RCAAP Repository

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

The excessive vibrations are common during the chamfering of valve seats and induce operator to reduce cutting speed and feed rate, causing reduction of the productivity. The objective of this work was to study the chamfering of the intake valve seats of the cylinder head of an internal combustion engine. The valve seats are machined with PCBN blades from sintered steel rings with 370-410 HB hardness. This work was developed in a partnership with the companies Fiat Powertrain Technologies and Mapal Tools. The justification to do this work is that there was a need to know better the influence of cutting speed, feed rate and PCBN blade geometry in the vibrations and roundness deviations resulting from the machining of the valve seats. With this knowledge, modifications were proposed in order to obtain a stable cut, higher productivity, lower cost and a better sealing of the combustion chamber, resulting in smaller emission of gases from the engine. The analysis carried out showed that the vibrations and roundness deviations tend to reduce when applying cutting speed between 80 and 100 m/min, feed rate between 0.04 and 0.08 mm/rev, using PCBN blades with T-chamfer cutting edge honing around 60 μm.

The use of compacted graphite iron - CGI is growing in the automobile industry, replacing several components that usually are manufactured in grey cast iron. However, due to its poor machinability when compared to grey cast iron, the production cost sometimes is not competitive. Several research about machinability of CGI has already been developed, mainly in turning, milling and drilling operations. Little has been done with regards to tapping process, which is a more complex operation. The main objective of this work is the investigation of the performance of cemented carbide taps when cutting CGI 450 ASTM. It was is used M13x1,5 taps with four straight flutes, TiAlN coated. The tests were carried out in dry conditions and using cutting fluid applied by MQF (minimal quantity of fluid) and overhead flow. The work was split into two parts. In the first, the cutting tools were used in the production line of Tupy S.A., to produce different wear levels. The second part was developed at the laboratory, when tool wear was measured and experiments were carried out to obtain cutting forces and torque. The results showed that the cutting forces and torque depend on the cutting parameters. Analysis in the scanning electron microscope and optical microscope to determine the wear mechanisms suggested that the main wear mechanisms are adhesion and abrasion. Experiments were also carried out to study the effect of some important aspects of the process like concentricity, feed rate, thread length and tool defects.

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

The present report describes the research work carried-out with the aim of developing, implementing and evaluating a three-dimensional modeling procedure of fluid-structure phenomena involving slender structures, such as beams, bars and cables. The novel approach adopted consists of the combination of the Cosserat theory applied to slender beams, which accounts for geometrical nonlinearity, and the Immersed Boundary methodology, which is used to represent the interactions between the structural and fluidic domains. The study is included in the scope of Vortex-Induced Vibrations, which is a topic of great interest in the oil industry, especially as related to the modeling of risers used for oil exploitation in deep seas. According to the Cosserat theory, the deformed configuration of the structure is described in terms of the displacement vector of the curved formed by the cross-sections center of area, and the orientation of a vector bases fixed to each cross-section, with respect to an inertial reference frame. The main advantage of this theory is that is geometrically exact. Finite element is employed for discretization of the equations of motion. According to the Immersed Boundary methodology, the solid-fluid interface forces are calculated by enforcing momentum balance to the fluid particles over the interface. The main features of the proposed methodology are evaluated by means of a number of numerical simulations, both in static and dynamic regimes, regarding the structural model, in a first step and the complete fluid-structure model, in a second step. The results obtained enable to evaluate the accuracy and the main advantages and shortcomings of the methodology, especially regarding the numerical aspects. Also, they enabled to put in evidence some relevant phenomenological aspects related to the dynamic behavior of cylindrical structures with various levels of bending flexibility, subjected to transverse flows characterized by different values of the Reynolds number.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Conselho Nacional de Desenvolvimento Científico e Tecnológico

The mathematical modeling of turbulent flows around complex moving geometries has always been an extensive area of practical applications and therefore takes place in the recent engineering research. A possible numerical method proposed to handle these problems is the so called Immersed Boundary Methods. This methodology is still under development and consists in separating the problem in two domains, a fixed Eulerian domain used to discretize the fluid equations and a Lagragian domain used to represent the solid/fluid interface. Since there is no geometric dependence between these two meshes, the immersed boundary method can easily handle moving or deformable bodies immersed in the fluid flow. This work presents an extension of the Virtual Physical Model, an immersed boundary methodology developed at the LTCM/UFU, to simulate fluid flows at high Reynolds numbers around moving or deformable bodies. The model was used in the simulation of immersed deformable bodies in laminar flows and was applied in shape optimization problems. Simulations of the turbulent flow past a pitching NACA 0012 airfoil was also presented. A brief comparative studied of three turbulence methodologies implemented with immersed boundary methods is also presented in this work. The results were compared with the experimental and numerical results available from literature, and a good physical coherence was obtained.