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Jan K. Spelt - One of the best experts on this subject based on the ideXlab platform.
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Jet properties and mixing chamber flow in a high-pressure Abrasive Slurry jet: part II—machining rates and CFD modeling
The International Journal of Advanced Manufacturing Technology, 2019Co-Authors: Michael Teti, Jan K. Spelt, Marcello PapiniAbstract:Part I of this two-part paper presented mixing chamber conditions and jet characteristics in a high-pressure Abrasive Slurry jet micro-machining (HASJM) system. The present paper describes the modeling of the Slurry entrainment process within the mixing chamber and mixing tube of the nozzle using computational fluid dynamics (CFD) and shows how the results can be used to explain and predict machining performance. The Slurry flow rate into the mixing chamber was found to have a large impact on the performance of the jet due to differences in the momentum of the high-velocity water and low-velocity Slurry. The erosive efficacy of the jet was assessed by machining channels and blind holes in aluminum 6061-T6. Differences in the centerline erosion rates of holes and channels for a given jet showed clear evidence of incubation and stagnation zone effects. The CFD models simulated various Slurry flow rates entering the mixing chamber as a result of the low pressure created by the central high-velocity jet of water. They predicted correctly an experimentally observed flooding condition in which Slurry completely filled the mixing chamber and mixing tube. The models could also identify the transient conditions leading to the onset of this flooding as the chamber first began to fill, which could not be identified experimentally. Flooding was found to significantly reduce the jet velocity, thus diminishing its erosive efficacy. The models also identified the operating conditions within the mixing chamber that produced boiling due to the low internal pressure generated by the central high-velocity jet of water. This boiling condition was found in part I to result in a wider jet exiting the mixing tube.
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Micro-machining with Abrasive Slurry-jets: effects of dissolved polymer concentration and nozzle design
The International Journal of Advanced Manufacturing Technology, 2019Co-Authors: Erwin Van Wijk, D. F. James, Marcello Papini, Jan K. SpeltAbstract:The resolution of features machined with Abrasive Slurry jets is dependent on the diameter of the erosion footprint on the workpiece and on the stability of the jet. Previous work has shown that the footprint size decreases, but the jet oscillation increases, with increasing polymer concentration. The present study investigated the effect of nozzle design on jet stability in Abrasive Slurry-jet micro-machining of glass using slurries with dissolved polymers. A variety of transparent acrylic nozzles were made with different geometries and a 180-μm sapphire orifice to study the oscillation of jets of water mixed with high molecular-weight polyethylene oxide. Fluorescent streak photography of the flows within the nozzles confirmed the presence of unstable vortices that can lead to jet oscillation. However, the dependence of these vortices on nozzle geometry and PEO concentration was unclear. Jet oscillation was then measured photographically and found to increase nonlinearly with polymer concentration for all nozzle geometries. These results were used to design and manufacture a new steel nozzle with a 30° tapered entrance region which reduced jet oscillation. Micro-channels were then machined in glass plates using a range of polymer slurries containing aluminium oxide particles. The polymer concentration that produced the best combination of a relatively small footprint while simultaneously minimizing the jet oscillation amplitude resulted in channels that were 11% narrower than reference channels machined with a pure water Slurry and a standard nozzle.
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jet properties and mixing chamber flow in a high pressure Abrasive Slurry jet part i measurement of jet and chamber conditions
The International Journal of Advanced Manufacturing Technology, 2018Co-Authors: Michael Teti, Jan K. Spelt, M PapiniAbstract:Techniques to enhance the performance of a high-pressure Abrasive Slurry jet micro-machining process (HASJM) were investigated by altering the conditions within the jet. The Slurry flow rate was controlled using six inlet tubes (cross-sectional areas of 0.2, 0.46, 1.27, 1.77, 3.08, and 4.51 mm2), and was found to have a large effect on the conditions within the mixing chamber. The tubes permitted the use of high-concentration Slurry solutions, which resulted in increased machining rates and the ability to machine glass targets without cracking by using a minimum particle concentration of 17 wt%. Slurry tubes producing large Slurry flow rates caused the mixing chamber to flood, resulting in a much lower jet velocity. The size of the smallest Slurry tube size that caused the mixing chamber to flood was dependent on the pump operating pressure, and varying from 1.27 mm2 at 134 MPa, to 1.5 mm2 at 233 MPa. Mixing chamber flooding significantly reduced the erosion rate of the jet and increased the machining time, as discussed in the second part of this two-part paper. Mixing chamber pressures were found to be low enough to cause boiling, which increased the jet diameter and the width of features that could be machined without a mask.
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erosive smoothing of Abrasive Slurry jet micro machined channels in glass pmma and sintered ceramics experiments and roughness model
Precision Engineering-journal of The International Societies for Precision Engineering and Nanotechnology, 2017Co-Authors: Kavin Kowsari, Jan K. Spelt, M Papini, J SchwartzentruberAbstract:Abstract Abrasive Slurry jet micro-machining (ASJM) was used to machine channels in glass, PMMA, zirconium tin titanate, and aluminum nitride. The channel roughness was measured as a function of the ASJM process parameters particle size, dose, impact velocity, and impact angle. The steady-state roughness of the channels was reached relatively quickly for typical ASJM Abrasive flow rates. The roughness of channels having depth-to-width aspect ratios up to about 0.25 could be reduced by approximately 35% compared to the roughest channel by decreasing particle impact velocity and angle. However, machining at such conditions reduced the specific erosion rate by 64% on average. It was therefore quicker to post-blast reference channels (225 nm average root mean square ( R rms ) roughness) using process parameters selected for peak removal. It was also found that the roughness of reference channels could be reduced by about 78% by post-blasting using 3 μm diameter silicon carbide particles at 15° jet incidence. The smoothest post-blasted channels had an R rms roughness of about 23 nm in glass, PMMA, and zirconium tin titanate, and 170 nm in aluminum nitride. Computational fluid dynamics was used to predict the particle impact conditions that were used in a model to predict the steady-state roughness due to ductile erosion with an average error of 12%.
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Selective removal of metallic layers from sintered ceramic and metallic plates using Abrasive Slurry-jet micro-machining
Journal of Manufacturing Processes, 2017Co-Authors: Kavin Kowsari, Marta Papini, Jan K. SpeltAbstract:Abrasive Slurry-jet micro-machining (ASJM) is a low-cost and relatively quick alternative for the selective removal of metallic layers compared to conventional processes such as chemical-mechanical planarization (CMP). The present study used a computational fluid dynamics (CFD)-aided methodology with over-lapping ASJM channel machining to predict the thickness of copper and nickel-phosphorous layers that could be removed without eroding the underlying ceramic or metallic substrate. High-viscosity soybean oil was used instead of water to eliminate undesirable erosion caused by the secondary Slurry flow adjacent to the primary footprint, thereby providing better control of the areas being eroded. Experiments and CFD models showed that the much larger boundary layer thickness of soybean oil reduced the particle velocities near the surface and modified particle trajectories so that erosion was minimized beyond the primary jet footprint where the flow moved mostly parallel to the target surface. CFD models were used to explain measured variations in the specific erosion rates found in single-pass channels of varying depths, brought about by the geometry of the machining front. It was found that the greater ability of viscous soybean oil to deflect the particles prior to impact caused the machining of relatively deep channels to be uneconomical, while the opposite trend was found using water. The generalized functions for the dependence of erosion on particle impact velocity and angle were measured experimentally for electrodeposited copper and nickel-phosphorous, and then used as inputs in CFD models to obtain erosion patterns. These were then calibrated and used in an existing superposition model for the prediction of the profile of channels machined using ASJM. In summary, the present work demonstrated that ASJM can be used to selectively remove metal layers deposited on both ceramic and metal substrates by controlling the process conditions.
M Papini - One of the best experts on this subject based on the ideXlab platform.
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measurement of Abrasive particle velocity and size distribution in high pressure Abrasive Slurry and water micro jets using a modified dual disc anemometer
Journal of Materials Processing Technology, 2019Co-Authors: Naser Haghbin, Ariana Khakpour, Jeff Schwartzentruber, M PapiniAbstract:Abstract In both Abrasive water jet (AWJ) and high pressure Abrasive Slurry jet (HASJ) machining, garnet Abrasive particles are mixed with water and the resulting jet can contain particles travelling with a wide range of velocities. Previous investigations have suggested that a dual disc anemometer (DDA) can be used to provide an assessment of the average particle velocity within the jets. This paper presents an in-depth analysis of the DDA test by considering the distribution and size of impact craters on the recording disc, and by modeling the size of the Slurry slug incident to it. Procedures are presented to assess the accuracy of the determined average velocity, and to determine the histogram of particle velocities within the jet. A modification to the anemometer is introduced which also allows determination of the particle size-velocity correlation. Results are presented for both HASJ and AWJ under typical process conditions, and compared to existing analytical models of Abrasive particle velocity from the literature, with good agreement.
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masked micro channel machining in aluminum alloy and borosilicate glass using Abrasive water jet micro machining
Journal of Manufacturing Processes, 2018Co-Authors: Naser Haghbin, Farbod Ahmadzadeh, M PapiniAbstract:Abstract Abrasive water jets (AWJs) have recently been used to mill unmasked features as narrow as 600 μm. This paper investigated the use of metal masks in order to decrease this minimum possible feature width in Al6061-T6 and borosilicate glass. Although there was under-etching on the channel sidewalls below the mask edges, it was nevertheless found that masked channels could be machined that were between 2–3 times narrower with 11% lower centerline roughness and 44% lower waviness than those created without masks. It was also found that increases in mask thickness led to increases in the channel centerline depth and width, and decreases in the centerline roughness and waviness. Increases in the Abrasive mass flow rate increased the channel width, but decreased the depth. Finally, the normalized instantaneous centerline erosion rates in the masked channels decreased faster with depth than in the unmasked cases. Reasons for these trends were discussed in terms of changes in Abrasive Slurry flow and in the size of the stagnation zone within the channels brought about by the masks. Overall, the study demonstrates that masked AWJ micro-machining of features as narrow as ∼150 μm wide is possible, thus demonstrating the feasibility of the technique for the manufacture of microfluidic and other components.
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jet properties and mixing chamber flow in a high pressure Abrasive Slurry jet part i measurement of jet and chamber conditions
The International Journal of Advanced Manufacturing Technology, 2018Co-Authors: Michael Teti, Jan K. Spelt, M PapiniAbstract:Techniques to enhance the performance of a high-pressure Abrasive Slurry jet micro-machining process (HASJM) were investigated by altering the conditions within the jet. The Slurry flow rate was controlled using six inlet tubes (cross-sectional areas of 0.2, 0.46, 1.27, 1.77, 3.08, and 4.51 mm2), and was found to have a large effect on the conditions within the mixing chamber. The tubes permitted the use of high-concentration Slurry solutions, which resulted in increased machining rates and the ability to machine glass targets without cracking by using a minimum particle concentration of 17 wt%. Slurry tubes producing large Slurry flow rates caused the mixing chamber to flood, resulting in a much lower jet velocity. The size of the smallest Slurry tube size that caused the mixing chamber to flood was dependent on the pump operating pressure, and varying from 1.27 mm2 at 134 MPa, to 1.5 mm2 at 233 MPa. Mixing chamber flooding significantly reduced the erosion rate of the jet and increased the machining time, as discussed in the second part of this two-part paper. Mixing chamber pressures were found to be low enough to cause boiling, which increased the jet diameter and the width of features that could be machined without a mask.
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erosive smoothing of Abrasive Slurry jet micro machined channels in glass pmma and sintered ceramics experiments and roughness model
Precision Engineering-journal of The International Societies for Precision Engineering and Nanotechnology, 2017Co-Authors: Kavin Kowsari, Jan K. Spelt, M Papini, J SchwartzentruberAbstract:Abstract Abrasive Slurry jet micro-machining (ASJM) was used to machine channels in glass, PMMA, zirconium tin titanate, and aluminum nitride. The channel roughness was measured as a function of the ASJM process parameters particle size, dose, impact velocity, and impact angle. The steady-state roughness of the channels was reached relatively quickly for typical ASJM Abrasive flow rates. The roughness of channels having depth-to-width aspect ratios up to about 0.25 could be reduced by approximately 35% compared to the roughest channel by decreasing particle impact velocity and angle. However, machining at such conditions reduced the specific erosion rate by 64% on average. It was therefore quicker to post-blast reference channels (225 nm average root mean square ( R rms ) roughness) using process parameters selected for peak removal. It was also found that the roughness of reference channels could be reduced by about 78% by post-blasting using 3 μm diameter silicon carbide particles at 15° jet incidence. The smoothest post-blasted channels had an R rms roughness of about 23 nm in glass, PMMA, and zirconium tin titanate, and 170 nm in aluminum nitride. Computational fluid dynamics was used to predict the particle impact conditions that were used in a model to predict the steady-state roughness due to ductile erosion with an average error of 12%.
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the effects of fluid vapor pressure and viscosity on the shapes of Abrasive Slurry jet micro machined holes and channels
International Journal of Machine Tools & Manufacture, 2016Co-Authors: Kavin Kowsari, Jan K. Spelt, M Papini, M H AminiAbstract:Abstract Abrasive Slurry jet micro-machining (ASJM) can etch micro-features such as holes and channels in virtually any material. Holes, and to a lesser extent, channels machined in brittle materials using ASJM typically suffer from substantial edge rounding near the opening. This study investigated the erosive mechanism responsible for the rounding in borosilicate glass and sintered zirconium tin titanate targets, and determined the process parameters capable of minimizing the effect. Computational fluid dynamics (CFD) showed that the rounding that occurred during ASJM with a water-based Slurry was due to the impact of particles accelerated by the formation and collapse of cavitation bubbles in regions where local pressures were below the vapor pressure of water. Further evidence of this was obtained by comparing the micro-topography in these regions with that produced by an ultrasonic cavitation apparatus in a water-particle Slurry. Cavitation-enhanced erosion in ASJM was minimized using liquids such as mineral or soybean oil that have relatively low vapor pressures, resulting in blind and through-holes having sharp entrance and exit holes in glass and sintered zirconium tin titanate. The increased viscosity of the test fluids also altered the particle trajectories observed in the CFD models, causing the cross-sectional shape of the holes to have flatter bottoms and steeper sidewalls. In ductile targets such as copper, edge rounding due to cavitation-enhanced erosion was found to be much smaller than in brittle targets. In glass channels, the use of a soybean oil-based Slurry eliminated the edge rounding and resulted in flatter bottoms, but increased the width by approximately 20%.
Kavin Kowsari - One of the best experts on this subject based on the ideXlab platform.
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erosive smoothing of Abrasive Slurry jet micro machined channels in glass pmma and sintered ceramics experiments and roughness model
Precision Engineering-journal of The International Societies for Precision Engineering and Nanotechnology, 2017Co-Authors: Kavin Kowsari, Jan K. Spelt, M Papini, J SchwartzentruberAbstract:Abstract Abrasive Slurry jet micro-machining (ASJM) was used to machine channels in glass, PMMA, zirconium tin titanate, and aluminum nitride. The channel roughness was measured as a function of the ASJM process parameters particle size, dose, impact velocity, and impact angle. The steady-state roughness of the channels was reached relatively quickly for typical ASJM Abrasive flow rates. The roughness of channels having depth-to-width aspect ratios up to about 0.25 could be reduced by approximately 35% compared to the roughest channel by decreasing particle impact velocity and angle. However, machining at such conditions reduced the specific erosion rate by 64% on average. It was therefore quicker to post-blast reference channels (225 nm average root mean square ( R rms ) roughness) using process parameters selected for peak removal. It was also found that the roughness of reference channels could be reduced by about 78% by post-blasting using 3 μm diameter silicon carbide particles at 15° jet incidence. The smoothest post-blasted channels had an R rms roughness of about 23 nm in glass, PMMA, and zirconium tin titanate, and 170 nm in aluminum nitride. Computational fluid dynamics was used to predict the particle impact conditions that were used in a model to predict the steady-state roughness due to ductile erosion with an average error of 12%.
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Selective removal of metallic layers from sintered ceramic and metallic plates using Abrasive Slurry-jet micro-machining
Journal of Manufacturing Processes, 2017Co-Authors: Kavin Kowsari, Marta Papini, Jan K. SpeltAbstract:Abrasive Slurry-jet micro-machining (ASJM) is a low-cost and relatively quick alternative for the selective removal of metallic layers compared to conventional processes such as chemical-mechanical planarization (CMP). The present study used a computational fluid dynamics (CFD)-aided methodology with over-lapping ASJM channel machining to predict the thickness of copper and nickel-phosphorous layers that could be removed without eroding the underlying ceramic or metallic substrate. High-viscosity soybean oil was used instead of water to eliminate undesirable erosion caused by the secondary Slurry flow adjacent to the primary footprint, thereby providing better control of the areas being eroded. Experiments and CFD models showed that the much larger boundary layer thickness of soybean oil reduced the particle velocities near the surface and modified particle trajectories so that erosion was minimized beyond the primary jet footprint where the flow moved mostly parallel to the target surface. CFD models were used to explain measured variations in the specific erosion rates found in single-pass channels of varying depths, brought about by the geometry of the machining front. It was found that the greater ability of viscous soybean oil to deflect the particles prior to impact caused the machining of relatively deep channels to be uneconomical, while the opposite trend was found using water. The generalized functions for the dependence of erosion on particle impact velocity and angle were measured experimentally for electrodeposited copper and nickel-phosphorous, and then used as inputs in CFD models to obtain erosion patterns. These were then calibrated and used in an existing superposition model for the prediction of the profile of channels machined using ASJM. In summary, the present work demonstrated that ASJM can be used to selectively remove metal layers deposited on both ceramic and metal substrates by controlling the process conditions.
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the effects of fluid vapor pressure and viscosity on the shapes of Abrasive Slurry jet micro machined holes and channels
International Journal of Machine Tools & Manufacture, 2016Co-Authors: Kavin Kowsari, Jan K. Spelt, M Papini, M H AminiAbstract:Abstract Abrasive Slurry jet micro-machining (ASJM) can etch micro-features such as holes and channels in virtually any material. Holes, and to a lesser extent, channels machined in brittle materials using ASJM typically suffer from substantial edge rounding near the opening. This study investigated the erosive mechanism responsible for the rounding in borosilicate glass and sintered zirconium tin titanate targets, and determined the process parameters capable of minimizing the effect. Computational fluid dynamics (CFD) showed that the rounding that occurred during ASJM with a water-based Slurry was due to the impact of particles accelerated by the formation and collapse of cavitation bubbles in regions where local pressures were below the vapor pressure of water. Further evidence of this was obtained by comparing the micro-topography in these regions with that produced by an ultrasonic cavitation apparatus in a water-particle Slurry. Cavitation-enhanced erosion in ASJM was minimized using liquids such as mineral or soybean oil that have relatively low vapor pressures, resulting in blind and through-holes having sharp entrance and exit holes in glass and sintered zirconium tin titanate. The increased viscosity of the test fluids also altered the particle trajectories observed in the CFD models, causing the cross-sectional shape of the holes to have flatter bottoms and steeper sidewalls. In ductile targets such as copper, edge rounding due to cavitation-enhanced erosion was found to be much smaller than in brittle targets. In glass channels, the use of a soybean oil-based Slurry eliminated the edge rounding and resulted in flatter bottoms, but increased the width by approximately 20%.
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calibrated cfd erosion modeling of Abrasive Slurry jet micro machining of channels in ductile materials
Journal of Manufacturing Processes, 2016Co-Authors: H Nouraei, Kavin Kowsari, Jan K. Spelt, M Papini, B. SamarehAbstract:Abstract Abrasive Slurry jet micro-machining (ASJM) uses a relatively high-speed jet of fine Abrasive Slurry to precisely machine controlled-depth micro-features such as channels. Existing surface evolution models, developed for air-driven erosion processes, cannot account for the effect of Slurry flow on the channel sidewall erosion that leads to the progressive channel widening observed in the ASJM of ductile materials. This paper presents a novel numerical–empirical model to predict the profiles of micro-channels in ductile materials (i.e. polymethylmethacrylate (PMMA), 6061-T6 aluminum alloy, 316L stainless steel and Ti–6Al–4V titanium alloy) using ASJM. The specific erosion rates of these materials were measured as a function of jet angle using a 10 μm nominal diameter aluminum oxide Slurry. The erosion rate-impact angle relations were corrected using computational fluid dynamic (CFD) models to account for the local impact angles and velocities of the particles. The erosion rate-impact angle relations were then used in three-dimensional CFD models to obtain the particle trajectories, impact angles, and velocities on a shallow eroded profile, and thus predict the erosion for deeper profiles. The model was verified by comparison with experiments which showed the previously-observed widening of the machined channels as the depth increased due to secondary erosion by particles impacting the channel sidewalls. The widening effect was found to be substantial in the PMMA but less important in Ti–6Al–4V titanium alloy due to its greater erosion resistance. The numerical–empirical approach could accurately estimate the widening and predicted the channel cross-sections up to an aspect ratio of approximately 1 with a maximum error of less than 5%.
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operating parameters to minimize feature size in Abrasive Slurry jet micro machining
Precision Engineering-journal of The International Societies for Precision Engineering and Nanotechnology, 2016Co-Authors: H Nouraei, Kavin Kowsari, Jan K. Spelt, M PapiniAbstract:Abstract In low-pressure Abrasive Slurry jet micro-machining (ASJM), an aqueous Slurry of Abrasive particles is used to erode features with relatively high resolution in a variety of brittle and ductile materials. The effects of ASJM operating parameters on the minimum size of micro-channels machined in borosilicate glass and polymethylmethacrylate (PMMA) were investigated experimentally and with CFD models. The operating parameters were found to have very different effects in these two materials due to fundamental differences in the erosion mechanisms. It was also found that, although the ASJM operating parameters could be adjusted to control the trajectory of particles and thereby reduce the size of the erosive jet footprint, this did not necessarily result in narrower channels, because of the oblique secondary impact of Abrasive particles on the channel sidewalls adjacent to the immediate footprint. For both glass and PMMA, the channel width increased with depth, but the channel widening by secondary oblique impacts was more substantial in PMMA due to its ductile erosive behavior. Increasing the particle kinetic energy widened the channels machined in both glass and PMMA for a given depth. Narrower channels could be machined for a given depth by: (i) increasing the Slurry temperature, (ii) reducing the jet impingement angle in both glass and PMMA, (iii) machining at a slower scan speeds in PMMA, but not in glass, (iv) using smaller orifices and particles, and (v) coating the target with a sacrificial surface layer.
Marcello Papini - One of the best experts on this subject based on the ideXlab platform.
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Jet properties and mixing chamber flow in a high-pressure Abrasive Slurry jet: part II—machining rates and CFD modeling
The International Journal of Advanced Manufacturing Technology, 2019Co-Authors: Michael Teti, Jan K. Spelt, Marcello PapiniAbstract:Part I of this two-part paper presented mixing chamber conditions and jet characteristics in a high-pressure Abrasive Slurry jet micro-machining (HASJM) system. The present paper describes the modeling of the Slurry entrainment process within the mixing chamber and mixing tube of the nozzle using computational fluid dynamics (CFD) and shows how the results can be used to explain and predict machining performance. The Slurry flow rate into the mixing chamber was found to have a large impact on the performance of the jet due to differences in the momentum of the high-velocity water and low-velocity Slurry. The erosive efficacy of the jet was assessed by machining channels and blind holes in aluminum 6061-T6. Differences in the centerline erosion rates of holes and channels for a given jet showed clear evidence of incubation and stagnation zone effects. The CFD models simulated various Slurry flow rates entering the mixing chamber as a result of the low pressure created by the central high-velocity jet of water. They predicted correctly an experimentally observed flooding condition in which Slurry completely filled the mixing chamber and mixing tube. The models could also identify the transient conditions leading to the onset of this flooding as the chamber first began to fill, which could not be identified experimentally. Flooding was found to significantly reduce the jet velocity, thus diminishing its erosive efficacy. The models also identified the operating conditions within the mixing chamber that produced boiling due to the low internal pressure generated by the central high-velocity jet of water. This boiling condition was found in part I to result in a wider jet exiting the mixing tube.
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Micro-machining with Abrasive Slurry-jets: effects of dissolved polymer concentration and nozzle design
The International Journal of Advanced Manufacturing Technology, 2019Co-Authors: Erwin Van Wijk, D. F. James, Marcello Papini, Jan K. SpeltAbstract:The resolution of features machined with Abrasive Slurry jets is dependent on the diameter of the erosion footprint on the workpiece and on the stability of the jet. Previous work has shown that the footprint size decreases, but the jet oscillation increases, with increasing polymer concentration. The present study investigated the effect of nozzle design on jet stability in Abrasive Slurry-jet micro-machining of glass using slurries with dissolved polymers. A variety of transparent acrylic nozzles were made with different geometries and a 180-μm sapphire orifice to study the oscillation of jets of water mixed with high molecular-weight polyethylene oxide. Fluorescent streak photography of the flows within the nozzles confirmed the presence of unstable vortices that can lead to jet oscillation. However, the dependence of these vortices on nozzle geometry and PEO concentration was unclear. Jet oscillation was then measured photographically and found to increase nonlinearly with polymer concentration for all nozzle geometries. These results were used to design and manufacture a new steel nozzle with a 30° tapered entrance region which reduced jet oscillation. Micro-channels were then machined in glass plates using a range of polymer slurries containing aluminium oxide particles. The polymer concentration that produced the best combination of a relatively small footprint while simultaneously minimizing the jet oscillation amplitude resulted in channels that were 11% narrower than reference channels machined with a pure water Slurry and a standard nozzle.
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CFD-aided prediction of the shape of Abrasive Slurry jet micro-machined channels in sintered ceramics
Ceramics International, 2016Co-Authors: Kavin Kowsari, H Nouraei, Marcello Papini, B. Samareh, Jan K. SpeltAbstract:Abstract The extreme hardness of sintered ceramics makes it difficult to machine them economically. Abrasive Slurry-jet micro-machining (ASJM), in which a target is eroded by the impingement of a micro-jet of water containing fine Abrasive particles, is a low-cost alternative for micro-machining of sintered ceramic materials without tool wear and thermal damage, and without the use of patterned masks. Existing profile prediction models could not account for changes in the flow field observed in the ASJM of sintered ceramics as channel depth increased. These changes in the flow of Abrasive particles fundamentally altered the channel profiles so that the specific erosion rate (mass of material removed per mass of erodent) of the channel centerline decreased with increasing depth and, when machined at 90° incidence, the profiles changed shape. Computational fluid dynamic (CFD) modeling was used to derive a generalized relation between channel geometry and erosive flow (the nonlinearity function), which was used in an existing numerical-empirical model to predict the depths, widths, and shapes of ASJM micro-channels in sintered ceramics; i.e. aluminum nitride (AlN), alumina (Al 2 O 3 ), and zirconium tin titanate (Zn–Sn–TiO 2 ). The specific erosion rate-particle impact angle and specific erosion rate-particle impact velocity relations, measured for 1 wt%, 10 μm-diameter alumina Slurry jet, were used in a CFD model of a first-pass channel to obtain the erosive pattern (erosive efficacy distribution) of the Slurry jet within a shallow ceramic channel. This shallow, first-pass erosion pattern was then generalized and used with the nonlinearity function to predict the shapes of deeper channels. The predicted depths in each of the three ceramics at any point on the cross-section were within 6% of those of measured channels up to a depth/width aspect ratio of about 0.5 for nozzle angles of both 90° and 45° in both the forward or backward channel-machining configurations.
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surface evolution models for Abrasive Slurry jet micro machining of channels and holes in glass
Wear, 2014Co-Authors: H Nouraei, Kavin Kowsari, Marcello Papini, Jan K. SpeltAbstract:Abstract Abrasive Slurry jet micro-machining (ASJM) uses a jet of Abrasive Slurry to erode features with relatively high resolution without the need for a patterned mask. The present study investigated the ability of a surface evolution model to predict the profiles of micro-channels and holes machined in borosilicate glass with a newly developed ASJM system. The system could produce micro-channels with depth and width variations along their length of less than 3%, and a channel-to-channel repeatability within 5%. The fundamental erosion rate of the borosilicate glass was measured as a function of impact angle using a Slurry of water mixed with a low concentration of 10 and 25 µm nominal diameter aluminum oxide particles. This erosion rate-impact angle relationship was used in an existing model developed previously for the Abrasive air jet micro-machining of brittle materials. The results demonstrated that, despite the differences in Abrasive flow patterns between air and Slurry based systems, the surface evolution model accurately predicted the profiles of micro-channels with a maximum error of 7% for aspect ratios (depth/width) of up to 5. The predicted profiles of holes were also in reasonable agreement with a maximum error of 14% for aspect ratios close to 1.
H Nouraei - One of the best experts on this subject based on the ideXlab platform.
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calibrated cfd erosion modeling of Abrasive Slurry jet micro machining of channels in ductile materials
Journal of Manufacturing Processes, 2016Co-Authors: H Nouraei, Kavin Kowsari, Jan K. Spelt, M Papini, B. SamarehAbstract:Abstract Abrasive Slurry jet micro-machining (ASJM) uses a relatively high-speed jet of fine Abrasive Slurry to precisely machine controlled-depth micro-features such as channels. Existing surface evolution models, developed for air-driven erosion processes, cannot account for the effect of Slurry flow on the channel sidewall erosion that leads to the progressive channel widening observed in the ASJM of ductile materials. This paper presents a novel numerical–empirical model to predict the profiles of micro-channels in ductile materials (i.e. polymethylmethacrylate (PMMA), 6061-T6 aluminum alloy, 316L stainless steel and Ti–6Al–4V titanium alloy) using ASJM. The specific erosion rates of these materials were measured as a function of jet angle using a 10 μm nominal diameter aluminum oxide Slurry. The erosion rate-impact angle relations were corrected using computational fluid dynamic (CFD) models to account for the local impact angles and velocities of the particles. The erosion rate-impact angle relations were then used in three-dimensional CFD models to obtain the particle trajectories, impact angles, and velocities on a shallow eroded profile, and thus predict the erosion for deeper profiles. The model was verified by comparison with experiments which showed the previously-observed widening of the machined channels as the depth increased due to secondary erosion by particles impacting the channel sidewalls. The widening effect was found to be substantial in the PMMA but less important in Ti–6Al–4V titanium alloy due to its greater erosion resistance. The numerical–empirical approach could accurately estimate the widening and predicted the channel cross-sections up to an aspect ratio of approximately 1 with a maximum error of less than 5%.
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operating parameters to minimize feature size in Abrasive Slurry jet micro machining
Precision Engineering-journal of The International Societies for Precision Engineering and Nanotechnology, 2016Co-Authors: H Nouraei, Kavin Kowsari, Jan K. Spelt, M PapiniAbstract:Abstract In low-pressure Abrasive Slurry jet micro-machining (ASJM), an aqueous Slurry of Abrasive particles is used to erode features with relatively high resolution in a variety of brittle and ductile materials. The effects of ASJM operating parameters on the minimum size of micro-channels machined in borosilicate glass and polymethylmethacrylate (PMMA) were investigated experimentally and with CFD models. The operating parameters were found to have very different effects in these two materials due to fundamental differences in the erosion mechanisms. It was also found that, although the ASJM operating parameters could be adjusted to control the trajectory of particles and thereby reduce the size of the erosive jet footprint, this did not necessarily result in narrower channels, because of the oblique secondary impact of Abrasive particles on the channel sidewalls adjacent to the immediate footprint. For both glass and PMMA, the channel width increased with depth, but the channel widening by secondary oblique impacts was more substantial in PMMA due to its ductile erosive behavior. Increasing the particle kinetic energy widened the channels machined in both glass and PMMA for a given depth. Narrower channels could be machined for a given depth by: (i) increasing the Slurry temperature, (ii) reducing the jet impingement angle in both glass and PMMA, (iii) machining at a slower scan speeds in PMMA, but not in glass, (iv) using smaller orifices and particles, and (v) coating the target with a sacrificial surface layer.
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CFD-aided prediction of the shape of Abrasive Slurry jet micro-machined channels in sintered ceramics
Ceramics International, 2016Co-Authors: Kavin Kowsari, H Nouraei, Marcello Papini, B. Samareh, Jan K. SpeltAbstract:Abstract The extreme hardness of sintered ceramics makes it difficult to machine them economically. Abrasive Slurry-jet micro-machining (ASJM), in which a target is eroded by the impingement of a micro-jet of water containing fine Abrasive particles, is a low-cost alternative for micro-machining of sintered ceramic materials without tool wear and thermal damage, and without the use of patterned masks. Existing profile prediction models could not account for changes in the flow field observed in the ASJM of sintered ceramics as channel depth increased. These changes in the flow of Abrasive particles fundamentally altered the channel profiles so that the specific erosion rate (mass of material removed per mass of erodent) of the channel centerline decreased with increasing depth and, when machined at 90° incidence, the profiles changed shape. Computational fluid dynamic (CFD) modeling was used to derive a generalized relation between channel geometry and erosive flow (the nonlinearity function), which was used in an existing numerical-empirical model to predict the depths, widths, and shapes of ASJM micro-channels in sintered ceramics; i.e. aluminum nitride (AlN), alumina (Al 2 O 3 ), and zirconium tin titanate (Zn–Sn–TiO 2 ). The specific erosion rate-particle impact angle and specific erosion rate-particle impact velocity relations, measured for 1 wt%, 10 μm-diameter alumina Slurry jet, were used in a CFD model of a first-pass channel to obtain the erosive pattern (erosive efficacy distribution) of the Slurry jet within a shallow ceramic channel. This shallow, first-pass erosion pattern was then generalized and used with the nonlinearity function to predict the shapes of deeper channels. The predicted depths in each of the three ceramics at any point on the cross-section were within 6% of those of measured channels up to a depth/width aspect ratio of about 0.5 for nozzle angles of both 90° and 45° in both the forward or backward channel-machining configurations.
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Abrasive enhanced electrochemical Slurry jet micro machining comparative experiments and synergistic effects
Journal of Materials Processing Technology, 2014Co-Authors: H Nouraei, Jan K. SpeltAbstract:Abstract Abrasive enhanced electrochemical Slurry-jet machining (ESJM) is presented as a new approach to the micro-machining of metals using a combination of Abrasive Slurry-jet machining (ASJM) and electrochemical jet machining (ECJM). A novel ESJM prototype was developed to generate a charged Slurry jet consisting of a mixture of Al2O3 Abrasive particles and an electrolytic solution of NaCl and NaNO3. A DC potential of 30 V was applied between the nozzle and specimen. A series of micro-channels were machined in Stellite 12 using ASJM, ECJM and ESJM processes to investigate the relative effects of erosion and anodic dissolution on the material removal rate and surface finish in the combined process of ESJM. The results illustrated that the ESJM process results in significantly greater target mass loss rate than the separate erosion and corrosion processes. The magnitude of the synergistic effect on the rate of mass loss was found to vary from positive to negative as the erosion component increased with increasing particle kinetic energy (jet pressure) and particle concentration. The roughness of the channels machined using ESJM was between that obtained with ASJM and ECJM. The roughness decreased as the erosion component of the total mass loss increased.
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Abrasive Slurry jet micro machining of holes in brittle and ductile materials
Journal of Materials Processing Technology, 2014Co-Authors: Kavin Kowsari, H Nouraei, D. F. James, Jan K. Spelt, M PapiniAbstract:Abstract This paper investigated the effects of elasticity and viscosity, induced by a dilute high-molecular-weight polymer solution, on the shape, depth, and diameter of micro-holes drilled in borosilicate glass and in plates of 6061-T6 aluminum alloy, 110 copper, and 316 stainless steel using low-pressure Abrasive Slurry jet micro-machining (ASJM). Holes were machined using aqueous jets with 1 wt% 10 μm Al 2 O 3 particles. The 180 μm sapphire orifice produced a 140 μm diameter jet at pressures of 4 and 7 MPa. When the jet contained 50 wppm of dissolved 8 million molecular weight polyethylene oxide (PEO), the blind holes in glass were approximately 20% narrower and 30% shallower than holes drilled without the polymer, using the same Abrasive concentration and pressure. The addition of PEO led to hole cross-sectional profiles that had a sharper edge at the glass surface and were more V-shaped compared with the U-shape of the holes produced without PEO. Hole symmetry in glass was maintained over depths ranging from about 80–900 μm by ensuring that the jets were aligned perpendicularly to within 0.2°. The changes in shape and size were brought about by normal stresses generated by the polymer. Jets containing this dissolved polymer were observed to oscillate laterally and non-periodically, with an amplitude reaching a value of 20 μm. For the first time, symmetric ASJM through-holes were drilled in a 3-mm-thick borosilicate glass plate without chipping around the exit edge. The depth of symmetric blind holes in metals was restricted to approximately 150 μm for jets with and without PEO. At greater depths, the holes became highly asymmetric, eroding in a specific direction to create a sub-surface slot. The asymmetry appeared to be caused by the extreme sensitivity of ductile materials to jet alignment. This sensitivity also caused the holes in metals to be less circular when PEO was included, apparently caused by the random jet oscillations induced by the polymer. Under identical conditions, hole depths increased in the order: borosilicate glass > 6061-T6 aluminum > 110 copper > 316 stainless steel. The edges of the holes in glass could be made sharper by machining through a sacrificial layer of glass or epoxy.
