1,721,111 research outputs found
Absenteeism and turnover performance analysis of multi-model and mixed-model assembly lines
No full textAssembly lines are characterised by high rates of turnover and absenteeism. Any case of absenteeism or turnover requires assigning a replacement worker who is often inexperienced. Learning process is crucial for increasing productivity in such replacement cases, but learning is dependent on the variety of product models produced on that line. The complexity effect of the tasks at the assembly station, owing to a multi-model pattern, can result in a forgetting curve. The current research investigates the absenteeism in various batch sizes of multi-model and mixed-model assembly lines, introducing an innovative adaptation of the learning and forgetting functions. Secondly, it analyses the assembly system performance through a simulation study, focusing on the models' commonality and models sequences in the case of new substitute workers. A case study and a simulation analysis are reported to validate the research
Design and simulation-based optimisation of a renewable energy system consisting of wind and hydrogen for the purpose of reliable electrification
No full textIn this study, design and simulation-based optimisation of a hybrid power system is investigated. The energy system is designed in such a way that when the electricity is produced from the wind power, it would either be transmitted into the grid for the purpose of medium or large-scale electrification or in the case of surplus electricity, it would be utilised for small-scale hydrogen production. The wind energy production transmitted to the grid is estimated with the optimum value of approximately 2,000 kWh per day. The hybrid energy system has been adjusted so that the incoming energy supplied from wind energy production powers the electrolyser thus producing hydrogen from the power plant. Through considering various ranges of design coefficients including hydrogen price, hydrogen production, electricity price and electricity transmitted to the grid by harnessing the wind power, the net monthly revenues reached a maximum level of € 1,974.87 per month
“Station-Sequence” parts feeding in mixed models assembly: Impact of variations and industry 4.0 possible solutions
Get PDFAbstract: Parts feeding is a complex logistic problem, stressed by the increasing product variety that
forces the assembly systems to manage a great number of models with a mixed model approach. In this
context a possible parts feeding policy is the “station-sequence”, sequences of parts supplied to the
assembly stations as function of the production models. This parts feeding policy can reduce stocks at the
assembly stations, but offers potential production stops due to its low robustness. Different external
elements can perturb the parts sequences (i.e. changing in production schedule, tasks times variation,
variable supply lead times, etc.). The aim of this paper is to study, through a simulation study and a
statistical analysis, the station-sequence part feeding policy considering its dynamic time-dependence the
impact of the model mix and time perturbations on the system performance. Authors discuss the possible
application of the real time events traceability, achievable through the I4.0 application, in order to
mitigate the variability influence on the system performances
Theoretical analysis of wind flow characteristics to investigate the mass and momentum parameters using a novel computational fluid dynamics-based approach
No full textIn this article, an experimental study of a wind turbine in a wind tunnel is performed. The objective has been to present a novel analytical computational fluid dynamics (CFD)-based approach through considering the residual levels of the mass and momentum parameters under effect of different air flow characteristics surrounding the wind turbine, which have an effect on the power losses, turbine’s performance and the economic viability. The involved decision variables are considered to be the wind velocity, the pressure and the turbulence. Evaluation of the convergence showed that the residual level for the maximum method is estimated to be approximately 10–1 to 10–3 times higher than the root mean square. Results also concluded that between two studied turbulence models, the turbulence eddy frequency is found to be more efficient compared with turbulence kinetic energy. In higher iterations compared with the initial iterations, a significant difference between the pressure and the Cartesian velocity components has occurred and the residual level of the velocity components indicated a more efficient convergence compared with the pressure. The overall environmental analysis concluded that on the basis of the CFD residual values, it would be possible to adequately determine the CFD efficiency of the wind energy system in a wind tunnel. It has been demonstrated that, among different decision variables, velocity components of the mass and momentum parameters and the turbulence eddy frequency were determined to produce further accurate results in comparison with the pressure and the turbulence kinetic energy
Assembly kits with variable part physical attributes: warehouse layout design and assignment procedure
No full textPurpose: The kitting feeding policy creates kits with the parts of each product to assemble. Each kit contains elements with heterogeneous physical properties imposing heterogeneous logistic facilities and management solutions for storage and handling. The purpose of this paper is to present and apply a two-step procedure to design the part warehouse layout and to assign locations in case of kitting with high-variety part attributes. The proposed procedure aims at reducing the kitting travelled distance, shortening the picker paths, best positioning the components in the warehouse to enhance the possibility of creating kits through a single corridor access. The saturation of the warehouse and the minimization of the required storage space are also considered. Design/methodology/approach: Starting from part categorization, the proposed two-step procedure, of general applicability, designs the component warehouse, sizing the corridors (Step 1) before clustering the kits in terms of part commonality and best-assigning clusters to corridors (Step 2) with the goal of reducing the travelled distance and saturating the available storage space. Findings: A comparison model considers the traditional versus the proposed warehouse layout highlighting the potential saving in the picker travelled distance. A case study taken from the harvesting machine agricultural sector exemplifies the applicability and the practical implications of this research. Originality/value: Elements of originality are the warehouse design strategy and the assignment model for parts based on their physical attributes and their occurrence in the assembly kits. Finally, the case study taken from industry, with a high number of components and part categories, adds value to the research making the proposed procedure able to address large-scale industrial problems
A tri-objective model for the manual assembly line design integrating economic, technical and ergonomic aspects
Get PDFSmart assembly lines are a milestone of Industry 4.0 allowing the efficient and effective production of complex products with an acceptable time-to-market. According to the literature and the standard practice, these lines are made of a set of equipped stations with a worker for each of them. Products flow the stations in sequence to perform their assembly cycle. Nowadays, the best design of assembly lines deals with the joint inclusion and best mix of multiple dimensions, often in conflict and requiring good trade-off solutions. This paper proposes and preliminary applies a tri-objective linear programming model to design a single-model smart assembly line aiming at optimizing the system annual equivalent cost, the time balance among the stations and, finally, the level of fatigue each worker is exposed. Details on the model boundaries are given together with its full mathematical formulation and linearization, to reduce its complexity. Finally, a preliminary case study links the model to practice showing its feasibility and potential benefit for the modern smart industries
Assembly line balancing for personalized production
Get PDFAssembly line balancing problems aim to an efficient and effective assignment of all the required
tasks to workstations in a flow oriented production system. Nowadays, assembly lines have to face the
manufacturing of extremely personalized products (e.g. cars) as requested by an increasingly higher portion
of the market demand. Several literature contributions focus on different balancing problems affected by
the wide variety of the final product, e.g. mixed and multi model assembly lines. However, no contribution
seems to tackle the personalized production of goods. Such products require to assemble a certain number
of tasks whatever the final product personalization is, and a variable number of optional of different type
determined by the specifications of every single costumer. This paper faces the generalized assembly of
personalized goods proposing an innovative two step methodology to optimize the workload balancing
between the assembly line stations, considering traditional tasks and the optional required by the product
personalization, which could occur with different frequencies and pairings. The first phase of the developed
methodology executes a clustering of product options required by the costumers based on a similarity
index. This phase leads to the definition of several sets of optional typically requested together by the
customer and with similar mounting time. The methodology second phase leverages the defined clusters
of optional. Indeed, optional of the same cluster shouldn’t be assigned to the same workstation to reduce
the overload or underload of the assembly operators. An integer programming model is proposed to assign
both traditional tasks and optional to stations, to maximize the assembly line balancing considering the
order frequency and assembly time of the clusterized optional. An industrial case study is adopted to test
and validate the proposed two steps methodology. The obtained results highlight a consistent time
balancing between assembly line workstations and a significant limitation of the operator overloads
Push/pull parts production policy optimization in the ato environment
Get PDFWithin the Assembly to Order (ATO) production strategy, the common approach is to produce the parts to assemble with a Push-Make to Stock policy.In recent decades, the effects of the modern Just in Time (JIT) moved to a Pull-Make to Order policy. Assembled parts characterized by wide variety and huge storage space utilization are critical, and a proper Push/Pull production policy definition is required. An appropriate balance of storage space utilization and setup times leads to the optimization of the production policy. The aim of this paper is to define a bi-objective math-ematical optimization model to assign the most suitable production policy to the parts within the production mix in an ATO industrial context. A numerical simulation and an operative case study showcases the model application, proving the industrial relevance of this research
AN ANALYTICAL MODEL TO EVALUATING THE IMPLEMENTATION OF A BATCH-PRODUCTION-ORIENTED LINE
No full textThis paper presents a new approach to evaluating the suitability of implementing a batch-production-oriented manufacturing line. The Characteristic Curve (CC) as introduced by Deming [Deming, D.D., 1959. When to shift to straight-line production. Harvard Business Review 38, 62–68.] is an efficient tool for determining the number of machines belonging to each station in single-model production lines. Because such an approach does not consider set-up times, it is inappropriate for batch-production-oriented lines. A new methodology is presented named Distributed Set-up times Characteristic Curve (DSCC) which enables application of the CC to manufacturing lines organized on a batch-production system. The innovation introduced is an analytical model able to consider frequent set-ups, such as those caused by batch switching. The importance of the proposed technique for production system designers is the speed of analysis and the possibility of avoiding simulations as presented in the case study application, where the optimal organization of a steel pipe manufacturing line is explored. Specifically, by analyzing technical and economical performance indicators, the optimal number of laser bits, curling machines, bar folders and welders belonging to manufacturing stations, along with the suggested size of production batches to be adopted, are evaluated
NUOVO APPROCCIO ALLA CURVA CARATTERISTICA DI PRODOTTO: PRODUZIONI IN LINEA MONOPRODOTTO PER LOTTI
No full textLa variabilità del mercato odierno richiede una continua evoluzione ed innovazione dei prodotti offerti ed una loro sempre più spinta diversificazione. L’introduzione del concetto d’automazione flessibile ha segnato il passaggio da politiche aziendali mirate alla produzione di grandi volumi di merci standardizzate a politiche “market-oriented”, all’interno delle quali ci si scontra sovente con una personalizzazione sempre più spinta dei prodotti offerti con il fine di soddisfare segmenti di mercato diversificati. In quest’ottica, l’obiettivo del presente lavoro è quello di proporre un nuovo approccio alla “curva caratteristica di prodotto” per estendere tale metodo di analisi alle situazioni aziendali che nella pratica si osservano più di frequente: decidere la convenienza del passaggio da una politica di produzione di tipo job-shop ad una di tipo flow-shop nel caso di produzione monoprodotto a lotti. In tale memoria, si è cercato di adattare il modello di Deming, di CCT (produzione monoprodotto in linea) a condizioni aziendali in cui i tempi di fermo impianto (per set-up, manutenzione ecc.) non possono essere trascurati nella normale pianificazione della produzione: lotto singolo monoprodotto ma con tempo di set-up rilevante rispetto al tempo disponibile e multilotto monoprodotto con fermo impianto obbligato tra due lotti consecutivi
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