Wear monitoring tool holder

In milling operations, tool failure due to excessive wear can result in operator injury, damage to machinery, the production of poor quality parts, or costly downtime. To eliminate such undesirable outcomes in machining processes, it is necessary to develop a method for monitoring tool health that can predict tool failure and indicate the current health status of the tool to the operator. Due to the limitations of mechanistic models, an approach incorporating real-time monitoring of tool health is required for practical implementation in a manufacturing environment. This paper examines the viability of an accelerometer-based real-time wear monitoring and tool failure prediction system incorporated into the tool holder of a vertical mill. The system is designed to be capable of autonomous operation and RF transmission to a remote computer for extensibility. A microprocessor mounted on a tool holder is responsible for collecting data from an on-board accelerometer, then analyzing the data using the Fast Fourier Transform. After a sample population of FFT bin magnitudes have been established, they are analyzed using an autoregressive algorithm which indicates acceptable tool health or impending failure based on the rate of change of the vibration dynamics associated with the tool pass frequency of the tool. If impending failure has been identified, LEDs mounted on the tool holder are illuminated. This system of tool monitoring also has the capability of simultaneously predicting failure and transmitting both collected data and tool health to a remote computer via an on-board RF module. A framework for sending commands to and collecting data from the remote tool holder has been constructed on the .NET framework, thereby providing extensibility for the system. The use of this library allows the development of customizable end-user selected visual analysis methods. The extensible capabilities of the system include use in an internet-based monitoring system where the wear state of a tool can be monitored from an off-site location or smart phone app, use with an automated ordering system for replacement tools, or use in automating tool changes in CNC mills. To address cost in industry, the system is constructed from commercially available off-the-shelf components. The cost-effective and autonomous nature of the system makes it an ideal candidate for small machine shops. Furthermore, the extensible nature of the system makes it an ideal candidate for large-scale manufacturing plants where off-site monitoring is required or where highly automated manufacturing processes are incorporated.