Papers by Author: Yan Xia Feng

Abstract: The profile of a single-pass milling can be assumed as a cosine curve. Therefore, the maximal depth model for single-pass milling is established which indicates the quantitative relationship between the AWJ single-pass milling depth and the milling parameters. The depth model of milled surface, which shows the effect of water pressure, standoff distance, lateral spacing, abrasive flow rate and the properties of the material on the AWJ milling depth, is established based on the maximal depth model for single-pass milling. The derived model is assessed by AWJ milling experiments. The results show that the milling depth increases with an increase in water pressure and standoff distance, and decreases with an increase in lateral spacing and traverse speed. The theoretical milling depth predicted by the mathematical model is good agreement with the experimental result.

Abstract: In this paper, an experimental evaluation of the surface microstructural integrity of Si3N4 ceramics milled with abrasive waterjet was studied. The results show that the surface residual stress resulting from abrasive waterjet milling process for ceramics is compressive, and the compressive residual stress ranges from negative 203MPa to negative 19.6MPa. The results also show that the water pressure, the standoff distance, nozzle traverse speed and the lateral spacing have strong effects on the surface residual stress. The results also show that there is some enhancement in the hardness of AWJ milling surface, and it is affected by milling process parameters. The micro-topography of the milled surface cross section shows that there is a thin deteriorative layer in milled layer, in which no obvious crack is observed. Since the surface residual stress is compressive and the surface hardness increases, the milled surface deteriorative layer by AWJ could improve the surface quality.

Abstract: In this paper, the micro-topography of the milled surface and chips are investigated, and the milling mechanisms of ceramics are analyzed. The results show that there are many deep and flat craters due to material fractures on the milled surface of Al2O3 ceramics and evidence of plastic flow is also observed around the craters. The milled surface of Si3N4 ceramics is smooth and even, and the trace of plastic flow can be observed. The abrasives after milling are very different from those before milling, which reflects the strong impact between abrasives and materials during the milling process. It is shown that the dominant milling mechanisms of ceramics are crack and exfoliating due to brittle fracture and plastic distortion according to the form of the chips.

Abstract: The machining performance of Al2O3 ceramics is studied by abrasive waterjet (AWJ) milling experiment. The machined surface characteristics and the effect of process parameters on machined surface quality are analyzed. The results showed that the nozzle traverse speed and traverse feed have a strong effect on the machined surface quality. The effect of process parameters on material volume removal rate and the milling depth is also researched. The results indicated that the material volume removal rate and the milling depth would be increased at the milling conditions of higher water pressure and bigger standoff distance. However, the milling depth will decrease at the milling conditions of higher traverse speed and higher traverse feed, and the material volume removal rate has a complex variation.

Abstract: Simulation of the velocity field of solid-liquid flow inside and outside the abrasive water jet nozzle was studied by the computational fluid dynamics software(CFD). The velocity field of the flow in the abrasive water jet (AWJ) nozzle was obtained. The results indicate that the swirl is produced in the nozzle and the abrasives are all distributed along the inner surface of the nozzle. The velocity at the center of the outlet face is the highest, while it is smallest at the both edge. The dispersion of the flow is happened when it flows out of the nozzle, but the flow velocity away from the outlet at a distance of about 4 times of the outlet diameter changes little. The fillet diameter, the inner cone angle, the length of mixing tube of the nozzle greatly affect the field of two-phase flow. The velocity of outlet increases with an increase in the fillet diameter, the flow becomes ease when the cone angle decreases, the mixing tube hampers the two-phase flowing.

Abstract: The surface characteristics of Si3N4 ceramics milled with abrasive waterjet milling technology is studied. The milled surface characteristics and the effect of process parameters on milled surface roughness are analyzed. The results show that the milled surface roughness ranges between 0.55 and 1.1um at the milling conditions under consideration and is changed with the change of process parameters. The milled surface roughness will be significantly decreased at the milling conditions of lower water pressure and larger lateral spacing. The effect of nozzle traverse speed on milled surface roughness is complex, but a traverse speed of 1000mm/min is the optimum speed for AWJ milling Si3N4 ceramics. The milled surface roughness first decreases then increases with an enhancement of standoff distance from 10mm to 30mm, and it also significantly decreases with the increase in abrasive mesh. Therefore, the medium standoff distance of 20mm and finer abrasive are the optimum conditions for AWJ milling Si3N4 ceramics with the process parameters under consideration.

Abstract: Simulation of the velocity field of gas-solid-liquid three-phase flow inside and outside the abrasive water jet nozzle was studied by the computational fluid dynamics software (CFD). The complicated velocity field of the flow in the abrasive water jet (AWJ) nozzle and the abrasive track in the nozzle were obtained. In the course of the simulation, the inter-phase drag exchange coefficient model uses Gidaspow model (gas-solid), Wen-yu model (water-solid), Schiller-Naumann model (water-gas) respectively. The simulation results indicate that the swirl is produced in the nozzle and the abrasives are accelerated and moved around the swirl, and they are all distributed along the inner surface of the nozzle, the gas is mostly distributed in the center of swirl. The dispersion of the flow happens when it flows out of the nozzle, it can be divided into three zones, that is core zone, middle zone and border zone. At the core zone the velocity changes little while the velocity changes greatly at the middle zone, the velocity fluctuates greatly at the border zone.

Abstract: Coloring stainless steel is a kind of corrosion-resistant and ornamental industry material. Whereas, the oxide film on stainless steel is sensitive to heat. At about 200
, the oxide film would be oxidized or dehydrated. With lesser cutting force and no thermal influence on target material, AWJ may be a suited method in cutting coloring stainless steel. In this paper, an experimental study on cutting coloring stainless steel by abrasive waterjet was carried out. By analyzing macroscopic features of kerfs, a damage model was established and a principle to optimize process parameters was presented.

Abstract: Abrasive waterjet (AWJ) machining is a new non-conventional machining technology. Compared with other conventional and non-conventional machining technologies, AWJ offers the following advantages: no thermal distortion, small machining force, high machining versatility, etc. Therefore this technology is regarded as a high potential technology in the field of machining difficult-to-cut materials. In this paper, a comprehensive review of research situation about the cutting performance, the cutting mechanism and the measures to improve the cutting quality is given. The application of abrasive waterjet machining in turning, milling and drilling is reviewed finally.

Abstract: Simulation on velocity field of gas-liquid flow in the abrasive water jet nozzle was studied by the computed fluid dynamics (CFD) software, The complex velocity field of the flow in the abrasive water jet nozzle can be obtained by means of simulation. The study on the effect of the nozzle inner cone angle on the velocity field shows that the cone angle affects the whirlpool’s intension and position of the whirlpool in the nozzle of abrasive water jet (AWJ), and it also affects velocity ‘s magnitude and distribution of the velocity on the cone surface.