Abrasive water and slurry jet micro-machining techniques for fabrication of molds containing raised free-standing micro-features

The demand for metallic micro-molds that can be used for inexpensive mass production of polymeric microfluidic chips is increasing. Existing manufacturing techniques such as soft-lithography and photolithography can require multiple time-consuming steps, especially when the aim is to create three-dimensional features. In this study, the feasibility of using abrasive water jet machining (AWJM) and abrasive slurry jet machining (ASJM) to fabricate such micro-molds in Al6061-T6 and SS316 was studied. Jet raster scans under various combinations of process parameters were used in order to machine micro-pockets containing free-standing structures, representing molds for casting microfluidic chips with channel networks. As expected, for both materials and using both ASJM and AWJM, the pocket roughness decreased as the distance between adjacent raster scans (step size) decreased, but the lowest waviness occurred at an intermediate step size. The best quality pockets were achieved on SS316 using ASJM with the intermediate step size and the highest possible slurry mass flow rate. Unmasked machining could not be used to fabricate molds with sharp-edged intersecting features, and a novel hybrid AWJM/ASJM masked machining technique was thus introduced. An undercut and an undesirable erosion near the edges of the mask formed if the position of the last raster scan closest to the mask was not carefully controlled. Possible reasons for these phenomena were discussed in terms of the likelihood of jet deflection off the machining kerf and mask, and the resulting erosion due to secondary slurry flow. By careful selection of the process parameters, it was demonstrated that high quality molds with both single and intersecting free-standing structures at multiple heights could be fabricated, thus making three-dimensional microfluidic chip mold fabrication feasible.     

Erosive smoothing of abrasive slurry-jet micro-machined channels in glass,PMMA, and sintered ceramics: Experiments and roughness model

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%.     

Modelling the erosion rate in micro abrasive air jet machining of glasses

Micro abrasive jet machining (MAJM) is an economical and efficient technology for micro-machining of brittle material like glasses. The erosion of brittle materials by solid micro-particles is a complex process in which material is removed from the target surface by brittle fractures. The rate of material removal is one of the most important quantities for a machining process. Predictive mathematical models for the erosion rates in micro-hole drilling and micro-channel cutting on glasses with an abrasive air jet are developed. A dimensional analysis technique is used to formulate the models as functions of the particle impact parameters, target material properties and the major process parameters that are known to affect the erosion process of brittle materials. The predictive capability of the models is assessed and verified by an experimental investigation covering a range of the common process parameters such as air pressure, abrasive mass flow rate, stand-off distance and machining time (for hole machining) or traverse speed (for channel machining). It shows that model predictions are in good agreement with the experimental results.     

电化学磁粒光整加工实验

从电化学磁粒光整加工对材料去除量和表面粗糙度影响规律的实验结果表明,由于磁粒加工过程中不断地去除钝化膜,使表面露出的新基体,从而进一步加速了电化学过程,实现表面整平,磁粒光整加工和电化学过程的复合,使光整加工效率和表面质量得到提高。     

微磨料浆体射流的浆体配制及钻孔性能研究

微磨料浆体射流技术是在微磨料水射流加工技术基础上发展起来的一种新技术。通过添加分散剂和悬浮剂来提高浆体的沉降稳定性;为了配制出优质钻孔浆体,研究了磨料质量浓度、磨料种类、分散剂体积分数和悬浮剂体积分数对钻孔加工的影响,并研究了分散剂体积分数和悬浮剂体积分数对浆体沉降稳定性的影响。研究结果表明：磨料质量浓度存在最佳取值;分散剂并非一定能改善颗粒的沉降稳定性,这与磨料种类、磨料质量浓度和分散剂体积分数等有关;悬浮剂能够改善浆体的悬浮性,其体积分数影响浆体的沉降稳定性和钻孔效果。     

Effect of workpiece properties on machinability in abrasive jet machining of ceramic materials

Abrasive jet machining (AJM), a specialized form of shot blasting using fine-grained abrasives, is an attractive micro-machining method for ceramic materials. In this paper, the machinability during the AJM process is compared to that given by the established models of solid particle erosion, in which the material removal is assumed to originate in the ideal crack formation system. However, it was clarified that the erosion models are not necessarily applicable to the AJM test results, because the relative hardness of the abrasive against the target material, which is not taken into account in the models, is critical in the micro-machining process. In contrast to conventional erosion by large-scale particles, no strength degradation occurs for the AJM surface, which is evidence that radial cracks do not propagate downwards as a result of particle impacts.     

Jet properties and mixing chamber flow in a high-pressure abrasive slurry jet: part I—measurement of jet and chamber conditions

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.     

三相射流去毛刺工艺的试验研究

金属切削毛刺是影响精密零件棱边质量及使用性能的主要因素之一。三相射流去毛刺技术是一种柔性工艺方法。三相射流去毛刺的作用过程和机理非常复杂,不仅与射流及作用条件有关,而且与材料的性质及毛刺的形状密切相关。通过正交试验,分析了三相射流工作条件对材料去除量和冲蚀深度的影响,讨论了磨料粒度与加工表面粗糙度的关系。     

激光冲击效应下的力学电化学微细刻蚀加工

在所构建的纳秒脉冲激光电化学加工系统中,利用激光辐照和脉冲电化学刻蚀复合的方法对铝合金进行了加工试验,研究了激光穿过溶液作用于物质时产生的力效应和电化学效应对加工质量的影响.试验结果表明:高能脉冲激光透过电解液辐照在工件表面时,激光在电解液中产生的冲击波力效应和射流冲击力效应会使工件发生弹性变形,从而改变电极电势,提高电流密度,加速了对工件的刻蚀.激光产生的力效应能够去除加工区的钝化层,使其发生电化学反应,而非加工区不发生反应,从而显著增强了电化学的定域蚀除能力.最后,利用力学电化学效应,在浓度为0.5 mol/L的NaNO3溶液中实现了线宽140 μm左右、深宽比较大的微细刻蚀加工,获得了较好的加工质量和成形精度.     

基于流体自激的磨料水射流加工仿真与实验

针对先进陶瓷材料的高效、精密加工,提出了一种基于流体自激的新型磨料水射流加工方法——自激振荡磨料水射流加工(SEO-AWJM).采用ANSYS Fluent大涡模拟模型进行了流体仿真,仿真结果表明:当入口流速为135 m/s,腔长为4 mm时,下游喷嘴出口脉冲率最大达到28.47％.射流束的脉冲特性使得工件表面停滞层周...     

磨料射流切割机的试验研究

本文介绍了前混合式磨料射流切割机的结构,工作原理以及用该机对金属和非金属材料进行的切割试验,指出射流工作压力、喷射靶距、喷嘴横移速度、磨料重量比浓度等是影响工作能力的主要因素,喷嘴直径及其内腔结构、磨料粒子尺寸等也是影响割缝宽度及表面形态的因素.试验对此表明,它比纯高压水射流和后混合式磨料射流切割机性能优越,是一种新型的、有广阔应用前景的工业切割设备.     

磨料水射流切割玻璃钢复合材料试验研究

磨料水射流对材料具有极强的冲蚀作用,并在冲蚀过程中不改变材料的力学、物理和化学性能,适于切割热敏、压敏、脆性和复合材料。文中选择压强、靶距、横移速度和砂流量四因素,试验研究了各因素对玻璃钢切割断面深度比值q的影响。在磨料流量为0．060kg／min、切割速度为650mm／min、靶距为5mm条件下,切割玻璃钢样件,没有出现分层和起鳞现象,切割表面光滑,充分证实了磨料水射流切割复合材料的优势。     

Abrasive waterjet machining simulation by SPH method

Abrasive waterjet machining (AWJM) is a non-conventional process. The mechanism of material removing in AWJM for ductile materials and existing erosion models are reviewed in this paper. To overcome the difficulties of fluid–solid interaction and extra-large deformation problem using finite element method (FEM), the SPH-coupled FEM modeling for abrasive waterjet machining simulation is presented, in which the abrasive waterjet is modeled by SPH particles and the target material is modeled by FE. The two parts interact through contact algorithm. The creativity of this model is multi-materials SPH particles, which contain abrasive and water and mix together uniformly. To build the model, a randomized algorithm is proposed. The material model for the abrasive is first presented. Utilizing this model, abrasive waterjet penetrating the target materials with high velocity is simulated and the mechanism of erosion is depicted. The relationship between the depth of penetration and jet parameters, including water pressure and traverse speed, etc., are analyzed based on the simulation. The results agree with the experimental data well. It will be a benefit to understand the abrasive waterjet cutting mechanism and optimize the operating parameters.     

磨料液体射流抛光技术研究进展

论述了磨料液体射流抛光过程中的材料去除机理,介绍了磨料液体射流加工系统平台的国内外研究成果。从速度变化、材料去除、表面演化、表面粗糙度、数值模拟五个方面阐述了磨料液体射流数学模型的构建状况。系统分析了主要工艺参数如磨粒动能、射流压力、磨料、喷射角度、喷射距离、添加剂对加工结果的影响规律,并总结了磨料液体射流抛光技术发展历程。最后针对其将来的研究方向与内容给出了进一步的建议与展望。     

磨料浆体射流切割机床及切割性能研究

将磨料浆体射流技术应用于切割领域，研制出相应的切割机床，避开了国外该项技术中的高压动密封问题，并对该机床的切割性能进行了正交试验，同时，将磨料浆体射流机床与前混合磨料水射流机床的切割性能进行了比较研究,　研究表明，影响磨料浆体射流切割性能的主要因素依次是切割速度、切割压力和靶距；在相同切割条件下，磨料浆体射流机床与前混合磨料水射流机床的切割力大致相同，但磨料浆体射流机床的切割质量明显好于后者，切割能耗大大低于后者。     

基于磨料水射流的螺杆转子加工新方法研究

螺杆转子传统加工过程中存在刀具磨损和过高切削热量等难题。为此,将具有无刀具磨损、切削热量低、绿色环保特点的磨料水射流加工方法引入螺杆转子加工研究之中,提出了磨料水射流多轴联动加工螺杆转子的新方法,以提高转子加工精度和效率。采用任意拉格朗日与欧拉方法构建了转子加工模拟模型,将模拟分析结果与实验数据进行比较,验证了模拟模型的正确性。最后,通过磨料对水射流多轴联动加工模拟结果的分析,证明了螺杆转子加工新方法的合理性。     

水射流加工中过程参数的多目标优化设计研究

针对水射流切割工艺中过程参数的优化选择进行了研究,考虑切割速率和比能消耗两个目标函数,采用改进非支配排序遗传算法(NSGAII)研究了多目标优化设计问题。根据Pareto最优解形成决策矩阵,基于信息熵法得到属性的权重,利用逼近理想解的排序方法(TOPSIS)进行多属性决策。讨论了一个木材切割过程中参数优化的算例,分析了喷嘴直径、间隙、压力等参数对切割速率和比能消耗的影响。综合采用多目标优化和多属性决策技术,可以迅速选择生产过程中的系统参数。     

Effect of impact angle on the slurry erosion–corrosion of 304L stainless steel

This communication describes an investigation of the effect of impact angle on slurry erosion–corrosion of stainless steel using a new slurry erosion rig. With the new apparatus, it is possible to measure the individual erosion events under impact as both electrochemical current/time transients, and mechanical transients through acoustic emission (AE) simultaneously. Each sharp rise observed in the electrochemical current transient under particle impact is accompanied by an AE event. These sharp current rises are attributed to the rupture or removal of the oxide film on the surface by the abrasive particles. The correlation between the current rise and the maximum of the AE event, although scattered, shows an increase with decreasing impact angle. The current transients due to individual erosion events show that on the average, the current rise is greater and the rise time is longer at oblique angles compared with those at normal incidence. The degree of denudation of the metal surface by individual particle impingements, the process which strips the surface of its passivity, increases at more oblique angles. Weight loss measurements demonstrate that the synergistic effect between erosion and corrosion is enhanced by a more oblique angle of impact. The origin of the synergism is discussed.     

淹没磨料水射流与非淹没磨料水射流冲蚀破岩效果比对分析

磨料水射流的冲蚀能力主要依赖于磨料颗粒所获得的能量,对非淹没磨料水射流和淹没磨料水射流的冲蚀实验结果进行比对,从能量角度和磨料颗粒速度变化角度分析了造成非淹没磨料水射流和淹没磨料水射流的冲蚀效果差异的原因。     

The drilling of Al2O3 using a pulsed DC supply with a rotary abrasive electrode by the electrochemical discharge process

The electrochemical discharge machining (ECDM) process has the potential to machine electrically non-conductive high-strength, high-temperature-resistant (HSHTR) ceramics, such as aluminum oxide (Al₂O₃). However, the conventional tool configurations and machining parameters show that the volume of material removed decreases with increasing machining depth and, finally, restricts the machining after a certain depth. To overcome this problem and to increase the volume of material removed during drilling operations on Al₂O₃, two different types of tool configurations, i.e., a spring-fed cylindrical hollow brass tool as a stationary electrode and a spring-fed cylindrical abrasive tool as a rotary electrode, were considered. The volume of material removed by each electrode was assessed under the influence of three parameters, namely, pulsed DC supply voltage, duty factor, and electrolyte conductivity, each at five different levels. The results revealed that the machining ability of the abrasive rotary electrode was better than the hollow stationary electrode, as it would enhance the cutting ability due to the presence of abrasive grains during machining.