This paper presents a performance assessment of the low-cost thin-disk piezoelectric diaphragm (PZT) for surface integrity monitoring in the grinding operation. PZT diaphragms are flexible, low-cost, and smart devices, making them promising for applications in manufacturing fields, such as in the grinding operation. To accomplish this, experimental grinding tests were carried out on workpieces of ceramic material covering from slight to severe machining conditions. A low-cost thin-disk PZT diaphragm was assessed, which was attached to the workpiece holder using a cyanoacrylate glue. In addition, a commercial and consolidated acoustic emission (AE) sensor was used as a baseline for comparative purpose. Likewise, surface roughness measurements were performed after grinding each workpiece to support the sensor monitoring system. Feature extraction using frequency spectrum and time domain analysis were applied to the sensor signals by means of fast Fourier transform (FFT), digital bandpass filters, root mean square (RMS) value, and power deviation (DPO) metric. The results indicate a clear relationship between the thin-disk PZT diaphragm and the conventional AE sensor for surface integrity monitoring in grinding, which proves the effectiveness and reliability of an innovative sensing device for the present application.

Sensor monitoring is widely used in modern industrial automation. Industries require efficient and cost-effective monitoring and control systems. Regarding monitoring, new low-cost piezoelectric sensors have been tested in order to monitor processes through the acoustic activity generated. However, these sensors present the difficulties of being very fragile and being glued directly to the structure, thus being single-use sensors. Thus, the objective of this paper is to present a simple, effective and low-cost approach to increase the robustness of piezoelectric transducers and allow their reuse, such as a commercial acoustic emission sensor. For this, a low-cost piezoelectric diaphragm was encapsulated and tested. The characterization of the sensors is the first step in the analysis of the feasibility of an industrial application. Therefore, the sensor was characterized by the pencil lead break (PLB) method, which is recognized for simplicity and repeatability. A piezoelectric diaphragm and a commercial acoustic emission sensor were used as a comparison. Ten PLB tests were performed on a ceramic surface. Time and frequency analysis demonstrated a clear relationship between the enclosed PZT and the other sensors. Based on the good correlation of the results, it was found that the low-cost enclosed PZT can be used in the monitoring of machining processes, presenting greater robustness and simplicity in practical application.

The interest of the scientific community for ultrasound techniques has increased in recent years due to its wide range of applications. A continuous effort of researchers and industries has been made in order to improve and increase the applicability of non-destructive evaluations (NDE). In this context, the monitoring of manufacturing processes, such as the grinding process, arises. This work proposes a novel technique of ultrasound monitoring (chirp-through-transmission) through low-cost piezoelectric diaphragms and digital signal processing. The proposed technique was applied to the monitoring of material removal during the grinding process. The technique is based on changes in ultrasonic waves when propagated through the material under study, with the difference that this technique does not use traditional parameters of ultrasonic techniques but digital signal processing (RMS and Counts). Furthermore, the novelty of the proposed technique is also the use of low-cost piezoelectric diaphragms in the emission and reception of ultrasonic waves, enabling the implementation of a low-cost monitoring system. The results show that the monitoring technique proposed in this work, when used in conjunction with the frequency band selection, is sensitive to the material removal in the grinding process and therefore presents an advance for monitoring the grinding processes.

Innovative monitoring systems based on sensor signals have emerged in recent years in view of their potential for diagnosing machining process conditions. In this context, preliminary applications of fast-response and low-cost piezoelectric diaphragms (PZT) have recently emerged in the grinding monitoring field. However, there is a lack of application regarding the grinding of ceramic materials. Thus, this work presents an analysis of the feasibility of using the acoustic emission signals obtained through the PZT diaphragm, together with digital signal processing in the time–frequency domain, in the monitoring of the surface quality of ceramic components during the surface grinding process. For comparative purpose, an acoustic emission (AE) sensor, commonly used in industry, was used as a baseline. The results obtained by the PZT diaphragm were similar to the results obtained using the AE sensor. The time–frequency analysis allowed to identify irregularities throughout the monitored process.

The Pencil Lead Break (PLB) method is used to reproduce an artificial source of acoustic emission. This method consists of breaking a pencil lead which has its size and thickness determined carefully in a certain angle in a surface. This break releases energy in the form of elastic stress waves which propagate through the structure and are captured and converted into electrical signals by a sensor fixed to the workpiece surface. The PLB method is very efficient in the characterization of acoustic emission sensors. In this paper, the effect of temperature variation in the acoustic emission sensor response was investigated through the PLB method and digital signal processing. The results show that in the frequency response not only the temperature but also the analyzed frequency bands are factors that influence the amplitude of the signals. When comparing signals at different temperatures, the magnitude difference in amplitude increases proportionally to the temperature.

The real-time monitoring of manufacturing processes is essential to achieve high-quality standards and uniformity at reduced costs. The monitoring of machining processes is usually performed by acoustic emission sensors, which measure the dynamic waves of mechanical stress that propagate through the material during the grinding process. This work studies the application of knock sensors, commonly used in the monitoring of combustion engines, as a low-cost and high-robustness alternative to acoustic emission sensors in the monitoring of the grinding process. Built to operate mechanically attached to the engine block, the knock sensor is resistant to high temperatures, liquids, and particles. In order to demonstrate the feasibility of the sensor, different tests were performed. By determining its resonant frequency, it was possible to identify the response curve of the sensor and its optimal operating range. The acoustic impulse test, generated by the pencil lead break technique, allowed the comparative analysis of the spectral performance between the acoustic emission sensor and the knock sensor. The performance of the knock sensor in an industrial environment was also verified in a case study. The results showed a similar spectral behavior between both sensors when subjected to the same stimulus, demonstrating the feasibility of using the knock sensor to monitor the grinding process.