RCAAP Repository

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

This study aims to monitor the cutting tools wear, during an end milling of VP80 steel and moreover use artificial neural networks (ANN) as a tool to predict the cutting condition. Therefore, the acoustic emission (AE) and the cutting power, were chosen as the techniques. Statistical parameters were extracted from the signals and compared with the maximum flank wear (VBBmáx). During the study, Sensis equipments were used to purchase the raw signal AE, and a sensor based on the Hall effect to the acquisition of the current, which will be posteriorly converted in effective cutting power. An end mill with R390-032A32-11M (Sandvik Coromant) specification and 32 mm in diameter was used. The inserts were coated with TiN and had R390-11 T3 10M-PH 1025 (Sandvik Coromant). During the life tests (40 in total) were acquired signals and carried out the wear measurement. The intention was try to relate them after tests conclusion and statistical parameters extraction of the signals. These parameters extracted was analyzed and those with had correlation with flank wear values were used in the training and validation of an ANN. The results show that skewness of the AE signal (frequency band 50-500 kHz), the RMS level extracted from power spectra of AE (frequency band 100-230 kHz) and the effective cutting power are correlated with wear. Furthermore, the use of these parameters as input values in an ANN, provides excellent feedback to the network while trying to predict have or not, working condition.

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Reaming is a machining process with relatively low cost and suitable when high quality holes are required. The purpose of this work is to evaluate the quality of the holes made in automotive valve guides, fabricated with sintered steel. This study was based on parameters of surface roughness, roundness and cylindricity deviations, obtained with uncoated carbide reamers. Cutting forces and vibrations in the system also were monitored. In order to determine the experimental tests, the Taguchi design was employed and the reamer geometry, cutting speed, feed rate and tool fixation method were varied. The results showed great influence of the tool holding method. The smaller roundness and cylindricity deviations were obtained using a four edge reamer, with pilot, fixed by hydro-mechanical mandrel and feed rate of 0,050 mm/edge. The used cutting speed range did not show significant influence.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Dynamic Vibration Absorbers (DVA) have been widely used for passive control of structural vibrations. In their simplest configurations, those devices have their mitigation capacity confined to narrow frequency bands, which limits, to a large extent, their practical effectiveness. In this work, it is proposed a methodology for the optimal design of a multimodal dynamic vibration absorber, intended to attenuate the amplitude levels around various resonance peaks simultaneously. The particular configuration considered is formed by blades containing circular disks in their tips. The optimization is performed taking into account design constraints. Moreover, the variability inherent to the construction of the base structure and of the DVA itself is considered aiming at obtaining robust designs in future studies. A technique for substructure coupling based on frequency response functions (FRFs) is used to evaluate the dynamic behavior of the coupled structure (base structure + DVA), given the FRFs of each substructure separately. The use of this technique enables the design of the DVA and the evaluation of its performance based solely on the use of experimental FRFs of the base structure, which makes numerical models unnecessary. Monte Carlo simulation is used to evaluate the influence of the uncertainties on the effectiveness of the multimodal DVA. The procedure is illustrated by numerical and experimental results obtained for a rectangular plate and hermetic compressor housing.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Machining experts sometimes come across with a question when using tool tips inserts: The use of one of the edges of an insert affects the performance of the others? Some of them comment that in squares inserts, for instance, the sequence of the tool edges used could affect their lives when machining. The reason for this is that worn edges would adversely affect the wear progress in the next adjacent edges. In order to avoid this, it is recommendable to index only the diagonal sequence of the cutting edges. Based on this hypothesis and because there is no scientific evidence to support it, squared carbide inserts with negative rake angle with eight edges were tested in turning of a microalloyed (HSLA) DIN 38MnSiVS5 steel. Tests were performed using all the possible edges sequences of one tool face in order to verify the possible influences in the tool edge lives. After using the upper face edges, the bottom face edges of the inserts were also tested. Tool flank wear was monitored during machining, criterion chosen as end of life. Replicas were made and the data were analyzed using the software Statistica 7.0 by differences between means with a significance level of 5%. The work also has a second phase of testing where the objective is to verify and compare the influence of the number of stops to measure the wear on tool life. The results showed that, statistically, it cannot be said that the wear of an edge affects the development of the wear, once therefore its life, on the adjacent edge of a square insert, i.e., they showed that the sequence of use of the edges does not influence the tool life of square inserts. However, one should mention that there was a wide dispersion in the results investigated. The results of the second phase of the research showed influential in the tool life. This means that the number of stops conducted to measure the wear influences the development of wear and consequently the tool life of square inserts.

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

The MIG/MAG process is nowadays the most important welding process. This is due to its high production capacity, characteristic searched by industries to improve their manufacturing processes. Thus, due to this process relevance, development of tools that helps to understanding how it works comes out as necessary, especially in relation to proper welding setting up. One tool for this task is the transfer mode map, which predicts the type of metal transfer according to the welding setting up. However, these maps, normally, are more scientific oriented rather that for practical purposes. In this context, the objective of this work was to map the transfer modes in such a way that welders, supervisors and engineers could be helped in the choice of the best setting up needed. For this purpose, a methodology was developed to provide more information than transfer modes according to the parameter setting up. The proposed mapping had the intention of obtaining transfer regions with proper operating characteristics (stable transfer resulting of appropriate welding conditions) and also information about weld bead conditions, production, thermal cycle and arc radiation. For each transfer mode looked for working at typical welding conditions, which mean that the contact tip-to-work distance was different for the two main transfer modes (short-circuit and spray). A large number of experiments was performed to map the transfers, with the objective to determine a stable operating regions of short-circuit and spray transfer mode using the ER70S-6 welding wire with three different shielding gases. After mapping, single-welded butt joint were carried-out using specific points of the maps instead of bead-on-plate. The proposed methodology was efficient in exterminating regions of operational stability, according to the experiments. It was also possible to have better welding geometries, in general, for setting ups within the map region of operational stability, but the results also depend on the shielding gas and the transfer mode. For setting ups outside the map region of operational stability the bead finish gets worse, except for spray transfer mode when working below the region of operational stability. The deposition efficiency is lower for setting ups outside the region and with gases containing higher levels of CO2, except for short-circuit transfer. The arc radiation intensity is lower in regions below the operational stability and higher above this position, but it is highly dependent of the arc length. Changes in the contact tip-to-work distance and/or in the power source inductance have no influence on the region of operational stability, except for short-circuit transfer, in which the contact tip-to-work distance is able to reduce the set voltage for this region.