金属增材制造液压阀块内部流道优化设计研究

液压阀块是液压系统的重要组成部分，采用锻造-钻铣传统方法加工的流道只能采用直孔形式并且管路交叉沟通不灵活。选区激光熔融增材制造克服了传统加工的限制，可实现两端盲孔流道加工、任意走向及任意曲率流道加工，并能剔除非必需质量，实现液压阀块的集成化、轻量化和节能化设计。与传统阀块相比，金属增材制造液压阀块体积降低30%以上，重量降低50%以上。但是金属增材制造受到悬垂部件阈值角度限制，传统圆形截面流道加工存在局部支撑结构，而阀块内部复杂流道的支撑结构很难去除，因此削弱了增材制造技术在轻量化和节能化方面的效果。以减少内部流道的辅助支撑为目标，提出采用异形截面流道的设计方案，通过理论分析和仿真对比，实现少支撑甚至零支撑的内部流道设计效果，为液压元件的增材制造技术提供理论支撑。     

基于增材制造的液压复杂流道轻量化设计与成形

 选区激光熔化（SLM）是一种金属增材制造技术,它利用激光逐层熔化金属粉末累加成形,在复杂零部件和轻量化结构成形上优势明显。分析了液压系统中复杂流道结构的典型特征,提出了传统加工流道局部压损过大、轻量化程度不足两个问题。基于SLM技术,进行了伺服阀集成块的设计成形,实现了集成块整体37%的减重,提取的典型流道仿真结果显示,压力损失降低了50%。最后提出了一种综合约束分析、模型设计和仿真评估的复杂液压流道轻量化设计方法,初步显示了增材制造液压集成块在轻量化和改善油液流动特性上的潜力。     

增减材复合制造加工FDM薄壁样件研究

研究了增减材复合制造加工熔融沉积成型(fused deposition modeling, FDM)薄壁零件的方法。结合增材制造和减材制造,改造传统独立双喷头3D打印机,修改右侧喷头为数控铣刀,在3D打印模型切片时对模型外轮廓进行识别和处理,生成数控加工代码,自动集成到3D打印G代码中,可对薄壁零件进行直接打印,并获得高精度的表面质量。对于薄壁复杂结构塑料零件的加工,通过改造的增减材打印机可以全自动生成复合加工G代码,大大提高了增减材复合制造的效率。     

基于增材制造的Y形流道压力损失建模研究

增材制造技术因其能够成形复杂结构而适用于高集成轻量化的液压系统,但增材制造成形流道的壁面粗糙度与传统钻削及铸造加工的流道不同,尤其是复杂管路系统中的流道分支结构,经典压力损失计算模型无法直接使用,迫切需要研究增材制造成形流道的压力损失数学模型。因此,以典型的流道分支结构——Y形流道为研究对象,应用伯努利方程、动量定理及达西公式建立其压力损失数学模型,并得到增材制造的成形角度对流道壁面粗糙度的影响。利用仿真分析分流比、分支角度及流道直径对压力损失的影响规律,初步验证Y形流道压力损失数学模型的准确性。搭建Y形流道压力损失测试试验台,利用增材制造加工Y形流道测试件,测定不同分流比、分支角度及流道直径下的流道压力损失。结果表明,不同参数下Y形流道压力损失数学模型计算结果与仿真分析结果平均误差均在9%之内,而不同参数下Y形流道压力损失数学模型计算结果与试验测试结果平均误差均在8%之内。研究成果可为增材制造成形低损耗管路的设计奠定基础。     

3D打印技术在航空铝合金薄壁零件上的应用

为解决薄壁结构件制造难题,以航空铝合金薄壁零件为研究对象,运用3D打印技术快速成型铝合金薄壁零件,并进行了尺寸检测、力学性能检测、表面质量和内部质量检测,结果表明:激光选区熔化成型的铝合金薄壁零件尺寸、力学性能、表面质量和内部质量均满足设计要求。     

基于Fluent液压集成块内部流场数据仿真

针对工程中的液压集成块,应用前处理软件Pro/E建立其内部流场的三维模型,应用ICEM对模型进行边界条件设定及网格划分,最后采用Fluent提供的κ-ε湍流模型对结构流场进行数值模拟。通过对流场的分析,找到了液流在集成块内部流道产生能量损失的原因,通过增大工艺孔尺寸、减少工艺孔数目和直角转弯结构等措施,可达到降低集成块内部流道能量损失的目的,为集成块内部结构优化提供了理论依据。     

基于增材制造的液压阀块流道过渡区优化研究

器件小型化和集成化发展趋势,对液压阀块设计提出了更高的要求。传统工艺加工阀块体内部流道,不但工艺复杂难加工,而且成形的流道流动特性有待提高。新型制造工艺增材制造一体化成形的特点使其在流道加工方面表现出很大的优越性。基于增材制造,对某一液压集成阀块的流道过渡区进行优化设计,利用Fluent仿真,对直线过渡、圆弧过渡、B样条曲线3种过渡方式连接的流道流动特性进行分析,B样条曲线过渡流道较直线过渡流道压力损失可降低55%以上,不同圆角半径的圆弧过渡流道较直线过渡流道压力损失可降低28%～56%,为基于增材制造的流道设计提供了必要的支持。     

增材制造成形液压流道沿程损失研究

选区激光熔化(Selective Laser Melting,SLM)作为一种金属增材制造技术,克服了传统加工方式下的成形限制,为液压元件与系统的设计提供了更大的自由度。流道是液压元件与系统的重要组成部分,而目前成形的无支撑圆形流道往往具有较低的轮廓精度和较高的表面粗糙度,这对液压系统的能量损失影响很大。利用SLM技术成形了具有不同直径的水平流道,测量了轮廓精度和表面粗糙度,设计了沿程压力损失测量装置,实验后分析了沿程阻力系数、雷诺数和直径之间的关系。结果表明,随着直径的增大,成形轮廓相对误差减小;成形流道下表皮粗糙度较其他面更高;相同工况下,沿程压力损失比传统加工流道更大。     

液压流道局部拓扑优化与增材制造

液压阀块是液压系统的重要组成部分,降低液压阀块的压力损失对实现液压系统节能化、提高功重比意义重大。选区激光熔化(Selective Laser Melting, SLM)技术是一种增材制造(Additive Manufacturing, AM)技术,基本突破了减材、等材等传统加工方式的设计约束,结合拓扑优化方法,可大大提高液压阀块及其流道的设计自由度。以降低流道局部压力损失为研究目标,对流道局部压力损失较大的拐弯处进行拓扑优化设计,并采用SLM技术成形,优化设计后流道的压力损失明显降低。进一步探究弯管压力损失的主要影响因素——迪恩涡,定量分析了拓扑优化流道降低压力损失的原理,结果表明,拓扑优化得到的变截面流域通过改变流域的弯曲程度,使迪恩涡对压力损失的影响降到最小,从而有效降低流域内的压力损失。对增材制造液压元件及其流道的设计具有重要指导意义。     

微纳增材制造微圆柱结构的形貌分析与工艺优化研究

针对目前亚像素微扫描的LCD式光固化3D打印技术在微纳结构增材制造中存在的典型打印瑕疵,通过优化打印工艺和分析打印结构,以提高打印成型质量和生产效率。首先,通过对打印材料后处理工艺研究,设计单因素试验并打印平板模型,分析后固化时长对零件硬度、粗糙度及形貌影响规律。其次,结合打印工艺参数,设计正交试验并打印圆柱阵列模型,分析打印层厚、曝光时间、振动次数对微圆柱成型的影响规律。结果表明：后固化时间在5～10 min时,后固化效果最优,此时表面粗糙度Ra值约为29 nm,邵氏硬度在88 HD左右。打印工艺参数对微圆柱直径尺寸影响大小排序为：曝光时间>打印层厚>振动次数。在均衡打印质量和打印效率的前提下,打印参数优化后,打印直径50 μm,高度210 μm的微圆柱结构应采用打印层厚10 μm,曝光时间2 500 ms,振动次数64 x的打印工艺参数。     

变截面涡旋盘高速铣削仿真加工与实验研究

为减小变截面涡旋盘涡旋齿的变形,提高加工精度,需确定合理的铣削参数。开展了变截面涡旋盘高速铣削仿真与实验研究以确定铣削参数的合理取值范围;选用HT250变截面涡旋盘为研究对象,研究了更接近实际的材料本构模型、刀-屑摩擦模型和热传导控制方程等关键技术;建立了变截面涡旋盘几何模型和简化后的二维铣削模型,利用ABAQUS软件仿真切屑成形过程及不同的铣削参数对铣削力、铣削热影响的变化曲线;通过多因素正交实验加工变截面涡旋盘。结果表明:当主轴转速为3500 r/min、每齿进给量为0.1 mm以及切削深度为2.5 mm时进行铣削更加合理。铣削变截面涡旋盘的研究为加工参数的选择提供了依据和参考;依据实验后所得的铣削参数进行铣削可减小铣削力、铣削温度及齿变形,提高了变截面涡旋盘的加工效率和质量。     

Prediction of roughness coefficient of a meandering open channel flow using Neuro-Fuzzy Inference System

Almost all the natural water resource channels meander. Accurate estimation of discharge capacity in a meander open channel is important from river engineering point of view. It helps the practitioners to provide essential information regarding flood mitigation, construction of hydraulic structures and prediction of sediment loads so as to plan for effective preventive measures. Reliable estimation of discharge capacity of a natural channel depends on selection of proper value of roughness in terms of Manning’s n. Evaluation of Manning’s n for a meandering channel is a complex procedure because of its dependence on many geometrical, hydraulic and surface parameters of the channel. Experimental investigation concerning the variation of roughness coefficient of meandering channels with flow depth, aspect ratio, slope and sinuosity are presented in this paper. An effort has been made to predict the roughness co-efficient of a meandering channel based on ANFIS. The results are compared with well established methods available in the literature. Statistical error analysis is also carried out to know the degree of accuracy of the models. Finally the present model is found to give better results as compared to others. It is concluded that, in practice ANFIS model can be used as a suitable and effective method to predict the non-linear relationship between roughness coefficient and the non-dimensional factors affecting it.     

Abrasive flow machining (AFM) finishing of conformal cooling channels created by selective laser melting (SLM)

Conformal cooling channels are widely adopted in the mold industry because of rapid and uniform cooling during injection molding. These complicated cooling channel geometries become feasible via selective laser melting (SLM) technology. However, the SLM fabricated internal channel surface shows high surface roughness of about 10 μm Ra. This rough surface can cause stress concentration, reducing the fatigue life of the mold. Therefore, the objective of this study is to investigate the surface finish of the SLM fabricated conformal channels by abrasive flow machining (AFM), which is widely used in the surface finishing of internal channels. To fulfill this objective, a combination of single/multiple and straight/helical channels for conformal cooling channel geometries are employed. Seven different types of conformal cooling channels (ø3mm) inside the bar are fabricated using SLM. The bar is put in the AFM fixture, and the internal channels are polished by flowing AFM media (ULV50%-54) through the channel at the same extrusion pressure of 80 bars for ten cycles. Fourteen bars (seven before AFM and seven after AFM) are machined to have the internal channel surfaces exposed for surface roughness measurement. Surface topographies of the exposed surfaces of seven types of internal channels are obtained using focus variation microscopy. The areal roughness parameters, such as arithmetical mean height (Sa) on the internal channel surfaces before and after AFM. By comparing SLM as-built conformal channel surfaces with AFM finished ones, AFM is shown to be effective in improving all SLM conformal cooling channels’ arithmetical mean height, Sa. Areal roughness parameters, such as developed interfacial area ratio (Sdr), root mean square gradient (Sdq), reduced peak height (Spk), reduced valley height (Svk), and skewness (Ssk), on those internal surfaces, were found to be sensitive to surface finishing by AFM.     

基于ANFIS的铝合金铣削加工表面粗糙度预测模型研究

分析以往建立表面粗糙度预测模型方法的不足，采用自适应神经模糊推理系统(ANFIS)建立了铝合金铣削加工表面粗糙度预测模型。经检验，该模型预测精度高，泛化能力强，且可简便预测铣削参数对已加工表面的表面粗糙度的影响，有助于准确认识已加工表面质量随铣削参数的变化规律，为切削参数的优选和表面质量的控制提供了依据。     

Stage-discharge relationship for slide gates installed in partially full pipes

Sluice/slide gates are widely used for flow depth control and flow discharge measurements in open channels. The hydraulic behavior of the sluice gates located in the rectangular open channels is well documented in the literature. This study reports the results of an investigation conducted to establish the stage-discharge relationship for the sluice gates located in horizontal, circular open channels/pipes under free outflow conditions. Different stage-discharge models were proposed based on the Buckingham's theorem of dimensional analysis and orifice theory. A comprehensive series of laboratory experiments (729 runs) were performed to study the sluice gates located at the middle, and at the end of two circular pipes. Using the data collected from two circular open channels of nominal diameters 20 and 30 cm, the proposed models were calibrated. For the middle slide gates, the experimental results showed that the discharge prediction can be improved by introducing the Reynolds number. For the slide gates located at the middle of the channel, the best proposed model has an average error of 1.40% with a maximum error of 7.12%. For the slide gates located at the end of the channel, the Reynolds number has no significant effect and best proposed model has an average error of 2.47% with a maximum error of 6.59%. The results also showed that the flow discharge of the end slide gate (with unconfined free jet under gravity) is higher than the flow discharge of the middle slide gate for the same gate opening areas and upstream flow depths. The proposed sluice/slide gate for circular open channels offers a simple and reliable discharge measurement approach with acceptable accuracy.     

Comparative study of conventional and micro WEDM based on machining of meso/micro Sized Spur Gear

This paper discusses the comparison of micro machining process using conventional and micro wire electrical discharge machining (WEDM) for fabrication of miniaturized components. Seventeen toothed miniaturized spur gear of 3.5 and 1.2 mm outside diameter were fabricated by conventional and micro WEDM respectively. The process parameters for both conventional and micro WEDM were optimized by preliminary experiments and analysis. The gears were investigated for the quality of surface finish and dimensional accuracy which were used as the criteria for the process evaluation. An average surface roughness (R_a) of 50 nm and dimensional accuracy of 0.1–1 μm were achieved in micro WEDM. Whenever applied conventional WEDM for meso/micro fabrication, a R_a surface roughness of 1.8 μm and dimensional accuracy of 2–3 μm were achieved. However, this level of surface roughness and dimensional accuracy are acceptable in many applications of micro engineering. A window of conventional WEDM consisting of low energy discharge parameters is identified for micromachining.     

Dimensional analyses and surface quality of the laser cutting process for engineering plastics

In this study, the effect of the CO₂ laser cutting process parameters (gas pressure, cutting speed, and laser power) on the dimensional accuracy and measured surface roughness of engineering plastic (PTFE and POM) materials was investigated. Cutting surface profile of specimens was examined by using an optical microscope. The surface quality of specimens was examined by measuring surface roughness and form error. Analysis of variance (ANOVA) and regression analyses are employed to assess the effect of the process parameters on the dimensional accuracy.     

Influence of process parameters on part quality and mechanical properties for DMLS and SLM with iron-based materials

Rapid manufacturing is an advanced manufacturing technology based on layer-by-layer manufacturing to produce a part. This paper presents experimental work carried out to investigate the effects of scan speed, layer thickness, and building direction on the following part features: dimensional error, surface roughness, and mechanical properties for DMLS with DS H20 powder and SLM with CL 20 powder (1.4404/AISI 316L). Findings were evaluated using ANOVA analysis. According to the experimental results, build direction has a significant effect on part quality, in terms of dimensional error and surface roughness. For the SLM process, the build direction has no influence on mechanical properties. Results of this research support industry estimating part quality and mechanical properties before the production of parts with additive manufacturing, using iron-based powders.     

Correlation between different cutting conditions,surface roughness and dimensional accuracy when ball end micro milling material measures with freeform surfaces

Abstract

Material measures are used to calibrate topography measuring instruments. Micro-milling is a suitable process for the manufacturing of areal material measures in particular of material measures featuring freeform surfaces. To improve their surface quality and to minimize their deviations from the target geometry, the cutting parameters feed per tooth respectively feed rate and spindle speed are examined in this study. Dependent on the varied parameters the deviation of the manufactured topography from its target geometry, the deviation to the nominal surface texture parameters and the short-wavelength roughness parameters are evaluated. Two different ball end micro-mills and two different target geometries are chosen to investigate whether the observed dependence on the varied parameters are valid independent from the tool and the target geometry. It is illustrated that the feed rate has a large influence on the dimensional accuracy: the dynamic properties of the axes are identified as reason for the decreasing amplitude with increasing feed rate. The spindle speed only influences the short wavelength roughness and has a minor influence on the surface quality.