Teresa P. Duarte

Research skills enhancement in future mechanical engineers

Nowadays, the Web is a common tool for students searching information about the subjects taught in the different university courses. Although this is a good tool for the first rapid knowledge, a deeper study is usually demanded.

Optimization of Ceramic Shells for Contact with Reactive Alloys

Companies are continuously under pressure to innovate their products and processes. In Portugal, there are already several examples of enterprises that have chosen research groups, associated to universities, to straighten collaboration seeking the development of new materials and advanced technological processes, to produce components with complex shapes, high surface quality, and others, at low cost, for continuously more demanding applications. Unfortunately, these cases are still a very small number, and many efforts have to be done to enlarge the collaboration university-companies. Ti and other reactive alloys are important groups of metals that are under intense and continuous research and development. For example, the high mechanical properties, low density, osteointegration behavior, corrosion resistance to fluids and tissues of the human body, the ability to be sterilized, and the possibility to obtain complex shapes, makes Ti a very attractive material for medical applications. The investment casting process, using lost wax or lost rapid prototyping models, allows designers a great amount of freedom and capacity to quickly produce castings of high dimensional accuracy and excellent surface quality suitable for different applications. Many of the castings obtained by this process are immediately ready for use, avoiding costly machining operations and joining processes, making the process very attractive to produce precision parts in Ti and other reactive alloys. However, the high reactivity of the Ti raises several compatibility problems with the traditional materials employed on the ceramic shells for casting steels and non ferrous alloys. The fragile surface layer obtained on the interface Ti-ceramic shell, result of the Ti reaction with oxygen and nitrogen of the shell, significantly reduces the mechanical properties of the cast parts, making them useless. The aim of the present work is the study of the interface properties of the Ti-ceramic shell, in order to be able to manufacture ceramic shells of low chemical reactivity for the investment casting process of reactive alloys, namely; titanium alloys, inconel, aluminotitanates, and others. Ceramic shells manufactured with calcium and yttria stabilized zirconia and other non reactive ceramics were employed and the metallic interface characterized in terms of microscopic and microhardness properties.

Conversion of rapid prototyping models into metallic tools by ceramic moulding - an indirect rapid tooling process

INEGI developed a process to convert models made by rapid prototyping or conventional techniques into metallic moulds. The main purpose is to rapidly obtain prototype tools by casting a metal into a ceramic mould produced by mixing in variable proportions, ceramic particles, a liquid binder and a catalyst added to start a sol-gel reaction. This liquid slurry is poured into the box containing the mould to be reproduced. After a short period of time the ceramic mixture acquires a rubber consistency. The pattern is removed from the ceramic mould, which is fired and sintered in order to generate an inert mould with the desired strength in which most alloys can be cast. The effect of ceramic materials (shape, granulometric distribution, chemical composition), sintering conditions (time and temperature) and casting conditions (mould preheating temperature and pouring temperature) were studied in order to obtain ceramic moulds and, subsequently, metallic moulds with tailored properties (accuracy reproduction of details, low roughness and high mechanical strength).

Development of Competitive Skills in Future Mechanical Engineers

Nowadays, the Web is a common tool for students searching information about the subjects taught in the different university courses. Although this is a good tool for the first rapid knowledge, a more deep study is usually demanded. After many years of teaching one course about ceramic and composite materials, the authors, used the Bologna reformulation of the mechanical engineering course to introduce new teaching methodologies based on continuous evaluation. One of the main innovations is one practical work that comprises the study of a recent ceramic scientific article, using all the actual available tools, elaboration of a scientific report, present the work and participate in a debate. With this innovative teaching method the enrolment of the students was enhanced with a better knowledge about the ceramics subject and the skills related with the CDIO competences.Copyright

Development of coated ceramic components for the aluminum industry

In general, due to ceramic’s high hardness, which makes machining operations extremely difficult and very expensive, ceramic components are formed in shapes very close to the final ones. Considering this, a manufacturing process, based on a sol-gel reaction that allows rapid production of ceramic components in the final shape with a low level of shrinkage was developed. Although the ceramics obtained presented good behavior in short-term contact with molten aluminum alloys, there was no guarantee that the components produced would have adequate continuous resistance to chemical and erosive wear by liquid metals. To enhance their resistance, the ceramic parts were coated by flame spray. Different powders and conditions were used to determine the degree of coating adhesion to the substrate. The coated specimens were then submerged in a molten aluminum bath, at different temperatures and time settings, to evaluate the interaction between the ceramic components and the molten aluminum alloys.

Development of low-cost customised hand prostheses by additive manufacturing

ABSTRACT The absence of hands makes human life very difficult. The development of prostheses becomes fundamental to improve living conditions. There are many types of prostheses ranging from the simplest ones, with only aesthetic function, to bionic, which have functionality closer to the human hand. Despite all actual technological progress, prices are still very high, making them inaccessible for a wide range of population. Therefore, the development of a low-cost prosthesis will allow simple actions like holding a cup, promoting a better quality of life of people without economic capacity to buy an expensive one. The e-NABLE project that aims to design and manufacture prosthetic hands in polymeric materials through additive manufacturing, tailored to meet user’s specific needs. These prostheses work by flexion and extension of the wrist that produces finger movements. Currently, the prostheses provided have some limitations and conceptual problems. This work contributes to overcome these problems.

Innovative Methodologies to Teach Materials and Manufacturing Processes in Mechanical Engineering

This chapter discusses some methodologies implemented in teaching materials and manufacturing processes at the Department of Mechanical Engineering, of Faculty of Engineering of University of Porto, Portugal, that aim to keep mechanical engineering students motivated and strongly enrolled in classes. Practical classes are structured around experimental works where students have the opportunity to design and perform different experiments, do research using databases, training presentations, do technical reports and posters, and visits to industrial companies. Although the experimental works are very demanding and time consuming, they are extremely appreciated by the students, leading to great motivation for learning and an uncommon enrolment in the curricular units. This chapter presents the methodologies adopted in teaching metallic and non-metallic materials, considering international criteria for engineering students, and learning outcomes and competences. Finally, different cases studies of implementation of this project based learning methodology are presented. These classes contribute to acquire solid technical knowledge and simultaneously, development of soft skills that are extremely important and appreciated by the companies.

The influence of face coat material on reactivity and fluidity of the Ti6Al4V and TiAl alloys during investment casting

Ti6Al4V alloy belongs to the most significant alloys within the conventional titanium alloys, namely for producing turbochargers impellers and human prostheses. TiAl alloys, because of its attractive properties, such as half density of any nickel-based alloys and excellent high temperature properties, exhibit excellent potential for aerospace turbines and turbocharger turbines application. Investment casting is a near net shape process with great interest for these kind of complex parts, but the processing of these alloys using this technique is still a challenge. In spite of these advantages, these alloys are highly reactive in their molten state, reacting with the ceramic shells used in investment casting, forming a hardened and brittle layer called alpha case on the cast alloy surface, rich in interstitial elements such as oxygen. It is commonly accepted that yttria-based face coats are the best solution for minimizing metal mold reaction, but this ceramic oxide is very expensive. So, the aim of this work is to test alternative materials to produce ceramic shells face coats. A test sample simulating both compressor wheels and turbines was developed and assembled in a wax tree for alpha case and fluidity evaluation. Reactivity studies were conducted based on microhardness measurements and microstructural analysis of γ-TiAl and Ti6Al4V standard test samples, casted in shells with different face coat materials: fused Y2O3, ZrSiO4, Al2O3, yttria (6%) stabilized ZrO2 and yttria stabilized ZrO2 with 10% fine Y2O3 (3–7 µm). The results obtained showed that fused Y2O3 face coat eliminates the alpha case, although affecting the fluidity, and γ-TiAl castings have more misruns blades than Ti6Al4V castings.

Development of Plaster Mixtures Formulations for Additive Manufacturing

Currently world abundancy and production of gypsum exceeds the threshold of 150 million tons per year, resulting in a low cost material. This reality leads to a massive use of plaster in construction, in mould casting, in agriculture as a way of land plaster or manufacture of models and moulds for processing of sanitary ceramics in long series. However, the industry is increasingly demanded to produce short or unit series and more complex components, where the use of conventional processes for this type of series leads to higher manufacturing time and production costs, in addition to significant waste of material. To meet the market demand, companies resort to means of production with models in thermoset resins, making this an expensive process due to the high cost of these materials. To fight these costs, the use of plaster combined with additive manufacturing processes (AM) and subsequent subtractive manufacturing (SM) would thus seem to be an economically viable solution. Despite the low cost of gypsum, the α-hemihydrate and β-hemihydrate without any additives have a very high setting time for the AM purposes, poor mechanical properties and weak resistance to sharp edges fragmentation, leading to a mismatch with machining processes. This work aims to create a family of gypsum plasters compatible with the processes described above, adding setting time accelerators and binders to the mixtures. Additivated plaster formulations were produced and tested with setting time accelerators such as K2SO4, CaCO3 or Zn2SO4 and binders based on vinyl or acrylic. Thus, it was possible to produce gypsum plasters with a reduction in the setting time up to 60% and an increase in flexural strength by 80%, compared to formulations without additives and depending on the selected hemihydrate and mixtures.