Comparison of Sensors Signal Quality when Drilling Inconel 718

Aero engines clearly differ from other propulsion systems used in general mechanical engineering particularly through the materials used and the extreme stresses that occur during operation. Boltholes in rotating turbine and compressor disks are among the most highly-stressed geometric features of jet-engines. For manufacturers of jet-engine components it is important to assess the quality of these at an early stage in the manufacturing of the product. The use of commercially available monitoring systems in hole-making has been successful in individual cases so far. Major reasons for this lack of effectiveness are the large material variations within one production batch, the overall difficult machinability of the materials applied, the small lot size which makes “teach-in” operations ineffective. Additional challenges occur during the implementation of monitoring systems in production. Here, the monitoring solution is judged predominantly by its robustness, its reliability against false alarms and its level of integration in the machine tool. A high level of integration can be achieved by using internal data, provided by the components of the machine tools themselves. The paper describes a new approach in real-time monitoring for drilling boltholes. In an experimental setup, process data origination from the NC of a Sinumeric 840D, collected by an OPC-Server had been processed. Comparing OPC data logging, DAU data logging and profibus data logging with respect to data quality, sample rate and real-time behaviour, profibus data logging appears to be the favourable choice. Compared to the price of many dedicated external sensors, all three methods to log internal data provide data access with small investments on a high level of integration. The experimental results indicate that OPC-data are suitable for tool wear monitoring and surface quality evaluation after drilling with solid carbide drills and face cutting reamers in Inconel718 workpieces.