Resumo em Inglês:

Precision cylindrical grinding is used extensively in the manufacture of precision components in the metal-mechanical industry in general. Modern CNC grinding machines have improved this process with respect to the positioning and rigidity of the machine-workpiece-tool system, allowing the production of high precision parts with low dimensional tolerances. Besides the difficulties inherent to the process, awareness has grown in recent years regarding the environmental issues of cutting fluids. As a response, the industry has begun to seek alternative lubrication and cooling methods. Among the various existing techniques, Minimum Quantity Lubrication (MQL) has been considered as an alternative. This technique can be understood as a combination of conventional lubrication and cooling methods and dry machining, in which a small quantity of lubricating oil mixed with compressed air flow is delivered in the wheel-workpiece interface. The MQL technique is already widely employed in machining processes with tools of defined geometry (e.g. turning), in which produces very satisfactory results. However, the MQL technique has been little explored in grinding processes (non-defined tool geometry), in which the really effective heat removal methods are required due to the frictional heat generation in the grinding zone. Consequently, the aim of this study was to evaluate the plunge cylindrical internal grinding operation when using the MQL technique and the conventional cooling method. Roughness and roundness were the outputparameters. As a result, it was found that the best values of roughness Ra were obtained with the conventional lubrication method. The MQL technique applied as proposed was not able to flush the chips away from the grinding zone, leading to the highest Ra values. No significant differences were detected among the cooling methods when analyzing the roundness results. The workpiece fixture method selected was responsible for the overall unsatisfactory results.

Resumo em Inglês:

The aim of this work is to study the primary control system of a hydropower plant in isolated mode. The power plant is modeled by differential equations and results are compared to field data from an actual hydropower plant, presenting deviations lower than 1.0%. The study of primary control system is conducted in order to define useful sets of parameters for controllers. Four controllers are studied: traditional, PI, PID and PI-PD. The performances are evaluated by stability criteria and a performance index. For the hydropower plant studied, the PI controller has the best performance.

Resumo em Inglês:

This paper presents the study on Taguchi's optimization methodology, which is applied to optimize cutting parameters in turning of age hardened Al6061-15% vol. SiC 25 µm particle size metal matrix composites with Cubic boron nitride inserts (CBN) KB-90 grade using steam as cutting fluid. Analysis of variance (ANOVA) is used to study the effect of process parameters on the machining process. This procedure eliminates the need for repeated experiments, time and conserves the material by the conventional procedure. The turning parameters evaluated are speed, feed, depth of cut, nozzle diameter and steam pressure. A series of experiments are conducted using PSG A141 lathe (2.2 KW) to relate the cutting parameters on surface roughness, tool wear, cutting force, feed force, and thrust force. The measured results were collected and analyzed with the help of the commercial software package MINITAB15. As well, an orthogonal array, signal-to-noise ratio is employed to analyze the influence of these parameters. The method could be useful in predicting surface roughness, tool wear, cutting force, feed force and thrust force as a function of cutting parameters. From the analysis using Taguchi's method, results indicate that among the all-significant parameters, steam pressure is the most significant parameter.

Resumo em Inglês:

In this paper, a theoretical analysis of the effects of couple stresses on the squeeze film lubrication between circular stepped plates is presented. Modified Reynolds type equation is derived for the couplestress fluids. Closed form solution is obtained. According to the results obtained, the influence of couple stresses enhances the squeeze film pressure, load carrying capacity, and decreases the response time as compared to classical Newtonian-lubricant case. The load carrying capacity decreases as step height increases.

Resumo em Inglês:

The aim of this paper is to perform a comparative study between different distance measures or metrics for use in nonlinear model updating using vibration test data. Four metrics derived from both frequency and time domain updating approaches are studied, including the harmonic balance method, the constitutive equation error, the restoring force surface and the Karhunen-Loève decomposition. In the first section, a benchmark model with local nonlinear stiffness is defined in order to illustrate each method. Secondly, each nonlinear updating metric is succinctly reviewed. Finally, the relative performances of the different metrics are investigated based on numerical simulations. These results allow us to characterize the applicability and limitations of the different approaches.

Resumo em Inglês:

In this work, the steps involved for the modelling of a reciprocating linear compressor are described in detail. The dynamics of the mechanical components are described with the help of multibody dynamics (rigid components) and finite elements method (flexible components). Some of the mechanical elements are supported by fluid film bearings, where the hydrodynamic interaction forces are described by the Reynolds equation. The system of nonlinear equations is numerically solved for three different restrictive conditions of the motion of the crank, where the third case takes into account lateral and tilting oscillations of the extremity of the crankshaft. The numerical results of the behaviour of the journal bearings for each case are presented giving some insights into design parameters such as, maximum oil film pressure, minimum oil film thickness, maximum vibration levels and dynamic reaction forces among machine components, looking for the optimization and application of active lubrication towards vibration reduction.

Resumo em Inglês:

The plunge cylindrical grinding operation has been widely employed in the manufacturing process of components which require excellent surface quality achieved within small ranges of dimensional tolerance. The sparkout time has proved to be an important parameter in this operation, contributing to obtain surfaces with high geometric and dimensional precision. This parameter, which is defined as the period in which there is no wheel radial feed, allows the elimination of elastic deformations that build up as the grinding wheel is fed. Experimentation with sparkout time was applied in the plunge cylindrical grinding operation and included the Minimum Quantity Lubrication (MQL)technique, which has proved to be an environmentally correct alternative, combining a small amount of lubricating oil with an intense flow rate of compressed air. The conventional lubrication and cooling method and the method involving the nozzle proposed by Webster [10] were also used. The results showed that longer sparkout times led to a decrease in tangential forces, wheel diametrical wear and surface roughness values for the MQL method.

Resumo em Inglês:

This paper presents subsurface hardening results of the low-carbon steel plate, deformed under industrial test conditions by punches manufactured in quenched and tempered AISI D2 steel, with and without TiN coating. The punches are 12º double shear angle shaped. A longer tool life was obtained in tools with TiN coatings applied by Physical Vapor Deposition (PVD) process. The depth of hardened layer generated through punching was different for the work piece and slug. In the workpieces, this layer was about 1.5 mm wide, whereas in the slugs no hardness stabilization values were observed up to 4 mm. Moreover, the presence of the TiN coating did not affect the subsurface hardening produced by punching. The results were discussed regarding the wear mechanisms and the role of TiN coating at the interface. Therefore, the thermal effects were not relevant during the punching tests.

Resumo em Inglês:

This work shows the resulting height and shape of the burrs produced by drilling holes with ratio L/D = 3. The tool used in the tests was the solid twist HSS drill coated with TiAlN, with diameter of 10 mm, to drill the microalloyed steel DIN 38MnS6. The height of the burr was studied under different lubricant/coolant systems, namely: dry machining, use of Minimum Quantity Lubrication (MQL) at the flow rate of 30 ml/h, and fluid applied in the conventional way (flooding). The following cutting fluids were used: vegetable oil (MQL), mineral oil (MQL and flooding) and semi-synthetic oil (flooding). The trials were carried out at two cutting speeds (45 and 60 m/min) and the criterion adopted for the end of the test was the catastrophic failure of the drill. The results showed that the height of the burr increases primarily with the wear of the tool and that this increase is almost exponential after 64% and 84% of drills life, for the speeds of 45 and 60 m/min, respectively. Furthermore, the results generally showed that the smallest burr height was obtained for the dry machining and the largest for the MQL systems.

Resumo em Inglês:

This paper describes the physical and rheological property mixtures of water and kaolinitic clay that form the interstitial fluid found in muds from inundations or torrential lava. Several compositions with varying volume concentrations (Cv) were tested in a high-precision R/S rheometer (shear rate x shear stress). The rheometric parameters such as critical stress, apparent viscosity and outflow curves were established. A detailed analysis of the possible thixotropic fluid (shear thinning) and preparation of the mixtures were carried out. Such mud-type mixtures were well adjusted to the Herschel-Bulkley rheologic model at 03 parameters namely τ =τ=τc + Kγn , where τ is the shear stress; τc the yield stress (or initial rigidity); k is the consistency term; n the flow index; and γ= du dy the deformation rate or shear rates. Considering that this is a thorough research that seeks to infer laws of friction on a canal taking into account the non-Newtonian rheology of the flowing material, it is observed that the tested mixturesspecifically keep away from the Newton model, though less for the Bingham model, and adjusted well to the Herschel-Bulkley model, especially for lower deformation rates. Finally, from a refined literature review on the subject, it was appropriate to describe in detail a wider range of deformation rates and overall behavior laws of the various parameters of the Herschel Bulkley as a function of the concentration by volume (Cv).

Resumo em Inglês:

The effectiveness of multiple tuned mass dampers (MTMD) for suppressing harmonically forced oscillations is studied in the paper. In particular the influence of possible connections between the masses of the damper on the main system performance is investigated using four different configurations of a double mass damper. For this, a minimax procedure, which considers all dampers parameters and variables, is used to optimize each configuration and compare their influence on the minimum value of the maximum magnification factor of the main system. A parametric study shows that small variations in the MTMD parameters and the way in which the masses are connected have a marked influence on the main system response. This sensitivity gives the designer more freedom in choosing the proper damper configuration in a practical situation.