Electromechanical impedance (EMI) technique has been employed in detection of structural failure in civil and mechanical structures because of its non-destructive property and easy implementation of small and inexpensive piezoelectric transducers that are attached to the structures, which lead to cost reduction as well as lesser dependence of manual inspection methods. In this technique, the capsule is excited by applying a sinusoidal voltage to generate waves to propagate throughout the structure. From the impedance signature of the structure without any damage, any structural change can be detected by measuring the electrical impedance of the piezoelectric (PZT) patch. Based on its real potentiality and because of its non-destructive characteristics, this work aimed to employ the EMI technique as the first alternative to monitor workpiece surface damages after grinding operation with a conventional abrasive grinding wheel. EMI measurements were performed by using a low-cost PZT transducer and under controlled environmental conditions. Microhardness and surface roughness of the machined surfaces, as well as grinding power, were also measured to detect any damage in the machined surface and to stablish relationship with the EMI technique. From the damage indices root mean square deviation (RMSD) and correlation coefficient deviation metric (CCDM), surface alterations on the ground surfaces were inferred by the EMI method. Also, it was observed a good correlation between the EMI technique and the other output parameters that were investigated in this work, such as surface roughness and power grinding, thereby posing as a non-destructive, low-cost, and viable technique to monitor workpiece surface damages in the grinding operation.
One of the major challenges in grinding is to conciliate the material removal rate with components free from damages. Due to the poor thermal conductivity of conventional grinding wheels, most of the heat generated during grinding is transferred to the workpiece surface and subsurface, which can cause thermal damages and impair the performance in service of machined components. Hence, it is very important to monitor the grinding process to ensure the quality of the machined parts. Thus, this work presents an innovative study comparing two indirect monitoring methods in monitoring surface integrity of steel during grinding: the acoustic emission technique and the electromechanical impedance technique. Worktable speed and radial depth of cut were used as input parameters. Visual inspection and scanning electron microscopy images of ground surfaces as well as microhardness were the output variables used to assess surface integrity and to establish a relationship with the acoustic emission and electromechanical impedance techniques. Since the acoustic emission signals are non-stationary in nature, these signals were analyzed in the time–frequency domain by applying the short-time Fourier transform and the continuous wavelet transform. The root mean square deviation index was extracted as feature from the acoustic emission and electromechanical impedance signals. Results showed that both techniques presented similar results. The root mean square deviation index showed a good correlation with alterations in surface integrity under the conditions investigated.
In a context where there is a continuous search for more environmentally friendly machining processes (for example, the implementation of the minimum quantity of lubrication-MQL-cooling-lubrication technique) and the constant concern with the high heat generation during the grinding process, there is still a lack of information about grinding of steel for molds and dies. Thus, the present work sought to evaluate the performance of tangential surface grinding of a steel for plastic injection molds, testing by two types of conventional abrasives (green silicon carbide and white aluminum oxide) under three different equivalent chip thicknesses. The performance of the MQL cooling-lubrication technique compared to the conventional one (flood coolant) was also evaluated. The output parameters to assess the surface integrity were the surface roughness (R a parameter), residual stresses and SEM images of the ground surfaces, as well as microhardness below the machined surface. The results shown that both conventional abrasives types have potential to be used in grinding of this steel, once low surface finish values (R a < 0.2 μm) and workpieces free of damages were fabricated. Silicon carbide (SiC) grinding wheel in general outperformed the aluminum oxide (Al 2 O 3) one in terms of surface roughness after machining under severest conditions (R a < 0.35 μm). Residual stresses were predominantly compressive irrespective of the cooling-lubrication technique and type of abrasive employed. Despite lower surface roughness and compressive residual stresses generated after grinding with the Al 2 O 3 grinding wheel, drop in hardness below the machined surface was observed, unlike when machining with SiC grinding wheel. MQL technique proved to be more effective than conventional coolant technique under the conditions investigated, irrespective of the grinding wheel used, and in some situations, it outperformed the conventional technique.
The effects of the feed rate and the axial and radial depth of cut in the up and down asymmetrical face milling with respect to workpiece about the orthogonal components (axial, radial and tangential) of the cutting force in the machining of cast iron DIN GGG50 with carbide inserts was evaluated. The spindle speed was remained constant. The cutting forces were acquired through a sensory system that consists of piezoelectric dynamometer, signal acquisition board and computer with appropriate software. In the end it was concluded that studies of machining forces provides a strong basis for understanding the kinematics and the dynamics of the tool and the cutting operation and it can be applied to optimize the cutting geometries and test the probabilities of tool distortions.
Resumo Os riscos envolvidos em função de deterioração de materiais e falhas de equipamentos devido à corrosão ou à corrosão associada a solicitações mecânicas vêm cada vez mais desafiando a engenharia na busca de novos materiais, ligas, revestimentos, inibidores e novas soluções de projetos e desenhos de equipamentos que ofereçam melhor desempenho e vida útil. O aço inoxidável duplex (AID) vem conquistando cada vez mais espaço justamente por possuir tais requisitos. Atribuem-se suas altas resistências à corrosão e mecânica à sua microestrutura balanceada em aproximadamente 50% de ferrita e 50% de austenita. No presente trabalho, chapas de AID UNS S31803 foram soldadas em chanfro de 45° pelo processo MIG/MAG curto circuito convencional, utilizando-se três diferentes energias de soldagem, na faixa de 0,5-0,8 kJ/mm. Os resultados mostraram que o efeito da energia de soldagem sobre a fração volumétrica de ferrita foi bem marcante na zona termicamente afetada (ZTA) e no metal de solda este efeito não foi tão pronunciado. As propriedades mecânicas de dureza e resistência à corrosão (corrosão intergranular) foram avaliadas em função da energia de soldagem empregada. Em geral, tanto a dureza como a resistência à corrosão intergranular não sofreram influência quando as diversas condições de soldagem foram comparadas.
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The search for continuous improvement of the processes and products offered to the market combined with continuous efforts to reduce energy consumption stimulates the development of techniques and tools geared towards their optimization. Thus, this manuscript describes the application of multivariate optimization in the process of face milling of DIN GGG 50 nodular cast iron by means of experimental design techniques, regression models, and Taguchi loss function. Three input parameters (axial “ap” and radial “ae” depth of cut, and feed-rate “f”) were used as controllable factors of the process and two output parameters (specific cuttingenergy “es” and roughnessaverage “Ra”) were considered as response variables. The output obtained as a result of optimization wases= 1.41 J/mm3andRa= 0.85 µm by applying the input parametersap= 2.34 mm,ae= 33.4 mm andf= 0.44 mm/rev.
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