Instantaneous Milling Force Model and Verification of Unequal Helix Angle End Mill

doi:10.3901/JME.2024.15.393

Abstract

Abstract: With the urgent demand for lightweight trends in aerospace, milling is an indispensable processing method for weak stiffness components such as frames. However, the instantaneous force changes during the milling process lead to vibration and machining deformation of weak stiffness components such as thin-walled structural components, which is the technical bottleneck. The unequal division of pitch and helix angle for end mills has been proven to be an effective method for suppressing chatter. However, changes in cutting force are the root cause of inducing process system chatter, and the mechanical behavior of milling weak stiffness structural components with unequal helix angle end mills has not yet been improved. Based on this, a mathematical model for instantaneous milling force of unequal helix angle end mills is established. Firstly, the angle position relationship under circumferential planarization of unequal helix angles is analyzed, and the influence of axial time-varying characteristics between cutting edges on the instantaneous cutting thickness at any axial position is studied. A force model of micro elements with unequal pitch is established and integrated axially to obtain a single edge instantaneous cutting force model. Secondly, the participation of unequal helix angle cutting edges in the cutting domain is analyzed, and a linear prediction method for milling force is proposed based on the superposition of multiple window functions when multiple cutting edges are simultaneously cut. Furthermore, the oblique transformation method after linear regression is used for coefficient calibration, a coefficient prediction method based on milling oblique transformation is obtained. Finally, validation experiments are conducted on dry milling of Ti-6Al-4V using a traditional end mill and an unequal helix angle end mill. The results show that under the linear regression method, the average error between the numerical solution of the traditional end milling cutter and the measured value in the feed direction F_y is 1.17%, and the average error in the cutting surface normal direction F_x is 2.09%. The average error of F_y obtained by the unequal helix angle end milling cutter using the milling oblique transformation method is 0.13%, which improves the prediction accuracy by 6.36% compared to the linear regression method. The axial time-varying characteristics between cutting edges caused by unequal helix angles are the fundamental reason for periodic changes in force signals and suppression of chatter.

Key words: milling, titanium alloy, weak stiffness, milling force, helix angle, pitch

CLC Number:

TH161

SHI Zhuang, LI Changhe, LIU Dewei, ZHANG Yanbin, QIN Aiguo, CAO Huajun, CHEN Yun. Instantaneous Milling Force Model and Verification of Unequal Helix Angle End Mill[J]. Journal of Mechanical Engineering, 2024, 60(15): 393-406.

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