Assembly line balancing problem is one of the most studied NP-Hard problems. NP-Hardness leads us to search for a good solution instead of the optimal solution especially for the big-size problems. Meta-heuristic algorithms are the search methods which are developed to find good solutions to the big-size and combinatorial problems. In this study, it is aimed at solving the multi-objective multi-model assembly line balancing problem of a company. A meta-heuristic algorithm is developed to solve the deterministic assembly line balancing problems. The algorithm developed is tested using the test problems in the literature and the the real life problem of the company as well. The results are analyzed and found to be promising and a solution is proposed for the firm.

In this study we focus on two-sided mixed-model assembly line balancing type-I problem. There is a production target for a fixed time horizon and the objective is to produce this amount with the minimum level of workforce. A mathematical model is developed to solve this problem in an optimal manner. For large scale problems, the mathematical model fails to give the optimal solution within reasonable computational times. Thus, a heuristic approach based on threshold accepting algorithm is presented. Both the mathematical model and the heuristic approach are executed to solve several example problems from the literature and a case study problem which is derived from the refrigerator production. Computational experiments are carried out using both approaches. It is observed that the heuristic procedure finds good solutions within very reasonable computational times.

In this study, we consider single model deterministic Assembly Line Balancing problem with task paralleling. The objective is to minimize the total cost which is composed of station opening cost and task dependent equipment cost. A branch and bound algorithm that allows two-level task paralleling is proposed. A heuristic algorithm is also developed both for obtaining efficient upper bounds to branch and bound and for achieving good approximate solutions for large sized problems. Computational experiments are conducted to investigate the effects of experimental parameters on the cost-related and algorithm-related performance measures. The exact algorithm results are compared to the proposed heuristic algorithm results, station paralleling results and optimal solutions without paralleling.

A diferença entre estações de trabalho é considerada desprezível em linhas de montagem tradicionais. Por outro lado, linhas de montagem heterogêneas consideram o problema de indústrias nas quais os tempos das tarefas variam de acordo com alguma característica a ser selecionada para a tarefa. No Problema de Balanceamento e Atribuição de Trabalhadores em Linhas de Montagem (do inglês Assembly Line Worker Assignment and Balancing Problem, ALWABP), os trabalhadores são responsáveis por estações de trabalho e de acordo com as suas habilidades, eles executam as tarefas em diferentes quantidades de tempo. Em alguns casos, os trabalhadores podem até ser incapazes de executar algumas tarefas. No Problema de Balanceamento de Linhas de Montagem Robóticas (do inglês Robotic Assembly Line Balancing Problem, RALBP), há diferentes tipos de robôs e o conjunto de tarefas de cada estação deve ser executada por um robô. Robôs do mesmo tipo podem ser usados múltiplas vezes. Nós propomos métodos exatos e heurísticos para a minimização do tempo de ciclo destes dois problemas, para um número fixo de estações. Os problemas têm características similares que são exploradas para produzir limitantes inferiores, métodos inferiores, models de programação inteira mista, e regras de redução e dominância. Para a estratégia de ramificação do método de branch-and-bound, entretanto, as diferenças entre os problemas forçam o uso de dois algoritmos diferentes. Uma estratégia orientada a tarefas tem os melhores resultados para o ALWABP-2, enquanto uma estratégia orientada a estações tem os melhores resultados para o RALBP-2. Nós mostramos que os limitantes inferiores, heurísticas, modelos de programação inteira mista e algoritmos de branch-and-bound para estes dois problemas são competitivos com os métodos do estado da arte da literatura. / The difference among workstations is assumed to be negligible in traditional assembly lines. Heterogeneous assembly lines consider the problem of industries in which the task times vary according to some property to be selected for the task. In the Assembly Line Worker Assignment and Balancing Problem (ALWABP), workers are assigned to workstations and according to their abilities, they execute tasks in different amounts of time. In some cases they can even be incapable of executing some tasks. In the Robotic Assembly Line Balancing Problem (RALBP) there are different types of robots and each station must be executed by a robot. Multiple robots of the same type may be used. We propose exact and heuristic methods for minimizing the cycle time of these two problems, for a fixed number of stations. The problems have similar characteristics that are explored to produce lower bounds, heuristic methods, mixed-integer programming models, and reduction and dominance rules. For the branching strategy of the branch-and-bound method, however, the differences among the problem force the use of two different algorithms. A task-oriented strategy has the best results for the ALWABP-2 while a station-oriented strategy has the best results for the RALBP-2. The lower bounds, heuristics, MIP models and branch-and-bound algorithms for these two problems are shown to be competitive with the state-of-the-art methods in the literature.

A diferença entre estações de trabalho é considerada desprezível em linhas de montagem tradicionais. Por outro lado, linhas de montagem heterogêneas consideram o problema de indústrias nas quais os tempos das tarefas variam de acordo com alguma característica a ser selecionada para a tarefa. No Problema de Balanceamento e Atribuição de Trabalhadores em Linhas de Montagem (do inglês Assembly Line Worker Assignment and Balancing Problem, ALWABP), os trabalhadores são responsáveis por estações de trabalho e de acordo com as suas habilidades, eles executam as tarefas em diferentes quantidades de tempo. Em alguns casos, os trabalhadores podem até ser incapazes de executar algumas tarefas. No Problema de Balanceamento de Linhas de Montagem Robóticas (do inglês Robotic Assembly Line Balancing Problem, RALBP), há diferentes tipos de robôs e o conjunto de tarefas de cada estação deve ser executada por um robô. Robôs do mesmo tipo podem ser usados múltiplas vezes. Nós propomos métodos exatos e heurísticos para a minimização do tempo de ciclo destes dois problemas, para um número fixo de estações. Os problemas têm características similares que são exploradas para produzir limitantes inferiores, métodos inferiores, models de programação inteira mista, e regras de redução e dominância. Para a estratégia de ramificação do método de branch-and-bound, entretanto, as diferenças entre os problemas forçam o uso de dois algoritmos diferentes. Uma estratégia orientada a tarefas tem os melhores resultados para o ALWABP-2, enquanto uma estratégia orientada a estações tem os melhores resultados para o RALBP-2. Nós mostramos que os limitantes inferiores, heurísticas, modelos de programação inteira mista e algoritmos de branch-and-bound para estes dois problemas são competitivos com os métodos do estado da arte da literatura. / The difference among workstations is assumed to be negligible in traditional assembly lines. Heterogeneous assembly lines consider the problem of industries in which the task times vary according to some property to be selected for the task. In the Assembly Line Worker Assignment and Balancing Problem (ALWABP), workers are assigned to workstations and according to their abilities, they execute tasks in different amounts of time. In some cases they can even be incapable of executing some tasks. In the Robotic Assembly Line Balancing Problem (RALBP) there are different types of robots and each station must be executed by a robot. Multiple robots of the same type may be used. We propose exact and heuristic methods for minimizing the cycle time of these two problems, for a fixed number of stations. The problems have similar characteristics that are explored to produce lower bounds, heuristic methods, mixed-integer programming models, and reduction and dominance rules. For the branching strategy of the branch-and-bound method, however, the differences among the problem force the use of two different algorithms. A task-oriented strategy has the best results for the ALWABP-2 while a station-oriented strategy has the best results for the RALBP-2. The lower bounds, heuristics, MIP models and branch-and-bound algorithms for these two problems are shown to be competitive with the state-of-the-art methods in the literature.

During the past decades, there have been an acceleration of customers’ needs of customized products. This have pressured many companies in offering customized products in order to reach customer satisfaction and keep growing and expanding their market share. Nowadays the competitive pressure between companies with the same product segment is increasing and the market requirements are changing rapidly. To handle this competition, many manufacturing companies are focusing on mass customized production. However, mass customization has been a topic of interest for many researchers. The focus has been in studying and understanding the complexity and the constrains that a company encounter when dealing with mass customized production in mostly the automotive industry. One of the constrains that have been less highlighted by researchers were the effects that mass customized production has on the output variation of production lines. Therefore, the purpose of this thesis is to investigate how to minimize output variations in mass customized production within assembly lines. To do that the researchers focused on studying the output variation in whitegoods industry instead of the automotive industry that captures most of the existing research. The study includes two main research questions. The first question was to identify the factors that affect the output variation in mass customized production. While the second question was to identify applicable solutions that can be used to stabilize the output. To ensure the reliability and validity of the research findings, the researchers used multiple case study combined with literature reviews. To answer the research questions several data collection techniques were used in the multiple case study conducted on two lines. Those data collection techniques were participating observations, document reviews, a semi-structured interview and many conversations with the affected persons. The findings from the case study for research question one showed consistency with the theories described in the theoretical background. This was evident because similar problems when it comes to output variations were defined in the theories. One problem was about the simplification of assembly line balancing problem that was evident in both case studies. This was an effect of the missing product family classification which created a high output variation because of the use of only one line balancing for all product variants. Another problem identified included functionality problems of machines because of performing wrong assembly or the use of the wrong component. There was as well the problem of missing or delayed components which was an effect of the lack of structure in the material picking and the deliveries performed for both lines. A combination of those factors created the experienced output variation on both lines. To deal with those problems and minimize the output variation, a solution approach was defined in the second research question. This approach was created together with the case company with the help of the theoretical background and it presents several steps to follow when attacking and resolving similar problems as presented above. The most important conclusion of this thesis is that, when dealing with output variation in mass customized production where people are performing the assembly, it is essential to provide the right conditions for them to ensure that they have the right knowledge base to perform the requested assembly.

A few years back, almost every garment manufacturer industry started implementing “lean Manufacturing.” Garments manufacturing is one of the oldest manufacturing systems, compromising a higher number of critical operations. The main performance indicators in the garment industry are the lead time, production rate, more wastage, and labor intensity. To remain competitive in the global market, the most important task for garments manufacturers is to reduce lead time and waste, which is also essential for productivity and long-term stable development. A headlong rush to reduce lead time and waste by turning into lean and responsive manufacturing has created an urgency for researchers and practitioners to apply new tools and techniques for discovering wastages. This thesis focuses on the application of value stream mapping in the garments industry to implement lean manufacturing system. Value stream mapping (VSM) helps visualize Material Flow and Information Flows of all components, cycle times, and utilization of resources. VSM is a proven lean technique in identifying and eliminating wastes in accommodation with similar or identical product routings. The research approach adopted in this thesis is abductive. Qualitative has been collected by the structured and semi-structured interviews. A single case observation has been made to use VSM as a lean tool to achieve productivity improvement at a selected garment company. Both current and future state mapping of cutting section and sewing line scenarios are discussed using value stream concepts. This was analyzed along with the process lead time as standard minute value (SMV) calculation and two gaps as productive time and non-productive.  Finally, gain in productivity (increase output pcs, less worker, less working hours), increased productive time, and reduce non-productive time was calculated.

Aim of diploma thesis “Lean production of electronics” is to apply lean production on workplaces in concrete company. Object of thesis is to orientate in lean production and apply its individual methods on workplace. First part of thesis is dealing with theoretical preparation, understanding lean production and methods of lean production. Second part is dealing with analyzing production processes, application of methods of lean production and designing workplaces.

Purpose – The purpose of the study is to explore how productivity can be improved in an assembly line in manufacturing industry. In order to fulfill the purpose, following three research questions have been formulated: 1. How can an assembly line be designed? 2. Which potential improvement areas can be found in an assembly line? 3. How can assembly line balancing be used to improve productivity? Method – A case study was performed in order to answer the research questions. A combination of quantitative and qualitative data have been collected. To build an understanding of existing theories and research within the study area, a literature study was conducted which formed a theoretical framework. Parallel to the literature study, empirical data was collected through a case study. Data collection methods included observations, document studies, time measurements and focus group meetings. The reviewed theories and the collected data were later analyzed and a result was generated. Findings – In order to improve productivity, Theory of Constraints enabled the identification of potential improvement areas. To address the improvement areas, Assembly Line Balancing was found an appropriate method. Through the case study it was found that through Assembly Line Balancing, a reduction of takt time can be achieved which opens up the possibility to increase the production volume. Also, when re-allocating operators between work tasks, a reduction in numbers of operators is possible which results in lower costs. By lowering costs and increasing production volume, improved productivity is achieved. Implications – This study presents an application of the two improvement methods Theory of Constraints and Assembly Line Balancing in a manufacturing industry. Therefore, the thesis can be used as a basis when performing improvement work related to reduction of takt time in other manufacturing industries, to gain a better understanding for the implementation of the studied methods. Limitations – One limitation of the study was the pandemic Covid-19, which enforced restrictions on the case company. This disturbed the conduction of the case study since less focus group meetings were conducted, and suggested improvements could not be tested. Another limitation was the limited study time frame. Consequently, the collected time measurements were relatively few and the study scope was delimited to only packaging activities. To increase reliability, a more extensive time frame is necessary. The analysis has been adopted to the situation at the case company. The conclusions may hence be biased, which could restrict to what extent the study can be generalized.

Purpose - This thesis aims to developing a decision-making tool which fits in a reconfigurable manufacturing system (RMS) milieu used to identify whether to introduce and produce a new product into an already existing assembly line or to invest in a new assembly line. To fulfil the purpose, four research questions were developed.  Which line balancing problem-solving techniques exist in the literature? Which investment costs can be considered vital for new assembly lines as a    consequence from new product introductions? Can a decision-making tool be designed to evaluate new product introductions which considers both line balancing KPIs and investment costs in an assembly line? To what extent can criteria in the RMS theory be linked with the attributes of the    designed decision-making tool to support its applicability? Method - Literature studies were performed in order to create a theoretical foundation for the thesis to stand upon, hence enabling the possibility to answer the research questions. The literature studies were structured to focus on selected topics, including reconfigurable manufacturing systems, line balancing, and assembly line investment costs. To answer the third research question, which involved creating a decision-making tool, a single-case study was carried out. The company chosen was within the automotive industry. Data was collected through interviews, document studies and a focus group. Findings & analysis - An investigation regarding which line balancing solving-techniques suit RMS and which assembly line investment costs are critical when  introducing new products has been made. The outputs from these  investigations set the foundation for developing a decision-making tool which enables fact-based decisions. To test the decision-making tool’s compatibility with reconfigurable manufacturing systems, an evaluation against established characteristics was performed. The evaluation identified two reconfigurable manufacturing system characteristic as having a direct correlation to the decision-making tool. These characteristics regarded scalability and convertibility. Conclusions - The industrial contribution of the thesis was a decision-making tool that enables fact-based decisions regarding whether to introduce a new product into an already existing assembly line or invest in a new assembly line. The academic contribution involved that the procedure for evaluating the tool was recognized as also being suitable for testing the reconfigurable correlation with other production development tools. Another contribution regards bridging the knowledge gaps of the classifications in line balancing-solving techniques and assembly line investment costs. Delimitations - One of the delimitations in the thesis involved solely focusing on developing and analysing a decision-making tool from an RMS perspective. Hence, other production systems were not in focus. Also, the thesis only covered the development of a decision-making tool for straight assembly lines, not U-shaped lines.