Cross-docking is an important transportation logistics strategy in supply chain management which reduces transportation costs, inventory holding costs, order-picking costs and response time. Careful planning is needed for successful cross-dock operations. Uncertainty in cross-dock problems is inevitable and needs to be addressed. Almost all research in the cross-dock area assumes determinism. This dissertation considers uncertainty in cross-dock problems and optimizes these problems under uncertainty. We consider uncertainty in processing times, using scenario-based and protection-based robust approaches. Using a heuristic method, we find a lower and upper bound and combine that with a meta-heuristic method to solve the problem. Also, we consider problems in two different industries (Goodwill and H-E-B) and address the uncertainties that happen frequently in their operations. The scenario-based robust optimization model for the unloading problem using a min max objective is presented with examples. A surrogate heuristic procedure is used to find a robust solution. Next, a two-space genetic algorithm, a meta-heuristic procedure, is applied to the unloading problem using the bounds obtained by the heuristic procedure. The results are closer to the optimal solution than those obtained by the two-space genetic algorithm without bounds. When compared with the regular genetic algorithm with bounds, the two-space algorithm performs well. The protection-based approach considers a limit on the number of coefficients allowed to change with data uncertainty, protecting against the degree of conservatism. The management of trucks and reduction of overtime pay in the cross-dock operations of Goodwill is addressed through two models and uncertainty is applied to those models. A combined cross-dock operations model together with demand is formulated and the uncertainties are discussed for H-E-B operations. This dissertation does not address the recycling operation within the cross-dock of Goodwill, or the uncertainty in H-E-B data. / text

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Cadeias de suprimentos podem ter operações seguindo diferentes estratégias de distribuição e a utilização de cada uma dessas estratégias pode resultar em diferentes operações e custos. A estratégia de cross-docking auxilia na redução dos custos de distribuição de produtos, consolidando cargas, e a redução de tempo e custos de armazenamento, uma vez que o tempo máximo de estoque permitido pela estratégia é de cerca de 24 horas. O objetivo deste trabalho é apresentar um modelo para o problema de cross-docking, em que cargas são entregues e reorganizadas de forma a atender a outras cargas que são coletadas e garantir que as janelas de tempo para início das operações sejam atendidas. Devido à falta de instâncias para o problema disponíveis na literatura, buscou-se gerar um benchmark e disponibilizá-las à comunidade científica. Uma vez que o problema é de difícil solução exata, um método heurístico para a resolução do problema foi desenvolvido. Os resultados mostraram que o modelo proposto resulta em boas soluções quando comparado ao modelo da literatura. O estudo de calibração do software IBM CPLEX mostrou que a calibração dos parâmetros pode resultar em melhores soluções e, por fim, a matheurística se mostrou competitiva com o CPLEX, principalmente para cenários em que a proporção de entregas e coletas diverge. / Supply chains may have operations which follow different distribution strategies and each one of these strategies may result in different operations and costs. The Cross-docking strategy helps to reduce the products distribution costs by consolidating loads and reducing storage costs as the maximum inventory time is approximately 24 hours. The aim of this research is to present a model for the cross-docking problem where loads are delivered and reorganized so as to cater for other loads that are collected and ensure that time windows are respected. Due to the lack of instances available in the literature, a benchmark was generated and was made available to the scientific community. As the problem is difficult to obtain the exact solution, a heuristic method was developed. The results showed that the proposed model has good solutions when compared to the literature model. A study of the IBM CPLEX software showed that tuning can result in better solutions and the matheuristcs was competitive with the software, mainly in scenarios where deliveries and pickups are very different.

[pt] As constantes mudanças no mercado levaram a um redirecionamento do foco empresarial para o consumidor final. Assim, as formas tradicionais de distribuição que empurravam a produção para o mercado, passaram a ser substituídas por novas formas onde o abastecimento é puxado pela necessidade de mercado. Entre estas novas formas de distribuição apresenta-se o sistema Cross Docking. Nesta dissertação, esse sistema será apresentado, buscando compreender sua estrutura e seus objetivos. O Cross Docking opera transferindo a mercadoria diretamente da área de recebimento para a área de embarque, sem armazená-la, buscando com isso oferecer melhores serviços e manter a oferta constante de produtos. Além disso, a pesquisa tem como objetivo identificar as vantagens e desvantagens do seu uso e os obstáculos de implementação. Será realizada também uma pesquisa de campo, onde uma observação simples da realidade terá como base a Empresa Brasileira de Correios e Telégrafos - ECT. Esta análise se deve ao fato da ECT operar de acordo com a filosofia do sistema Cross Docking, ou seja, as encomendas urgentes fluem pelo centro de distribuição, sendo imediatamente transferidas para as docas de expedição, sem paradas. Dessa forma, a pesquisa busca realizar um diagnóstico da distribuição utilizando-se como referência a ECT. Para essa empresa são avaliados tanto o seu desempenho operacional como a execução dos seus serviços de encomendas expressas, com base nos dois índices de performance utilizados pela própria empresa: produtividade e qualidade (nível de serviço). / [en] The frequent changes in the market turned any company`s focus to the final consumer. So, the ordinary distribution techniques, which usually pushed the production to the market, has being replaced by new techniques, where the product supplies are pulled by the market needs. One of these new ways of distribution is the Cross Docking system. This master`s thesis will present this system, in order to understand its structure and its aims. The Cross Docking concept immediately transfers the merchandise received at the point of reception, to the point of delivery, with the minimum time in between. So, this system can offer better service levels and keep a constant supply of products. In addition, this research has the purpose of identifying the main advantages and disadvantages derived from the use of this system and the main obstacles for its implementation. It will also make a field research, which will have the Empresa Brasileira de Correios e Telégrafos - ECT - as a basis for a simple observation of the reality. That is because the ECT operates with the same philosophy of the Cross Docking system, in which orders do not stay inside the Distribution Center but are immediately transferred to the outbound docks. So, this research has the purpose of diagnosing the distribution system, using the express services of ECT as the field research case study and the performance indexes such as, productivity and service level.

Cadeias de suprimentos podem ter operações seguindo diferentes estratégias de distribuição e a utilização de cada uma dessas estratégias pode resultar em diferentes operações e custos. A estratégia de cross-docking auxilia na redução dos custos de distribuição de produtos, consolidando cargas, e a redução de tempo e custos de armazenamento, uma vez que o tempo máximo de estoque permitido pela estratégia é de cerca de 24 horas. O objetivo deste trabalho é apresentar um modelo para o problema de cross-docking, em que cargas são entregues e reorganizadas de forma a atender a outras cargas que são coletadas e garantir que as janelas de tempo para início das operações sejam atendidas. Devido à falta de instâncias para o problema disponíveis na literatura, buscou-se gerar um benchmark e disponibilizá-las à comunidade científica. Uma vez que o problema é de difícil solução exata, um método heurístico para a resolução do problema foi desenvolvido. Os resultados mostraram que o modelo proposto resulta em boas soluções quando comparado ao modelo da literatura. O estudo de calibração do software IBM CPLEX mostrou que a calibração dos parâmetros pode resultar em melhores soluções e, por fim, a matheurística se mostrou competitiva com o CPLEX, principalmente para cenários em que a proporção de entregas e coletas diverge. / Supply chains may have operations which follow different distribution strategies and each one of these strategies may result in different operations and costs. The Cross-docking strategy helps to reduce the products distribution costs by consolidating loads and reducing storage costs as the maximum inventory time is approximately 24 hours. The aim of this research is to present a model for the cross-docking problem where loads are delivered and reorganized so as to cater for other loads that are collected and ensure that time windows are respected. Due to the lack of instances available in the literature, a benchmark was generated and was made available to the scientific community. As the problem is difficult to obtain the exact solution, a heuristic method was developed. The results showed that the proposed model has good solutions when compared to the literature model. A study of the IBM CPLEX software showed that tuning can result in better solutions and the matheuristcs was competitive with the software, mainly in scenarios where deliveries and pickups are very different.

Bring Frigo transporterar och distribuerar kylda och frysta livsmedel inom Sverige och övriga Norden genom ett temperaturkontrollerat nätverk av fordon, kyllager, fryslager och terminaler. En av Bring Frigo:s terminaler är belägen i Linköping dit livsmedel som ska distribueras till eller från Östergötland ankommer för att lastas om mellan fjärr- och distributionsbilar. Idag räcker kapaciteten på terminalen i Linköping precis till för att kunna hantera det flöde av livsmedel som passerar genom terminalen. Då Bring Frigo nyligen ingått en affär med en större svensk matgrossist om att distribuera matgrossistens livsmedel inom Östergötland i sitt befintliga transportnätverk behöver terminalens kapacitet utökas för att detta ska vara möjligt. I samband med denna förändring vill Bring Frigo passa på att ta fram riktlinjer för hur omlastningsprocessen kan optimeras. Bring Frigo önskar erhålla riktlinjer för vart livsmedlen temporärt ska placeras inne i terminalen under omlastningsprocessen och hur lastbilar ska tilldelas lastkajer så att transportsträckan inne i terminalen hålls så kort som möjligt. Som ett första steg för att besvara var livsmedlen temporärt bör placeras inne i terminalen utformades en intern layout över den tilltänkta ombyggda terminalen. Därefter utvecklades och implementerades en heuristik som, utifrån den framtagna layouten och historiska data över livsmedelsflödet genom terminalen, tog fram var olika livsmedel temporärt bör placeras inne i terminalen och hur tilldelningen av lastkajer bör ske så att erfordrad transportsträcka hålls så kort som möjligt under omlastningsprocessen. Med hjälp av de resultat som erhölls från heuristiken formulerades specifika riktlinjer för respektive arbetsdag. Riktlinjerna för respektive dag delades vidare in i två olika nivåer beroende på om dagen kategoriserades som en dag med normal eller hög arbetsnivå utifrån totala antalet lastbärare som förväntas passera terminalen den aktuella dagen. Slutsatsen av studien är att de riktlinjer som utformats för omlastningsprocessen på terminalen bör reducera den erfordrade transportsträckan av livsmedel inne på terminalen och på så sätt effektivisera omlastningsprocessen, men att detta inte kan säkerställas i och med att historiska data använts som indata till heuristiken.

The current logistics chains must be designed to copy with short life cycles of products, high stock velocity, low degree of predictability etc. The conditions for accuracy, reliability and flexibility of deliveries at the markets have been changing, and that is why it is inevitable to seek new alternative methods that would lead to higher efficiency levels, remaining competitiveness and, at the same time, fulfil the needs and wishes of customers. In this paper I focuse on cross-docking which is a newer distribution method. In the first part of the paper, I try to determine the principles of this operation in distribution, identify individual types of cross-docking and in detail describe the assumptions and conditions under which the method should be implemented to reach the requested results. The paper then continues with an analysis of the current position of cross-docking and there are given several examples of demand driven supply chains that have been using this distribution method at a certain point. These examples are followed with a discussion on current options and problems of implementing cross-docking in the case of retailers and manufacturers.

Supply chain network design involves location decisions for production facilities and distribution centers. We consider a make-to-order supply chain environment where distribution centers serve as crossdocking terminals. Long waiting times may occur at a cross-docking terminal, unless sucient handling capacity is installed. In this study, we deal with a facility location problem with congestion eects at distribution centers. Along with location decisions, we make capacity allocation (service rate) and demand allocation decisions so that the total cost, including facility opening, transportation and congestion costs, is minimized. Response time to customer orders is a critical performance measure for a supply chain network. The decisions like where the plants and distribution centers are located aect the response time of the system. Response time is more sensitive to these decisions in a make-to-order business environment. In a distribution network where distribution centers function as cross-docking terminals, capacity or the service rate decisions also aect the response time performance. This study is closely related to a recent work Vidyarthi et al. (2009) which models distribution centers asM/G/1 queuing systems. They use the average waiting time formula ofM/G/1 queuing model. Thus, the average waiting time at a distribution center is a nonlinear function of the demand rate allocated to and the service rate available at the distribution center. The authors Vidyarthi et al. (2009) propose a linear approximation approach and a Lagrangian based heuristic for the problem. Dierent than the solution approach proposed in Vidyarthi et al. (2009), we propose a closed form formulation for the problem. In particular, we show that the waiting time function derived from M/G/1 queuing model can be represented via second order conic inequalities. Then, the problem becomes a mixed integer second order cone programming problem which can be solved by using commercial branch-and-bound software such as IBM ILOG CPLEX. Our computational tests show that proposed reformulation can be solved in reasonable CPU times for practical size instances.

Syfte – Rapportens syfte är att undersöka förbättringsmöjligheter av materialhantering mellan in-och utlastning på en cross-docking terminal. Baserat på syftet har två frågeställningar formulerats. Vilka aktiviteter ingår i materialhantering? Hur kan materialhanteringen effektiviseras? Metod – Studien har genomfört en förstudie på fallföretaget för att definiera ett problemområde. Utifrån problemområdet har syfte och frågeställningar formulerats. Fallstudien och litteraturgenomgång har genomförts parallellt för att skapa en abduktiv ansats. De inhämtade teorier från litteraturstudierna ligger stöd för det teoretiska ramverket.  Resultat – Flera slöserier identifierades under studien vilket påverkar den interna materialhanteringen. Inom de primära cross-docking aktiviteterna existerar slöserier vilket behöver elimineras för en effektivisering ska genomföras. Studien lyfter även vikten av ett fungerande informationsflöde för en effektiv materialhantering.  Implikationer – Eftersom problemområdet redan har etablerade teorier har ingen ny forskning genomförts. Däremot har studien inriktat sig på en annan synvinkel, där förhållandet mellan informationsflöde och materialflöde studerats.  Begränsningar – Begreppet materialhantering är brett och innefattar även materialhantering utanför terminalen. Rapporten har begränsat sig till enbart den interna materialhanteringen. Studien begränsar sig till enbart ett fallföretag vilket påverkar generaliserbarheten.  Nyckelord – Cross-docking, Materialhantering, Materialflöde, Informationsflöde.

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