微磨料空气射流加工玻璃微流道结构研究

采用微磨料气射流加工技术(MAJM),对普通硅酸盐玻璃进行微流道槽加工.对通过掩膜加工与非掩膜加工效果相比较,得出在掩膜加工过程中,由于磨料的二次反弹冲蚀作用,所加工出的槽,槽壁较陡;在掩膜加工过程中,改变喷射距离、喷射压力、喷嘴移动速度和磨料流量四个加工参数,对加工槽的轮廓、加工过程中的材料去除率、磨料的流量效应进行研究,得出当喷射距离为4 mm,喷射压力为0.5 MPa,喷嘴移动速度为1.0 mm/s,磨料流量为0.117 g/s时,加工效果最好.通过倾斜喷射与掩膜加工相结合,研究了磨料磨粒的二次反弹冲蚀现象,为复杂三维微结构的加工,提供了一种新方法.     

Cut Front Geometry Characterization in Cutting Applications of Brass with Abrasive Water Jet

Abrasive water jet (AWJ) cutting is an advanced manufacturing process for machining hard to cut materials. In this study, brass-353 samples of different thicknesses were cut by AWJ using different feed rates to identify the relationships between depth of cut (material thickness), feed rate, and deflection of cutting edge geometry. The effects of material thickness on the AWJ cut surface roughness were investigated and discussed. Deflection of cutting edge geometry in AWJ cutting process was assessed. Cutting edge geometry was characterized by analyzing the surface properties of cut samples.     

A study of abrasive waterjet cutting of metallic coated sheet steels

A study of Abrasive Waterjet (AWJ) cutting of metallic coated sheet steels is presented based on a statistically designed experiment. It shows that AWJ cutting is a viable technology for processing metallic coated sheet steels with good productivity and kerf quality. A scanning electron microscopy analysis indicates that micromachining and plastic deformation are the dominant cutting phenomena in sheet steel processing. Plausible trends and relationships between kerf characteristics and process parameters are discussed. It is found that an optimum water pressure together with small standoff distance between the nozzle and workpiece may be used, while the traverse speed should be selected as high as possible for through cuts in order to increase the cutting rate. Empirical models for kerf geometry and quality are finally established for the prediction and optimization of AWJ cutting performance.     

Influence of kinematic operating parameters on kerf geometry in abrasive waterjet machining of silicon carbide ceramics

Silicon carbide (SiC) is extensively used for manufacturing of highly engineered parts due to its high hardness, low coefficient of friction, wear resistance and high decomposition temperature. However, generating 3D surfaces (e.g. pockets) in such structural ceramics by conventional machining is a difficult task. In this context, abrasive waterjet (AWJ) machining, with its capability to cut any material with low specific cutting forces, seems to be the “ideal” processing technique for such materials; nevertheless machining 3D shapes by AWJ milling is still in its infancy. 3D shapes can be generated by “enveloping” them with successions of jet footprints (kerf geometries) generated by varying the process operating parameters. To enable this, the present work investigates the influence of key kinematic operating parameters (i.e. α-jet impingement angle and v-jet feed rate) on the kerf geometry and its dimensional characteristics. Furthermore, the kerf generation mechanism under multi-pass jet erosion was analysed to get control over erosion depth in multi-pass machining. It was found that by varying α (90°–40°), the symmetric/asymmetric kerf geometry is intimately dependent on the variation of standoff distance (SOD), abrasive particle velocity distributions and their local impact angles accounted across the jet footprint. Variation in v influences the exposure time of material to jet and enhances the erosion capability of abrasives impacting at shallow angle that results in different erosion rates along the kerf profile; this combined effect leads to departure of kerf geometry from simple cosine profile approximation to more elliptical type with the decrease of feed speed. Further, at lower jet feed rates, the depth of erosion increased and the low energy abrasive particles along trailing edge of jet plume get enough time to erode the material that results in variation of slope of kerf walls and hence, overall geometry. Based on these observations, the multi-pass trials showed that the successive passes have to account for both the local impact angles of abrasive particles as well as the actual SOD (SOD+initial kerf depth). In this way, by understanding the influence of key kinematic operating parameters (α and v) on the kerf geometry and its dimensional characteristics, the paper establishes a good basis for developing strategies for controlled 3D AWJ machining of complex shapes.     

便携式磨料水射流系统切割X60钢的试验研究

磨料水射流切割技术能够满足油气储运设备设施应急抢修切割的需求。通过切割试验研究了便携式磨料水射流切割系统对管线钢的切割特性,得到压力、靶距和横移速度对切割深度的影响关系,提出了切割深度预测模型。结果表明:切割深度与切割压力成正比,与靶距和横移速度成反比。切割深度模型对切割结果预测的最大误差为15.04%,最小误差为0.87%,平均误差为5.98%,表明切割深度模型在一定参数范围内能够有效指导切割工艺的制定。     

Improving the cut surface qualities using different controlled nozzle oscillation techniques

One of the principle deficiencies of the abrasive water jet (AWJ) cutting process is wavy striations on the generated cut surface in relatively thick workpieces. A desirable surface finish can be obtained only when the thickness of the workpiece is less than the depth of the smooth zone. Due to the limitation of the waterjet pressures from the current pumping technology, minimisation of striations without the sacrifice of the cutting speed and so increasing the smooth zone depth would constitute a marked improvement in the AWJ machining. In this study, different nozzle oscillation cutting techniques were developed to optimise the AWJ machining process. A comparative study was conducted using different surface texture parameters among straight cutting and different oscillation cutting methods under the same input cutting parameters. Detailed analyses of the cutting results indicate that a significant enhancement in the cut surface quality was obtained by using the controlled cutting nozzle oscillation techniques.     

微磨料空气射流加工技术的发展

微磨料空气射流加工(MAJM)技术是对硬脆材料进行微细加工的一种非常有潜力的技术，特别是对复杂的三维微细结构的加工。微磨料空气射流加工技术是基于传统的喷砂技术发展起来的，通过由空气喷射磨料微粒形成高速气流冲击工件表面而去除工件材料。与其它的加工技术相比，微磨料空气射流加工具有环境友好、易于控制、无热影响区、切口质量好等优点。本文介绍了此技术的基本加工原理、特点以及加工过程中的影响因素，论述了微磨料空气射流加工的材料冲蚀机理和切口特征。重点分析了一些主要的加工参数，例如空气压力、磨料材料、尺寸、供给率、喷嘴的形状和尺寸、喷射距离以及工件材料，对切削性能和切口特征的影响。并提出了微磨料空气射流加工技术中有待进一步深入开展的研究工作。     

磨料射流铣削工艺参数优化

目的对表面粗糙度和材料去除率作为输出参数的磨料水射流铣削45#钢过程进行研究,旨在寻找最优加工参数。方法对射流去除材料机理进行了分析,设计并进行了以磨料粒度、射流压力、横向进给距离、靶距为加工工艺参数的田氏正交实验。采用Minitab对不同实验参数组合下磨料水射流加工45#钢的表面粗糙度、材料去除效率进行了数据分析,并从材料去除机理方面,对4种加工工艺参数对于铣削表面质量和材料去除效率的影响程度和影响趋势,以及各因素之间的交互作用进行了分析。结果对射流铣削面表面粗糙度影响较显著的因素是横向进给距离,射流压力次之;对于材料去除效率,磨料粒径的影响最显著,横向进给距离次之。结论综合材料去除效率和表面粗糙度值,选出最优加工参数:磨料粒径2000目,射流压力120~160 MPa,喷嘴横移距离1.0~1.5 mm,靶距约30 mm。     

后混合水射流喷丸工艺对18CrNiMo7-6渗碳钢表面性能的影响

目的探究不同后混合水射流喷丸工艺对18Cr Ni Mo7-6渗碳钢表面性能的影响。方法运用超景深三维显微系统、三维表面形貌测量系统、X射线残余应力分析仪及HV-1000显微硬度计等,对后混合水射流喷丸前后试样的表面形貌、表面粗糙度、残余应力及显微硬度随层深的变化情况进行分析。结果后混合水射流喷丸时,弹丸和水会对试样表层产生一定的冲蚀、磨损、剪切作用,使试样表面产生新的凹坑。表面粗糙度Ra值随着喷射压力P及喷射靶距H的增加而增大,随着喷嘴移动速度v的增加而减小。试样显微硬度最大值都出现在表面,且随层深的增加,硬度值逐渐减小,喷射压力P=300 MPa时,表面硬度值达到62.8HRC,比试样初始表面硬度值增加了7.35%。试样材料所能引入的残余压应力具有固有最大值σmirs,当引入的残余压应力未达到σmirs时,所产生的最大残余压应力值σmcrs随喷射压力P的增加而增大,但随喷射靶距H和喷嘴移动速度v的改变变化不大。当引入的残余压应力达到σmirs时,所产生的最大残余压应力值σmcrs即为σmirs,不再改变,但是最大残余压应力距表面距离值zm仍会随着喷射压力P的增加而增大。结论后混合水射流喷丸后,试样表面粗糙度变化较大,表层显微硬度有一定提高。残余应力的分布主要与喷射压力P有关,而与喷射靶距H和喷嘴移动速度v关系不大。     

An investigation on kerf characteristics in abrasive waterjet cutting of layered composites

Layered composites are “difficult-to-machine” materials as it is inhomogeneous due to the matrix properties, fibre orientation, and relative volume fraction of matrix. Abrasive waterjet cutting has proven to be a viable technique to machine such materials compared to conventional machining. This paper presents an investigation on the kerf taper angle, an important cutting performance measure, generated by abrasive waterjet (AWJ) technique to machine two types of composites: epoxy pre-impregnated graphite woven fabric and glass epoxy. Comprehensive factorial design of experiments was carried out in varying the traverse speed, abrasive flow rate, standoff distance and water pressure. Using the dimensional technique and adopting the energy conservation approach, the kerf taper angle has been related to the operating parameters in a form of a predictive model. Verification of the model for using it as a practical guideline has been found to agree with the experiments.     

基于量纲分析法的一种磨料水射流打孔模型

水射流的加工过程中非常复杂,涉及到许多参数,对其模型的描述也较为困难。运用量纲分析法,选取对加工过程中影响较大的参数,忽略影响很小的因素,建立了水射流打孔过程的新数学模型,并通过试验验证该模型的误差仅为3%～10%。     

超声辅助磨料水射流加工机制及去除模型研究

为了增强磨料水射流的加工效果,设计了超声辅助微细磨料水射流加工系统。通过喷嘴内变幅杆的超声振动,将声能与射流压力能叠加,增强磨料水射流的脉动行为,形成脉冲射流。通过数值计算的方法研究了流场轴线上的声压分布及磨粒在流场中的运动特性,探究了脉冲射流的加工机制及硬脆材料去除机制。通过切槽实验分析了系统压力、振幅及靶距对冲蚀深度的影响规律,实验结果证明,施加超声振动可有效降低系统压力,最佳靶距为8～10 mm。基于实验结果,利用MATLAB建立了硬脆材料的去除深度预测模型。     

Analysis and modelling of particle velocities in micro-abrasive air jet

Abrasive jet micromachining (AJM) is a non-traditional technology that can effectively remove hard and brittle materials at high cut quality. A key requisite in modelling the AJM process is to determine the velocities of abrasive particles. In this paper, a theoretical analysis for particle velocities within a micro-abrasive air jet is presented and the associated particle velocity models are developed. The particle velocities at the nozzle exit are determined based on the nozzle length, particle mean diameter, particle density, air density and air flow velocity. The distribution of particle velocities along the jet centerline downstream from the nozzle and the particle velocity profile at a jet cross-section are also modelled considering surrounding air entrainment and air-particle interaction. A numerical solution to the models is developed to determine the particle velocities by dividing the nozzle and the jet flow in air into small segments along the jet axial direction. The developed models are finally verified by comparing the calculated particle velocities with those from a particle image velocimetry (PIV) measurement of the velocity distribution in micro-abrasive air jets. It is shown that the model calculations and the corresponding experimental results are in good agreement with less than 4% average errors.     

基于LS-DYNA仿真的射流加工参数分析

目的通过LS-DYNA对磨料射流冲蚀切削进行仿真,研究相关工艺参数对切削参数的影响。方法采用磨料水射流对Al_2O_3陶瓷进行了单点冲蚀仿真和切削仿真研究,其中水和磨料粒子采用SPH方法建模,氧化铝陶瓷工件采用FEM方法建模,并通过SPH-FEM耦合算法,实现射流冲蚀切削过程的仿真。结果分析射流冲蚀过程仿真和切削过程仿真可知,射流加工前期,由于射流中磨粒碰撞与反弹,使壁面成不规则"V"型。初始阶段,切深随计算时间呈线性增加,同时壁面对磨粒产生制约作用,从而使加工处的孔深基本不再增加。由于磨粒在冲蚀处壁面底部的冲蚀作用,使凹坑底部宽度增加并迅速趋于稳定。同时切削仿真与冲蚀仿真也存在一定区别,主要由于切削过程设定了移动速度。结论将仿真结果与实验结果进行比较可知,切削深度随着泵压的增大而成线性增大,切深随磨料流量的增大而增大,随靶距和横移速度的增大而减小。其中切深与磨料流量、靶距、横移速度均为非线性关系,工件最大切深与计算时间不呈线性关系增长。     

A study on surface roughness in abrasive waterjet machining process using artificial neural networks and regression analysis method

In the present study, artificial neural network (ANN) and regression model were developed to predict surface roughness in abrasive waterjet machining (AWJ) process. In the development of predictive models, machining parameters of traverse speed, waterjet pressure, standoff distance, abrasive grit size and abrasive flow rate were considered as model variables. For this purpose, Taguchi's design of experiments was carried out in order to collect surface roughness values. A feed forward neural network based on back propagation was made up of 13 input neurons, 22 hidden neurons and one output neuron. The 13 sets of data were randomly selected from orthogonal array for training and residuals were used to check the performance. Analysis of variance (ANOVA) and F-test were used to check the validity of regression model and to determine the significant parameter affecting the surface roughness. The statistical analysis showed that the waterjet pressure was an utmost parameter on surface roughness. The microstructures of machined surfaces were also studied by scanning electron microscopy (SEM). The SEM investigations revealed that AWJ machining produced three distinct zones along the cut surface of AA 7075 aluminium alloy and surface striations and waviness were increased significantly with jet pressure.     

Kerf characteristics in abrasive waterjet cutting of ceramic materials

An abrasive water jet (AWJ) can provide a more effective means for precision cutting of ceramic materials as compared with conventional machining methods, but many aspects about this cutting technology are still under flux and development. In this study, experimental techniques based on statistical experimental design principles and theoretical investigations were conducted to study AWJ cutting of alumina-based ceramics. Semi-empirical cutting depth equations are determined for the prediction and optimization of the AWJ cutting performance. Topographical characteristics of uncut-through kerf and the effects of various parameters are discussed. In addition, visualization studies are conducted to develop further understanding of the macromechanics of the AWJ cutting process.     

Modelling of Abrasive Waterjet Machining: A New Approach

Abrasive waterjet (AWJ) machining is one of the recent non-traditional methods starting to be used widely in industry for material removal of different materials. The cutting performance of AWJ is achieved by a very high speed, small-scale erosion process. In this paper, a modified form of Finnie's model for erosion is developed for application to AWJ. This modified form is able to deal with curved surfaces rather than flat surfaces only. Furthermore, the new modelling approach is capable of simulating multiple particle erosion. This approach uses standard material properties and requires no calibration constants. The modelled results agreed well with both experimental and analytical data.     

Abrasive enhanced electrochemical slurry jet micro-machining: Comparative experiments and synergistic effects

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.     

Erosion resistance of laser clad Ti-6Al-4V/WC composite for waterjet tooling

In waterjet operations, milled surfaces are left with some undesirable dimensional artefacts, thus the use of abrasion resistant mask has been proposed to improve the surface quality of machined components. In this study, the erosion performance of laser clad Ti-6Al-4V/WC composite coating subjected to plain water jet (PWJ) and abrasive water jet (AWJ) impacts to evaluate its potentials for use as waterjet impact resistant mask material and coating on components was investigated. Results showed that composite with 76 wt.% WC composition subjected to PWJ and AWJ impacts offered resistance to erosion up to 13 and 8 times that of wrought Ti-6Al-4V respectively. Scanning electron microscopy (SEM) examination of the eroded composite surfaces showed that the erosion mechanism under PWJ impacts is based on the formation of erosion pits, tunnels and deep cavities especially in the interface between the WC particles and the composite matrix owing to lateral outflow jetting and hydraulic penetration. Composite suffered ploughing of the composite matrix, lateral cracking and chipping of embedded WC particles and WC pull-out under AWJ impacts. The composite performance is attributed to the embedded WC particles and the uniformly distributed nano-sized reaction products (TiC and W) reinforcing the ductile β-Ti composite matrix, with its mean hardness enhanced to 6.1 GPa. The capability of the Ti-6Al-4V/WC composite coating was demonstrated by effective replication of a pattern on a composite mask to an aluminium plate subjected to selective milling by PWJ with an overall depth of 344 μm. Thus, composite cladding for tooling purpose would make it possible to enhance the lifetime of jigs and fixtures and promote rapid machining using the water jet technique.     

Electrochemical micromachining using flat electrolyte jet

This paper describes the development of a novel machining method capable of micro-milling and electrochemical turning using a flat electrolyte jet. The workpiece is machined locally in the area hit by the jet which moves when an electrical current is applied to it. Use of a flat jet in place of a cylindrical jet improves milling speed, and turning process is realized by the flat jet hitting the surface of the rotating cylindrical workpiece. Since depth of cut can be determined by the electrical current or dwelling time of the jet on the surface, there is no need for precise positioning of the nozzle against the workpiece.