磨粒流抛光伺服阀阀芯喷嘴的颗粒冲蚀磨损研究

伺服阀是伺服控制系统中的一种核心伺服控制元件,阀芯喷嘴的内表面质量往往会直接影响伺服阀的使用性能。目前传统的加工工艺方法难以保证其质量及合格率,磨粒流抛光技术为改善伺服阀阀芯喷嘴的表面质量提供了有效的技术方案。以磨粒流抛光伺服阀阀芯喷嘴为研究对象,根据冲蚀磨损机理采用离散相模型对阀芯喷嘴通道内的颗粒进行数值模拟分析,研究分析了不同入口速度、颗粒粒径以及温度对颗粒冲蚀磨损性能的影响,得出颗粒的冲蚀磨损量随着入口速度、颗粒粒径以及温度的增加而增加,对阀芯喷嘴磨粒流抛光技术的发展具有重要的理论意义和工程应用价值。     

基于大涡模拟的伺服阀喷嘴磨粒流抛光数值研究

现代机械零件发展的越来越精密,对零件表面要求也越来越高。为了降低微小孔的表面粗糙度,提高表面质量,选择伺服阀阀芯喷嘴作为研究对象,基于mixture多相流模型和大涡数值模拟(LES)方法,通过构建伺服阀喷嘴三维模型,运用流体力学理论知识,分别从不同进口速度下的动压和湍流粘度对伺服阀喷嘴进行流态仿真分析,并且对不同速度下的流体的涡旋分布状态进行了分析对比。通过数值研究可知,适当增加进口速度,可以提高磨粒流在抛光时的平均速度,从而提高磨粒流抛光光整加工能力。     

大涡模拟Smagorinsky模型用于磨粒流精密加工喷嘴的质量控制研究

为研究固液两相磨粒流加工喷嘴小孔过程中的流场分布、涡旋形成规律及涡旋的存在对磨粒流加工的影响机制,采用Smagorinsky亚格子模型对磨粒流加工喷嘴小孔的流道进行大涡数值模拟,并使用磨粒流对变直径喷嘴工件进行加工试验。数值模拟发现磨粒流流体中磨粒与壁面的碰撞与剪切作用随流体的速度增大而增大,同一截面的速度存在速度差,其中还伴随涡旋的存在;通过试验研究发现：经固液两相磨粒流加工后的喷嘴小孔表面质量得到明显提高,喷嘴经过四次不同入口速度的磨粒流加工后大孔处表面粗糙度Ra由1.24 μm降至0.542 μm,小孔处表面粗糙度Ra由1.21 μm降至0.437 μm。结论显示固液两相磨粒流加工技术可有效提高被加工喷嘴工件的内表面质量,加工时同一截面的速度存在速度差,速度差的存在利于涡旋的形成,涡旋的存在利于提高磨粒流加工过程的剪切作用,有助于获得高质量的喷嘴小孔内通道表面。     

固液两相磨粒流研抛工艺优化及质量影响

为研究磨粒流对异形腔孔内壁表面以及微小孔的研抛去毛刺等的作用效果,探讨了研抛过程中磨粒流各工艺参数与加工质量间的作用关系。以共轨管这种非直线管为研究对象,对磨粒流抛光共轨管过程进行数值模拟研究,探索各工艺参数对磨粒流研抛的影响。数值模拟结果表明:控制碳化硅体积分数可以改变磨粒流研抛过程中的粘温特性,从而可以控制磨粒流的研抛质量。然后采用正交方法设计实验方案,实验过程中,采集抛光过程中温度和粘度的变化数据,分析磨粒流研抛中粘温特性对磨粒流研抛质量的影响。试验与数值模拟结果表明,在磨粒流研抛共轨管过程中SiC的体积分数比出口压力的极差秩大,磨粒流研抛确实可有效改善工件表面质量。而且本文还进一步得出在本试验条件下,磨粒流研抛共轨管的最佳工艺参数:出口压力为5 MPa,SiC体积分数为0.25%,SiC目数为80,同时获得了表面粗糙度与体积分数的回归方程,可用于指导磨粒流实际研抛生产工作。     

前置级冲蚀磨损对射流偏转板伺服阀的影响

射流偏转板伺服阀前置级油液高速流动时,油液中的颗粒物会对伺服阀前置级产生冲蚀磨损导致伺服阀的性能下降。采用数值仿真的方法对冲蚀磨损前后射流偏转板伺服阀前置级流场进行计算,通过曲线拟合得到两接收孔压差与偏转板位移的关系;将其与射流偏转板伺服阀的AMESim模型结合分析冲蚀磨损前后伺服阀位移及空载流量的变化。结果表明:冲蚀磨损导致射流偏转板伺服阀前置级两接收孔压差减小;在相同的输入条件下射流偏转板伺服阀阀芯位移减小,空载流量降低。     

铝合金手机外壳超精密镜面加工工艺的实验研究

通过工艺实验研究超精密镜面研抛技术在铝合金手机外壳精密超精密镜面加工中的应用,获得表面粗糙度为R a0.026μm的铝合金加工表面。通过优化研抛压力、研抛盘转速、研磨垫质地和硬度、磨料磨粒大小等参数的匹配组合,能够有效提高加工效率、改善加工表面质量,减小表面粗糙度值。     

汽轮机喷嘴环磨粒流抛光工艺参数优化

为解决大型汽轮机喷嘴环磨粒流抛光的工艺技术问题,研究了喷嘴环磨粒流抛光工艺,分析了抛光工艺因素对表面质量的影响。根据喷嘴环结构的特点,结合抛光压力损失规律,设计了喷嘴环磨粒流抛光专用夹具;利用ANSYS有限元软件对叶片进行压力载荷静态分析,确定了合理的磨粒流抛光压强范围;采用信噪比实验设计法对工艺参数进行分析,得出工艺参数对表面粗糙度的影响关系及最优抛光工艺参数。通过实验验证可知,喷嘴环表面质量得到显著提升,可满足喷嘴环抛光表面粗糙度小于0.4μm以及允许变形量小于0.1mm的图纸要求。     

海水泵球型配流阀冲蚀磨损的数值模拟研究

海水中存在大量污染物,其中悬沙颗粒会对海水液压元件造成不同程度的冲蚀磨损;配流阀的冲蚀磨损会降低海水泵的容积效率,使用离散项模型对水介质下悬沙颗粒对海水泵配流阀的冲蚀磨损现象进行数值模拟计算,研究阀口开度与入口流速对球型配流阀阀芯及阀座冲蚀磨损的影响.结果表明:不同阀口开度下阀座表面的冲蚀位置有明显差异,而阀芯表面冲蚀...     

水压伺服阀液压桥路的正交设计与分析

提出了一种前置级采用两级串联固定阻尼孔的双喷嘴挡板水压伺服桥路模型,并对其进行了参量敏感性分析。探讨了喷嘴挡板位移、阀芯运动速度与阀芯两端压力的关系;运用正交设计方法研究了喷嘴直径、串联固定阻尼孔直径、阀芯直径及其运动速度、喷嘴挡板与喷嘴之间初始距离等参量对水压桥路特性的影响。结果表明,喷嘴直径以及喷嘴与挡板之间中位距离越小,阀芯与阀套之间配合间隙越大,阀芯直径越大,阀芯与阀套之间叠合长度越短,压力源压力越高,桥路控制的线性度越好;对于采用二级节流的水压伺服桥路,第一级固定阻尼孔直径越小,第二级固定阻尼孔直径越大,喷嘴前端流道直径越小,阀芯与阀套之间配合间隙以及阀芯直径越大,桥路响应就越快。这些研究结果为水压伺服阀样机的研制奠定了理论基础。     

磨粒流加工壁面效应研究

数值模拟了圆柱内表面的初始粗糙度、入口流速和内孔直径对壁面流场压力、局部压差及剪切力的影响规律,分析了入口处流场速度和剪切力的形成过程,从磨粒切削作用角度剖析了圆柱内表面入口处过抛现象的形成原因,结合磨粒流加工试验揭示了各参数对壁面效应的影响规律。理论分析和试验结果表明：增大圆孔直径或减小入口流速能有效改善磨粒流流场压力的均匀性,初始表面粗糙度对流场压力数值及其局部压差有微弱影响;入口处圆孔壁面速度突变引起剪切力突变,从而导致磨粒流加工过抛现象;初始表面粗糙度Ra=0.296μm时有利于减弱磨粒流加工的壁面效应,而Ra=4.273μm时有利于提高材料去除速率。     

喷油嘴微孔磨粒流抛光数值模拟与试验

以喷油嘴喷孔为研究对象,采用kε固液两相Mixture湍流模型对磨粒流抛光过程中流场分布规律进行数值模拟,并通过正交试验探索了抛光压力、磨料浓度、磨粒粒径及加工时间等工艺参数对被抛光微孔表面粗糙度的影响规律。结果表明：喷油嘴微孔磨粒流单向循环抛光加工有利于改善喷孔结构;流道表面粗糙度与各加工参数均成负相关关系,且受抛光压力及磨料浓度影响显著。通过试验获得了最优参数组合,在此条件下喷油嘴微孔表面粗糙度值(Ra)由初始的1.16μm降至0.20μm。     

Effects of particle size, polishing pad and contact pressure in free abrasive polishing

The objective of this research is to better understand the mechanisms of material removal in the free abrasive polishing process. Experiments were carried out to understand the effects of particle size, polishing pad and nominal contact pressure on the wear rate and surface roughness of the polished surface. A theoretical model was developed to predict the relationship between the polishing parameters and the wear rate for the case of hard abrasive particles sandwiched between a soft pad and a workpiece (softer than the abrasive particles). Experimental results and theoretical predictions indicate that the wear rate increases with an increase in particle size, hardness of polishing pad and nominal contact pressure, and with a decrease in elastic modulus of the polishing pad. Surface roughness increases with an increase in particle size and hardness of polishing pad, and nominal contact pressure has little effect on the roughness. A dimensionless parameter, wear index which combines all of the preceding parameters, was introduced to give a semi-quantitative prediction for the wear rate in free abrasive polishing. It is also suggested that when polishing hard material, in order to achieve a high materials removal rate and a smooth surface, it is preferable to use diamond as the polishing particles because of their high deformation resistance.     

三相旋流抛光磨粒运动的测量与微气泡补偿

研究了气液固三相旋流流场抛光机理和规律。设计了三入口的抛光加工流道,对气液固三相旋流抛光流场进行了数值模拟。基于模拟结果设计了气液固三相磨粒流旋流流场测量平台,并通过粒子图像测速法(PIV)测量了微气泡补偿条件下气液固三相旋流抛光的流场参数,获得了微气泡补偿区域流场的运动图像、速度矢量图和涡量图。PIV测量试验数据显示:在微气泡补偿区域,磨粒速度主要集中在30m/s到80m/s,同一测量点高速磨粒出现频率明显增加,少数磨粒速度达到100m/s以上;磨粒平均速度从33.8m/s增大到44.2m/s,经4h抛光后硅片表面最大粗糙度从10.4μm下降到1.3μm。理论和试验研究表明,气液固三相旋流抛光流场中微气泡溃灭引发的空化冲击效应可增大磨粒动能,提高抛光效率,实现B区域的均匀化抛光。     

粘结Fe＋SiC磁性磨料的研究

研究了粘结Fe SiC磁性磨料的成分、粒度以及研磨时间对几种钢件研磨表面粗糙度的影响,并通过扫描电镜分析研磨表面形貌,探讨了研磨机理。试验结果表明：该磁性磨料具有良好的研磨效果,而磨磨机理是SiC粒子对钢件表面的低应力磨料磨削。     

Study of solid particle erosion on AISI D2 using angular silicon carbide and steel round grit particles

Abstract

In this study, the performance of AISI D2 steel subjected to solid particle erosion tests was analysed. This material has applications for tools and dies for blanking, wood milling cutters, cold-extruding and other operations requiring high compressive strength and excellent wear resistance. The erosion tests performed by using a rig developed according to some parameters of the ASTM G76-95 standard. Two abrasive were used, angular silicon carbide (SiC) and steel round grit, both, with a particle size of 400–420 μm. This allowed comparing the erosion severity of each abrasive particle. The tests were conducted using four different incident angles 30, 45, 60 and 90° with a particle velocity of 24±2 m s^?1 and a flow rate of 21±2·5 g min^?1 for silicon carbide and 48·5±3·5 g min^?1 for the steel round grit. The exposure testing time was 10 min. Subsequently, the surface damage was analysed with a scanning electron microscope (SEM) to identify the wear mechanisms. Additionally, atomic force microscopy (AFM) was conducted in order to obtain roughness of the surface damage at 60°. The results indicated that higher amount of mass loss was obtained by angular silicon carbide particles.     

A novel polishing method for single-crystal silicon using the cavitation rotary abrasive flow

Traditional low-pressure abrasive flow polishing can produce highly smooth surfaces, but the efficiency of this method is too low for polishing of hard-brittle materials parts. This paper proposes a novel cavitation rotary abrasive flow polishing (CRAFP) method. The energy generated from the cavitation bubble collapse is used to increase the kinetic energy of the abrasive particles in the low-pressure abrasive flow and the motion randomness of the abrasive particles near the wall; thereby, the efficiency and quality of low-pressure abrasive flow polishing are improved. The CRAFP mechanism was first introduced, and then the characteristics of the CRAFP process were investigated using computational fluid dynamics (CFD)-based abrasive flow simulation. Subsequently, a single-crystal silicon wafer polishing test was carried outperformed to verify the validity of the CRAFP method. The polishing results were compared with those of the traditional low-pressure abrasive flow polishing method. After 8 h of polishing using the CRAFP method and the traditional low-pressure abrasive flow polishing method, the surface roughness of the workpiece decreased to7.87 nm and 10.53 nm, respectively. Furthermore, by starting at similar initial roughness values, the polishing time required to reduce the roughness to 12 nm was 3.5 h and 6 h, respectively. The experimental results demonstrated that CRAFP can satisfy the surface requirements of single-crystal silicon (R_a < 12 nm) and exhibit high polishing efficiency and good quality.     

硅晶片化学机械抛光材料去除机制与模型

通过分析软质层的形成、作用以及纳米磨料的自身变形对材料去除的影响，改进了CMP过程的接触力学模型；分析了纳米磨料自身变形量对磨料嵌入硅晶片基体材料的深度的影响，以及纳米磨料硬度对抛光表面粗糙度的影响。结果表明：软质层的存在增加了单个纳米磨料所去除材料的体积，且对基体材料有保护作用，减小了纳米磨料嵌入基体材料的深度；纳米磨料的自身变形抵消了纳米磨料嵌入基体材料的切削深度，从而也决定了抛光表面的粗糙度；纳米磨料的自身变形量与纳米磨料的硬度有关，硬度低的纳米磨料自身变形量大，因而切削深度小，抛光后表面的粗糙度值低。     

CMP behavior of alumina/metatitanic acid core–shell abrasives on sapphire substrates

The abrasive is one of the important influencing factors during the chemical mechanical polishing (CMP) process. Although α-alumina is one of the most commonly used sapphire polishing abrasives due to its high hardness, it often results in surface damage. To receive lower surface roughness and high material removal rate, a common approach is to modify the surface of alumina. In this work, a series of alumina/metatitanic acid composite abrasives with core–shell structure were synthesized. The CMP performances of the pure alumina and alumina/metatitanic acid core–shell abrasives on sapphire substrates were investigated after polishing under the same conditions. Experimental results indicate that the alumina/metatitanic acid core–shell abrasives can not only improve the surface quality, but also further enhance the material removal rate. Furthermore, through the X-ray photoelectron spectroscopy test, this study investigated the chemical effect mechanism of the alumina/metatitanic acid core–shell abrasives in sapphire CMP. The results show that solid-state chemical reactions occur between metatitanic acid shell and sapphire surface during CMP process. We also investigated the mechanical friction mechanism through abrasive wear and adhesive wear.     

高压磨料水喷嘴磨损实验研究

本文采用硬质合金和陶瓷材料制成喷嘴．在高压水设备上进行了磨损实验研究。结果表明，影响其耐磨性主要因素是喷嘴材料、表面硬度及高压磨料水工艺参数。同时采扫描电镜对喷嘴磨损表面进行了分析。