On-line & Real-time Monitoring System Of Micro-hole Drilling Based On Virtual Instruments

With the development of mechanical-electronic products for accurate, integral and miniature applications, there is an increasing need for micro-holes. At present there are many methods for machining micro-holes, however, machining by using drills tends to be the most useful in practice. When drills are used to machine micro-holes there is the serious drawback in that the drill is mechanically weak and breaks easily, resulting in short-lived working drills. Besides this drawback, the statistical scatter of micro-drill lives is large and it is very difficulty to predict just how long the working life of a micro-drill might be. This is important from the point of drill breakage results in part of the broken drill remaining trapped in the workpiece. Often it is impossible to extract this trapped part thereby causing workpiece wastage. This can be, to a considerable extent, achieved by controlling the cutting forces (The term 'cutting force' will be imply torque as well as thrust throughout the paper), for which the concerned system should be modeled.Force signal was measured by using a dynamometer installed in the machining system. The workpiece was fixed on the dynamometer. The data collected by a data-acquisition card were transmitted to a PC, where they were stored for further processing. A microcontroller interfaced to the PC through an RS-232 serial interface was used to control stepping motor through a power amplifier, and implements the series communication. The sensor signals were first amplified by a dynamic resistance strain instrument and then were interfaced to the PC. The collected data, cutting force, were further processed, displayed on the monitor and stored in the disk. The cutting forces were calibrated by the static parameter got through least square methods. The frequency domain of the systematic signals before drilling was analyzed, and the invalid signals could be excluded by the digital filtering method. The analysis of time domain and frequency domain during the drilling process indicated that the breaking of micro drills could be predicated by observing the static signals.It was the first time to built up the required modules of the on-line micro-drilling monitoring system by using the LabVIEW, one important software for developing virtual instruments. The modules composed the platform of the on-line and real-time monitoring system. The appropriate program from the LabVIEW can collect the signal, store the data, display the data real time and redisplay the data, moreover, it can completely take the place of the traditional hard wares such as the oscillograph, filter and FFT. In addition, this on-line micro-drilling monitoring system can create executable file (.EXE file) which can run without the LabVIEW condition.On-line and real-time monitoring of machining of micro-holes was investigated. The monitoring was carried out to measure drilling torques and thrusts. Under the present work, limit values of drilling torques and thrusts are both Weibull distribution. Critical value of drilling torques and thrusts for the monitoring is obtained from liability function. From the critical value, process of machining of micro-holes is monitored, presenting breaking of micro-drills. So that, the use of micro-drills can be improved from the present work. Therefore, using as a basis a reliability investigation of cutting force's limit value, reliability functions for micro-drills should be established to supply the necessary information as to when working drilling should be changed.