Repositório RCAAP

Information concerning the critical variables of the bleaching process (transformation of a raw fabric into bleached) by pad-steam is scarce, since it is considered a recent process in the textile industry. One hundred percent fine cotton fabrics present great difficulties in the standardization of bleaching across different production batches, which is even more complex when the fabric composition provided by the supplier is unknown. Thus, one carried out an evaluation of the variables that influence color yield in the bleaching process by pad-steam. The conditions used consisted of the reintroduction of the process of desizing by pad-batch, as well as washing and bleaching by pad-steam. The other variable changed was the chemical recipes (desizing and bleaching). As result of this research, the variables which most influenced color performance were the degree of whiteness (Berger) and the pH of extraction. Hence, a change in the production process for this type of 100% fine cotton is required. In this work, a statistical control was performed on the characteristics of the product obtained, which compared results before and during the study. The suggestions for improvement, some of which have already been implemented, are also presented. The results were then compared, enabling one to observe a significant improvement.

Supported by the concepts and definitions of Standard Work methodology, which underpins Lean Thinking philosophy and Kaizen, the study described in this article was developed at a company in the automotive sector, more specifically directed at a production line manufacturing components for air-conditioning systems. The main objectives were to standardize operations, decrease or eliminate the number of activities those are not generating added-value, enhance productivity and associate continuous improvement actions to the processes at hand in order to eliminate waste. After the implementation of a few simple changes - the standardization of operations, adjustments and allocations of workstations – one was able to tailor the production objectives and cycle times to the line’s capacity. The productivity and efficiency of both machines and workers was also increased. Due to the elimination of waste and generation of value, from the customer’s perspective, one was able to raise the OEE (Overall Equipment Effectiveness) general average by 16%, from 70% to 86%.

This paper concerns work carried with a view to reduce defect occurrence rate in the spray painting lines of MDF (medium density fibre cluster-medium density fibreboard) parts of a multinational mobile manufacturing. The determination of the causes for the excessive rejection values is elusive for the multiplicity of factors and parameters involved and the dispersion of application times, not always sufficiently or properly documented. A process analysis methodology was applied to diagnose possible causes of defect occurrences. Considering that the highest defect rate concerned impurities, data collected over a six months’ period was analysed using SPSS to find the correlation between parameters, to find optimal limits of some parameters and evidence of their influence. Kaizen-Lean actions were discussed and implemented conducing to an effective reduction of the existing impurities defect rate, which decreased ninefold related with initial work values.

This work was carried out at Continental tyre factory in Portugal, regarding the APEX machines production process, with the main goal of improving of their performance and product quality rate. Main possible causes of defect generation were identified and proposals to enhance the functioning of the bead APEX production process were also carried out. By applying Six Sigma, variables that influence the quality of the production were identified. DMAIC cycle (Define, Measure, Analyse, Improve and Control) was applied in the process analysis, enabling a structured analysis and the identification of different causes that negatively affect the process studied and consequently allowed the identification of opportunities for improvement. With the help of the DMAIC method, a series of experiments were developed in order to achieve improvements in product quality rate and process control and stabilization.

The automotive industry is one of the most competitive sectors, in which rigour, flexibility, quality and agility constitute the critical factors of success. Warehouse activities and their associated costs play a vital role in logistic functions. Their optimisation and performance assessment may result in substantial value gains for the company. This study was developed at Continental Mabor, with the purpose of developing a proposal to restructure and optimise the company’s warehouse. An analysis of the existing warehouse was carried out and the respective proposals were subsequently presented. The main goal of these proposals was to improve the efficiency of warehouse functions, reduce stock quantities and enhance the capacity to meet customer’s demand. A warehouse management system (WMS) was installed and a suitable bin management solution was defined. This system consisted of a basic WMS to support stock inventory and its location. In addition, this system envisaged warehouse performance and included elements such as the inventory management Key Performance Indicator (KPI) and warehouse productivity.

The automotive sector constitutes one of the most demanding activities in the global market, since it requires a constant increase in productivity, both in the automobile industry as well as in the companies whose manufacture its components. This sector is currently set within an economic framework where there is a relentless search for costs reduction and an increase in productivity with minimal investment. In order to meet these requirements, companies have sought to optimise their products and processes to ensure higher profits. This study was developed with the purpose of enhancing procedures in the maintenance sector regarding a company which supplies air-conditioning tubes to the automotive sector. The main objective was to increase its machines and equipment availability through the implementation of autonomous maintenance. Due to the undertaken improvements, there was a 10% increase in the monthly indicator of equipment availability on line AA3 at the company where the study was carried out. This, in turn, resulted in an increase of 8% in OEE (Overall Equipment Effectiveness) during the same time period, which was chiefly due to a reduction both in machine breakdown rates, as well as in the MTTR (Mean Time To Repair) on the same line.

The management of energy resources for islanded operation is of crucial importance for the successful use of renewable energy sources. A Virtual Power Producer (VPP) can optimally operate the resources taking into account the maintenance, operation and load control considering all the involved cost. This paper presents the methodology approach to formulate and solve the problem of determining the optimal resource allocation applied to a real case study in Budapest Tech’s. The problem is formulated as a mixed-integer linear programming model (MILP) and solved by a deterministic optimization technique CPLEX-based implemented in General Algebraic Modeling Systems (GAMS). The problem has also been solved by Evolutionary Particle Swarm Optimization (EPSO). The obtained results are presented and compared.

This study was undertaken at a Small and Medium-sized Enterprise (SME) in the metalworking sector, where Lean Management has been implemented through several Lean Tools (LT) and their variations. This study comprised two main goals. The first involved demonstrating which LT allow the highest impact during the implementation phase, thus producing great influence both in terms of organization and operational results, as well as in the context of employees’ motivation. The second goal consisted of introducing procedure changes based on the Management of Human Resources through Lean Leadership tools. By implementing these two objectives, one was able to achieve an increase of 8,5% in machine occupancy rate, and a reduction of 27,9% regarding the costs of defective products per hour.

This study aims to design a new warehouse layout as a solution to the warehouse’s main problem: lack of space to store all the materials in stock. Besides the existing warehouse building, which currently presents an unsuitable layout for the storage of large volumes, there is a second area right next to the first to increase the storage area. The two buildings were re-dimensioned to accommodate a great quantity of stock, enabling one to transform the warehouse building into an industrial warehouse with appropriate storage methods. The final layout increased the storage area by 64%, from a total of 1.471,41 m2 to 2.414,22 m2 overall.

This work proposes a multi-criteria decision making model to assist in the choice of a strategic plan for a world-class company. The Balanced Scorecard (BSC) is a support tool of Beyond Budgeting that translates a company’s vision and strategy into a coherent set of performance measures. However, it does not provide help in choosing a strategic plan. The selection of a strategic plan involves multiple goals and objectives that are often conflicting and incommensurable. This paper proposes an integrated Analytic Hierarchy Process-Goal Programming (AHP-GP) approach to select such a plan. This approach comprises two stages. In the first stage, the AHP is used to evaluate the relative importance of the initiatives with respect to financial indicators/KPIs; while in the second stage a GP model incorporating the AHP priority scores is developed. The GP model selects a set of initiatives that maximizes the earnings before interest and taxes (EBIT) and minimizes the Capital Employed (CE). The proposed method was evaluated through a case study.

Today’s society is technologically advanced, the world is just a click away and our companies’ customers have easy access to all the information. Therefore, they are increasingly demanding, wanting more and better at a lower cost. Using as a case study a shipping company, a system of Customer Relationship Management (CRM) was analysed to verify what reasons led to its abandonment and to realise what to do to reverse such situation. In this industry product differentiation is practically null, so the customer’s choice comes down to price. However, customers are paying more attention to customer service, therefore companies are developing stronger relationships with them. The construction of such relationships implies data collection on the client, from which one can offer services of greater value. This may lead to partnerships and competitive advantages. Thus, the use of CRM tools is being promoted for CRM tools present themselves as a valuable asset. In the end, suggestions are presented, ranging from improvements to the existing system, to more complex suggestions, costlier or breaking with the existing mode of relationship and dialogue between company and customers, but that, in the future, will certainly translate into advantages over competing companies.

Zamak is a light-weight alloy presenting very good properties for parts not requiring high mechanical strength. Due to its low melting temperature, this alloy is perfectly suitable for complex shape parts because it is easily moulded by high-pressure die casting process. Industrial parts usually do not require perfect look but this alloy can be also suitable for aesthetic parts, requiring complex finishing processes.The challenge embraced by this work aims to optimize the injection parameters and mould configuration of a Zamak alloy aesthetic part, to be obtained through a single injected casting operation, minimizing finishing operations. In order to obtain healthy, defect-free Zamak parts with a good aesthetic appearance, it was necessary to study the problem and then try to find the best possible solution. Thus, a study was carried out about the high-pressure die casting process and corresponding parameters. Throughout the work, and in order to solve the problem, numerical simulations were carried out using the SolidCast™ software, studying the material flow into the mould and corresponding fusion lines, and empirical tests were carried out in order to correlate the results with the parameters. Changes in the mould were also performed. After the experiences, it was possible to draw some guidelines in order to achieve better results in the Zamak high-pressure die casting process of complex aesthetic parts, allowing for save time in next approaches.

Pultrusion is a versatile continuous high speed production technology allowing the production of fibre reinforced complex profiles. Thermosetting resins are normally used as matrices in the production of structural constant cross section profiles. Although only recently thermoplastic matrices have been used in long and continuous fibre reinforced composites replacing with success thermosetting matrices, the number of their applications is increasing due to their better ecological and mechanical performance. Composites with thermoplastic matrices offers increased fracture toughness, higher impact tolerance, short processing cycle time and excellent environmental stability. They are recyclable, post-formable and can be joined by welding. The use of long/continuous fibre reinforced thermoplastic matrix composites involves, however, great technological and scientific challenges since thermoplastics present much higher viscosity than thermosettings, which makes much difficult and complex the impregnation of reinforcements and consolidation tasks. [1] In this work continuous fibres reinforced thermoplastic matrix towpregs were produced using equipment developed by the Institute for Polymers and Composites (IPC). The processing of the towpregs was made by pultrusion, in a developed prototype equipment existing in the Engineering School of the Polytechnic Institute of Porto (ISEP). Different thermoplastic matrices and fibres raw-materials were used in this study to manufacture pultruded composites for commercial applications (glass and carbon fibre/ polypropylene) and for advanced markets (carbon fibre/Primospire®). To improve the temperature distribution profile in heating die, different modifications were performed. In order to optimize both processes, towpregs production and pultruded composites profiles were analysed to determine the influence of the most relevant processing parameters in the final properties. The final pultruded composite profiles were submitted to mechanical tests to obtain the relevant properties.

The biggest advantagein the use of thermoplastic composites is the possibility of recycling and reprocessing, which is not possible with thermosetting composites. The shorter manufacturing cycle time and lower chemical emissions are, as well, other advantages. The use of thermoplastic matrix composites creates new engineering challenges concerning the manufacturing due to their high viscisity during manufacture. For all the advantages that these materials present, it becomes useful to study and evolve the universe of composites in the direction of thermoplastics. In this work, continuous fiber thermoplastic composites were produced and transformed by pultrusion and heated compression moulding. The manufactured composites were then tested, and mechanical properties were determined and studied.

This chapter considers sandwiched composites used in aerospace applications. It discusses new developments in the types of face and core materials, production methods and joining and repair techniques. It also discusses various properties as well as their main design methods. Both existing and future applications of sandwiched composites are discussed.

In the energy management of the isolated operation of small power system, the economic scheduling of the generation units is a crucial problem. Applying right timing can maximize the performance of the supply. The optimal operation of a wind turbine, a solar unit, a fuel cell and a storage battery is searched by a mixed-integer linear programming implemented in General Algebraic Modeling Systems (GAMS). A Virtual Power Producer (VPP) can optimal operate the generation units, assured the good functioning of equipment, including the maintenance, operation cost and the generation measurement and control. A central control at system allows a VPP to manage the optimal generation and their load control. The application of methodology to a real case study in Budapest Tech, demonstrates the effectiveness of this method to solve the optimal isolated dispatch of the DC micro-grid renewable energy park. The problem has been converged in 0.09 s and 30 iterations.

The aim of this work is to produce and optimize the processing of carbon fibres thermoplastic matrix pre-impregnated materials (towpregs and PCT´s). Pultrusion and heated compression moulding were the selected manufacturing methods for processing all carbon fibres thermoplastic matrix pre-impregnated materials into composite parts. The optimization of those processes was made by studying the influence of the most relevant processing parameters in the final properties of the produced carbon fibres thermoplastic matrix pre-impregnated materials and composites. The method of Taguchi / DOE (Design of Experiments) was used to achieve this aim as it allowed making more rational choices of processing windows. The composite relevant mechanical properties were determined and studied. The final composites were also submitted to SEM microscopy analysis.

Historically, thermoset resins have dominated the composite industry but they start to be replaced by thermoplastics. In this study two different thermoplastic matrix carbon reinforced pre-impregnated materials were used, one produced in our laboratories (towpreg) and another obtained from coextrusion process (PCT). Carbon fibre and two different thermoplastic matrices (polypropylene and PRIMOSPIRE®) were selected for the production of the pre-impregnated materials. Heated compression moulding and pultrusion were the two manufacturing technologies used to obtain composite plates and profiles for study. The optimization of those processes was made by studying the influence of the most relevant processing parameters in the final properties of the produced carbon fibres thermoplastic matrix pre-impregnated materials and composites. The composite relevant mechanical properties were determined and the final composites were submitted to Dynamic Mechanical Analysis (DMA), Scanning Electron Microscope (SEM), optical microscopy and calcination tests. The determination of the fiber volume fraction of all studied composite was obtained comparing the results of thermogravimetric analysis (TGA), SEM and calcination tests.

This paper presents an experimental study that aims to compare the practical performance of well-known metaheuristics for solving the parameter estimation problem in a dynamic systems context. The metaheuristics produce good quality approximations to the global solution of a finite small-dimensional nonlinear programming problem that emerges from the application of the sequential numerical direct method to the parameter estimation problem. Using statistical hypotheses testing, significant differences in the performance of the metaheuristics, in terms of the average objective function values and average CPU time, are determined. Furthermore, the best obtained solutions are graphically compared in relative terms by means of the performance profiles. The numerical comparisons with other results in the literature show that the tested metaheuristics are effective in achieving good quality solutions with a reduced computational effort.

Thermoplastic matrix composites are receiving increasing interest in last years. This is due to several advantageous properties and speed of processing of these materials as compared to their thermoset counterparts. Among thermoplastic composites, Long Fibre Thermoplastics (LFTs) have seen the fastest growth, mainly due to developments in the automotive sector [0, 2]. LFTs combine the (semi-)structural material properties of long (>1 cm) fibres, with the ease and speed of thermoplastic processing. This paper reports a study of a novel low-cost LFT technology and resulting composites. A patented powder-coating machine [3, 4] able to produce continuously pre-impregnated materials directly from fibre rovings and polymer powders was used to process glass-fibre reinforced polypropylene (GF/PP) towpregs. Such pre-impregnated materials were then chopped and used to make LFTs in a patented low-cost piston-blender developed by the Centre of Lightweight Structures, TUD-TNO, the Netherlands [5, 6]. The work allowed studying the most relevant towpreg production parameters and establishing the processing window needed to obtain a good quality GF/PP powder coated material. Finally, the processing window that allows producing LFTs of good quality in the piston-blender and the mechanical properties of final stamped GF/PP composite parts were also determined.