THE APPLICATION OF ACOUSTIC-EMISSION FOR PRECISION DRILLING PROCESS MONITORING

Precision drilling is a process where a close tolerance hole can be pr oduced with a special drill bit without subsequent reaming. Producing a hole without reaming results in less overall processing time during hole preparation. Precision drilling is best accomplished by a robot w ith a computer controlled drilling end effector due to the high degree of process control required. Some aspects of the process, such as spi ndle speed, feed rate, and peck cycles, can easily be controlled by a computer controlled end effector. Other variables, such as drill bit w ear, chipping, and point geometry variation, cannot be controlled with the end effector. These variables affect the diameter of the hole but cannot be detected unless the hole or the drill bit is manually inspe cted. It is not practical to stop the process and check the diameter a fter every hole. Therefore, a means to perform real time drilling proc ess monitoring is required to detect if an oversized hole is being dri lled. The primary objective of this research was to correlate the diam eter of a hole drilled in steel with any acoustic emission (AE) signal measurement parameter. The secondary objective was to correlate drill bit lip height variation, which has a significant influence on the di ameter of a hole, with any AE signal measurement parameter. The result s of this study showed that acoustic emission could only be correlated to hole diameter variations if those variations were related to the l ip height variations. However, AE energy and RMS were correlated to li p height variations under a wide variety of conditions. (C) 1998 Elsev ier Science Ltd. All rights reserved.