<p>Many types of services are provided using some equipment or machines, e.g. transportation systems using vehicles. Designs of these systems require capacity decisions, e.g., the number of vehicles. In my dissertation, I use many-server and conventional heavy-traffic limit theory to derive asymptotically optimal capacity decisions, giving the desired level of delay and availability performance with minimum investment. The results provide near-optimal solutions and insights to otherwise analytically intractable problems.</p> <p>The dissertation will comprise two essays. In the first essay, &ldquoAsymptotic Analysis of Delay-based Performance Metrics and Optimal Capacity Decisions for the Machine Repair Problem with Spares,&rdquo I study the M/M/R machine repair problem with spares. This system can be represented by a closed queuing network. Applications include fleet vehicles' repair and backup capacity, warranty services' staffing and spare items investment decisions. For these types of systems, customer satisfaction is essential; thus, the delays until replacements of broken units are even more important than delays until the repair initiations of the units. Moreover, the service contract may include conditions on not only the fill rate but also the probability of acceptable delay (delay being less than a specified threshold value).</p> <p>I address these concerns by expressing delays in terms of the broken-machines process; scaling this process by the number of required operating machines (or the number of customers in the system); and using many-server limit theorems (limits taken as the number of customers goes to infinity) to obtain the limiting expected delay and probability of acceptable delay for both delay until replacement and repair initiation. These results lead to an approximate optimization problem to decide on the repair and backup-capacity investment giving the minimum expected cost rate, subject to a constraint on the acceptable delay probability. Using the characteristics of the scaled broken-machines process, we obtain insights about the relationship between quality of service and capacity decisions. Inspired by the call-center literature, we categorize capacity level choice as efficiency-driven, quality-driven, or quality- and efficiency-driven. Hence, our study extends the conventional call center staffing problem to joint staffing and backup provisioning. Moreover, to our knowledge, the machine-repair problem literature has focused mainly on mean and fill rate measures of performance for steady-state cost analysis. This approach provides complex, nonlinear expressions not possible to solve analytically. The contribution of this essay to the machine-repair literature is the construction of delay-distribution approximations and a near-optimal analytical solution. Among the interesting results, we find that for capacity levels leading to very high utilization of both spares and repair capacity, the limiting distribution of delay until replacement depends on one type of resource only, the repair capacity investment.</p> <p>In the second essay, &ldquoDiffusion Approximations and Near-Optimal Design of a Make-to-Stock Queue with Perishable Goods and Impatient Customers,&rdquo I study a make-to-stock system with perishable inventory and impatient customers as a two-sided queue with abandonment from both sides. This model describes many consumer goods, where not only spoilage but also theft and damage can occur. We will refer to positive jobs as individual products on the shelf and negative jobs as backlogged customers. In this sense, an arriving negative job provides the service to a waiting positive job, and vice versa. Jobs that must wait in queue before potential matching are subject to abandonment. Under certain assumptions on the magnitude of the abandonment rates and the scaled difference between the two arrival rates (products and customers), we suggest approximations to the system dynamics such as average inventory, backorders, and fill rate via conventional heavy traffic limit theory.</p> <p>We find that the approximate limiting queue length distribution is a normalized weighted average of two truncated normal distributions and then extend our results to analyze make-to-stock queues with/without perishability and limiting inventory space by inducing thresholds on the production (positive) side of the queue. Finally, we develop conjectures for the queue-length distribution for a non-Markovian system with general arrival streams. We take production rate as the decision variable and suggest near-optimal solutions.</p> / Dissertation

Submitted by ROBSON FLÁVIO CASTRO null (robson.afl@gmail.com) on 2016-05-04T14:03:14Z No. of bitstreams: 1 ROBSON_CASTRO_AUTOARQUIVAMENTO.pdf: 19394323 bytes, checksum: 7e472e92d451cc588e98cedecc565eba (MD5) / Approved for entry into archive by Juliano Benedito Ferreira (julianoferreira@reitoria.unesp.br) on 2016-05-06T14:50:11Z (GMT) No. of bitstreams: 1 castro_rf_me_bauru.pdf: 19394323 bytes, checksum: 7e472e92d451cc588e98cedecc565eba (MD5) / Made available in DSpace on 2016-05-06T14:50:11Z (GMT). No. of bitstreams: 1 castro_rf_me_bauru.pdf: 19394323 bytes, checksum: 7e472e92d451cc588e98cedecc565eba (MD5) Previous issue date: 2016-03-29 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Por meio de experimentos baseados em simulação computacional, este trabalho tem como objetivo avaliar o desempenho do Sistema de Coordenação de Ordens (SCO) Simplified Drum-Buffer-Rope (S-DBR) aplicado a ambientes de produção para estoque, denominado Make-to-Availability (MTA). Composto por um conjunto de técnicas, o MTA visa maximizar o nível de serviço a partir da garantia de estoques de produtos acabados para pronta entrega. Nesta pesquisa, são criadas derivações do MTA com as retiradas das técnicas Gerenciamento do Pulmão, Priorização pelo Status do Pulmão e Carga Planejada. O desempenho das derivações é comparado com o MTA em sua forma completa. Para tanto, quatro indicadores de desempenho são utilizados: fill rate, estoque em processo, estoque de produtos acabados e tempo de reposição. Quatro cenários foram simulados, variando as taxas médias de demanda e o coeficiente de variação dos tempos de processamento. O MTA não obteve o melhor desempenho em nenhum dos indicadores, nos quatro cenários, porém a retirada das técnicas não trouxe melhoras significativas na disponibilidade dos produtos, e em alguns casos aumentou extremamente os níveis de estoque e o tempo de reposição. Ao final as técnicas se mostraram importantes para manter a disponibilidade dos produtos com menores níveis de estoque e menor tempo de reposição. / Through experiments with computer simulation, this work aims to evaluate the performance of an Ordering System Coordinator (OSC), Simplified Drum-Buffer-Rope applied to a make to stock environment, called Make-To-Availability (MTA). Composed of a set of techniques, the MTA aims to maximize the level of service from the supply guarantee for immediate delivery. In this research, MTA derivations are created pulling out the techniques Buffer Management, Status of Buffer Prioritization and Planned Load. The performance of derivations was compared with MTA in its complete form. For this purpose, four performance indicators were utilized: fill rate, work in process, finished goods inventory and reposition time. Four scenarios were simulated, with different median demand rates and the coefficient of variation of the process time. The MTA does not obtain the best performance in any indicator, at the four scenarios, however the pulling out of techniques does not bring significant improvement on product availability, and in some cases, stocks and reposition time greatly increased. In the end, the techniques have shown important to keep the availability of products with lower stocks and smaller reposition time.

A high level of competition in the food industry, specifically in the Middle East and the UK has forced companies to improve their processes by reducing lead time, waste, and costs and increasing production efficiency. The main challenge to the achievement of the process improvement objectives is the high level of process variability. Therefore, this research investigates the different types of variability in food production system and proposes a methodology to reduce the effect variability in food production system. The variability can be caused by several factors, for instance, in biscuit production lines variability can be induced due to short breakdown and long breakdown, variable processing times, variable temperature, etc. The proposed approach addresses process time variability issues associated with both make-to-stock (MTS) and make-to-order (MTO) manufacturing environments using an iterated approach. The proposed methodology integrates process mapping, (which is a lean tool for identifying value added and non-value added activities), discrete event simulation (to mirror the real production line), Taguchi orthogonal arrays (to generate different scenarios in order to investigate the effect of variability on the simulation model), correlation analysis (to identify the highest variability factors), and the rule based system (to improve food production system performance based on identified key performance indicators (KPIs)). The research uses a biscuit production line as a case study to validate the proposed methodology. The application of the proposed approach determines that the highest effected KPI is %working. The results showed that after implementation of the rule-based system, key performance improved in high variable areas. Results analysis based on before scenario shows that %working performance indicator is highly effected by variable temperature, speed, and breakdown factors for high variable areas such as baking, cooling, aligning, and packing. Based on identified factors and high variable areas, rules are developed by applying standardisation setting (SOP, WI, PP) in high variable areas and the results shows %working improved in baking by 4.78%, in cooling by 16.06%, in aligning by 0.35%, in packing machine1 by 2.5%, in packing machine2 by 2.37%, in packaging1 by 3.35%, and in packaging2 by 3.16%. The integrated method allow quick response , control the environment without production interruption, reduce number of experiments , and reducing variability in high variable areas, which narrowed the improvement in the required areas and increased its effectiveness.

Introduktion: Små till medelstora företag (SME) innefattar 99.9% av alla aktiva verksamheter i Sverige. SME:s är företag som har begränsade ekonomiska resurser. Begränsade resurser kan leda till att verksamheter producerar produkter till lager i rädslan om att gå miste om leveranser, vilket skapar ett uppbundet kapital i färdigvarulagret. Syftet med studien är att undersöka om make to order (MTO) kan användas av SME:s för att reducera kapitalbindning i färdigvarulagret och undersöka vilka utmaningar det finns med att implementera MTO.  FF1: Hur kan MTO användas som ett verktyg för att reducera kapitalbindningen hos SME:s? FF2: Vilka utmaningar finns det med att implementera MTO för SME:s?  Metod: En fallstudie har genomförts hos ett producerande mikroföretag. Data har samlats in genom observationer, intervjuer och dokument. För grund till den teoretiska referensramen har en litteraturstudie genomförts. Litteraturstudien samlade in data genom vetenskapliga artiklar och böcker som har använts för att analyser den insamlade empirin från fallstudien.   Resultat: Studiens resultat har kommit fram till att MTO kan användas som ett verktyg hos SME:s som har en hög kapitalbindning och inte kan utesluta ett färdigvarulager. För att reducera kapitalbindningen kan därmed en hybrid mellan MTO och MTS (make to stock) användas. Studien har ytterligare kommit fram till att det finns tre huvud utmaningar med att implementera MTO. De tre utmaningarna är ställtider, oförutsägbara händelser och förändringar.

Industrialization of construction is a business strategy to significantly improve competitiveness. However, the organization structure of the construction firms needs to support the new production system. The knowledge on why and how this business development can be accomplished is scarce, both within academia and in business practice. This research seeks to fill this knowledge gap. The purpose of organization structure and the production system have is to coordinate the firm’s processes and control the work performing resources. Information is one of the most fundamental dimensions for steering and controlling the work. The different information types are determined by the firm’s product customization strategy and the production system flexibility. Further, diverse information types are managed in different extent by the organizational steering mechanisms. Consequently, firms with dissimilar customization strategy or production flexibility should organizationally be designed differently in order to be efficient. The developed model identifies four generic production topologies: “engineer-to-order” (ETO), “manufacture-to-order” (MTO), “assembly-to-order” (ATO), and “make-standard-products” (MSP). The differences between the topologies can be related to the location of the “customer-order-decoupling-point” (CODP) in the product realization process; and to what extent the upstream and downstream processes continuously use stored information or process information to accomplish the work of each product order. The model predicts which organization structure mechanisms that should be used for which processes for each production topology. It is the specific configuration of the mechanisms that gives each production topology their organizational capability. The model has been validated by case studies in four organizations, each representing one of the four generic production topologies. Three cases considered housing and one studied truck manufacturing. It has been shown that the conventional housing firms have an ETO-production topology, while industrialized housing firms belonging to one of the others, i.e. MTO, ATO or MSP. The reason is that ETO-firms rely on crafts-based production to manage the work, while the other topologies base their steering mechanisms on industrial principles. These two types of production are fundamentally different, which also explain the need for different organization structures. The research complements previous knowledge and significantly increases the ability to predict, analyze and explain an organization’s design and behavior. The model can be used in practice to guide business development work and performance improvement programs. / <p>Research funder: SBUF (The development fund of the Swedish construction industry). QC 20131113</p>

Purpose – Globalization affects all producing companies with increased complexity in production, stock management and never ending customer demands. The customers of today have a greater range of suppliers than before with even more products to choose from which puts the customer in a strong position. One of many important subjects that companies need to work with to keep their competitiveness strong against each other is to work with continuous improvements in production- and inventory management. This study therefore reviews tied up capital in stock and suggest adequate procedures, which could be applied to decrease the tied up capital.   Method –In order to fulfil the purpose a case study is conducted. Two central research questions are chosen for the study to investigate in a case company. The data collected contains of secondary data, observations and interviews. To accomplish the purpose a theoretical framework has been put together.   Findings – Reducing variations in production and re-designing of the daily production plan is presented as the two procedures with the purpose to achieve a decrease in tied up capital for stock kept units. The study describes these two procedures in general in order to make the solution applicable into various manufacturing company. Further the study claims that gaining flow efficiency should be prioritized instead of resource efficiency, which could be accomplished by the two procedures.    Implications – The study contributes to verifying production theories, foremost about variations in production, Lean manufacturing and the technique of Lead-time mapping.   Limitations – In order to apply the procedures with precision and efficiency some further data and extended studies needs to be performed. This study is performed in a generalizing point of view, which may influence the results.  The study does not capture every aspect of affecting circumstances that might be needed for a successful implementation of suggested procedures.   Keywords – Tied up capital, Lead-time, Lean, Lead-time mapping, Variations, Flow efficiency, Postponement, Just-in-Time, Make-to-stock and Make-to-order. / Syfte – Globaliseringen har gjort att kunden har ett högre utbud att välja mellan och kan därmed ställa högre krav på tillverkande verksamheter. För att fortsatt vara konkurrenskraftig måste verksamheter ständigt utveckla den interna produktion- och materialstyrningen. Studiens ämnar därmed undersöka orsaken till uppkomsten av bundet kapital i lager samt finna potentiella åtgärder som kan vidtas inom verksamheten för att på ett hållbart sätt minska bundet kapital i lager.   Metod – För att uppfylla studiens syfte tillämpas fallstudie. Studien utgår från två frågeställningar som besvaras med hjälp av data från ett fallföretag. Data som samlas är hämtad från sekundärdata, observationer och intervjuer. Därtill har ett teoretiskt ramverk upprättats vilken studien utgår ifrån.   Resultat – Minska variationer samt utförande av en mer detaljerad planering presenteras som studiens två åtgärdsförslag för att minska bundet kapital i lager. Studien beskriver övergripande potentiella tillvägagångssätt för att åstadkomma förslagen. Studien konstaterar att flödeseffektivitet med fördel bör prioriteras framför resurseffektiviteten i verksamheten, vilket uppfylls med hjälp av åtgärdsförslagen.   Implikationer – Studien bidrar inte till nya teorier men verifierar befintliga teorier främst kring variationer i tillverkning, Lean och ledtidskartläggning.   Begränsningar – För att åtgärdsförslagen i studiens resultat ska kunna tillämpas krävs ytterligare data och fördjupade studier för att garantera att samtliga aspekter ska fångas in samt att orsak och påverkan av åtgärderna ska kunna kartläggas. Studien bygger på generaliserande antaganden vilket ger ett generaliserat resultat.   Nyckelord – Lean, Ledtid, Ledtidskartläggning, Variationer, Flödeseffektivitet, Senareläggning, Just-in-Time, Make-to-order och Bundet kapital.

Bakgrund: Dagens marknader har med tiden tenderat att bli mer globala vilket i sin tur har ökat konkurrensen mellan företag. Detta har inneburit att många industriorganisationer har behövt förändra sig för att vara konkurrenskraftiga på marknaden. Ett koncept som idag genomsyrar många företag är lean vilket bygger på att maximera användandet av sina resurser, eliminera slöserier och skapa en effektivare tillverkning. Genom att arbeta med lean kan företag uppnå snabbare genomloppstider. Syfte: Syftet med studien är att kartlägga Press Kogyos propellerprocess för att kunna identifiera icke-värdeadderande aktiviteter i processen. Vidare kommer studien bidra Press Kogyo med förslag gällande hur en effektivare material- och produktionsstyrning kan reducera genomloppstiden i propellerprocessen. För att studien ska uppnå teoretisk relevans är ytterligare ett syfte med studien att bidra med teori kring hur tillverkande företag, med en funktionell layout, kan reducera de nackdelar som finns med layouten med effektivare material- och produktionsstyrning. Genomförande: Studien har delats upp i tre forskningsfrågor. De två första forskningsfrågorna var specifikt inriktade mot det studerade företaget medan den tredje forskningsfrågan var mer generellt ställd mot tillverkande företag med funktionell layout. Studien har genomförts som en fallstudie och präglats av kvalitativa forskningsmetoder. Empiriska data har samlats in genom intervjuer, observationer samt en fokusgrupp. För första forskningsfrågan skapades processkartor och VSM-kartor. Dessa i samband med diverse intervjuer låg till grund för att identifiera icke-värdeadderande aktiviteter/slöserier i propellerprocessen vilka påverkade genomloppstiden. För forskningsfråga två applicerades teori kring material-och För tillverkande industriföretag kan en reducering av genomloppstid generera diverse fördelar. Några av dessa fördelar är: minskat antal produkter i arbete, bättre kvalité, minskade kostnader, bättre prognoser, ökad flexibilitet samt minskad ledtid gentemot kund. Press Kogyo har under en längre period upplevt en problematik kring en av deras processer. Problematiken har legat i att de inte vetat om vilka icke- värdeadderade aktiviteter som finns i processen samt hur de påverkar genomloppstiden.   produktionsstyrning i syfte att reducera de icke-värdeadderande aktiviteterna/slöserier som identifierats och följaktligen reducera genomloppstider i processen. Gällande forskningsfråga tre genomfördes intervjuer med det studerade företaget och ett annat tillverkande företag med funktionell layout. Författarna ämnade att genom dessa intervjuer besvara hur tillverkande företag med en funktionell layout kan reducera de nackdelar som finns med den layouten med hjälp av effektiv material- och produktionsstyrning. Slutsats: I studien identifierades sju slöserier där väntan ansågs vara det slöseri vilket mest påverkade genomloppstiden i propellerprocessen. För att eliminera alla slöserier och framförallt väntan applicerades teori kring material- och produktionsstyrning med fokus på production activity control (PAC). Den teori vilken användes skapade också en teoretisk modell vilken kan vara en bra grund när företag med funktionell layout vill effektivisera sin planering. Vissa delar av den teoretiska modellen användes också senare i studien där den användes för att reducera de nackdelar vilka kan finnas med en funktionell layout. / Background: Today's markets have over time tended to become more global, which in turn has increased competition between companies. This has meant that many industry organizations have had to change in order to be competitive in the market. A concept that today permeates many companies is the lean practice, which is based on maximizing the use of resources, eliminating waste, and creating more efficient production. By working with lean, companies can achieve faster throughput time. For manufacturing industrial companies, a reduction in throughput time can generate various benefits. Some of these advantages are: reduced number of products in work, better quality, reduced costs, better forecasts, increased flexibility and reduced lead time towards customers.Press Kogyo has for a long period experienced problems with one of their processes. The main problem has been that they do not know what non-value-added activities/waste that can be found in the process and how these activitiesaffect the total throughput time of the process. Purpose: The purpose of the study is to map Press Kogyo's propeller process in order to be able to identify non-value-adding activities in the process. Furthermore, the study will provide Press Kogyo with proposals regarding how more efficient material and production control can reduce the throughput time in the propeller process. In order for the study to achieve theoretical relevance, another purpose of the study is to contribute with theories about how manufacturing companies, with a functional layout, can reduce the disadvantages of the layout with more efficient material and production control. Methodology: The study has been divided into three research questions. The first two research questions were specifically aimed at Press Kogyo, while the third research question was more generally directed at manufacturing companies with a functional layout. The study was conducted as a case study and was characterized by qualitative research methods. Empirical data has been collected through interviews, observations, and a focus group. For the first research question, process maps and VSM maps were created. This together with various interviews created the foundation for identifying non-value-adding activities/waste in the propeller process which affected the throughput time. For research question two, theory of material and production control was applied in order to reduce the non-value-adding activities/waste and consequently reduce throughput time in the process. Regarding research question three, interviews were conducted with Press Kogyo and another manufacturing company with a functional layout. The authors intended to, through these interviews, find answers to how manufacturing companies with a functional layout can reduce the disadvantages of the layout with the help of efficient material and production control. Conclusions: In the study, seven wastes were identified where “wait” was considered to be the waste that affected throughput time the most in the propeller process. To eliminate all waste and specifically the waste “wait”, methods and theories regarding material and production control was applied with a focus on production activity control (PAC). All the different theories that was used also created a theoretical model which can be a good basis for planning when companies with a functional layout want to find ways tostreamline their planning. Some parts of the theoretical model were also used later in the study where it was used to reduce the disadvantages that may exist with a functional layout