“Innovations in Abrasive Products for Precision Grinding”, written by Dr. John Webster, Cool-Grind Technologies and Marc Tricard, QED Technologies, is a review of recent developments in the design and manufacture of precision, fixed-abrasive tools. The Keynote paper was presented at the 2004 CIRP, in Poland. The paper looks at the role of each component within the “engineered composite”, with examples showing how the components have been enhanced to achieve their current high levels of performance. The paper also looks at examples where innovations in the abrasive tool have enabled the development of innovative abrasive processes. A vision of future abrasive product developments is also presented by the authors. The section on sensor-integrated grinding wheels is shown below:
Sensor-integrated wheels
In the quest for lower process cost and improved quality, machine tool companies and end users are increasingly integrating sensors into grinding machine systems for in-process and post-process control. Typically, these sensors measure displacement, motor power, grinding force, vibration and acoustic emission (AE). In some cases, the outputs from these sensors are used to indirectly predict the conditions occurring within the grinding arc. To improve the measurement accuracy, it is advantageous to make these measurements within the grinding zone and transmit them to a signal processing system. Three University research teams have developed innovative cBN wheel hubs with integral sensors to monitor the grinding process.
Varghese and Malkin [1] integrated an AE sensor into the aluminium hub of the wheel, and fixed a force transducer underneath one of the cBN segments. Using Digital Signal Processing (DSP) and Radio Frequency Transmission (RFT), both signals were received by a host computer. Force monitoring was successfully applied to identify wheel rounding during truing. The AE signal was found to be sensitive to grinding and truing parameters, and could identify initial wheel-work contact to help minimize air grinding time. The technology behind this wheel has been patented [67].
Karpuschewski et al [2 based their grinding monitoring system on an AE sensor-integrated wheel by Wakuda et al [3]. They showed that the wheel and signal processing system could be used to reliably detect events, such as: wheel-work contact, for reduced cycle time; and wheel-dresser contact, to ensure the minimum number of truing passes are given. The ground part surface finish was also monitored by the integral AE sensor. With the help of a fuzzy neural system, based on parameters calculated from sensor data, a roughness prediction can be achieved.
Figure 1. Sensor integrated wheel [4]
Boehm et al [4] integrated temperature, vibration and force sensors into their wheel. The temperature sensor was proved to have sufficient response time (20-50 ns) to measure the temperature close to the grinding zone, and can be compensated for changing abrasive layer thickness with time. The piezoelectric force and vibration, thin-film, sensors are still being perfected for this application. Figure 1 shows a schematic of the wheel.
The ‘Sensor Integrated’ wheel concept needs to be embraced by machine tool manufactures, in order to become seamlessly embedded into the process control, and not considered as a retrofit. Future designs must also consider the easy removal and replacement of glued vitrified cBN segments, without causing damage to the hub each time.
References
[1] Varghese, B., and Malkin, S., 2000, Development of a Sensor Integrated ‘Intelligent’ Grinding Wheel for In-Process Monitoring, Annals of the CIRP, 49/1:231-234.
[2] Malkin, S., August 5 2003, Grinding Wheel System, US Patent 6,602,109.
[3] Wakuda, M, Inasaki, I., Ogawa, K., and Takahara, M., 1993, Monitoring of the grinding Process with an AE Sensor Integrated cBN Wheel, Journal of Advanced Automation Technology, 5/4:179-184.
[4] Boehm, C., Seedorf, T., Meyer, L., Brinksmeier, E., and Binder, J., 2001, Temperature and Force Sensor Integrated Grinding Wheel for Process Monitoring, Abrasives