Resumo em Inglês:

Wire electrical discharge machining (WEDM) is extensively used in machining of materials when precision is of major factor. Selection of optimum machining parameter combinations for obtaining higher accuracy is a challenging task in WEDM due to the presence of a large number of process variables and complex stochastic process mechanisms. In the present work, WEDM of titanium alloy (Ti6Al4V) is experimentally studied. The behavior of eight control parameters such as Ignition pulse current (A), Short pulse duration(B), Time between two pulses(C), Servo speed(D), Servo reference voltage(E), Injection pressure(F), Wire speed(G) and Wire tension(H) on surface finish was studied using Taguchi parameter design. A mathematical model is developed by means of linear regression analysis to establish relationship between control parameters and surface finish as process response. An attempt is made to optimize the surface roughness prediction model using Genetic Algorithm (GA). Optimum values of control parameters at level A1, B1, C1, D3, E1, F3, G2, H3 for the selected range and workpiece material are obtained.

Resumo em Inglês:

TiN/TiAlN multilayers were deposited by radio frequency, r.f., reactive magnetron sputtering by using titanium and aluminum targets with 10 cm diameter and 99.99% purity in an argon/nitrogen atmosphere, applying a substrate temperature of 300 ºC. WC inserts were used as substrates to improve the mechanical and tribological properties of TiN/TiAlN multilayered coatings compared to other types of coatings like TiAlN monolayers and to manage greater efficiency of these coatings in different industrial applications, such as machining, and extrusion. Their physical, mechanical, and tribological characteristics were investigated, including cutting tests with AISI 4340 hardened steel (50 HRC) to assess wear as a function of the period and number of bilayers. A comparison of the properties of TiCN-Al2O3-TiN monolayers coatings and the [TiN/TiAlN]300 multilayers with individual layer thicknesses of 10 nm revealed a decrease of flank wear (around 33%) for [TiN/TiAlN]300 multilayers and a reduction of flank wear (around 13%) for coatings with 300 layers when is compared with [TiN/TiAlN]200 coatings. They also showed better machining properties onto hardened AISI 4340 steel pieces, when compared to uncoated WC inserts. These results open the possibility of using [TiN/TiAlN] multilayers as new coatings for tool machining with excellent industrial performance.

Resumo em Inglês:

This paper addresses the reliability-based calibration of partial safety factors for Brazilian design codes NBR8681:2003 (Actions and Safety of Structures) and NBR8800:2008 (Design of Steel and Steel-Concrete Composite Structures). To the author's knowledge, these codes have never been subject to reliability-based calibration of partial and load combination factors. This paper represents a first effort in reaching this goal. The present calibration effort is based on actual data for wind loads in south east of Brazil, but uses mainly international data for other problem parameters. So far, the investigation is limited to structural steel members. The investigation leads to a set of optimized partial safety factors, which are compared to partial factors currently used in Brazilian design codes. Results show that the optimized set of partial factors leads to more uniform reliability for different design situations and load combinations. The investigation includes an analysis of the economical impact of replacing the current set of partial factors by the calibrated factors found in this paper. It is shown that, with an optimized set of partial safety factors, it is possible to maintain the current level of reliability and still produce a 5% average reduction in expenditure with structural materials, nationwide. The paper also points to general similarities between Brazilian design codes, the new generation of EUROCODES and American ANSI/AISC codes. These codes are compared in terms of their ability to produce uniform reliability for different design situations.

Resumo em Inglês:

The acquirements and potentiality universe of cleaning, heating and/or sputtering effects caused by plasma species bombardment phenomenon on the surface characteristics and finishing of manufactured parts treated in DC abnormal glow discharge opens a new research and development field, called here of Plasma Assisted Parts' Manufacturing (PAP'M). The adequate control of the sputtering mechanism allows the production of different kinds of surface. Therefore, the design of rough or smooth surface, presenting a modified distribution of surface porosity and texturing could be idealized, in accordance with the desired surface characteristics, as the parts are simultaneously sintered and treated. The first part (out of two) of this work performed in hollow cathode discharge (HCD) presents the results of the surface morphology's changes in the pressed iron samples and in the internal surfaces of the external cathodes as a function of the sintering time and temperature. Potential applications include small diameters' cylindrical parts and components like axles, pins, pivots, and tubes and pipes presenting small internal diameters. Sputtering effects were quantified by means of mass loss and Ra and Rz roughness measurements and qualified by means of SEM. The overall work comprises the study of different parameters, including sintering time and temperature (Part I), and inter-cathode distance and pressure (Part II). Results indicate the sputtering mechanism in HCD sintering and surface texturing treatments could be adequately controlled as a function of the plasma parameters, comprising an important contribution to the development of green technologies for surface texturing, surface engineering, and part's manufacturing.

Resumo em Inglês:

The acquirements and potentiality universe of cleaning, heating and/or sputtering effects caused by plasma species bombardment phenomenon on the surface characteristics and finishing of manufactured parts treated in DC abnormal glow discharge opens a new research and development field, called here of Plasma Assisted Parts' Manufacturing (PAP'M). The adequate control of the sputtering mechanism allows the obtainment of different kinds of surface. Therefore, the design of rough or smooth surface, presenting a modified distribution of surface porosity and texturing could be idealized, in accordance with the desired surface characteristics, as the parts are simultaneously sintered and treated. This is the second part (out of two) of the work performed in hollow cathode discharge (HCD) and it presents the first results of the surface morphology's changes in the pressed iron samples and in the internal surface of the external cathode as a function of the inter-cathode distance and gas pressure. Potential applications include small diameters' cylindrical parts and components like axles, pins, pivots, and tubes and pipes presenting small internal diameters. Sputtering effects were quantified by means of mass loss, and Ra and Rz roughness measurements and qualified by means of SEM. Results indicate the sputtering mechanism is highly dependent of the hollow cathode effect, in HCD sintering and surface texturing treatments, comprising an important contribution to the development of green technologies for surface texturing, surface engineering, and part's manufacturing.

Resumo em Inglês:

Industry worldwide has been marked by intense competition in recent years, placing companies under ever increasing pressure to improve the efficiency of their product processes. In addition to efficiency, precision is an extremely important factor, allowing companies to maintain standards and procedures aligned with international standards. One of the finishing processes most widely utilized for the manufacturing of mechanical precision components is grinding, and one of the principal criteria for evaluating the final quality of a product is its surface, which is influenced mainly by thermal and mechanical factors. Thus, the objective of this work was to investigate the intrinsic relationship between the surface quality of ground workpieces and the behavior of the corresponding acoustic emission and grinding power signals in the surface grinding processes, using artificial neural networks. The surface quality of workpieces was analyzed based on parameters of surface grinding burn, surface roughness and microhardness. The use of artifice-al neural networks in the characterization of the surface quality ground workpieces was found to yield good results, constituting an interesting proposal for the implementation of intelligent systems in industrial environments.

Resumo em Inglês:

Tapping operations on hardened steels have always been a great challenge. Dry machining and two cooling systems were used when tapping hardened AISI H13 (53 HRC). Embedded thermocouples were used for temperature measurement close to the thread diameter in the radial and axial direction. A FEA model was used to evaluate the heat "Q", and coefficient of convection "h". The lowest temperature peak occurred with the flooded system, followed by the MQL, and dry condition. The heat and coefficient of convection increased when using the flooded system, followed by the MQL, compared to the dry condition. Those values were also in accordance with early published works, using different techniques.

Resumo em Inglês:

In this study, experimental verification of a proposed extrusion die profile design approach, which aims to satisfy microstructural criteria at maximum production speed and minimum left out material in the die cavity, is presented. The design problem is formulated as a nonlinear programming problem, which is solved using genetic algorithm (GA). Selection of the processing parameters is carried out using dynamic material modeling (DMM). Microstructural study reveals considerable grain refinement in the extruded tube.

Resumo em Inglês:

The stability of holonomic mobile manipulator can be improved effectively based on the stability twist constraint (STC). However, nonholonomic mobile manipulators are much more popular. In this paper, the stability of a nonholonomic mobile manipulator is improved with STC consideration. However, the constraint of nonholonomic mobility will affect the orientation of mobile base. Numerical simulations results are carried out for the nonholonomic mobile manipulator with different initial states to track the same trajectory of the end-effector.

Resumo em Inglês:

Cast irons are important engineering materials, which possess a wide range of attractive properties. Their properties are significantly dependent on the microstructure of the cast, cast iron components. A way of controlling the microstructure of cast iron is through the control of cooling rates during solidification. To control cooling rate mould properties are important. This paper presents the report of a study of the effects of additions of iron filings to green moulding sand on the microstructure of grey cast iron. Five sand samples were prepared with different Fe content ranging from 1 wt% to 5 wt%. A control sand sample, which had no iron content, was also prepared. The properties of the sand samples were tested and used to cast some grey cast iron samples whose microstructure were observed by optical microscopy. The results show that addition of Fe filing does not have any adverse effects on the properties of green moulding sand; however, the microstructures show a dependence on heat storage capacity of the mould.

Resumo em Inglês:

This paper studies the effect of design variables vector on automatic aerodynamic shape optimization in the adjoint method. Three shape techniques are studied: surface points, relations of the NACA 4-digit airfoil series and Hicks-Henne "Bump" Functions. First, this paper presents the complete formulation of the optimal design problem for the Euler equations. Second, the implementation of these surface representation methods are explored. Finally, results are presented for inverse and drag minimization problems. The results show that the mechanism, value and the trend of drag reduction during the optimization strongly affected by the type of design vector.

Resumo em Inglês:

In this work, we introduce an inverse formulation to be applied in the identification of a rheological parameter associated to non-Newtonian fluids. It is built upon a creeping flow through a 4 to 1 axisymmetric abrupt contraction. The fluid is modeled by the Generalized Newtonian Fluid constitutive equation. The viscosity function is based on the one proposed by Souza Mendes et al. (1995). It predicts an extensional elastic behavior, controlled by a rheological parameter q , which is the parameter determined via the proposed identification procedure. The numerical solution of the forward problem, needed in the iterative procedure introduced by the inverse formulation, is obtained through the finite volume method. A sensitivity analysis is also performed to evaluate the effect of the parameter q on the dimensionless pressure drop through the contraction. The optimization algorithm is based on an iterative method to find the minimum of the cost function, which is given by the least square difference between numerical and experimental values of the dimensionless pressure drop. The gradient method was used to update the parameter q , starting from the cost function gradient. The results obtained with the sensitivity analysis validated the adequacy of the proposed cost function, which is a key aspect on the identification formulation. Moreover, it shows that the method provides an attractive alternative for estimation of rheological properties.