzed providing the necessary results for the study. Finally, from the results shown, it can be inferred that variability on the functioning of the line does have an impact on human performance overall. However, due the complexity of the manufacturing system, impact in human performance might not be as regular as initially thought. / Trots decennier av automatiseringsinitiativ utgör manuell montering fortfarande en av de mest kostnadseffektiva metoderna i scenarier med hög produktsortiment och komplex geometri. Den representerar 50% av den totala produktionstiden och 20% av den totala produktionskostnaden. Att förstå mänsklig prestanda och dess inverkan i monteringsledningen är nyckeln för att förbättra den totala prestandan hos en monteringslinje. Utöver detta avhandlingsarbete, genom att studera avvikelserna som uppstår i linjen, syftar det till att förstå hur mänskliga arbetstagare påverkas av vissa fungerande aspekter av monteringslinjen. För att göra det har tre olika inflytningsfaktorer valts och sedan observerat dess inverkan i mänsklig prestation: i. Hur tidigare händelser som uppstår i linjen påverkar arbetarens nuvarande åtgärder. ii. Hur påverkar planerade stopp arbetstagarens nuvarande åtgärder. iii. Hur påverkar teoretisk cykeltid arbetarens prestation. För att observera dessa inflytningsrelationer har det använts data som samlats in i butiksgolvetfrån SCANIAs Manufacturing Execution System (MES). Genom att tillämpa metoder för Knowledge Discovery i Database (KDD) har data indexerats och analyseras vilket ger de nödvändiga resultaten för studien. Slutligen kan det framgå av de visade resultaten att variationen i linjens funktion har en inverkan på den mänskliga prestationen övergripande. På grund av tillverkningssystemets komplexitet kan emellertid effekten i mänsklig prestanda inte vara så regelbunden som ursprungligen tänkt.

Purpose – The purpose of this master thesis was to enhance the knowledge of the relationship between digital tools and innovation speed. By doing so, adding to literature on innovation speed and digital tools.     Method – The method used in this study was a comparative case study with five case companies from a variety of industries in Sweden and Denmark. Data were collected and analysed in three waves, 1) explorative interviews used to set the scope of the study, 2) semi-structured interviews used to answer the research questions, 3) validatory interviews to validate the collected data and results.  Findings – The result culminated in the identification of seven effects derived from the use digital tools which had an impact on innovation speed (I.e., Automation, knowledge exchange, visualisation, experimentation and iteration, data management, competence, and trust).   Theoretical contribution – This master’s thesis main contribution to current literature is, by not viewing digital tools as a homogeneous group, enhancing the understanding of how digital tools affect the innovation process. Furthermore, applying the perspective of differences between types of digital tools, this thesis also contributes to understanding digital tools impact on innovation speed.  Practical implications – This thesis contributes to managers by suggesting different context to consider when implementing new digital tools for an accelerated innovation process. The study concludes that there are three main notions for managers to keep in mind when implementing tools in the innovation process. Firstly, to ensure that the complexity of the tool doesn’t exceed the internal capabilities. Secondly, to implement the tools in the phases which enables the most advantages. Thirdly, to have a process in place for managing data.  Limitations of the study – This study has focused on a small number of case companies, where the focus was on gathering in-depth data instead of quantifying findings. Future studies could therefore benefit from validating the findings with a larger sample pool. / Syfte – Syftet med detta examensarbete var att öka kunskapen om sambandet mellan digitala verktyg och innovationshastighet. Genom att göra det, bidra till både litteratur om innovationshastighet och digitala verktyg.  Metod – Metoden som användes i denna studie var en fallstudie med fem företag från en mängd olika branscher i Sverige och Danmark. Data samlades in och analyserades i tre vågor, 1) explorativa intervjuer som användes för att fastställa studiens omfattning, 2) semistrukturerade intervjuer som användes för att besvara forskningsfrågorna, 3) validerande intervjuer för att validera insamlad data och resultat.  Resultat – Resultatet kulminerade i identifieringen av sju effekter som härstammar från användningen av digitala verktyg som hade en inverkan på innovationshastigheten (dvs automation, kunskapsutbyte, visualisering, experimentering och iteration, datahantering, kompetens och tillit).  Teoretiskt bidrag – Den här masteruppsatsens huvudsakliga bidrag till aktuell litteratur är, genom att inte se digitala verktyg som en homogen grupp, en ökad förståelse för hur digitala verktyg påverkar innovationsprocessen. Genom att tillämpa perspektivet av skillnader mellan typer av digitala verktyg, bidrar denna avhandling också till att förstå digitala verktygs inverkan på innovationshastighet.  Praktiska implikationer – Den här avhandlingen bidrar till chefer genom att föreslå olika sammanhang att tänka på när de implementerar nya digitala verktyg för en accelererad innovationsprocess. Studien drar slutsatsen att det finns tre huvudsakliga områden för chefer att tänka på när de implementerar verktyg i innovationsprocessen. För det första för att säkerställa att verktygets komplexitet inte överstiger de interna funktionerna. För det andra att implementera verktygen i de faser som möjliggör flest fördelar. För det tredje att ha en process på plats för att hantera data.  Studiens begränsningar – Denna studie har fokuserat på ett litet antal fallföretag, där fokus låg på att samla in djupgående data istället för att kvantifiera resultat. Framtida studier kan därför dra nytta av att validera resultaten med ett större urval.

Ett signalställverk används för säker styrning av tågtrafiken. Ett datorställverk säkerställer atttåg kan framföras på en järnvägssträcka genom att låsa tågvägar och även förhindra otillåtnakombinationer av tågvägar. Kopplingen mellan de olika delarna på en bangård (objekten) ochställverket utförs med hjälp av Object Controllers (OC). Den svenska benämningen för OC ärutdelar. Spårledningar är bangårdsobjekt som används för att detektera positionen av tåg på enspecifik järnvägssträcka. Ställverk 95 ska ersätta Ställverk 85 på Östra Station. Detta arbete ska genom enlitteraturstudie och en systemanalys undersöka vilka effekter detta får på fördröjningarna i 75Hz växelströmsspårledningen (SASIB) och tonfrekvensspårledningen DigiCode, tillsammansmed fördröjningarna från Object Controller System (JZU840 och OCS950). Detta utfördesmed syftet om att ta reda på hur cykeltiden i Ställverk 95 påverkas av fördröjningarna frånspårledningarna och OC. Cykeltiden är tiden det tar för signalställverket att få enstatusuppdatering från OC, till att signalställverket skickar nya kommandon som ska utförasav objekten. Orsaken till tilläggsfördröjningarna för spårledningarna är en följd av kontaktstudsar.Kontaktstudsarna uppstår när spårledningsreläerna ändrar position och innebär att ankaret ireläet inte stannar av direkt utan studsar för att sedan stabilisera. Om reläet i spårledningarnasnabbare kan garantera en absolut lägesändring, är det möjligt att minska cykeltiden och ökakapaciteten på Östra Station. / Railway interlocking is used for safe control of train traffic. A computer based interlockingsystem ensures that trains can be driven on a railway line by locking train paths and preventingunauthorized combinations of train paths. The connection between the different parts of a yard(objects) and the interlocking system is performed with the help of Object Controllers (OC).The Swedish name for OC is “utdelar”. Track circuits are railway objects used for thedetection of trains on a specific railway section. EBILOCK 950 will replace EBILOCK 850 at Östra Station. Through a literature study and asystem analysis, this work will investigate the effects this has on delays in the 75 Hz AC trackcircuit (SASIB) and the audio frequency track circuit DigiCode, together with the delays fromthe Object Controller Systems, JZU840 and OCS950. This was done with the aim of findingout how the cycle time in EBILOCK 950 is affected by the delays from the track circuits andOC. The cycle time is the time it takes for the interlocking system to receive a status updatefrom OC, until the interlocking system sends new commands to be executed by the objects. The reason for the additional delays for the track circuits is a consequence of contact bounces.The contact bounces occur when the track circuit relay change position and means that thearmature in the relay does not stop immediately but bounces and the stabilizes. If the relay inthe track circuits can guarantee an absolute change of position more quickly, it is possible toreduce the cycle time and increase the capacity at Östra Station.

Volvo GTO is one of the strongest brands in the truck industry, with a long and proud history of world-leading innovations. The factory in Skövde produces diesel engines of various sizes to Volvo GTO. The project has been carried out on the processing part of grovdel crankshaft. Where the objective was to construct a simulation model that reflects flows 0, 1 and 2 on the crankshaft grovdel order to produce the best driving style for the size of the batches and sequences, focusing on PIA, between the stock and conversion-up times. A theoretical study intervention gave knowledge to the methodology to ensure that the data is collected and processed correctly. The data were collected in an Excel document, which was integrated with the simulation model for an overview and adjustments would be possible. The simulation program, Siemens Plant Simulation 12 used in the construction of the complex model of the three flows, which where verified and validated against the real flows. Optimization on the simulation model was made with a high and a low demand for crankshafts. Several objects were taken into consideration as: minimal waiting processing Findel, minimal setup time and minimal total-PIA from a truly viable perspective. The optimization showed a possible production planning in order to best be able to run such large batches as possible with reduced readjustment time and for delays of production in processing rawflows to not occur in the refined flow. For maximum capacity in the company there are two different optimal solutions one solution focused on reducing setup time and the second solution to minimize the number of additional production hours per week. Discrete simulation of production flows are being used to support production planning and simulation model is created for the continued use of the Volvo GTO, either in simulation group or future researches and theses in collaboration with the University of Skövde. The project objectives were achieved with good results and resulted as a standing basis for future planning of batches and sequences of processing crankshaft Volvo GTO.