线电极微幅振动电解线切割研究

通过线电极叠加轴向微振动促进加工间隙中的电解产物排除,改善线电极电解线切割的稳定性,提高加工效率。自行研制线电极微幅振动电解加工系统,阐述线电极微幅振动电解加工原理,建立加工间隙产物排除的数学模型,揭示线电极叠加轴向微幅振动是排除电解产物、更新电解液的有效途径之一,分析线电极叠加轴向微幅振动对加工稳定性、加工效率和加工精度的影响。针对线电极叠加轴向微幅振动和不叠加振动两种情况进行了对比试验,试验结果表明,振幅8μm、频率10Hz的振动参数有利于改善线电极电解线切割稳定性,提高加工效率。与不叠加振动相比,线电极叠加轴向微幅振动情况下,线电极电解线切割可以在较小的电压、脉冲宽度和较大的脉冲周期下稳定进行,有效地缩小切缝宽度,提高了加工精度。采用优化后的振动参数和加工参数,在不锈钢工件(0Cr18Ni9)上加工出12μm的微缝以及形状复杂的微渐开线齿轮和微螺旋结构。     

窄缝精密电解加工的实验研究

通过在理论上分析窄缝电解加工中片状电极和丝状电极对加工间隙和流场分布的影响,提出了采用小直径丝状电极提高加工精度和改善加工稳定性的方法。文中分别进行了片状电极和丝状电极之间、不同直径丝状电极之间的窄缝电解加工对比试验。结果表明,小直径丝状电极可以减小电解液流过电极丝产生的涡流死水区,改善加工区内的电解液更新和电解产物的排除,提高加工精度和加工过程的稳定性。     

电极平动式电解孔加工技术研究

从电解液流动角度对影响电解孔加工过程的主要原因进行了分析 ,提出利用电极平动来改善电解加工过程稳定性和提高加工精度 ,研制了电极平动系统 ,进行了加工试验。试验结果表明 ,电极的平动运动使得电解液分布变得均匀 ,消除了空穴和分离流等弊端 ,改进了过程稳定性 ,显著提高了加工精度。     

用高转速微电极电解钻削深小孔

针对难切削材料的深小孔加工,提出一种有效排屑、迅速补充电解液的新工艺——高转速微螺旋电极电解钻削加工工艺,并对该工艺进行了机理分析与试验研究。研究了电极转速、电压、脉冲频率、进给速度等工艺参数对深小孔电解钻削加工精度和稳定性的影响,提出合理匹配上述参数可在较高加工效率下获得高的加工精度和加工稳定性。基于硬质合金微螺旋电极用自行研制的高精度微细电解系统成功地在高温镍基合金GH4169上加工出了一组孔径小于0.5mm、深径比大于10、形貌较好,锥度较小,侧壁陡直,进出口边缘锐利的深小孔。试验结果表明,高速电解钻削加工工艺在深小孔加工方面很有潜力。     

微细电解加工实验研究

采用基于电化学腐蚀法制作直径80μm、长度3000μm的微细电极,分别使用微细圆柱电极和微细螺旋电极进行了加工实验,实验研究丧明微细螺旋电极在孔和槽的加工中比微细圆柱电极具有更快的加工速度以及更小的加工间隙.螺旋结构在加工中有助于排出加工间隙内电解产物,显著地提高了加工效率、加工精度及加工过程的稳定性.     

阳极振动辅助微细电解线切割技术

在微细电解线切割加工过程中,工具线电极与工件之间的加工间隙在微米量级,因此,电解加工产物的及时输运是微细电解线切割加工中极为关键的问题。提出在线电极进行轴向往复运动的同时叠加阳极低频微幅振动的方法,促进加工间隙内产物排出,提高加工精度与加工稳定性。探讨加工间隙内电解产物影响微细电解线切割加工精度的机理,研究线电极往复运动条件下阳极振动对加工间隙内产物排出效率的影响。试验结果表明提高阳极的振动频率和振动幅值可以改善微细电解线切割的加工精度和加工稳定性;阳极叠加振动较阳极无振动的切缝更宽、更均匀。采用优化参数加工出宽度4.28 μm的微缝、微槽以及方螺旋结构。     

纳秒脉冲微细电化学加工的理论及试验

根据电化学反应原理,探讨纳秒脉冲电化学加工的特点及其实现微细加工的机理.建立纳秒脉冲微细电化学加工的理论模型,并分析电解液浓度、加工间隙、脉冲参数和加工电压等因素对微细电解加工的影响作用.构建微细电化学加工系统,包括微细加工机床、纳秒脉冲电源、电解液循环系统、运动控制部分和加工检测部分.试验研究了超短脉冲的电压幅值和脉冲宽度对侧面加工间隙的影响,结果表明减小脉冲宽度和降低加工电压可以提高微细电解加工的精度.在自制的微细电化学机床上,实现工具电极和工件微结构的连续加工.将加工间隙控制在5 μm以内,加工出中间有20 μm×30 μm×30 μm棱台的微型腔和30 μm槽宽的十字形孔,分析加工起始点对成形精度的影响,并提出解决方法.试验证明纳秒脉冲微细电解加工可以很好地满足微机电系统(Micro electromechanical system,MEMS)微器件的加工要求.     

微热管内壁非连续微结构微细电解加工法及其实现

针对1μm～1mm的微热管内壁非连续微结构加工困难,加工工艺稳定性和定域性差等问题,提出了一种基于变截面多线螺旋电极微细电解加工微热管内壁非连续微结构的新方法。针对所提出的新方法,研制出了一种微细电解加工机床,通过对其机床本体及结构原理、控制系统、电解液系统三方面的全面设计实现了微热管内壁非连续微结构的电解加工成型。     

管电极电解加工工艺过程稳定性研究

为提高管电极电解加工的稳定性,对管电极电解加工的极间流场进行建模仿真,分析底面流场分布与加工稳定性的关系。仿真所得到的底面压强分布变化规律表明,侧面间隙、底面间隙以及电解液流速均对底面流场分布有重大影响,从而影响管电极电解加工的过程稳定性。结合仿真分析,通过对影响加工稳定性的主要工艺参数,如绝缘层的涂覆厚度、工具进给速度、电解液供液压力进行优化,减少深小孔加工中火花、短路等现象的发生。采用优化的参数,利用群电极成功加工出深宽比为2的7×7小孔阵列,加工过程稳定,孔径均匀。     

振动进给对微尺度群缝电解加工过程的影响

为精确控制振动进给运动,研制了多参数可调的电解加工振动进给装置系统。通过对工具阴极振动进给方式对电解加工间隙内电解产物排出、电解液流场稳定性影响的分析,以剃须刀网罩上的微尺度阵列群缝的电解加工为研究对象开展了系列工艺试验,研究了振动进给的运动参数对微尺度群缝的平均缝宽、侧壁锥度的影响,据此优选了工艺参数,并成功批量加工出了缝宽为0.26mm、侧壁锥度小于5%的微尺度阵列群缝。试验结果证明,振动进给能够有效提高微尺度群缝的电解加工精度和加工过程稳定性。     

微细群缝的精密电解加工研究

以某辐射状分布微细群缝结构的电解加工为研究对象，讨论了电解液、工件材料、加工速度等因素对加工精度的影响，结合研制的加工电极设计流场分布，优化加工参数，实现了以较高的效率加工出缝宽小至0．27mm的微细群缝结构，缝宽一致均匀，加工稳定性和重复性均好。     

端面型槽广义对数螺旋线的通用模型与应用

为解决流体润滑端面型槽设计中经典型线形状优化受限的问题,提出一种广义对数螺旋线模型,获得了斜直线、圆弧线、抛物线和椭圆曲线等经典几何型线的广义螺旋线表达式,掌握了不同参数条件下广义对数螺旋线的几何共性及演变规律。以气体推力轴承为例,对比分析了高速条件下广义螺旋角的分布规律和变化幅值对推力轴承承载性能的影响规律,结果表明:广义对数螺旋线具有很强的几何表征能力,从外径至内径侧流道渐扩的广义对数螺旋槽端面具有最大的气膜承载力。     

焊接卷筒稳定性计算方法研究

经实验证明,传统的卷筒设计和稳定性校核方法是很保守的。本文庆分考虑绳 槽对稳定性的影响,把绳槽作为环筋加到卷筒壁厚中,且它并不参与纵向的承载,提出了一种新的稳定性校核准则。数值计算与理论结果基本是一致的。     

轴向倾斜式周向槽处理机匣对压缩机的扩稳效果研究

针对某亚音速轴流压缩机转子进行周向槽处理机匣的数值模拟.相对于原始的径向式处理机匣,周向槽前倾63.4°,可以在更低的效率损失情况下获得更大的稳定裕度.流场分析表明:周向槽轴向前倾改变了槽内的气流流动结构,减小了流动损失,降低了槽的径向输运能力,增加了周向输运能力,扩稳效果更好.     

An analysis of the effect of journal bearings with helical grooves on the stability of a vertically mounted canned motor pump

An analysis of a vibration problem encountered on a vertically mounted, canned motor pump is described. Details are given of the flush water lubrication system and the two laminated pf resin journal bearings with helical grooves. The vibrational behaviour is described and attributed to bearing instability. A stability analysis based upon a finite element model of the rotor and finite difference solution to the bearing equations is discussed. Particular emphasis is given to the data available and the assumptions that had to be made. The role of the circumferential supply pressure in influencing stability id highlighted and the effect on stability and lubricant axial flow rate of the start of the start position and number of helical grooves is demonstrated. The effect of increased bearing clearance is also discussed. A recommendation to replace the single groove by a bearing with two grooves for the upper bearing is the main conclusion     

Analysis of a hydrodynamic seal with helical grooves

High speed turbogenerators are generally gas cooled and hydrodynamic seals are often used to prevent cooling gas leakage. The seal needs to run essentially at a low eccentricity in order to maintain an uninterrupted oil film all around the shaft. The flow of the oil towards the gas side should be minimized to avoid the contamination of oil with gas.The hydrodynamic seal studied consists of two lands, one on the gas side with helical grooves and the other exposed to ambient air with a wedge. The two lands are separated by a circumferential oil supply groove. The leakage of oil towards the gas side was investigated for different helical groove parameters such as the number of grooves, the helix angle and the groove depth. The effects of these parameters on the performance of the hydrodynamic seal in terms of load support, induced moment, attitude angle, temperature rise and friction force are reported. Equations governing the fluid flow were solved by the finite element method.     

Effect of Axially Grooved Oil Seals on the Leakage Flow and Stability of a Centrifugal Compressor

The results of an analytical investigation are given for the effect of axially grooved floating oil ring seals on the leakage flow and stability of a centrifugal gas compressor. The finite element method was used to solve the non-linear and coupled hydrodynamic and thermal equations for pressure and temperature distributions in the oil seal ring with and without the axial grooves. The peturbation technique was used to obtain the static and dynamic characteristics of the oil seal. The results for selected cases of axial grooving are presented in graphical form for operation at various eccentricities. The non-dimensional leakage flow results correlate well with previously published results calculated by narrow groove theory. The stability of a multi-stage gas compressor is evaluated for different configurations of the oil seal grooving geometry. The compressor rotor shaft finite element model includes a multi-level analysis for the oil seal rings that permits the evaluation of the floating seal influence on the total system stability. Results are given for both low and high-pressure sealing conditions, which simulate test stand and field operating conditions. The results show that the added grooves enhance the stable operation of the rotor system for low-pressure fixed seal conditions arid reduce the system stability at lower eccentricities for low-pressure floating seal conditions. In high pressure conditions the added grooves enhance the stability of the system for both fixed and floating seal conditions.     

Flow field design and experimental investigation of electrochemical machining on blisk cascade passage

Electrochemical machining (ECM) provides an economical and effective way for machining heat-resistant, high-strength materials into complex shapes that are difficult to machine using conventional methods. It has been applied in several industries, especially aerospace, to manufacture blisk. The electrolyte flow field is a critical factor in ECM process stability and precision. To improve the process stability and the efficiency of blisk cascade passages, ECM with a radial feeding electrode, a rational electrolyte flow mode for electrochemical machining called “Π shape flow mode”, is discussed in the paper. Three flow field models are described separately in this report: traditional lateral flow mode, positive flow mode and Π-shaped flow mode, and the electrolyte velocity and pressure distribution vectors for each flow mode are calculated by means of a finite element fluid analysis method. The simulation results show that the electrolyte flow is more uniform with the Π-shaped flow mode. The deformation of the cathode, which is caused by the pressure difference, is also analysed in this report. The cascade passage ECM with a radial feeding electrode was experimentally tested out to evaluate the rationality of the flow field, and the fluctuation of current during the process was less than 1 %, which means that the process that uses the Π-shaped flow mode is stable. The feeding velocity of the cathode with the Π-shaped flow mode is approximately 70 % higher than that with the other two flow modes, and the incidences of short circuiting are obviously decreased. The surface roughness of the blisk hub is only 0.15 μm, and the machining error of the hub is less than 0.1 mm. The results demonstrate that using the Π-shaped flow mode can enhance the quality, stability and efficiency of blisk cascade passage ECM.     

钛合金深窄槽可控振动辅助电解加工试验研究

为提高TB6钛合金深窄槽电解加工精度,基于电场仿真分析方法,研究了不同加工方式深窄槽侧壁电流密度和电化学溶解速度分布规律,并采用工艺试验方法对持续进给、振动进给、脉冲与振动耦合3种加工方式进行对比研究。试验结果表明：振动频率和持续进给速度固定时,提高振幅能够显著降低槽宽标准差,提高深窄槽加工一致性;持续进给速度相同时,脉冲与振动耦合的平均槽宽和槽宽标准差均较小,加工精度更高。采用脉冲与振动耦合加工方式,深窄槽入口处平均槽宽为2.62 mm,沿深度方向平均槽宽为2.73 mm,入口处槽宽标准差为0.05 mm,沿深度方向槽宽标准差为0.03 mm。     

Load performance analysis of three‐pad fixing pad aerodynamic journal bearings with parabolic grooves

Three‐pad fixing pad aerodynamic journal bearings (TPFPAJBs) have been widely used in precision instruments due to their low friction, high stability and non‐pollution. In order to improve the load performance of TPFPAJBs, parabolic grooves are opened in the bearing pad surfaces. By opening parabolic grooves in various bearing pad surfaces, the effects of the orientation angle, distance, width and depth of the grooves on the load performance of micro‐grooved TPFPAJBs can be investigated. The numerical results show that the location of the micro‐grooved bearing pads can greatly affect the load performance of micro‐grooved TPFPAJBs. When the given bearing pad surface is grooved, the effects of the bearing number and width‐to‐diameter ratio on the load performance of micro‐grooved TPFPAJBs can be studied. The bearing number and width‐to‐diameter ratio are observed to have significant influences on the load performance of micro‐grooved TPFPAJBs. Copyright © 2015 John Wiley & Sons, Ltd.