Investigation on a aluminium oxide cutting tool with an internal magnetohydrodynamic coolant

This study aims to investigate the design, analysis and performance of an aluminium oxide cutting insert with an internal cooling channel fabricated through an additive manufacturing route. The study is conducted using a developed thermomechanical numerical model combined with controlled experiments. Liquid gallium as an internal coolant, combined with permanent magnets to generate a homogeneous magnetic field, forms the basis of a heat transfer mechanism through a magnetohydrodynamic drive. Thus, allowing enhanced heat transfer within the boundaries of the defined geometrical structure of the internal channel, without the need for external coolants or mechanical power input. Chapter 1 describes the background and defines the problem in terms of heat transfer in the cutting tool, and specifically relating to aluminium oxide. Chapter 2 describes the current state of the art in internal cooling tools and lists the challenges posed in developing new technologies to address the heat generation problem. Chapter 3 is a detailed account of the fabrication of the cutting insert. The development and design of the cutting tool and the internal cooling mechanism are discussed. The design approach and iterative steps in optimisation are discussed along with results of mechanical analysis and characterisation studies to ascertain the suitability for the intended application. Chapter 4 introduces the magnetohydrodynamic cooling system and the underlying theory based on Maxwell’s Law’s of electromagnetism coupled with Navier stokes equations for fluidic behaviour. Experiments are conducted to measure the strength of the magnetic field, with subsequent development of the numerical model and simulation of the fluid velocity vectors. Chapter 5 is based on the full development of the numerical model and the simulation of heat transfer through the cutting tool. A fluidic model is developed and analysed with resultant data presented for a series of three variant cutting conditions relating to heat transfer in the cutting tool.
Chapter 6 describes the results of the experimental machining tests using the integrated magnetohydrodynamic internal cooling system. Experimental results showed with the cutting speed at Vc=250 m min-1, the corner wear VBc rate observed was 75µm with the coolant off, and 48µm with the coolant on. This represents a decrease of 36% in tool wear. When the cutting speed was increased to Vc=900 m min-1, the corner wear VBc rate showed 357µm with the coolant off, and 246µm with the coolant on. This represents a decrease of 31% in tool wear. The results clearly indicate liquid gallium outperforms as a heat transfer agent, and by extension reduces tool wear, in all cutting speed variations. To provide further validation of the new internal cooling system, experimental tests were compared against the results of the liquid gallium coolant versus external liquid water coolant. The results showed at Vc=250 m min-1, the difference between the tool wear rate reduction with the internal coolant relative to the external coolant was 29%. When the cutting speed was increased to Vc=900 m min-1, the difference observed between the internal liquid gallium coolant relative to the external coolant was 16%. Moreover, it was found that as the cutting speed increases, the heat increases, and the effectiveness of the heat transfer rate also increases accordingly.
The numerical models developed along with the experimental tests results obtained support the hypothesis that liquid gallium can transfer heat through an internal cooling mechanism in ceramic inserts and in doing so, reduce tool wear.