Repositório RCAAP

The relationship between the film generation and the coefficient of friction in grease lubricated contacts was investigated. Ball-on-disc tests were performed under different operating conditions: entrainment speed, lubricant temperature and surface roughness. The tests were performed with fully formulated greases and their base oils. The greases were formulated with different thickener types and also different base oils natures and viscosities. Film thickness measurements were performed in ball-on-glass disc tests, and Stribeck curves were measured in ball-on-steel disc tests with discs of different roughness. The role of the thickener and the base oil nature/viscosity on the film thickness and coefficient of friction was addressed and the greases’ performance was compared based on their formulation.

The maintenance management is a topic of strategic importance for automotive manufacturers. In fact, an effective maintenance process and a preventive maintenance (PM) procedure can significantly reduce the risk of equipment failures that can lead to downtime on the production lines. However, due to the complexity of an automotive production system, the risk of failure on a crucial piece of the production equipment cannot be entirely avoided. The study made in this paper aims at improving the availability of a critical production line through the total productive maintenance (TPM) methodology and supported by Lean Maintenance tools. An analysis is made of the initial condition of the line where the main problems are identified by employing several tools for this purpose, such as Mean Time between Failures (MTBF), Mean Time to Repair (MTTR), Overall Equipment Efficiency (OEE) and Availability (A). In response to the identified problems, an action plan is developed and implemented in order to find the root cause of the high number of malfunctions and faults in one of the line’s equipment with the use of 5S tools, visual management, and maintenance progress, as well as the development of a training program to increase operators’ skills. The results of such actions were positive as the line became more organized, the value of the MTBF increased, the MTTR value decreased, and consequently the overall availability increased.

The increasing competitiveness installed in the automotive industry implies continuous improvements in all fields of knowledge and action. Thus, it is very important to be aware of the wastes generate across all the productive and logistics operations. In this regard, and considering the production process of command cables for the automotive industry, it was detected that a significant volume of lubricant is wasted during the task of introducing grease into the spiral used in the command cables utilized to drive the doors, windows and brakes of motor vehicles. The industrial operation was carefully followed leading to identify the main causes of the wastes and a brainstorming was carried out allowing the discussion of new ideas on how to overcome the problem. A novel equipment was developed, being also cared all the logistics around the supplying task. The new solution developed, as well as the redefinition of the logistic process of supplying the lubricating grease to the production lines, made it possible to make the process more flexible for the admission of different grease packs, as well as a better utilization of the existing grease in the reservoirs, resulting in a cut of grease waste by more than 70%. It was also produced a prototype of the grease supply system, which allowed validate the previously developed system.

Due to the globalization of markets, the industrial competitiveness has increased significantly in the recent years. Within this scope, the transportation of products inside industrial parks acquires special relevancy. One of the solutions is the use of autonomous guided vehicles. This work presents the design of a modular autonomous vehicle, capable of carrying heavy loads, which will improve the performance of industrial parks. This is a compact vehicle with low associated costs and good transport speeds. A drive system was designed, which will be capable of transporting the proposed loads. This design was carried out using simulations of the transport with loads, either in plane ground or in an industrial park. A structural analysis to the vehicle was also undertaken by the Finite Element Method, showing the points of the structure that require reinforcement for the different load cases. Finally, the required corrections were implemented, giving to the structure the ability to carry the desired loads. The end result was an autonomous vehicle with capacity to safely transport the imposed loads in the most efficient possible manner.

This paper presents an integrated system that helps both retail companies and electricity consumers on the definition of the best retail contracts and tariffs. This integrated system is composed by a Decision Support System (DSS) based on a Consumer Characterization Framework (CCF). The CCF is based on data mining techniques, applied to obtain useful knowledge about electricity consumers from large amounts of consumption data. This knowledge is acquired following an innovative and systematic approach able to identify different consumers’ classes, represented by a load profile, and its characterization using decision trees. The framework generates inputs to use in the knowledge base and in the database of the DSS. The rule sets derived from the decision trees are integrated in the knowledge base of the DSS. The load profiles together with the information about contracts and electricity prices form the database of the DSS. This DSS is able to perform the classification of different consumers, present its load profile and test different electricity tariffs and contracts. The final outputs of the DSS are a comparative economic analysis between different contracts and advice about the most economic contract to each consumer class. The presentation of the DSS is completed with an application example using a real data base of consumers from the Portuguese distribution company.

The automotive industry, like many other industries, uses a wide range of parts produced by the die-cast process. Parts like engine blocks, wheel spacers, alternator housings and command cable terminals, are made by die casting with different kinds of materials like aluminium and zinc alloys. Despite being a reliable process both in terms of quantity and quality, it is very important to keep the process parameters controlled, in order to achieve a minimum percentage of defective parts, which may be caused by several factors such as, porosities, segregations, incomplete fill, soldering, cracks, etc. The main goal of the die casting industry is to achieve the zero per cent defects target, a goal that goes along with the automotive industry and its quality system, and to accomplish this objective the stakeholders need to invest in research and development. In the casting industry, for instance, it is very important to have a complete knowledge of the entire process developed inside the casting machine, from the melting pot to the die, in order to obtain data so one can improve the filling parameters, machine parts, and moulds. The focus of the presented study is the improvement of the methodologies used to design moulds for control cable terminals in Zamak alloys. The work starts by characterizing the flow happening inside the mould at the moment of cavity fill by analysing computer fluid dynamics simulations (CFD). The study proceeds by quantifying the porosities detected on cut terminal surfaces, and the ultimate goal is achieved with the modification of molten metal flow systems, like channels and sprues, and the introduction of venting systems, with a resource to mathematical and geometrical calculus developed in MATLAB® specifically for that purpose. The paper ends with the validation of the improvements, by comparing the initial results with the ones obtained through an improved mould, building bases for novel design concepts of moulds for this kind of parts, as well as new studies trying to improve the results now achieved.

Cohesive zone modelling (CZM) is widespread for the strength analysis of bonded joints. The fracture toughness (GC) is required to use CZM. A scarcely studied mixed-mode test is the Asymmetric Tapered Double-Cantilever Beam (ATDCB), which merges a Tapered Double-Cantilever Beam (TDCB) adherend with a Double-Cantilever Beam (DCB) adherend. This work addresses the ATDCB test to estimate the fracture envelope of a structural adhesive. TDCB and End-Notched Flexure (ENF) tests were also performed to acquire the tensile (GIC) and shear fracture toughness (GIIC), respectively. Numerically, mixed-mode CZM laws were constructed based on the obtained data, and the results were compared with experiments, to validate the CZM laws and the mixed mode propagation criterion. As a result, the best damage propagation criterion for mixed mode was estimated and validated.

The growing globalization of the different types of market requires that companies invest, in a recurrent way, to optimize and improve all the processes inherent to their activities. Aluminium extrusion is the main industrial process used to create profiles of a fixed cross-section. This process requires appropriate processing parameters to be used, in order to produce diverse profiles and high-quality products. The company’s ability to adapt and improve the productive process are differentiating factors against the competition. Thus, understand the main operations and dynamics of the companies is crucial. This work presents an empirical study concerning the extrusion process of a Portuguese company in the aluminium sector. By analysing a real data base provided by the company, the main objective is to model the aluminium extrusion process. Taking into account the variables that most influence the extrusion of different profiles, the aim is to minimize the production of scrap. First, by studying the literature in the subject, the variables that most contribute to scrap production were identified. Since the database provided by the company did not present all the variables described in literature, proxy variables were considered. Next, a multivariate linear regression model for explaining the amount of scrap taking as explanatory the identified variables was estimated. With this analysis, it was possible to identify levels of significance of the variables under study, and therefore understand how each of the variables contributes to the increase or decrease of the amount of scrap on the production of aluminium profiles. The results show that variables concerning with extrusion temperature, time, speed, pressure and die geometry are crucial to improve and control the scrap production. The obtained model will be improved, in future work, by including further variables of the extrusion process. Furthermore, factor analysis and GHML methodologies will also be considered for explaining the production of scrap and therefore improve the production process.

The effect of organophilic clay (C15A) in PP compatibilized polymer (PP/PP-g-MA) through rheological experimental results is presented. This study focusses on the description of the rheological behaviour of the organophilic layers along the screws of a twin screw extruder by melting process, varying the screw profile as well as the processing conditions, namely screw speed, temperature and feed rate. Different levels of dispersion were found along the screws for all conditions and positions analyzed by rheology. The qualitative analysis of the images obtained by transmission electron microscopy, reinforced the results. Furthermore, the effects of the processing conditions on dispersion of C15A layers along the screw profile are analyzed using multiple linear regression techniques. The results show statistically significant differences of all rheology measures for all the processing conditions and positions along the extruder.

Adhesively-bonded joints have become more efficient due to the improvement of adhesives’ characteristics. On the other hand, with the use of composites in structures it is possible to reduce weight. Due to this, new techniques are being explored, including adhesively-bonding different materials. Nowadays, in many high performance structures, it is necessary to combine composite materials with other light-weighted metals such as aluminium or titanium. This work reports on an experimental and numerical study for hybrid scarf joints between composite and aluminium adherends, and considering different values of the scarf angle (α). The numerical analysis by Finite Elements (FE), using the software Abaqus®, enabled the obtainment of peel (σy) and shear stresses (τxy), which are then used to discuss the strength between different joint configurations. Cohesive zone modelling (CZM) was used to predict the joint strength and the results were compared to the experiments for validation. The joints’ behaviour was highly dependent on α, and CZM were validated for the design process of hybrid scarf joints.

Manufacturing industries are currently experiencing important changes towards digitization and autonomous production control, which is known as Industry 4.0. However, the profitability of some companies, namely Small and Medium Enterprises (SMEs), and of some industrial sectors does not allow for great investments, meaning that is necessary to undertake simple changes that potentially can lead to significant gains. This is the case for the metalwork company under study, where wastes related to the large parts movement and non-conformities detected before and after the parts delivered to the customers have been identified. The elimination of these wastes can contribute to a significant increase in the profitability of the company. The use and integration of several Lean tools made it possible to achieve this goal for this company. Amongst other improvements on productivity and waste reducing, a 59% reduction in the time required to move parts of up to 1000 kg, a reduction of 2.04% on the external non-conformities (i.e. on non-conformities detected outside the company) and 3.99% on the internal non-conformities, was achieved.

The deep knowledge about manufacturing processes, as well as their optimization, present themselves as indispensable factors in the search for the best product quality. It is this point of view of continuous improvement that makes companies in profitable and sustainable way. This paper presents a study about unwinding tension of textile cords in the cap ply manufacturing process, using machines called cap-strips for production. In this work, tension can be understood as the tensile force exerted on the cord. This study determines the influence of unwinding tension on the physical and shrinkage properties of the cord, as well as on the properties of cap ply, namely green adhesion and peel adhesion. Furthermore, the impact of cord tension on tire uniformity and the manufacturing process itself was also studied. All conclusions are based on the performed experiments and the execution of statistical tests. This work allows to conclude that the unwinding tension of the textile cords have some impact on the cap ply properties but have no influence on the tire uniformity.

Cohesive zone modelling (CZM) is widely used for predicting the strength of adhesive joints. The key variable for crack path modelling is the critical strain energy release rate (GC), which can be separated into the tensile (GIC) and shear (GIIC) components. In shear, the End Notched Flexure (ENF) test is widespread. However, other test methods exist and could be a viable replacement. This work aims to make a numerical evaluation between the ENF and Four-Point End Notched Flexure (4ENF) tests to determine GIIC of a ductile adhesive (SikaForce® 7752) and to provide shear CZM laws for further application in design. An inverse technique was used to obtain the shear CZM laws of the adhesive. It was concluded that the GIIC values obtained by the ENF and 4ENF tests are in good agreement. The numerical analysis led to unique shear CZM laws for both tests, with similar results.

Purpose: This study comprised two main goals. The first goal demonstrates how LT (Lean Tools) allows the highest impact during the implementation phase.The second goal consisted of introducing procedure changes based on the Management of Human Resources through Lean Leadership tool. The target for these two objectives is to achieve an increase of 5% in machine occupancy rate and a reduction of 10% regarding the costs of defective products per hour. Methodology/Approach: The research methodology is a Action-Research/Research-Action developed by Professor Kurt Lewin of MIT that goes through cycles of five stages: Diagnosis; Planning; Implementation; Evaluation, Conclusions. Findings: Regarding the two objectives above mentioned, it was observed an increase of 8.5% in machine occupancy rate and a reduction of 27.9% regarding the costs per hour of defective products. It was created an additional motivation in the employees and very satisfying results in every production. Research Limitation/implication: The study is limited to a Portuguese Small and Medium-sized Enterprise (SME) in the metalworking sector. Originality/Value of paper: Lean tools can be rapidly and easily implemented and quickly understood by the workers. With that implementation, the occupation of the machines has increased and the defects and their costs have decreased, so the added value grows.

In the last decade, it has been common to observe a competition between coatings achieved via physical vapor deposition (PVD) and chemical vapor deposition (CVD) techniques on cutting tools used in machining processes. The tool’s substrate material can immediately condition the coating process selection. However, there are also materials capabe of adapting to any of the coating processes. Hence, the capabilities demonstrated by a given coating when created with one technique or another are usually different due to the intrinsic characteristics of each coating process, such as temperature and stress levels. In this work, to study the machining behavior of a super duplex stainless steel, PVD- and CVD-coated tungsten carbide inserts with different coatings were used in order to identify the wear mechanisms that affect each of the coatings and the workpiece’s surface quality, evaluated through different roughness parameters. The vibration level produced throughout the various tests was also registered in an attempt to associate the type of coating or insert failure with the level of vibrations generated in the CNC (Computer Numeric Control) machining spindle. This allowed us to conclude that the tools coated with TiAlN via PVD showed better wear behavior, as well as creating workpiece surfaces with less roughness. Thus, it was clear that this coating presents strong advantages in the machining of the super duplex stainless steel chosen for this work, being an innovative work due to the combination of materials used and the approach in terms of vibration analysis applied to milling

The Information and Communication Technology (ICT) provide new strategies for disseminating information and new communication models in order to change attitudes and human behaviour concerning to education. Nowadays the internet is crucial as a means of communication and information sharing. To education or tutorship will be required to use ICT, supported on the internet, to establish the communication of teacher-student and student-student, disseminating the content of the subjects, and as a way of teaching and learning process. This paper presents an intelligent tutor that aims to be a tool to support teaching and learning in the field of the electrical engineering project.

The machining process evolution has been accompanied by the improvement of tool performance, being this mainly due to the development of thin coatings, mono and multi-layered, providing the most appropriate set of properties for each machining condition. On the other hand, duplex stainless steels have registered a strong increase in demand, which, in many cases, requires the use of machining processes in order to obtain the final shape accurately. Taking into account these two aspects, this paper aims essentially to evaluate the performance of two cutting inserts with PVD and CVD coatings, used in rough milling operations of duplex stainless steel. The cutting parameters and machining conditions were those recommended by the manufacturer and were kept unchanged in all performed tests. The behavior of the PVD- and CVD-coated cutting tools was assessed using three different facets: (a) surface roughness analysis, (b) tool wear evaluation, and (c) the monitoring of vibration levels produced during each test. CVD (TiN/TiCN/Al2O3)-coated inserts showed very good suitability to be used as tools for roughing milling operations when machining super duplex stainless steels.

The food industry is increasingly demanding in terms of the quality and appearance of its product packages. The present study focuses on identifying the main wear mechanisms developed during the stamping process of these packages. During the stamping process, the presence of a tin layer on the surface of the sheet used creates difficulties in the stamping due to the transfer of material from the sheet to the tool, addition of the coefficient of friction, and premature wear of some surfaces of the tool where the contact is more pronounced. In order to understand and avoid these phenomena, a TiAlN coating deposited by a physical vapor deposition (PVD) process was used, which was studied in the laboratory to analyze the evolution of the friction force on the contact and to verify the reaction of the coating on contact with tinplate. Afterwards, the tool was coated and practical tests were performed on the stamping. The obtained results allow confirmation of a significant improvement of the wear behavior of the tool when provided with the coating and also verify that this coating presented better wear resistance than others previously tested in the same working conditions.

The purpose of this paper is to examine settings for the Open Innovation Arena. In greater depth, this paper aims to analyse and reveal which factors influence the formation of an appropriate arena for doing open innovation and furthermore to prescribe how a firm can create an effective arena to gain access to external knowledge. This paper presents a review on open innovation literature with the purpose of examining the current understanding of factors influencing a firm’s capacity to embrace and practice open innovation as well as understanding what is critical when fitting outside systems. It presents the results of a survey conducted among 25 researchers from INESC TEC, the Portuguese Institute for Systems and Computer Engineering, Technology, and Science. The study concludes that conditions, namely culture, leadership and strategy, are the main drivers to an open innovation arena, highlighting culture as the most important one.

The main advantage of welding cast iron is to recover parts by repairing defects induced by casting processes (porosities, etc.), before they enter their working cycle, as well as repair cracks or fractures when already in service. This method contributes to decreased foundry industrial waste and avoids the additional energy costs of their immediate recycling. Therefore, it is necessary to have a welded joint with similar or better characteristics than the parent material. The major problem of welding cast iron is that this material has a very high content of carbon in comparison to steel (≈3%). Therefore, when it is heated by the very high temperatures from arc welding and during its process of solidification, very hard and brittle phases originate, known as ledeburite and martensite, and appear in the partially melted zone and in the heat-affected zone. Eventually, this problem can be solved by implementing heat treatments such as preheat or post weld heat treatments under specific parameters. Therefore, in this study, the aim is to collect data about the effects of heat treatments performed at different temperatures on welded joints of high strength ductile cast iron (SiboDur® 450), and to evaluate the effects of heat treatments performed at diverse temperatures on welded joints of this type of material, using Shield Metal Arc Welding and nickel electrodes. Mechanical strength, hardness, and microstructure were analyzed, showing that the best mechanical strength in the joint (380 MPa) was obtained using two passes of E C Ni-Cl (ISO EN 1071:2015) filler metal and post weld heat treatments (PWHT) of 400 °C for two hours.