Multiphase Flow and Wear in the Cutting Head of Ultra-high Pressure Abrasive Water Jet

Abrasive water jet cutting technology is widely applied in the materials processing today and attracts great attention from scholars, but many phenomena concerned are not well understood, especially in the internal jet flow of the cutting head at the condition of ultra-high pressure. The multiphase flow in the cutting head is numerically simulated to study the abrasive motion mechanism and wear inside the cutting head at the pressure beyond 300 MPa. Visible predictions of the particles trajectories and wear rate in the cutting head are presented. The influences of the abrasive physical properties, size of the jewel orifice and the operating pressure on the trajectories are discussed. Based on the simulation, a wear experiment is carried out under the corresponding pressures. The simulation and experimental results show that the flow in the mixing chamber is composed of the jet core zone and the disturbance zone, both affect the particles trajectories. The mixing efficiency drops with the increase of the abrasive granularity. The abrasive density determines the response of particles to the effects of different flow zones, the abrasive with medium density gives the best general performance. Increasing the operating pressure or using the jewel with a smaller orifice improves the coherency of p articles trajectories but increases the wear rate of the jewel holder at the same time. Walls of the jewel holder, the entrance of the mixing chamber and the convergence part of the mixing tube are subject to wear out. The computational and experimental results give a qualitative consistency which proves that this numerical method can provide a reliable and visible cognition of the flow characteristics of ultra-high pressure abrasive water jet. The investigation is benefit for improving the machining properties of water jet cutting systems and the optimization design of the cutting head.

Energy Consumption in Comminution of Mica with Cavitation Abrasive Water Jet

We have studied the efficiency of energy consumption in the comminution of mica powder with cavitation abrasive water jet technology. The energy required to create new surfaces in the comminution of mica powder with cavitation abrasive water jet was calculated,in order to estimate its efficiency of energy consumption. The particle size distribution and the specific surface area were measured by applying a JEM-200CX transmission electron microscope and an Autosorb-1 automatic surface area analyzer. The study results show that the efficiency of energy consumed in creating new surface areas is as high as 2.92%,or 4.94% with the aid of cavitation in the comminution of mica powder. This efficiency will decrease with an increase in the number of comminutions. After three comminutions,the efficien-cies will become 1.91% and 2.29% for comminution without cavitation and with cavitation,respectively. The abrasive water jet technology is an effective way for comminution of mica powder.

Numerical Simulation Research of Liquid-Solid Two-Phase Flow in Abrasive Water Jet Nozzle

According to the Lagrange discrete phase model of multiphase flow, mathematical model of the abrasive water-jet （AWJ） nozzle based on the multi-phase movement was introduced, then the boundary conditions was determined and the liquid-solid turbulence which is isothermal, can not be compressed and steadystate in the cone-cylinder nozzles of the export of the pre-mixed AWJ was simulated applying the software FLUENT. The results showed that： the axial velocity and dynamic pressure of the continuous phase in the nozzle were axial symmetry notable, and at the axis had a extreme point; abrasive accelerated at two points, in front contractive segment, the rate increased rapidly, and in the back straight one, the speed accelerated slowly. The length of the cylinder is 100 mm, the diameter of the nozzle is 8 mm, and the angle of the cone is 15°. There is a extreme point of the rate at the point 10 mm in the established model. The results of simulation laid the foundation for optimizing the nozzle structure, improving efficiency and developing the nozzle.

Portable mixed abrasive water jet equipment for rescue in high gas mine shaft

In order to rescue a trapped miner and clean out roadways quickly in a high gas mine shaft after a mining mishap, a special portable cold-cutting equipment is needed, the main technology parameters were calculated according to the advanced cold-cutting technology of high pressure abrasive water jet and the portable mixed abrasive water jet equipment （PAWE） was designed to meet the needs of emergency rescue in high gas mine shafts. Tested the PAWE in a high gas environment, and the result shows that the maximum cutting depth of solid iron pipe is 18 mm and the recoilforce of the sprayer is 28.9 N under the conditions that actual cutting pressure is 29 MPa, starting target distance is 10 ram, cutting speed is 180 mm/min and concentration of abrasive is 32%. The course of the experiment in the high gas environment was smooth and continuous, without any explosion. The PAWE is easy to move and operate, but the nozzle which was worn badly in the sprayer should be changed every 8 minutes.

Performance of recycling abrasives in rock cutting by abrasive water jet

Rock cutting performance of recycling abrasives was investigated in terms of cutting depth, kerf width, kerf taper angle and surface roughness. Gravity separation technique was employed to separate the abrasives and the rock particles. The recycling abrasive particles were then dried and sieved for determination of their disintegration behaviors. Before each cutting with recycling abrasives, the abrasive particles less than 106 ?m were screened out. It is revealed that a considerable amount of used abrasives can be effectively reused in the rock cutting. The reusabilities of abrasives are determined as 81.77%, 57.50%, 34.37% and 17.72% after the first, second, third and fourth cuttings, respectively. Additionally, it is determined that recycling must be restricted three times due to the excessive disintegration of abrasives with further recycling. Moreover, it is concluded that cutting depth, kerf width and surface roughness decreases with recycling. No clear trend is found between the kerf taper angle and recycling. Particle size distribution is determined as an important parameter for improving the cutting performance of recycling abrasives.

Rapid manufacturing of SiC molds with micro-sized holes using abrasive water jet

Silicon carbide (SiC) is highly wear resistant with good mechanical properties, including high temperature strength, excellent chemical resistance, and high thermal conductivity and thermal shock resistance. SiC molds, which can be produced with diverse microstructural features, are now widely used in glass molding owing to their excellent characteristics, and also have potential applicability in IT industries. SiC molds are traditionally fabricated by silicon micromachining or dicing. The fabrication cost of silicon micromachining is very high, however, because several expensive masks are needed. Furthermore, the fabrication time is very long. Meanwhile, it is difficult to make micro-patterned molds with arbitrary shapes using dicing saws. Abrasive water jet (AWJ) is widely applied to cut and drill very brittle, soft and fibrous materials. It offers high energy density, the absence of a heat affected zone(HAZ), high performance, and an environment friendly process. In spite of these advantages, micro-hole drilling via conventional AWJ processing suffers from notable shortcomings. We proposed a new abrasive supplying method of AWJ. The proposed method reduces frosting phenomena, and provides micro-machining of AWJ. The characteristics of a hole machined was investigated by the proposed AWJ process according to the ratio of water and abrasives. With the optimal experimental conditions, 3×3 array SiC molds with the diameter of 700 μm and depth of 900 μm were successfully manufactured.

Experimental study on landscape of CFRP cutting by abrasive water jet

To investigate the influence of operation parameters of abrasive water jet on surface roughness of carbon fiber reinforced plastic(CFRP),experimental studies were conducted.The three-dimensional landscape of cutting front was reconstructed according to the measured data byμscan laser confocal microscopy.Fourier spectral analysis was also adopted to study surface structure in detail.It is found that the morphology of cutting front is similar to that of other materials.In the smooth cutting zone,the fluctuation of amplitudes of surface profile is gentler,compared with that in the rough cutting zone.The lower part of the rough cutting zone was characterized by the periodical appearance of peaks and valleys.The roughness of surface increases with the increase of depth.While in the smooth cutting zone and part of rough cutting zone,roughness increases with the increase of traverse speed.For the thickness of samples,in the smooth cutting zone,the roughness increases with the increase of depth.The dominant harmonic component in the surface profile is concentrated in a narrow range from 0 to 10 Hz,and the relatively higher density of frequency from 10 to 50 Hz is shown in the rough cutting zone,which is caused by the interaction between perpendicular abrasive water jet and reflect jet.

Comminution of Mica by Cavitation Abrasive Water Jet

The comminution of mica with an abrasive water jet is mainly based on three knids of effects, that is, high-speed collision, cavitating effect and shearing effect. Cavitation abrasive water jet was applied for the comminution of mica because cavitation abrasive water jet can make full use of the three effects mentioned above. Besides high speed impacting among particles,cavitation and shearing were also enhanced due to the divergent angle at the outlet of the cavitation nozzle.A JME-200CX transmission electron microscope was used for observing the size distribution of particles.Variance analysis on the experimental results indicates that the effect of cavitation is much more significant than that of collision.The effect of pressure on comminution results becomes less with the decrease of the particle size.

Orthogonal design of experiment and analysis of abrasive water jet cutting on carbon fiber reinforced composites

The carbon fiber reinforced composite is a new type of composite material with an excellent property in strength and elastic modulus,and has found extensive applications in aerospace,energy,automotive industry and so on.However,this composite has a strict requirement on processing techniques,for example,brittle damage or delamination often exists in conventional processing techniques.Abrasive water jet machining technology is a new type of green machining technique with distinct advantages such as high-energy and thermal distortion free.The use of abrasive water jet technique to process carbon fiber composite materials has become a popular trend since it can significantly improve the processing accuracy and surface quality of carbon fiber composite materials.However,there are too many parameters that affect the quality of an abrasive water jet machining.At present,few studies are carried out on the parameter optimization of such a machining process,which leads to the unstable quality of surface processing.In this paper,orthogonal design of experiment and regression analysis were employed to establish the empirical model between cutting surface roughness and machining process parameters.Then a verified model was used to optimize the machining process parameters for abrasive water jet cutting carbon fiber reinforced composites.

INVESTIGATION ON NEW TYPE OF DOUBLY BLENDING ABRASIVE WATER JET NOZZLE SYSTEM WITH HIGHER PERFORMANCE

Based on the two existing abrasive water-jet（AWJ） systems, the dia-jet （or pre-jet） and the post-jet, a new type of abrasive water-jet system is put forward, which combines the dia-jet＇s advantage, low operating system pressure, slender stream jet, and more concentrative abrasive in the blended stream, with merits of post-jet, the less sophisticate apparatus, successive supply of abrasives. The theoretic analysis is brought out in detail, and the nozzle system structure is concisely illustrated. Its relevant experiment results are demonstrated, proving that this new system is effective in various aspects, enlarging penetrating capability without raising system pressure, saving machining power supply, lessening energy loss, etc.

Research and application of water jet technology in well completion and stimulation in China

In recent years, rapid progress in the use of high pressure water jets （HPWJ） has been made in oil and gas well drilling, completion, and stimulation; and good results have been achieved in field applications. Advances in technologies and developments of well completion and stimulation with hydrajet are reviewed in this paper. Experiments were conducted to study the characteristics of abrasive water jetting and to optimize jet parameters, which can provide methods for the well completion and hydrajet fracturing. Deep-penetrating hydrajet perforating can create a 2-3 m clean hole with a diameter of 20-35 mm. Multilayer hydrajet fracturing is a process whereby multiple layers are stimulated in a single run without using mechanical packers, thereby reducing operation procedure and risk. Multilateral radial wells can be drilled using hydraulic jetting up to 100 m in length. The technique to remove sand particles and plugs with rotating self-resonating cavitating water jets in horizontal wellbores has been developed and oilfield-tested, which shows promising, cost effective prospects.

基于GA-GRNN的AWJ强化3D打印AlSi10Mg表面性能实验研究

为提高磨料水射流(Abrasive Water Jet,AWJ)强化工艺对3D打印AlSi10Mg表面性能的强化效果预测的准确性及高效性,首先开展磨料水射流强化AlSi10Mg表面强化实验;然后分别以表面硬度和表面残余应力作为目标,基于遗传算法-广义回归神经网络(Genetic Algorithm-Generalized Ragression Neural Network,GA-GRNN)对实验数据样本进行训练,建立3D打印AlSi10Mg表面性能预测模型;最后,利用遗传算法对建立的神经网络预测模型中的AWJ强化主要参数进行优化。研究结果表明,经过磨料水射流强化后的AlSi10Mg表面硬度与表面残余应力均得到有效提高;建立的GA-GRNN预测模型与校验值误差在2.3%以内,具有较高的准确性;经遗传算法优化后,得到表面硬度最佳参数组合:射流压力为33 MPa,磨料粒径为0.15 mm,靶距为12.4 mm,此时表面硬度为159.25HV;表面残余应力最佳参数组合:射流压力为40 MPa,磨料粒径为0.13 mm,靶距为15 mm,此时表面残余应力为-137.4 MPa。为后续磨料水射流强化零件表面的参数选择提供数据支撑。

MAWJ喷嘴流场数值模拟及磨损预估研究

为得到湍流场流动和喷嘴磨损的特征,该文对喷嘴内液-固两相湍流流场进行数值模拟。利用液-固两相湍流控制方程,建立喷嘴内流场的二维仿真模型,采用交错网格和有限差分法离散方程,通过SIMPLEC法求解。运用FLUENT软件分析速度场、颗粒分布规律、颗粒运动轨迹以及射流特性,得到两相分离流动、出口中心处射流速度最大、颗粒沿管壁分布的特点。研究喷嘴形状与尺寸参数对喷嘴内部流场的影响,结果表明收敛锥角小、聚焦管长的喷嘴,喷射出的射流动能更大,但对喷嘴的磨损也最严重。喷嘴聚焦管出口壁面的磨损率达到1.1×10-4以上,磨损深度在4.7×10-4mm以上,且呈现递增趋势。研究为优化MAWJ。

基于MAWJ刀具钝化表面质量的模型研究

为了获得微磨料水射流加工参数与刀具钝化质量之间的关系,采用正交试验设计方法进行刀具钝化试验研究。利用MikroCAD三维光学测量仪,可以获得刀具表面微观结构和切削刃刃口钝圆半径。基于多元逐步回归分析法,建立刀具钝化表面粗糙度的预测模型,选择射流压力、横移速度、磨料流量、磨料粒度、靶距作为模型变量。利用方差分析和F检验验证回归模型的有效性以及确定影响表面粗糙度的钝化参数,实现微磨料水射流钝化参数的优化。研究结果表明,磨料流量是钝化表面粗糙度最主要的影响因素,预测模型的最大相对误差仅为7.55%。

陶瓷等脆硬板材的磨粒水射流(AWJ)切割技术

陶瓷等脆硬材料板材在普通方法切割加工时容易破碎,也不能切割加工出特别复杂的形状和图案。分析磨料水射流技术原理和材料去除机理,重点介绍几种脆硬材料的水磨料射流切割应用示例,并总结其技术优势和推广意义。

基于MAWJ刀具钝化钝圆半径的回归分析

为得到微磨料水射流加工参数与刀具钝圆半径之间的关系,综合考虑射流压力、横移速度、磨料流量、磨料粒度、靶距5个主要参数对刀具钝化钝圆半径的影响,采用正交试验设计方法设计试验。使用MATLAB软件对试验结果进行方差分析并建立回归模型,得到影响钝圆半径的主要钝化参数和回归模型方程。研究结果表明:磨料流量、横移速度和磨料粒度是影响钝圆半径的主要因素,而射流压力和靶距对其影响较小,可能是由于取值过于密集导致;由回归分析得到的预测模型能够很好地预测钝圆半径的值,其最大相对误差小于7.59%。

基于声发射的超声辅助AWJ冲蚀实验研究

超声辅助磨料水射流具有良好的流动特性,有效提高了射流的加工效率与精度。为了进一步研究其冲蚀能力,通过实验研究了超声辅助磨料水射流(AWJ)冲蚀动态响应规律,基于声发射检测技术研究了超声辅助磨料水射流冲蚀动态响应情况,对信号进行采集处理,分析了射流压力、靶距以及超声振幅等参数对其冲蚀动态响应的影响规律。结果表明:声信号随着射流压力的增大而不断增强,冲蚀深度不断增大;随着靶距与超声振幅的不断增大,声信号呈现先变强后变弱的趋势,冲蚀深度先增大后减小,即存在最佳靶距与最佳超声振幅;声信号频率主要分布于0~200kHz之间。

基于GABP神经网络的超声辅助AWJ冲蚀深度预测及参数优化

多孔HAP生物陶瓷材料硬度低、脆性大,传统生物陶瓷零件切削加工方法容易产生细小裂纹、应力集中等缺陷,微细磨料水射流加工技术可有效解决这些难题。本文采用超声辅助微细磨料水射流对多孔的HAP生物陶瓷块进行加工试验。基于GABP神经网络方法,利用获得试验数据样本来训练和检测GABP神经网络,建立了加工参数如系统压力、靶距、振幅等的微细磨料水射流冲蚀深度预测模型,预测误差和为0.007044,利用遗传算法进行参数寻优,较传统BP神经网络误差和降低了61.506%,大大提高了预测精度,实现了不同参数组合下冲蚀深度的预测。该预测和优化结果表明,当采用系统压力为25MPa,靶距为7.576mm,振幅为13.883μm时,可以获得最大冲蚀深度,其值为3.296mm。

Air flow exploration of abrasive feed tube

An abrasive water-jet cutting process is one in which water pressure is raised to a very high pressure and forced through a very small orifice to form a very thin high speed jet beam. This thin jet beam is then directed through a chamber and then fed into a secondary nozzle, or mixing tube. During this process, a vacuum is generated in the cham- ber, and garnet abrasives and air are pulled into the chamber, through an abrasive feed tube, and mixes with this high speed stream of water. Because of the restrictions introduced by the abrasive feed tube geometry, a vacuum gradient is generated along the tube. Although this phenomenon has been recog- nized and utilized as a way to monitor nozzle condition and abrasive flowing conditions, yet, until now, conditions inside the abrasive feed line have not been completely understood. A possible reason is that conditions inside the abrasive feed line are complicated. Not only compressible flow but also multi- phase, multi-component flow has been involved in inside of abrasive feed tube. This paper explored various aspects of the vacuum creation process in both the mixing chamber and the abrasive feed tube. Based on an experimental exploration, an analytical framework is presented to allow theoretical calculations of vacuum conditions in the abrasive feed tube.

含磨料脉冲射流破岩效果试验研究

为探究脉冲磨料水射流的破岩效果,选用五种不同强度的硬岩,开展了脉冲纯水/磨料水射流破岩试验,并以冲蚀孔尺寸为指标,将脉冲纯水/磨料水射流的破岩效果同连续纯水/磨料水射流进行了对比。结果表明:连续磨料水射流冲蚀岩体过程主要依赖磨料粒子的磨削作用,而脉冲磨料水射流则是连续的水锤效应和磨料粒子磨削作用的叠加;无磨料粒子时,连续水射流破岩主要依赖射流初期的单个水锤效应,而脉冲水射流则是多个连续的水锤压力持续冲击岩石,导致岩体表面出现破碎区。