# Evaluation of Tool Wear Characteristics and Machining Performance During Longitudinal–Torsional Ultrasonic Vibration Drilling of Al/Ti Stacks

## TL;DR

This paper evaluates how longitudinal-torsional ultrasonic vibration drilling improves drilling performance and reduces tool wear when working with Al/Ti stacks in aerospace manufacturing.

## Contribution

The study introduces a novel drilling method combining axial and tangential vibrations to enhance drilling performance and reduce wear in heterogeneous Al/Ti stacks.

## Key findings

- LTUVD significantly reduces thrust force and improves chip breaking in titanium layers.
- LTUVD mitigates tool wear and enhances hole wall surface quality compared to conventional methods.
- SEM and EDS analyses show LTUVD suppresses thermal and adhesive wear, extending tool life.

## Abstract

Al/Ti stacks are widely used in aerospace manufacturing due to their heterogeneous and multi-property material characteristics. However, during integrated hole-making processes, the significant differences in material properties often induce abrupt variations in cutting force, leading to uneven loading along the cutting edge and non-uniform tool wear. These issues complicate the drilling process and severely hinder the advancement of manufacturing and assembly technologies for aerospace components. To address these issues, longitudinal–torsional ultrasonic vibration drilling (LTUVD) is implemented in drilling of Al/Ti stacks, which superimposes high-frequency axial and tangential vibrations onto conventional drilling, enabling a spatial elliptical cutting trajectory and periodic material separation. A spatial kinematic model of LTUVD is developed to analyze the effects of key parameters on the tool motion trajectory and chip variations. Drilling experiments are conducted on Al/Ti stacks at a defined cutting condition (30 m/min, 0.1 mm/rev) to compare the performance of conventional drilling (CD), ultrasonic vibration-assisted drilling (UVAD), and LTUVD under various conditions. The results show that LTUVD can significantly outperform the other two methods in reducing thrust force, chip breaking (especially in the titanium layer), mitigating tool wear, and improving hole wall surface quality. In addition, scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) analyses further reveal that LTUVD can effectively suppress thermal and adhesive wear, thereby extending tool life.