Improvement of the workpiece surface and process stability through coolant lubricant pulsation

08/29/2022

For turning deep contours, the use of boring bars is the industrial standard. Due to the high projection length of a boring bar when machining deep contours, it is particularly susceptible to vibration. A high susceptibility to vibration favors unstable process behavior (chatter) even at low feed rates and shallow cutting depths. To avoid chatter, the cutting depth and feed rate must be reduced and the largest possible boring bar diameter must be used. A previously untapped potential lies in the frequently used cooling lubricant. For this reason, TAM Tools GmbH (Goldberg), in cooperation with the IFW, is researching in the "KSS-Puls" research project to what extent cooling lubricant passed through the boring bar can be used to reduce vibration.

The coolant flow generates a force at the outlet bore of the cooling channel of the boring bar. In order to use the coolant flow for vibration reduction, it should be pulsed in such a way that this pulsation force is superimposed with the passive force of the process to form a destructive interference. However, optimal superposition is not necessarily sufficient to produce sufficiently high vibration damping. If the pulsation force is too small in relation to the passive force, no significant effect can be expected. If, on the other hand, the pulsation force becomes too large, vibration can in turn be excited by the pulsation itself. The aim is therefore to match the pulsation force and the pulsation frequency to the dynamic component of the passive force.

To optimize the desired force transmission between the workpiece and the tool, the geometry of the boring bar cooling channel is optimized and the pulsation system used to pulse the coolant is designed. The cooling channel is simulated in a flow simulation model with different input parameters in order to determine the parameter with the greatest influence via a multiple regression analysis. The input parameters considered here are the angle of the exit hole to the central hole of the cooling channel, the diameter of both holes, and the flow rate directed into the drill rod. These parameters were chosen because the angle determines the force vector and the bore diameters as well as the volume flow affect the local flow velocities and pressures.

In experimental investigations, a force of Fpuls = 100 N could already be exerted at a pulsation frequency of f = 30 Hz without optimizing the cooling channel of the boring bar. This is already more than twice the dynamic component of the passive force without pulsation, which is why in the next experiments the pulsation force should be reduced by reducing the inlet pressure.

Contact:

For further information, please contact Moritz Wickmann, Institute of Production Engineering and Machine Tools at Leibniz Universität Hannover, by phone +49 (0) 511 762 12190 or by e-mail Wickmann@ifw.uni-hannover.de

Published by Moritz Wickmann

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