Detection of workpiece hardness variation from controller signals in milling operations

In this study, an approach to detect and counteract the workpiece material hardness variation in milling operations through the use of controller signals is developed. In order to control the workpiece material hardness variation, steel specimens are subjected to end-quenching, which introduces a controlled hardness gradient to the workpieces. This gradient is then detected from the controller signals without using an additional sensor. It is shown that the process parameters can be adjusted to avoid chatter arising from the increasing hardness, and the productivity can be increased by modifying the process parameters according to the local material hardness.