Removal mechanisms during fluid jet polishing of amorphous materials with diamond particles
Mechanical Process Engineering
Fluid Mechanics
Final Report Abstract
The fluid jet polishing process (FJP) is analysed specifically for machining hard amorphous surfaces employing abrasive suspension jet impingement. The behaviour of the suspension jet and the particles in an FJP process has been investigated by computational fluid dynamics (CFD) and experimental methods (for instance, high-speed videography). From erosion experiments with suspension jet application, white light interferometry has been applied to identify the characteristics of the eroded surface (depth and volume) of the workpiece. Some high-speed video recordings have shown inhomogeneities in the nozzle exit jet flow, such as the twist motion of the fluid jet and its non-transparent aspect. Macroscopic characteristics of the impinging jet flow have been identified, such as the formation of the hydraulic jump and its position. The position of the hydraulic jump was used to validate the numerical model for the main characteristics of the impinging jet flow. The behaviour of particles in the impinging suspension jet flow has been analysed by CFD techniques. Particle trajectories and particle motions are strongly affected by the liquid backflow near the stagnation region. As the particles approximate the stagnation region, the decrease in the impact angle of particles and strong reduction of the kinetic energy (due to the deceleration of particles) cause changes in the abrasion effects. This analysis is essential since it allows to identify where the particles are impacting the workpiece surface and under which conditions (impact velocity and angle), allowing to design finishing approaches and optimise the performance of the fluid jet polishing process. Despite the large number of particles impinging directly in the stagnation zone, a low material removal rate has been observed in the experiments in this region due to the relatively low impact velocity and kinetic energy of the particles. The material removal rate is more significant in the further downstream regions, especially in which the wall shear stress increases and particle kinetic energy presents its maxima. The investigation provided a deeper understanding of the fluid suspension jet impingement behaviour, the particle dynamics in the jet, and the particle-surface interactions. However, the numerical process model may be improved (the erosion model needs to be implemented) for further investigations in order to establish correlations between the microscopic fluid particle dynamic characteristics and the macroscopic operating process parameters.
Publications
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Close-loop Controlled Jet Polishing System for Generating Nano-Scale Roughness Optical Surfaces. Micro/Nano Manufacturing: SIG Meeting 2021, November 2021, Raaba, Austria.
Yongli Qi, Lizoel Buss, Oltmann Riemer & Udo Fritsching
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Numerical Investigation of Fluid Jet Impingement Applied to Polishing Processes of Amorphous Materials. Jahrestreffen der ProcessNet-Fachgruppe Mehrphasenströmung, March 2021, Paderborn, Germany.
Lizoel Buss, Yongli Qi, Oltmann Riemer & Udo Fritsching
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Numerical Investigations of the Fluid Behaviour on the Impingement Workpiece Surface in the Fluid Jet Polishing Process. Jahrestreffen der ProcessNet-Fachgruppe Mehrphasenströmung, February 2022, Leipzig, Germany.
Lizoel Buss, Yongli Qi, Oltmann Riemer & Udo Fritsching
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Towards an Understanding of Multiphase Fluid Dynamics of a Microfluid Jet Polishing Process: A Numerical Analysis. Fluids, 7(3), 119.
Buss, Lizoel; Qi, Yongli; Heidhoff, Julian; Riemer, Oltmann & Fritsching, Udo
