Laser-Assisted Turning Of Difficult-To-Cut Aluminium With Silicon Carbide Metal Matrix Composites (Al/SiC MMC)

Abstract

An extensive literature review was conducted on the machinability of Aluminium/SiCp metal matrix composite in conventional turning, laser-assisted turning, ultrasonic-assisted turning, and simultaneous laser and ultrasonic-assisted turning modes. Factors influencing machinability include the material's composition and fabrication method, machining parameters, laser parameters, and cutting tools. These factors contribute to cutting force, tool life, machining quality, cutting temperature, chip formation, and surface integrity. The hypothesis for this work is that the hybrid simultaneous machining method, combining laser and ultrasonic-assisted machining, will improve material machinability compared to conventional machining and each individual-assisted turning method. The work was divided into two phases. The first phase involves the hybrid and simultaneous LUAT (laser and ultrasonic-assisted turning) system via experiment and simulation. It focused on the temperature distribution of laser heating due to rotation velocity (25 and 50 m/min), laser spot size (1 and 1.5 mm), and laser power (280-600 W). This phase also assessed machinability as influenced by laser power and ultrasonic vibration. Phase two dealt with optimising laser-assisted turning, consisting of two sub-phases. The initial sub-phase evaluated the improved machinability of laser-assisted turning at a common laser power (600 W) but with a small laser spot (1 mm), considering cutting parameters (material removal rate, cutting velocity, feed rate, and cutting tool). The final sub-phase investigated an adaptive circumferential distance between the cutting point and laser spot (7, 14, and 21 mm) at different laser powers (300, 600, 900 W) and material removal rates (2400, 7200, 14400 mm³/min). The results of Phase-1 indicated that simultaneous laser and ultrasonic-assisted turning improved machinability, demonstrated by 20–67% less cutting force, significantly lower von Mises stress, 25% less plastic strain, and a 44% lower chip compression ratio. The laser heating study showed that a smaller laser spot and lower cutting velocity resulted in higher temperatures at the laser spot. However, the circumferential distance between the laser spot and the cutting point significantly influenced heat loss and the temperature drop towards the cutting tool. The results from the initial part of Phase-2 indicated that the material removal rate significantly impacts the effect of laser heating on the machinability of the workpiece. Lower material removal rates demonstrated better improvement in machinability compared to higher removal rates, as evidenced by a significant reduction in specific cutting energy (3–25%), improved surface quality, and less tool wear. The crystallographic image revealed a 71% increase in aluminium grain size during laser-assisted turning, indicating easier machinability. The PCD cutting tool exhibited significantly less wear compared to the tungsten carbide tool during LAT, surpassing 0.3 mm in the first pass. However, the tungsten carbide tool provided a better surface finish. The final part of Phase-2 provided increased evidence that increasing rotating velocity is more beneficial for retaining heat from the laser spot compared to elevating laser power. Reducing the distance between the cutting point and the laser spot improves machinability but risks directly heating the cutting tool. The smallest distance between the laser spot and the cutting point leads to a peak temperature at the cutting zone, which worsens machining and chips the cutting tool rake face. Conversely, a laser spot too far from the cutting zone is inefficient in delivering the heating needed to improve machinability. An optimal distance was derived for three different laser powers (300, 600, and 900 W) and three material removal rates.

Date of Award	20 Mar 2025
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Paul Mativenga (Main Supervisor), Lin Li (Co Supervisor) & Zhu Liu (Co Supervisor)