Estudo da qualidade micrográfica de juntas soldadas em ligas de alumínio pelo processo MIG

O objetivo desta dissertação de mestrado é o estudo da qualidade micrográfica de juntas soldadas em ligas de alumínio pelo processo MIG robotizado. O ciclo de tratamentos realizados foi constituído por solubilização, têmpera e envelhecimento artificial. Também foi definido um intervalo de espera entre os dois últimos tratamentos afim de avaliar o efeito de um possível envelhecimento natural. Para definição do quadro de variáveis recorreu-se a literatura e a trabalhos antigos, para a solubilização foram definidas 3 temperaturas: 480, 500 e 520ºC, e tempos de 30, 60 e 90 minutos. O intervalo de espera entre a têmpera e o envelhecimento foi de 0, 12 e 24 horas. E por último, as variáveis definidas para o tratamento de envelhecimento artificial foram temperaturas de 160, 175 e 190ºC, e tempos de 6, 14 e 20 horas. Utilizando o método das matrizes ortogonais de Taguchi, definiu-se que, para o número de parâmetros selecionados, seriam necessários 18 ensaios diferentes. Para realização do estudo foram soldadas chapas da liga AA6082-T6, através do processo MIG robotizado, a seguir foram cortadas as amostras e realizados os tratamentos térmicos. Na sequência as amostras, foram caracterizadas por microscopia ótica e por medição das microdurezas na junta soldada. Verificou-se que a temperatura de solubilização tem efeito sobre os valores de dureza, amostras solubilizadas a 520ºC indicam durezas cerca de 13% maiores quando comparadas as amostras que foram solubilizadas a 480ºC. Além disso, comparando a amostra que atingiu o maior valor de microdureza com uma amostra com ausência de tratamento térmico, constatou-se um aumento de 43% na dureza média da peça.The objective of this dissertation is the study of the micrographic quality of joints welded in aluminum alloys by the robotized MIG process. The treatments cycle consisted of solubilization, quenching, and artificial aging. It was also defined as a waiting interval between the last two treatments in order to evaluate the effect of possible natural aging. For the definition of the table of variables, we used the literature and the old works. For solubilization, 3 temperatures were defined: 480, 500 and 520ºC, and times of 30, 60 and 90 minutes. The wait time between quenching and aging was 0, 12 and 24 hours. And finally, the variables defined for the treatment of artificial aging were temperatures of 160, 175 and 190ºC, and times of 6, 14 and 20 hours. Using the Taguchi orthogonal matrix method, it was defined that for the number of selected parameters, 18 different tests would be required. For the study, plates of the AA6082-T6 alloy were soldered through the robotized MIG process, then the samples were cut, and the thermal treatments were carried out. After the heat treatments, the samples were characterized by optical microscopy and microhardness measurement in the welded joint. It was found that the solubilization temperature influences the hardness values, samples solubilized at 520ºC indicated hardnesses about 13% higher when compared to samples that were solubilized at 480ºC. In addition, comparing the sample that reached the highest microhardness value with a sample with no heat treatment, a 43% increase in the average hardness of the part was observed

Texturing methods of abrasive grinding wheels: a systematic review

Creating textures on abrasive wheels is a strategy that allows a significant improvement in grinding operations. The reduction of the internal stresses in the workpiece and the temperature during the grinding operation generates an increase in the dimensional accuracy of the workpiece and a longer tool life. Textured abrasive wheels can be produced in many different ways. Depending on the processing method, the dimensional accuracy of the tool and its applicability is changed. Some methods can produce tools with three-dimensional grooves; there are also methods that are employed for the re-texturing of grooves after the grooved zone wears out. In the literature, the benefits of textured grinding wheels over traditional wheels have been extensively discussed. However, information on the particularities of texturing methods is still lacking. To clarify the advantages, limitations, and main advances regarding each of the groove production methods, the authors of this article carried out a systematic review. The objective of this work is to establish the factors that are affected by groove production methods and the technological advances in this area. The benefits and drawbacks of various grooving techniques are then reviewed, and potential study areas are indicated.This research was funded by FCT national funds, under the national support to R&D units grant, through the reference projects UIDB/04436/2020, UIDP/04436/2020, UIDB/00690/2020, UIDP/00690/2020, and SusTEC (LA/P/0007/2020). This work is within the scope of the Sharlane Costa Ph.D. degree in progress, financially supported by the Portuguese Foundation for Science and Technology (FCT) through the PhD grant reference 2021.07352.BDinfo:eu-repo/semantics/publishedVersio

Texturing methods of abrasive grinding wheels: a systematic review

Creating textures on abrasive wheels is a strategy that allows a significant improvement in grinding operations. The reduction of the internal stresses in the workpiece and the temperature during the grinding operation generates an increase in the dimensional accuracy of the workpiece and a longer tool life. Textured abrasive wheels can be produced in many different ways. Depending on the processing method, the dimensional accuracy of the tool and its applicability is changed. Some methods can produce tools with three-dimensional grooves; there are also methods that are employed for the re-texturing of grooves after the grooved zone wears out. In the literature, the benefits of textured grinding wheels over traditional wheels have been extensively discussed. However, information on the particularities of texturing methods is still lacking. To clarify the advantages, limitations, and main advances regarding each of the groove production methods, the authors of this article carried out a systematic review. The objective of this work is to establish the factors that are affected by groove production methods and the technological advances in this area. The benefits and drawbacks of various grooving techniques are then reviewed, and potential study areas are indicated.This research was funded by FCT national funds, under the national support to R&D units grant, through the reference projects UIDB/04436/2020, UIDP/04436/2020, UIDB/00690/2020, UIDP/00690/2020, and SusTEC (LA/P/0007/2020). This work is within the scope of the Sharlane Costa Ph.D. degree in progress, financially supported by the Portuguese Foundation for Science and Technology (FCT) through the PhD grant reference 2021.07352.BD

Experimental and numerical study to minimize the residual stresses in welding of 6082-T6 aluminum alloy

One of the most important negative consequence in the fusion welding processes is the generation of tensile residual stresses in welded joints. The main goals of this work are to determine the optimal combination of welding parameters to minimize the residual stress level and the influence of each welding parameter in that feature to weld 6082-T6 aluminum alloy plates using the GMAW welding process. To achieve these goals was implemented the Taguchi orthogonal array (L27) to define the design of numerical and experimental tests. All combinations were simulated in the Simufactwelding 6.0 software, from which it was possible to obtain the values of maximum residual stresses. The data treatment was carried out, reaching the combination of levels for each parameter. With ANOVA analysis was found that the parameter with the greatest influence in the residual stress generation was the welding speed, while the parameter with the least influence was the torch angle. Also, to minimize the residual stresses it was observed that the optimal combination of welding parameters is welding current intensity of 202 A, welding speed of 10 mm/s, and 30° of inclination of the angular torch. The two simulations that resulted in the highest and lowest residual stresses were validated experimentally by the hole drilling method to measure the residual stresses.info:eu-repo/semantics/publishedVersio

Effect of grooves and their geometry on the wear behavior of structured grinding wheels

The dry and wet wear behavior of different structured abrasive grinding wheels, with different grooves geometry, were investigated and compared with an unstructured abrasive composite. It was found that the grooves, as well as their geometry, play a decisive role in the wear behavior of abrasive composites.This work is within the scope of the Sharlane Costa Ph.D. degree in progress, financially supported by the Portuguese Foundation for Science and Technology (FCT) through the PhD grant reference 2021.07352.BD; this work is also supported by FCT national funds, under the national support to R&D units grant, through the reference project UIDB/04436/2020 and UIDP/04436/2020

Simulation-based optimization of fluid distribution for enhanced grinding performance

Grinding fluids play a crucial role in removing heat and debris during grinding processes. Their distribution directly affects the grinding results, particularly in reaching the contact zone between the wheel and workpiece [1]. Our study introduces a novel approach utilizing wheels with internal channels to distribute grinding fluid from the center of the wheel to the workpiece, aiming to reduce the air barrier phenomenon [2] and to control heat generation in the grinding zone. Through computational simulations, the fluid's distribution and spreading were evaluated through different internal cooling channel configurations. The findings offer valuable insights into enhancing fluid distribution strategies for optimizing cooling systems design in grinding operations.This work was supported by Portuguese FCT, under the reference project UIDB/04436/2020 (CMEMS center/LABBELS Associate Lab.); a PhD grant reference 2021.07352.BD, funded by FCT/MCTES (PIDDAC), granted to CIMO (UIDB/00690/2020 and UIDP/00690/2020), and SusTEC (LA/P/0007/2020

Control of the dimensional variation adjusting the thermal drying cycle of abrasive composites with incorporated PLA

In composite production, during the thermal drying cycle (T<100ºC), size variation of the composite material occurs due to thermal expansion and water elimination. However, when incorporating PLA components, produced by additive manufacturing, into the abrasive composite, the dimensional variation of the set is very large due to the higher polymer thermal expansion. During this stage, this composite, still in the green state, could not have the sufficient mechanical strength to withstand dimensional variations. These can result in crack formation. Therefore, the proper thermal cycle is a critical step. To define the convenient heating rate during the drying of composites with a PLA piece, thermomechanical analyzes were conducted. Three different heating ramps were tested, 0.1, 0.5, and 2.0 ºC/min in the most critical phase of dimensional change (up to 60 ºC), after this temperature the heating continues at 2 ºC/min. The results indicate that the slower the heating rate, the higher the absorption of the polymer's expansion by the composite. In the slower heating rate (0.1 ºC/min) it was possible to minimize the dimensional variation of the samples by more than 94%.This work is supported by FCT national funds, under the national support to R&D units grant, through the reference project UIDB/04436/2020 and UIDP/04436/2020. This work is also within the scope of the Sharlane Costa Ph.D. degree in progress, financially supported by the Portuguese Foundation for Science and Technology (FCT) through the PhD grant reference 2021.07352.BD. The authors are grateful to the Foundation for Science and Technology (FCT, Portugal) for financial support through national funds FCT/MCTES (PIDDAC) to CIMO (UIDB/00690/2020 and UIDP/00690/2020) and SusTEC (LA/P/0007/2020).info:eu-repo/semantics/publishedVersio

Dimensional variations on drying of composite components for abrasive wheels

Abrasive wheels are composed of abrasive grains, vitreous bond precursors and a temporary binder that, normally, includes a liquid part to give consistency and plasticity to the green body [1]. During the drying thermal cycle, there are length variations in the material caused by thermal expansion and water elimination. These can originate the formation of cracks in the composite. In this work, the effect of the amount of water added to the vitreous precursor and the organic additive (dextrin) was analyzed, up to 80 °C, by Thermomechanical Analysis and Dynamic Mechanical Analysis in compression mode. Firstly, it was observed that the vitreous bond precursor does not significantly contribute to the length variation of the composite (< 0.05%) in the drying process. Figure 1a presents the dimensional variation for dextrin with different H2O contents. Initially, the added water is incorporated into the dextrin molecules, as water of hydration (zone Z1). Sample with 7.0% H2O presents an expansion, up to ~47 °C, followed by a contraction. As the water content in the samples increases, free water begins to form and, therefore, the shrinkage generated by the water evaporation occurs (zone Z2) becoming the predominant effect. The trend lines of samples with water content in the range 22-30%, converge to a value of ~ 15 ± 1% of H2O as the transition zone to free water formation. Compression tests (figure 1b) show that the two types of water incorporation in dextrin have a different effect: inducing a transition from a mainly elastic to a plastic deformation behavior. The necessary water content to guarantee the plasticity of the mixture without subjecting the composite to excessive dimensional variations during the drying step, was determined. Excess of water increases the global dimensional variation on drying and can induce formation of cracks.This work is within the scope of the Sharlane Costa Ph.D. degree in pro-gress, financially supported by the Portuguese Foundation for Science and Technology (FCT) through the PhD grant reference 2021.07352.BD. This work is also supported by FCT national funds, under the national support to R&D units grant, through the reference project UIDB/04436/2020 and UIDP/04436/202

Micrographic study of weded joints in aluminium allows by mig process

The objective of this work is to analyze and evaluate the influence of thermal treatments of solubilization, tempering and aging sequence, made in the 6082 - T6 alloy, previously welded by the MIG (Metal Inert Gas) welding process. In this work, a microscopically analysis of the welded and a thermally treated joint is realized, to evaluate the microstructure quality and the results found by varying the time and temperature during the treatment. In addition, it is intended to verify the influence of the waiting time amongst the heat treatment of quenching and artificial aging.info:eu-repo/semantics/publishedVersio

Effect of distance between grooves on the wear of structured grinding wheels

During roughing and surface finishing operations a lot of heat is generated in the grinding wheel/workpiece contact zone. The surface structuring/texturing of abrasive wheels has been a proposal to reduce the operating temperature. In this work, three spiral grooved abrasive discs were produced, with different distances between grooves. The wear behavior of structured grinding wheels was evaluated by lubricated pin-on-disc tests. Results show that the inclusion of grooves, and the reduction of the distance between them, allows a more efficient lubrication of pin/disc contact zone, reducing the temperature in this zone while wear debris are eliminated, thus modifying the wear conditions