Repositório RCAAP

The automotive component industry has grown steadily in the last decade. The automation of the manufacturing processes has boosted an increase in the production rates of the components, and also contributed to a significant increase in quality. Automation has also contributed significantly to an increase in the production rate, as well as the process flexibility and reliability of the products obtained in the manufacture of spiral tubes used in control cables normally used for the operation of doors, brakes, glass handling, etc.. Currently, the manufacturing process of these components can be performed in a completely automated way, which proves the importance of automation in this sector. This work intends to present the development of a new solution for transporting conduits along an automatic production line, where several operations are carried out on the control cable spirals, namely cutting, deburring, punching of terminals at the ends and insertion of a tube starter, to sample noises during operation. An innovative transport system of the main sub-product (conduits) was developed along the line, which has a much higher reliability than previously recorded, also reducing the setup time required by 97%. The stoppages of the equipment due to problems with the conduits transportation process were also drastically reduced. The solution found is extremely simple and economical, allowing the reuse of numerous parts already used in the previous solution, with the consequent benefits in terms of resources reutilization. As an economical solution, it can be easily adaptable to other similar production processes, inducing very appreciable productivity gains.

Partindo da premissa que sugere que um professor é também um investigador, este artigo pretende explorar essa ‘faceta profissional’, mas a partir da experiência de alguns estudantes aquando da frequência de um mestrado profissionalizante para a docência. Para tal, e recorrendo ao programa informático MAXQDA 2018, analisamos o conteúdo de 25 relatórios de estágios de alunos do Mestrado em Educação Pré-Escolar e Ensino do 1.º Ciclo do Ensino Básico selecionados aleatoriamente, tendo atentado em elementos vários, como as temáticas educativas investigadas, as motivações subjacentes às pesquisas ou a concertação entre os pressupostos metodológicos assumidos e os objetivos de investigação definidos.No final, duas ou três considerações ganharam destaque: aqueles futuros docentes, para além de vivenciarem um momento elementar para o desenvolvimento da sua literacia investigativa, reconhecendo as várias dimensões inerentes ao processo, nem sempre são capazes de discernir a prática investigativa da prática pedagógica ou, ainda, distintos métodos de investigação.

This paper studies Optimal Intelligent Supervisory Control System (OISCS) model for the design of control systems which can work in the presence of cyber-physical elements with privacy protection. The development of such architecture has the possibility of providing new ways of integrated control into systems where large amounts of fast computation are not easily available, either due to limitations on power, physical size or choice of computing elements.

Physical vapour deposition (PVD) is a well-known technology that is widely used for the deposition of thin films regarding many demands, namely tribological behaviour improvement, optical enhancement, visual/esthetic upgrading, and many other fields, with a wide range of applications already being perfectly established. Machining tools are, probably, one of the most common applications of this deposition technique, sometimes used together with chemical vapour deposition (CVD) in order to increase their lifespan, decreasing friction, and improving thermal properties. However, the CVD process is carried out at higher temperatures, inducing higher stresses in the coatings and substrate, being used essentially only when the required coating needs to be deposited using this process. In order to improve this technique, several studies have been carried out optimizing the PVD technique by increasing plasma ionization, decreasing dark areas (zones where there is no deposition into the reactor), improving targets use, enhancing atomic bombardment efficiency, or even increasing the deposition rate and optimizing the selection of gases. These studies reveal a huge potential in changing parameters to improve thin film quality, increasing as well the adhesion to the substrate. However, the process of improving energy efficiency regarding the industrial context has not been studied as deeply as required. This study aims to proceed to a review regarding the improvements already studied in order to optimize the sputtering PVD process, trying to relate these improvements with the industrial requirements as a function of product development and market demand.

The technological evolution in the last century also required an evolution of materials and coatings. Therefore, it was necessary to make mechanical components subject to heavy wear more reliable, improving their mechanical strength and durability. Surfaces can contribute decisively to extending the lifespan of mechanical components. Chemical vapor deposition (CVD) and physical vapor deposition (PVD) technologies have emerged to meet the new requirements that have enabled a remarkable improvement in the morphology, composition and structure of films as well as an improved adhesion to the substrate allowing a greater number of diversified applications. Thin films deposition using PVD coatings has been contributing to tribological improvement, protecting their surfaces from wear and corrosion, as well as enhancing their appearance. This process can be an advantage over other processes due to their excellent properties and environmental friendly behavior, which gives rise to a large number of studies in mathematical modelling and numerical simulation, like finite element method (FEM) and computational fluid dynamics (CFD). This review intends to contribute to a better PVD process knowledge, in the fluids and heat area, using CFD simulation methods focusing on the process energy efficiency improvement regarding the industrial context with the sputtering technique.

Productivity is a key factor for companies manufacturing parts and sets to the automotive industry. Automation plays an important role in this matter, allowing development of entire manufacturing cells without the direct need of workers. Even in countries where the labour cost is relatively low, it becomes necessary to improve the level of automation applied to manufacture cells and reduce the dependence of the human labour unpredictability, also increasing the quality and reducing the costs. This case study was developed based on an industrial request in order to improve a semi-automatic cell devoted to seat suspension mat manufacturing. The original cell allows several automatic operations but it needs two workers for two specific operations not considered in the initial design. Thus, new concepts of wire feeding and manipulation were developed in order to allow a better material flow throughout the cell. The new cell was designed and built with success, allowing obtain a fully-automated system, which leads to a better productivity and reliability of the manufacturing process.

The use of hydrogen as an alternative to fossil fuels for vehicle propulsion is already a reality. However, due to its physical characteristics, storage is still a challenge. There is an innovative way, presented in this study, to store hydrogen in conventional vehicles propelled by spark-ignition reciprocating engines and fuel cells, using hydrogen as fuel; the storage of hydrogen will be at high pressure within small spheres randomly packed in a tank, like the conventional tank of fuel used nowadays in current vehicles. Therefore, the main purpose of the present study is to assess the performance of this storage system and compare it to others already applied by car manufacturers in their cars. In order to evaluate the performance of this storage system, some parameters were taken into account: The energy stored by volume and stored by weight, hydrogen leakage, and compliance with current standards. This system is safer than conventional storage systems since hydrogen is stored inside small spheres containing small amounts of hydrogen. Besides, its gravimetric energy density (GED) is threefold and the volumetric energy density (VED) is about half when compared with homologous values for conventional systems, and both exceed the targets set by the U.S. Department of Energy. Regarding the leakage of hydrogen, it complies with the European Standards, provided a suitable choice of materials and dimensions is made.

Water is an important resource for human beings, yet there are inhabited places tormented by the scarcity of it. The present study is concerned with places where, seemingly, the best way to get water is through solar distillers. These places should have, typically, high values of solar irradiation and a lack of human and economic resources to build and operate complex equipment. A set of sites scattered around the world was chosen, and then the presumed productivity and thermal efficiency that solar distillers would have if they were installed at these places was calculated. The mathematical model used with this purpose assumes steady-state operation; the values of mass of water distilled and distiller efficiency were calculated for every hour, but the results presented are annual averages. Then, an economic study was made based on local costs of construction materials for the distillers, the workforce, and the prices of water to predict the payback time of solar distillers. Finally, a study on environmental impact, particularly in terms of greenhouse gas (GHG) emissions, was made to compare reverse osmosis (RO) with solar distillation. For the sites studied, typical values of annual water output are in the range of 414 dm3/m2, for Évora, up to 696 dm3/m2, for Faya Largeau; the minimum efficiency was found for Évora, as 11.5%, and the maximum efficiency was found for Tessalit, as 15.2%. Payback times are very high, regardless of the areas of the globe where solar distillers are implanted. Regarding GHG emissions, solar distillation is preferable to RO.

Advanced coatings play an important role in a wide range of industrial applications. These coatings are commonly used in machining tools due to their high hardness and wear resistance, but also can be applied in jewellery and decorative purposes. Deposition techniques have seen a strong evolution as result of the directly related devices, control evolution and software. Several variants have been developed around the main techniques: arc evaporation and sputtering. The coatings produced present significant differences in their characteristics, namely in terms of structure, mechanical properties and surface morphology. Depending on the substrate material and application, the deposition process needs to be properly selected, providing the particular characteristics requested. This paper intends to do a critical review of the evolution of the advanced coatings deposition process, mainly focused on the Physical Vapour Deposition (PVD) process, particularly in the Magnetron Sputtering technique, which is able to produce smooth surfaces, using lower temperatures, presenting excellent mechanical and tribological properties and having very good adhesion to the main materials used as substrate.

The metal packaging industry used for food application has undergone drastic changes in the demands of its final consumers. The raw material for these packages, is a low carbon steel coated with a thin layer of tin (2,0 g/m2), also known as tinplate. The stamping process of these packages occurs at room temperature and is critically influenced by the tin transfer from the steel surface to the tool surface, mainly due to the tin softness. This problem is easily solved using lubrification but the purpose of this study will be the reduction or even absence of lubricants during the process in order to comply with costumers’ requirements. A successful way to minimize the consumption of lubricants is to use tools which are coated with PVD (Physical Vapour Deposition) advanced coatings deposited with unbalanced magnetron sputtering technique. Thin WC (Tungsten Carbide) and CrCN (Chromium Carbonitride) coatings were deposited using PVD on tool stamping steel – AISI D2. Block on ring tribological tests were performed on the coatings against tinplate counterface in order to investigate their wear performance, with particular emphasis on the material transfer (tin) phenomena during the sliding tests. The results allowed for selecting the best coating tested with a view to avoid the tin adhesion to the die.

Physical Vapour Deposition (PVD) is a process usually used for the production of advanced coatings regarding its application in several industrial and current products, such as optical lens, moulds and dies, decorative parts or tools. This process has several variants due to its strong evolution along the last decades. The process is commonly assisted by plasma, creating a particular low pressure and medium temperature atmosphere, which is responsible for the transition of atomic particles between the target and the parts to be coated into a vacuum reactor. Several parameters are directly affecting the deposition, namely the substrate temperature, pressure inside the reactor, assisting gases used, type of current, power supply, bias, substrate and target materials, samples holder and corresponding rotation, deposition time, among others. Many mathematical models have been developed in order to allow the generation of numerical simulation applications, trying to combine parameters and expect the corresponding results. Numerical simulation applications were created around the mathematical models previously developed, which can play an important role in the prediction of the coating properties and structure. This paper intends to describe the numerical simulation evolution in the last years, namely the use of Finite Elements Method (FEM) and Computational Fluid Dynamics (CFD).

This paper presents a Unit Commitment model with reactive power compensation that has been solved by Genetic Algorithm (GA) optimization techniques. The GA has been developed a computational tools programmed/coded in MATLAB. The main objective is to find the best generations scheduling whose active power losses are minimal and the reactive power to be compensated, subjected to the power system technical constraints. Those are: full AC power flow equations, active and reactive power generation constraints. All constraints that have been represented in the objective function are weighted with a penalty factors. The IEEE 14-bus system has been used as test case to demonstrate the effectiveness of the proposed algorithm. Results and conclusions are dully drawn.

This paper explores the use of a multi-objective approach through the implementation of a numerical direct multiple shooting (MS) method to solve optimal control problems (OCP). When a direct MS method is used to solve the OCP, a set of `continuity constraints' emerges and should be satisfied together with the other algebraic mixed states and control constraints. To minimize the objective function and satisfy all the constraint conditions, the finite-dimensional optimization problem is reformulated as a multi-objective problem with three objectives to be optimized. An illustrative example is included to show that the present methodology is worth pursuing.

A direct multiple shooting (MS) method is implemented to solve optimal control problems (OCP) in the Mayer form. The use of an MS method gives rise to the so-called ‘continuity conditions’ that must be satisfied together with general algebraic equality and inequality constraints. The resulting finite nonlinear optimization problem is solved by a first-order descent method based on the filter methodology. In the equivalent tri-objective problem, the descent method aims to minimize the objective function, the violation of the ‘continuity conditions’ and the violation of the algebraic constraints simultaneously. The preliminary numerical experiments carried out with a set of benchmark OCP are encouraging.

This work proposes a multi-criteria decision making approach to help assessing and selecting suppliers in the olive oil sector. Olive oil is a protected agricultural product, by region and origin certificate. Therefore to select a supplier, it is of utter importance to inspect and test (taste, colour, smell, density, among others) the olive oil in addition to the supplying company. The identification of possible suppliers was done in two stages: firstly, the region of origin from which to choose possible suppliers was identified and then potential suppliers were evaluated on a set of characteristics for which minimum threshold values were set. From this study, which is not part of the research reported here, we were able to identify the suppliers of interest. Due to the several characteristics and characteristic dimensions used to choose a supplier we resort to the Analytic Hierarchy Process to rank them, this way allowing for a better choice. The rank obtained is robust as the top ranked supplier remains the same for any reasonable change in the criteria weighs and in the evaluation of the suppliers on each criterion. The involved company found the results of value, as well as the lessons learned by addressing the supplier evaluation problem using a more systematic approach.

Absenteeism is defined as the absence of a worker from his or her workplace during a normal day’s work schedule and is seen as a problem which companies face every day. The absence of an employee can result in a significant drop in productivity and the company’s daily revenue can be negatively impacted by it, which when multiplied by the absence of multiple workers in different days can have a harmful impact on the company’s financial situation. However, most managers neither understand nor have looked into the causes of their absence issue. This study took place at a company which produces cork stoppers, which deals with a problem of high absenteeism that costs around 1,200,000€ per year to the company. The main goal of this study is to identify the sectors in this com- pany which have the highest percentage of absenteeism, quantify its impact on related outcomes and diagnose its causes. The results of this study show that most absenteeism occurs in production areas and the causes are related to musculo- skeletal problems. The consequences involve various costs to the company, some of them difficult to quantify.

The absenteeism related to health and safety at work is a serious issue in the manufacturing process, and some industries can be dangerous work fields with a high level of accidents. It is important to understand what causes the accident and, if possible, apply standard procedures to minimize the risk of accidents and subsequent absenteeism. This study aims to assess the impact of the implementation of occupa-tional health and safety procedures on company absenteeism. In the compa-ny where the study took place, most work accidents and absenteeism hap-pened in the production area, with workers who directly handle raw materi-als and machines. As a result, an HSE manager was hired in order to reduce accidents by putting in place several hygiene and security measures and procedures. The results of these measures as well as absenteeism data were studied and con-clusions regarding company performance were drawn

The focus of the current study was to set the benchmark for designing school furniture for Portuguese primary schools, taking into account the characterization and analysis of a previously selected sample of students. Considering the anthropometric data of the Portuguese children with ages between six and ten years old and its treatment, it was possible to set benchmarks for the design of school furniture for Portuguese primary schools, as well as to develop a methodological guide for adjusting the furniture according to the student’s stature. The obtained results seem to be very relevant as they provide a scientific basis for the design and compatible with the anthropometric dimensions of the considered population of users.

Pultrusion is a widely known technique for production of constant cross-section profiles, such as bars, L-shape or T-shape profiles, as well as structural tubes in polymer matrix composite materials. In some applications, requirements are demanding for profiles able to provide better thermal or sound insulation or needing a slightly higher moment of inertia without increasing the ratio between weight and strength. In such cases, hybrid pultruded profiles with core based on preforms are a possible solution. After obtaining prototypes according to the methodologies described in a previous work, and as a complement to that work, it is necessary to verify if the properties of these hybrid profiles correspond to the initial expectations, by performing destructive and non-destructive tests. Thus, tensile, compression and bending tests were performed, in order to verify the mechanical benefits achieved through the core introduction into the hollow profile and to analyse the added value brought by these new products. These values, once properly validated, can be added to existing databases related to structural calculation programs, enabling to get the adequate values for calculations regarding this kind of profiles. In addition, thermal and acoustic insulation tests were performed, in order to quantify the physical improvements achieved regarding these properties, which are extremely important in specific applications linked to the civil construction and public works, among many others. The cored profiles showed a strong adhesion between the profile and any kind of core tested as well as improved properties in terms of thermal insulation and moment of inertia. However, the sound insulation did not present significant improvements, probably due to GFRP profile external rigidity and consequent reflection.

Hybrid pultrusion is a process that can be used to fabricate different products, enclosing distinct techniques and materials. Its development comes from the need to obtain properties' reinforcement of the structural profiles obtained by pultrusion, allowing its application into specific situations, such as thermal or acoustic insulation or to increase the product's moment of inertia, without having a proportional weight increase. In this work was developed based on a novel idea of manufacturing pultruded pipes around preforms of good thermal and/or acoustic insulator materials, such as cork and polyurethane foam. However, the same terminology was already used to describe fabrication techniques in which pultruded structural profiles were combined with concrete structures in order to increase the mechanical and/or flexural resistance, diminishing the total weight. Nevertheless, no industrial equipment is currently available on the market regarding the production of hybrid pultruded products based on preforms. Thus, novel equipment has been designed to provide a good connection with a conventional existing pultrusion machine, allowing the production of pultruded pipes that involve cork and polyurethane foam preforms in a continuous way. The equipment has been developed and tested, enable obtaining hybrid pultruded products that can be applied in several situations where flexural strength, acoustic or thermal insulation must be improved relatively to conventional pultruded products, broadening the market for this type of structural products. The manufacturing equipment is prepared to work without permanent workers, needing to be refilled every 60 min and showed to be competitive, being able to add value to the conventional profiles already on the market. Preliminary tests were carried out showing clearly the improvement of the mechanical strength, thermal insulation and acoustic insulation capacities.