The key objective of the case study is to help students understand the nuances of assembly line design without having to manage a huge problem context. The case study provides a platform for an ...engaging discussion on assembly line balancing and related concepts. The case is developed in a setting of an auto subassembly manufacturer that currently operates two lines. The management is confronted with a situation in which the production requirements are increased. The management needs to decide between hiring additional workers, reconfiguring the assembly lines, or both to meet the new demand. The production manager suggests a simple linear allocation of resources based on demand. Its validity and various other options are investigated to manage the projected volume. The following considerations are used to evaluate each option: capacity utilization, labor utilization and flexibility of operations, cost of overtime, cost of new recruitment, and inventory. As an extension, we also discuss the trade-offs involved in level-production strategy and a market-driven strategy when the demand profile is variable.
This paper deals with an optimization problem that arises when a new paced simple assembly line has to be designed subject to a limited number of available workstations, cycle time constraint, and ...precedence relations between necessary assembly tasks. The studied problem, referred to as SALPB-S, consists in assigning the set of tasks to workstations so as to find the most robust line configuration (or solution) under task time variability. The robustness of solution is measured via its stability radius, i.e., as the maximal amplitude of deviations for task time nominal values that do not violate the solution feasibility. In this work, the concept of stability radius is considered for two well-known norms: ℓ1 and ℓ∞. For each norm, the problem is proven to be strongly NP-hard and a mixed-integer linear program (MILP) is proposed for addressing it. To accelerate the seeking of optimal solutions, an upper bound on the stability radius is devised and integrated into the corresponding MILP. Computational results are reported on a collection of instances derived from classic benchmark data used in the literature for the Simple Assembly Line Balancing Problem.
► Ergonomic characteristics on the upper extremity were considered. ► Ergonomic measures were formulated as linear functions of assembly task assignment. ► Assembly line design model was built ...incorporating the linearized ergonomic measures. ► The linear model enables utilizing existing efficient solution methods. ► The new model enables considering ergonomics in early stage of assembly line design.
Work-related musculoskeletal disorders (WMSDs) are common occupational diseases among assembly workers due to repetitive motions or heavy workloads. The conventional approaches to decreasing WMSDs in assembly workers usually focus on individual assembly work at the station level. These approaches, however, do not pay enough attention to work allocation at the whole assembly line level such as balancing ergonomic burdens among workers by proper work assignment. This paper presents a methodology that can be used to integrate ergonomic measures of upper extremities into assembly line design problems. Linear models are developed to link work-worker assignment to the upper extremity ergonomic measures based on a guideline from American Conference of Governmental Industrial Hygienists. These linear models allow ergonomic and productivity measures to be integrated as a mixed-integer programming model. The case studies of this paper show the new model can effectively balance and control exposure levels in the upper extremity while not significantly decreasing line efficiency. This research shows the potential to reduce the need of numerous task adjustments for ergonomic improvement after initial assembly line design in conventional trial-and-error based assembly task adjustment. Furthermore, these linearization methods can be generalized in order to incorporate other ergonomic measures in tabulated forms into assembly line design problems.
A realistic and accurate product cost estimation is of high importance during the design phases of products and assembly lines. This paper presents a methodology that aims at supporting decision ...makers during the design phases of assembly lines by taking into consideration product designs, processes and resources alternatives. First, we introduce a new variant of the Assembly Line Balancing and Equipment Selection Problem, in which Product Design Alternatives are considered. Since the ability to estimate product costs provides grounds for making better decisions, a new detailed cost model whose aim is to translate the complex and interrelated consequences of product design and manufacturing technologies and processes choice into one single cost metric is proposed. In order to solve the problem under study, 34 Multi-Objective Algorithms were developed. The list of developed algorithms includes variants of Evolutionary Algorithms, Ant Colony Optimisation, Artificial Bee Colony, Cuckoo Search Optimisation, Flower Pollination Algorithm, Bat Algorithm and Particle Swarm Optimisation. The performances of all these algorithms are compared based on fifty well-known problem instances in accordance with four multi-objective quality indicators. Finally, the algorithms are ranked using a nonparametric statistical test.
•An adaptable multi-agent systems has to allow the modelling of the dependencies between relevant elements of the assembly line planning.•Virtual collaboration for modelling problem model relevant ...elements, objectives and constraints, requires a robust conflict search.•The acceptance of the solutions only corresponds to the optimal solution when the problem is described perfectly.•The perfect collective problem description increases the graph complexity and outsources the solution search to the problem definition.•The solution search speed using genetic algorithm is shown to be dependent on the graph complexity and the graph flow.
Assembly line planning is the interface between agents of different professions, competencies, skills and experiences. Each agent is characterized by specific objectives and constraints, that must be considered when different products and processes are merged across multiple levels of various decision making units. A systemic platform for the dependencies of goals, constraining relationships of elements to be assigned and the interdependencies to properties of the elements is designed. Hereby, the objectives and the constraints are evaluated and mapped within the assembly line planning (ALP) process, resulting in a comprehensive graph with the processes, structures, resources and their properties with its dependencies. The dependencies include time criteria but also technical, processual, ergonomic, qualitative, part-dependent along with resource-dependent, structural constraints. The dependency map is integrated within an existing ALP process to achieve a temporal precedence on the incoming and outgoing information resulting in a dynamic process oriented presentation of the objectives and constraints. The elements of the dependency map are categorized and analysed based on the evaluations and a problem model is created for the presented ALP problem. The problem model is solved using a genetic algorithm which is parameterized in accordance to the problem model complexity and characteristic.
Automated assembly lines are a fundamental part of today’s manufacturing industry. Due to shortening product life cycles and an increasing number of product variants, assembly lines have to be ...designed with increasing frequency. Currently, all design decisions are based on the knowledge and expertise of engineers and the design process results in a high amount of manual effort. This paper therefore presents an approach to making the knowledge of these experts explicit and using it as the basis for the automated planning of multi-station assembly lines. The proposed planning method includes the scheduling of the assembly line and the selection of resources and their positioning into a feasible layout.
Assembly lines and cellular manufacturing systems (CMSs) design have been widely used in the literature. However the integration of these manufacturing concepts is neglected in an environment where ...parts need to be assembled after production in different shops. In this paper, a comprehensive quadratic assignment problem is developed for the assignment of machines of each part manufacturing cell, sub-assembly tasks of each sub-assembly cell as well as the assignment of different cells and final assembly tasks within the shop floor in their relevant predetermined locations. A genetic algorithm (GA) as well as a memetic algorithm (MA) consisting of the proposed GA and Tabu search (TS) algorithm are proposed and implemented on different size numerical examples. The obtained results show the efficiency of both algorithms to reach near optimal solutions compared to the optimal solution of small-sized problems.
Purpose
– The paper aims to focus on in-house part logistics design and management for assembly systems in which supermarket storage is adopted and coupled with an automated transportation system. In ...this context, this work aims to assess the transportation mode selection problem to speed up the preliminary design phase.
Design/methodology/approach
– The paper is divided into two main parts. The first one provides and discusses a new conceptual framework derived from the authors’ experience in the field and from previous published works. The framework aims to support managers in problem comprehension by setting three problem sub-phases, key input parameters and qualitative guidelines without losing sight of the big picture. The second part focuses on the transportation mode selection sub-phase by assessing an analytical study followed by a multi-scenario analysis.
Findings
– The final outcome of this work is a decision support matrix capable of setting technical guidelines that are helpful to managers and practitioners to speed up the transportation mode selection problem in the preliminary phases.
Originality/value
– This work is beneficial for supporting managers in understanding the main decisional steps involved in the design of a part-feeding system with a supermarket by discussing the three problem sub-phases and key input parameters and providing both qualitative and quantitative guidelines. Moreover, this study explores the transportation mode selection problem, which is not yet largely explored in the published literature.
Purpose
The purpose of this paper is to present the process of balancing a mixed-model assembly line by incorporating unskilled temporary workers who enhance productivity. The authors develop three ...models to minimize the sum of the workstation costs and the labor costs of skilled and unskilled temporary workers, cycle time and potential work overloads.
Design/methodology/approach
This paper deals with the problem of designing an integrated mixed-model assembly line with the assignment of skilled and unskilled temporary workers. Three mathematical models are developed using integer linear programming and mixed integer linear programming. In addition, a hybrid genetic algorithm that minimizes total operation costs is developed.
Findings
Computational experiments demonstrate the superiority of the hybrid genetic algorithm over the mathematical model and reveal managerial insights. The experiments show the trade-off between the labor costs of unskilled temporary workers and the operation costs of workstations.
Originality/value
The developed models are based on practical features of a real-world problem, including simultaneous assignments of workers and precedence restrictions for tasks. Special genetic operators and heuristic algorithms are used to ensure the feasibility of solutions and make the hybrid genetic algorithm efficient. Through a case study, the authors demonstrated the validity of employing unskilled temporary workers in an assembly line.
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