This is a bachelor thesis which handles a balancing problem in a manual assembly line for mixed models. Many product variations that are assembled in an assembly line have different cycle times in each operation in the process. The products that are assembled in the line have also large variations in their lead times. This leads to large balancing losses leading to reduced productivity and efficiency. Many balancing losses occur due to the inefficient time that one of the products causes. Other balancing losses occur due to bottlenecks that occur in some operations. The purpose of this study is to investigate the balancing losses in a manual assembly line with mixed models. The goal is to develop a proposal for a balanced layout, as well as to minimize balancing losses and waste and maximize productivity as much as possible. Two research questions have been developed as guidelines for the study: RQ1: What factors can lead to balancing losses in a mixed-model assembly line? RQ2: How can a mixed-model assembly line be balanced without leading to other types of losses? The study is a case study that looks for problems in one case company. It is based on a literature study and the collection of real-world data, which has been collected at the case company by observations, interviews and documents that include data about production times and balancing reports.  A proposal on how balancing losses can be reduced in the best possible way has been developed. The inefficient time has been reduced and the assembly line has become more efficient and productive. With help of this improvement proposal, other types of losses could be avoided, such as losses of human resources and financial resources. This study aimed to reduce the balancing losses that one product causes in the assembly line. No rebalancing of the other products was done, but other products were considered so that the balancing of the product does not lead to extra imbalance on the other products in the line. It was important for the fall company to be able to implement a solution that does not lead to a lot of other losses. Based on the three solutions proposed, this solution was the most suitable for what the company wants. A new layout for the product’s stations has been proposed. With this layout, efficiency will increase, and downtime will decrease, thus increasing productivity. Proposal three shows that it is possible to balance a mixed-model assembly line, by terminating a product and removing it earlier from the assembly line.   Keywords: Line balancing, manual assembly, balancing loss, mixed products, mixed-model assembly / Det här är ett examensarbete på grundnivå, som behandlar ett balanseringsproblem i en manuell monteringslinje för mixade modeller. Det monteras många produktkonfigurationer som har olika cykeltider i varje station i processen. Produkterna som monteras i linan har även stora variationer i deras ledtider. Detta medför stora balanseringsförluster som leder till minskad produktivitet och effektivitet. Många balanseringsförluster uppstår på grund av den ineffektiva tiden som en av produkterna orsakar. Andra balanseringsförluster uppstår på grund av flaskhalsar som förekommer i vissa stationer.  Syftet med denna studie är att undersöka balansringsförlusterna i en manuell monteringslinje med mixade modeller. Målet är att ta fram ett förslag på en balanserad layout, samt att minimera balanseringsförlusterna och slöseri och maximera produktiviteten så mycket som möjligt.   Två forskningsfrågor har tagits fram som riktlinjer för studien: F1: Vilka faktorer kan leda till balanseringsförluster i en mixad-modellmonteringslinje?  F2: Hur kan en mixad-modellmonteringslina balanseras utan att leda till andra typer av förluster? Studien är en fallstudie som undersöker problem hos ett fallföretag. Studien är baserad på en initial litteraturstudie och insamlad data, som har samlats in från fallföretaget via observationer, intervjuer samt dokument med data om produktionstider och balansrapporter.  Ett förslag på hur balanseringsförlusterna kan minskas på bästa möjliga sätt har tagits fram. Den ineffektiva tiden har minskats och monteringslinan har blivit effektivare och produktivare. Med hjälp av det här förbättringsförslaget, kunde andra typer av förluster undvikas, som exempelvis förluster av mänskliga resurser och ekonomiska resurser.   Denna studie är gjord för att minska balanseringsförlusterna som en av produkterna orsakar i monteringslinjen. Ingen ombalansering på de andra produkterna gjordes, men det togs hänsyn till andra produkter så att balanseringen av den produkten inte leder till extra obalans på de andra produkter i linan. Det var viktigt för fallföretaget att kunna implementera en lösning som inte leder till massa andra förluster. Utifrån de tre lösningarna som föreslagits var denna lösning den mest lämplig för vad företaget önskar sig. En ny layout på produktens stationer har tagits fram. Med denna layout kommer effektiviteten att öka och dötiden minska, och därmed ökas produktiviteten. Förslag tre visar sig att det är möjligt att kunna balansera en mixad-modellmonteringslina, genom att avsluta en produkt och ta ut den tidigare ur monteringslinan.   Nyckelord: Line balancing, manuell montering, balanseringsförluster, mixed products, mixed-model assembly line.

The thesis addresses the mixed model assembly line sequencing and outbound logistics planning problems in the automotive industry at the operational level. Different from the sequential decision-making procedure used in practice, the thesis proposes a scheme that integrates production sequencing and logistics planning. Mixed integer programs are established for the production sequencing, logistics planning, and integrated problems. The integrated model cannot be solved by commercial solvers in a reasonable amount of time. After studying the optimality properties of the product mode, the thesis proposes a modified integrated model. The results of numerical experiments and simulations demonstrate the benefit of the integration by comparing the modified integrated model with two sequential schemes, the Production-First-Scheme and the Logistics-First-Scheme.

The demand for increased diversity, reduced cycle time, and reduced work-in-process has caused increased popularity of mixed-model assembly lines. These lines combine the productivity of an assembly line and the flexibility of a job shop. The mixed-model assembly line allows setup time between models to be zero. Large lines mixed-model assembly lines require a timely, near-optimal method. A well balanced line reduces worker idle time and simplifies the mixed-model assembly line sequencing problem. Prior attempts to solve the balancing problem have been in-adequate. Heuristic techniques are too simple to find near-optimal solutions and yield only one solution. An exhaustive search requires too much processing time. Simulated Annealing works well, but yields only one solution per run and the solutions may vary because of the random nature of the Simulated Annealing process. Multiple runs are required to get more than one solution, each run requiring some amount of time which depends on problem size. If only one run is performed, the solution achieved may be far from optimal. In addition, Simulated Annealing requires different parameters depending on the size of the problem. The Genetic Algorithm (GA) is a probabilistic heuristic search strategy. In most cases, it begins with a population of random solutions. Then the population is reproduced using crossover and mutation with the fittest solutions having a higher probability of being parents. The idea is survival of the fittest, poor or unfit solutions do not reproduce and are replaced by better or fitter solutions. The final generation should yield multiple near optimal solutions. The objective of this study is to investigate the Genetic Algorithm and its performance compared to Simulated Annealing for large mixed-model assembly lines. The results will show that the Genetic Algorithm will perform comparably to the Simulated Annealing. The Genetic Algorithm will be used to solve various mixed-model assembly line problems to discover the correct parameters to solve any mixed-model assembly line balancing problem. / Master of Science

Purpose - The purpose of the bachelor thesis is to describe the relationship between Third-party logistics (3PL) suppliers and car assemblers under Just-in-sequence (JIS). The paper refers to a case in the Spanish automotive industry and the main target is to identify and analyse the potential problems between both parts and explain how they work together. Methodology – The paper is based on a case study research, with the aid of interviews with people of the industry and participant-observations, to explain how this part of the supply chain works, the relationships along the chain and the difficulties of sequencing. Results – The paper identifies and analyses the potential problems between both parts and relates how a mistake from one of them can affect the other one. Then, the results are discussed and associated with some concepts of the theoretical framework. Limitations - The results of this case study can only be related to the Spanish automotive industry, for car assemblers that work under a JIS context with several 3PL suppliers. The case study only identifies and analyses the problems, solutions and measures for managing them are not provided.

Purpose – The purpose of the study is to propose a framework for standardized workstations with focus on operators work activities and material presentation on a mixed-model assembly line. In order to fulfill the purpose, it was decomposed into three research questions: Research question 1: What problems in existing manual workstations can be identified, regarding work activities and material presentation? Research question 2: What can be considered regarding operators' work activities in creation of standardized workstations for a mixed-model assembly line? Research question 3: What can facilitate the work performance and ergonomics of operators when designing material presentation for standardized workstations for a mixed-model assembly line? Methodology – This study was carried out inductively through analysis of empirical data from a case study against existing theories from a literature study. Theories were in the areas of mixed-model assembly line, workstation design, material presentation, work activities, ergonomics and human aspect, and standardization and flexibility. To gather empirical data, a document study, observations and interviews were conducted at one case company. Findings – The study resulted in a framework for work activities and material presentation in standardized workstations on a mixed-model assembly line within the perspectives of ergonomics, standardization and non-value-added work. Results indicated on decreased efficiency if the involvement of human factor and standardization were insufficient in the workstation design, by increased non-value- added work and decreased ergonomics. Implications – The proposed framework intended to support companies to merge assembly lines into a mixed-model assembly line with low automation. Limitations – The framework in this study only focused on workstations' workactivities and material presentation. Workstations are linked to more than these two areas therefore should more areas be included in merging assembly lines. This framework had the perspectives of ergonomics, standardization and non-value-added work, more perspectives should be considered in a merger.

Volvo CE at Hallsberg, Sweden is specialized in the production of cabs for construction equipment. The organization employs the one-line (mixed-model assembly) method, where cabs for different products are all assembled on the same main line. Operations on the main line are not standardized for all products. The future vision of the company is to establish the fishbone factory concept, where the diversity is introduced in sub-flows and variation is reduced on the main line.This is primarily to reduce balancing losses and eventually reduce the total throughput time of the plant. The thesis work focuses on a new product known as the Next Gen Cab. These cabs are designed to support the fishbone factory concept. Next Gen cabs comprise of physical modules that provide different customer features, but are designed with standard interference and toolpoints. They follow the common architecture approach. The aim of this thesis work is to develop an assembly setup for the production of the front module within the next gen cabs, and investigate a suitable material feeding technique. The work also focuses on the transition phase, which comprise of the production of both existing and Next Gen cabs. The methodology used for the work includes the understanding of the current state to determine possibilities of utilizing the existing setup. The report explains part and process similarities between the existing cabs and Next Gen cabs which aids in the development of an assembly setup through line balancing. Two material feeding concepts have been developed and a framework has been established for part presentation at Point-of-Use. It is followed by a comparison of the concepts based on factors such as kitting time, headcount cost, stock value and required investment. The concepts are evaluated and finally, a conclusion is made along with a recommendation on how the company can proceed when the new products are introduced. / Volvo CE i Hallsberg, Sverige är specialiserat på produktion av hytter för entreprenadmaskiner. Organisationen använder en enkellinje metod (blandad-modellmontering), där alla hytter för olika produkter monteras på samma huvudlinje. Operationerna på huvudlinjen är inte standardiserad för alla produkter. Framtidsvisionen för företaget är att etablera fiskbensfabrikskonceptet, där mångfalden införs i delflöden och variationen minskas påhuvudlinjen. Detta är främst för att minska balanseringsförlusterna och så småningom minska anläggningens totala genomströmningstid. Examensarbetet fokuserar på en ny produkt som kallas Next Gen Cab. Dessa hytter är utformade för att stödja fiskbensfabrikskonceptet. NextGen-hytterna består av fysiska moduler som ger olika kundfunktioner, men är utformade med standardkopplingar och verktygspunkter. De följer den gemensamma arkitekturstrategin. Syftet med detta examensarbete är att utveckla ett monteringsupplägg för framställning av frontmodulen inom next gen hytter, och undersöka lämplig materialmatningsteknik. Arbetet fokuserar också på övergångsfasen, som består av produktion av både befintliga och NextGen-hytter. Metoden som används för arbetet inkluderar förståelse för det aktuella tillståndet för att bestämma möjligheterna att använda den befintliga uppställningen. Rapporten förklarar likheter mellan delar och processer för de befintliga hytterna och Next Gen-hytterna vilket hjälper till att utveckla en monteringsuppställning genom linjebalansering. Två materialförsörjningskoncept har utvecklats och ett ramverk har skapats för delpresentation vid Point of-Use. Detta följs av en jämförelse av koncepten baserat på faktorer som ”kittnings”-tid, antal anställda, aktievärde och nödvändiga investeringar. Koncepten utvärderas och utmynnar i en slutsats tillsammans med en rekommendation om hur företaget kan gå vidare när de nya produkterna introduceras.

Dans cette thèse, nous considérons le problème du séquencement sur une ligne de montage multi-modèles de véhicules industriels. Pour équilibrer au mieux la charge dynamique des opérateurs, la minimisation de la somme des retards à l’issue de chaque véhicule est proposée.Deux approches peuvent être utilisées pour optimiser le lissage de charge dans un problème de séquencement : l’utilisation directe des temps opératoires ou le respect de règles. La plupart des travaux appliqués à l’industrie automobile utilisent l’approche de respect de règles. Une originalité de ce travail est d’utiliser l’approche de la prise en compte directe des temps opératoires.L’étude de la littérature de ce problème a dévoilé deux lacunes dans les travaux précédents : l’essentiel des travaux modélisent un seul type d’opérateurs d’une part, et proposent des heuristiques ou des métaheuristiques pour résoudre ces problèmes, d’autre part. L’originalité de ce travail est de tester des méthodes exactes pour des instances industrielles et de modéliser le fonctionnement de trois différents types d’opérateurs spécifiques au cas industriel.Deux méthodes exactes sont développées : la programmation linéaire mixte et la programmation dynamique. Une étude expérimentale des facteurs de complexité sur des instances académiques des deux modèles est développée. Les modèles sont aussi testés sur des instances du cas d’étude.Par ailleurs, le problème est traité par deux méthodes approchées : une heuristique basée sur la programmation dynamique d’une part, et des métaheuristiques (algorithme génétique, recuit simulé et un couplage des deux) d’autre part. Les deux approches sont testées sur des instances académiques et des instances du cas d’étude.Ce travail a permis d’apporter une solution intéressante d’un point de vue industriel puisqu’il prend en compte les caractéristiques de la ligne de montage (opérateurs spécifiques) et améliore significativement la qualité du séquencement en un temps de calcul raisonnable. / In this thesis, the problem of sequencing mixed model assembly lines (MMAL) is considered. Our goal is to determine the sequence of products to minimize the work overload. This problem is known as the mixed model assembly line sequencing problem with work overload minimization (MMSP-W). This work is based on an industrial case study of a truck assembly line.Two approaches can be used to minimize the work overload: the use of task operation times or the respect of sequencing rules. Most of the earlier works applied in car industry use the latter approach. The originality of this work is to employ the task operation times for the generation of the product sequence in a MMAL.The literature review has highlighted two main gaps in previous works: most of the papers consider a single type of operators, and propose heuristics or metaheuristics to solve the problem. The originality of this work is to test exact methods for industrial case instances and to model three different types of operators.Two exact methods are developed: the mixed integer linear programming and dynamic programming. The models are tested on industrial case study instances. An experimental study is developed for both approaches in order to understand the complexity factors.Moreover, the problem is treated by two approximate methods: a heuristic based on dynamic programming and metaheuristics (genetic algorithm, simulated annealing and a hybrid method based on both genetic algorithm and simulated annealing). All approaches are tested on academic instances and on real data from the industrial case study.

Cette thèse, réalisée en collaboration avec le Groupe Renault dans le cadre d’un projet d’automatisation du kitting, s’intéresse à l’optimisation du processus de kitting en termes de maximisation du temps de cycle. Pour cela, nous étudions différentes configurations de système de kitting hybride avec robots(s) et opérateur(s) travaillant en série et séparés par un stock de découplage. Le(s) robot(s) commence(nt) la préparation des kits de pièces puis le(s) opérateur(s) se trouvant dans la partie manuelle du kitting récupère(nt) cette préparation et la complète(nt) avec les pièces affectées à cette zone.Notre objectif est de développer un outil d’aide à la décision permettant d’évaluer la performance d’un kitting hybride et de simuler son fonctionnement dans une configuration donnée (layout, politique de picking, etc.) avant son déploiement physique.Tout d’abord, à travers une modélisation des opérationsélémentaires de kitting effectuées par des robots et des opérateurs (prise et dépose, déplacement, etc.), nous proposons un modèle de temps de cycle permettant d’évaluer la performance du système hybride en termes de temps de cycle. Ensuite, nous développons un modèle d’affectation de pièces (PLMNE) permettant de les répartir entre kitting robotisé et manuel. L’objectif est de minimiser les temps de cycle et d’équilibrer la charge de travail entre les deux modes de kitting. Le modèle est appliqué à deux études de cas pratiques issues d’une usine Renault. Les résultats permettent d’identifier les paramètres qui impactent le plus les temps de cycle et le choix d’affectation des pièces entre kitting automatisé et manuel. Enfin, nous développons un modèle de simulation afin de calculer la taille optimale du stock de découplage entre kitting automatisé et manuel dans le but de maximiser la cadence du système hybride de kitting. / In this thesis, conducted with Renault in the context of a kitting automation project, we are interested in the optimisation of kitting processes in terms of cycle time maximisation. To do so, we study different configurations of hybrid robot-operator kitting systems where robots (two types of robots considered) and operators are connected in series by an intermediate buffer (to decouple their activities). The robotic kitting area starts the preparation of kits then the operators in the manual kitting area retrieve the preparation of robots and complete with the remaining parts.Our objective is to develop a decision-making tool that assesses the hybrid system performance in a given configuration (layout, picking policy, etc.).First, through a modelling of elementary kitting operations performed by robots and operators (pick and place, travel, etc.), we develop a cycle time model to assess the performance of hybrid kitting systems. Then, we develop an assignment model that assigns parts (formulated as a mixed integer linear programming (MILP) problem) either to robotic or manual kitting areas with the objective of minimising cycle times and balancing workload between them. The model is applied to two case studies pertaining to a Renault plant. This analysis identifies the parameters that influence cycle times and the choice between robotic and manual kitting. Finally, we develop a simulation model to find the optimal buffer size between robotic and manual kitting so that throughput is maximised.