Grinding is considered one of the last processes in precision parts manufacturing, which makes it indispensable to have a reliable monitoring system to evaluate workpiece surface integrity. This paper proposes the use of the electromechanical impedance (EMI) method to monitor the surface grinding operation in real time, particularly the surface integrity of the ground workpiece. The EMI method stands out for its simplicity and for using low-cost components such as PZT (lead zirconate titanate) piezoelectric transducers. In order to assess the feasibility of applying the EMI method to the grinding process, experimental tests were performed on a surface grinder using a CBN grinding wheel and a SAE 1020 steel workpiece, with PZT transducers mounted on the workpiece and its holder. During the grinding process, the electrical impedance of the transducers was measured and damage indices conventionally used in the EMI method were calculated and compared with workpiece wear, indicating the surface condition of the workpiece. The experimental results indicate that the EMI method can be an efficient and cost-effective alternative for monitoring precision workpieces during the surface grinding process.

The grinding operation gives workpieces their final finish, minimizing surface roughness through the interaction between the abrasive grains of a tool (grinding wheel) and the workpiece. However, excessive grinding wheel wear due to friction renders the tool unsuitable for further use, thus requiring the dressing operation to remove and/or sharpen the cutting edges of the worn grains to render them reusable. The purpose of this study was to monitor the dressing operation using the acoustic emission (AE) signal and statistics derived from this signal, classifying the grinding wheel as sharp or dull by means of artificial neural networks. An aluminum oxide wheel installed on a surface grinding machine, a signal acquisition system, and a single-point dresser were used in the experiments. Tests were performed varying overlap ratios and dressing depths. The root mean square values and two additional statistics were calculated based on the raw AE data. A multilayer perceptron neural network was used with the Levenberg-Marquardt learning algorithm, whose inputs were the aforementioned statistics. The results indicate that this method was successful in classifying the conditions of the grinding wheel in the dressing process, identifying the tool as ''sharp'' (with cutting capacity) or ''dull'' (with loss of cutting capacity), thus reducing the time and cost of the operation and minimizing excessive removal of abrasive material from the grinding wheel.

Monitoring the grinding of ceramics using the vibration signal has been presented as an alternative for the diagnosis of the workpiece surface. This paper has the objective of studying the vibration signal through spectral analysis in order to monitor the grinding process, and looking for the best parameters that could be related to the surface integrity in the finished workpieces of ceramics. Thus, grinding tests were carried out on alumina ceramic specimens in different depths of cut. The workpieces were evaluated after grinding process by measuring the surface roughness Ra and confocal microscopy. For monitoring was used an accelerometer and vibration signal was collected by an oscilloscope. Digital signal processing techniques were performed, identifying a range of frequencies between 800 Hz and 2 kHz that best correlate with the condition of the machined ceramic. There was a correlation between the vibration and the integrity of the ceramics workpiece after grinding process. Moreover, the increase of the vibration is directly proportional to the surface roughness each cutting depth used. It follows that the vibration can be used to monitor the grinding of ceramics due to their relationship with the condition of the workpieces.

RESUMOO uso de dressadores desgastados pode proporcionar uma menor agressividade para o rebolo, causando um aumento das forças de corte e a perda mais rápida de afiação dos grãos que por consequência compromete a qualidade final da peça a ser usinada. Por outro lado, um método de monitoramento do processo de dressagem em tempo real, que permita identificar o momento em que o dressador esteja desgastado, e assim seja substituído, é algo que pode ser de grande importância para o processo de retificação, visando garantir a qualidade e precisão das peças usinadas. Dessa forma, esse trabalho teve como objetivo avaliar o desgaste do dressador de ponta única, por meio da análise espectral do sinal de vibração durante o processo de dressagem. Para isso, ensaios de dressagem foram realizados, utilizando uma retificadora plana e variáveis de entrada um rebolo de óxido de alumínio, um dressador de ponta única de diamante sintético do tipo CVD (Chemical Vapour Deposition), profundidade de dressagem de 40 µm; velocidade do dressador de 3,45 mm/s e o grau de recobrimento U d igual a 1 no início da dressagem. As variáveis de saída foram a aquisição dos sinais de vibração por meio de um acelerômetro fixo no suporte do dressador, coletados por um osciloscópio e as medições do desgaste do dressador por meio de um microscópio. Por meio da análise espectral do sinal de vibração, em três condições de uso, sendo, nova, meia vida e desgastado, utilizando o método Welch e a Transformada Rápida de Fourier (FFT), foi possível identificar faixas de frequência entre 1 kHz e 8 kHz, em que a amplitude aumentava em função do desgaste do dressador. Foi constatado que o aumento da atividade de vibração é diretamente proporcional ao desgaste do dressador CVD. Foi possível identificar faixas de frequências que melhor caracterizam tal situação, como nos trechos de 2 kHz a 4 kHz e de 6 kHz e 8 kHz. Os resultados indicam a possibilidade de implementação de um sistema de monitoramento em tempo real, a partir do uso de filtros digitais nessas faixas de frequência.Palavras-chave: Operação de dressagem; dressador CVD; desgaste do dressador; vibração; análise espectral; monitoramento. ABSTRACTThe use of dressers worn can provide a less aggressive to the grinding wheels, causing an increase in cutting forces and a more rapid loss of grinding grain consequently compromise the final quality of the workpiece to

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