Estimation of Engagement Conditions Using an Ann Pattern Recognition System on the Base of a Sensory Tool Holder

Abstract

Knowledge of the tool wear state in machining has become an important issue in research and industrial application. Current systems use the spindle power or cutting force as measured variable and refer it to a taught set point. However, this method lacks the ability to adapt to new work piece geometries. This new approach focusses on the tool instead of the workpiece, and uses a sensory tool holder with integrated strain gauges. Process monitoring that is based on the increasing effect of tool wear on the cutting force requires online information of the current engagement conditions to normalize the force information. The research shown in this paper hence presents a method to estimate the width of cut in end milling. The signal of the bending torque of the tool holder in the XY-plane shows a characteristic shape for each respective engagement condition. An analytically describable relationship has been found between these shapes for different engagement conditions. On the base of this relationship, an ANN was taught to estimate the width of cut without prior knowledge of the cutting path. The results show an accurate estimation for a wide range of cutting parameters.

Process monitoring in end milling using polar figures

“…A more recent approach shown by Bergs and Goetz uses the bending moments in two perpendicular directions of the tool coordinate system to plot two-dimensional figures that correspond to the engagement conditions [26]. They use the points of maximum curvature of these figures to train an artificial neural network that estimates the current width of cut.…”

“…This system relies on a sensory tool holder with integrated strain gauges that delivers characteristic polar figures derived from the bending moments of the tool holder. These polar figures can be used to determine the engagement conditions [26]. The engagement conditions determine the chip thickness and width of chip, thus having a significant influence on the cutting force.…”

“…However, these systems rely on piezoelectric dynamometers and have mostly been shown for laboratory conditions only. A new method that uses strain gauges which are integrated into a sensory tool holder has been shown by Bergs and Goetz and was used for the current research [26]. The following Chapter 2.1 will outline the analytical relationship between the polar figures obtained by the sensory tool holder and the engagement conditions of the end milling process.…”

“…The following Chapter 2.1 will outline the analytical relationship between the polar figures obtained by the sensory tool holder and the engagement conditions of the end milling process. Chapter 2.2 shows the identification algorithms based on [26].…”

“…The shape of the polar figure is strongly related to the geometry of the tool and the engagement conditions of the milling process, i.e. the width and depth of cut [26]. It is therefore possible to monitor the current engagement conditions of a milling process based on the polar figures.…”