Interference and grinding characteristics in ultra-precision grinding of thin-walled complex structural component using a ball-end grinding wheel

As for ultra-precision grinding of difficult-to-process thin-walled complex components with ball-end grinding wheels, interference is easy to occur. According to screw theory and grinding kinematics, a mathematical model is established to investigate the interference and grinding characteristics of the ball-end wheel. The relationship between grinding wheel inclination angle, C axis rotation angle, grinding position angle and grinding wheel wear are analyzed. As the grinding wheel inclination angle increases, the C axis rotatable range decreases and the grinding position angle increases. The grinding position angle and wheel radius wear show a negative correlation with the C axis rotation angle. Therefore, a trajectory planning criteria for increasing grinding speed as much as possible under the premise of avoiding interference is proposed to design the grinding trajectory. Then grinding point distribution on the ball-end wheel is calculated, and the grinding characteristics, grinding speed and maximum undeformed chip thickness, are investigated. Finally, a complex structural component can be ground without interference, and surface roughness and profile accuracy are improved to 40.2 nm and 0.399 μm, compared with 556 nm and 3.427 μm before ultra-precision grinding. The mathematical model can provide theoretical guidance for the analysis of interference and grinding characteristics in complex components grinding to improve its grinding quality.     

航空面齿轮磨削碟形砂轮修整方法及误差分析

根据面齿轮专用磨齿机的机械结构,提出了偏置曲线修整方法,设计了砂轮修整装置,并运用VERICUT软件进行修整加工仿真.推导了含各类修整误差情况下面齿轮的齿面方程表达式,并运用MATLAB软件生成了齿面误差云图,为修整过程的误差补偿提供了理论参考.最后进行了磨削及检测试验,将检测结果与误差云图对比,分析可能产生这种误差的原因,并在修整过程中进行误差补偿,使齿面最大法向误差值减少了31.14%,面齿轮齿形精度得到了提高.      

航空齿轮磨削加工安装偏心误差补偿研究

磨齿加工时齿坯几何中心与回转工作台轴心存在安装偏心误差,降低了磨齿加工精度。以数控成型砂轮磨齿机工作原理为基础,建立偏心误差磨削加工几何模型;提出安装偏心误差补偿法,建立偏心误差补偿数学模型,通过数学模型求出磨削砂轮在X、Y两个方向的进给补偿增量;以YK73125数控成型砂轮磨齿机为例,进行安装偏心误差补偿实验,齿轮的左右齿面单个齿距极限偏差绝对值分别减小了0.9μm和1.6μm,齿距累积总偏差绝对值分别减小了49.6μm和43.3μm。结果表明:安装偏心误差与单个齿距偏差和齿距累积总偏差成正比;采用安装偏心误差补偿进行磨齿加工,有效地减小了单个齿距偏差和齿距累积总偏差,齿轮的精度有所提高。     

Grindability and Surface Integrity of Cast Nickel-based Superalloy in Creep Feed Grinding with Brazed CBN Abrasive Wheels

The technique of creep feed grinding is most suitable for geometrical shaping, and therefore has been expected to improve effectively material removal rate and surface quality of components with complex profile. This article studies experimentally the effects of process parameters (i.e. wheel speed, workpiece speed and depth of cut) on the grindability and surface integrity of cast nickel-based superalloys, i.e. K424, during creep feed grinding with brazed cubic boron nitride (CBN) abrasive wheels. Some important factors, such as grinding force and temperature, specific grinding energy, size stability, surface topography, microhardness and microstructure alteration of the sub-surface, residual stresses, are investigated in detail. The results show that during creep feed grinding with brazed CBN wheels, low grinding temperature at about 100 °C is obtained though the specific grinding energy of nickel-based superalloys is high up to 200-300 J/mm³. A combination of wheel speed 22.5 m/s, workpiece speed 0.1 m/min, depth of cut 0.2 mm accomplishes the straight grooves with the expected dimensional accuracy. Moreover, the compressive residual stresses are formed in the burn-free and crack-free ground surface.     

Performance evaluation of creep feed grinding of γ-TiAl intermetallics with electroplated diamond wheels

This paper evaluates the performance of creep feed grinding γ-TiAl intermetallic (Ti-45Al-2Mn-2Nb) using electroplated diamond wheels. Firstly, a comparative analysis with the grinding results by using electroplated CBN wheels was conducted, mainly involving abrasive wheel wear behavior and maximum material removal rate below surface burn limit. It was found that the diamond wheel would produce much better grinding results including lower wheel wear rate and higher maximum material removal rate. Then the surface integrity obtained at different level of material removal rate was characterized with the utilization of the diamond wheel. The poor ductility of this γ-TiAl intermetallic material was found to have a marginal effect on the surface integrity, as no severe surface defects such as material pullout were generated during the stable wheel wear stage. For the involved operating parameters, a deformation layer was produced with ∼10 μm or more in thickness depending on the material removal rate used. Meanwhile, a work-hardened layer extending to more than 100 μm was produced with a maximum microhardness of above 520 HV_0.05 (bulk value 360 HV_0.05). The residual stress remained compressive, with a value of above −100 MPa and even up to −500 MPa for an elevated material removal rate. Shearing chip was the main chip type, indicating good wheel sharpness in the grinding process.     

Investigation on surface integrity of electron beam melted Ti-6Al-4 V by precision grinding and electropolishing

Electron beam melting (EBM), as an excellent Additive Manufacturing (AM) technology, enables the printing of Ti-6Al-4 V alloy for a wide range of applications such as aerospace and biomechanical industries. It improves functionality and integrity of components and negates complexities in assembly processes. However, due to the poor surface and sub-surface integrity represented by the rough surface finish and low dimensional accuracy, achieving a favorable surface condition is quite challenging. Therefore, post processing becomes essential for these electron beam melted (EBM-ed) Ti-6Al-4 V alloys. Being the most common technique to improve such parts, milling of Ti-6Al-4 V alloy is very challenging and resulting tool wear issues, due to its unique material properties. Thus, this paper presents a comprehensive study on the surface integrity of EBM-ed Ti-6Al-4 V parts processed by precision grinding and electropolishing, aiming to qualitatively and quantitatively clarify the interrelation between process parameters and processed surface quality. The surface and subsurface characteristics such as profile accuracy, surface roughness, microstructure, defective layer and residual stress before and after post processing were compared and evaluated. The results show that by precision grinding, the profile accuracy was improved from over 300 µm PV to 7 µm PV, while surface roughness (R_a) was reduced from 30 µm to about 2 µm. The layer with partially melt particles was removed, but introduced a deformed subsurface layer with more residual stress. Then by applying electropolishing, the residual stress was released and the deformed layer was removed. In addition, R_a was further reduced to 0.65 µm. The research can serve as a reference for the integration of post machining processes with AM.     

Analysis of grinding mechanics and improved grinding force model based on randomized grain geometric characteristics

Too high grinding force will lead to a large increase in specific grinding energy, resulting in high temperature in grinding zone, especially for the aerospace difficult cutting metal materials,seriously affecting the surface quality and accuracy. At present, the theoretical models of grinding force are mostly based on the assumption of uniform or simplified morphological characteristics of grains, which is inconsistent with the actual grains. Especially for non-engineering grinding wheel,most g...     

整体叶盘弹性磨具抛光轨迹关键规划方法

为使得弹性磨具(砂布轮)在抛光中和叶片型面有效切合,提高抛光质量和抛光效率,研究了弹性磨具抛光轨迹规划方法,给出了抛光行距、抛光步长、刀轴矢量的计算方法。该抛光轨迹规划方法使得柔性主轴机构在抛光过程中保持合理的位姿,确保弹性磨具不仅与叶片型面有效贴合,而且使得弹性磨具抛光力方向与抛光点位法矢方向基本一致。试验结果表明:抛光后叶片表面粗糙度小于0.4μm,叶型轮廓度在公差范围内,能够满足整体叶盘叶片型面抛光要求。     

A trajectory planning method on error compensation of residual height for aero-engine blades of robotic belt grinding

While the traditional trajectory planning methods are used in robotic belt grinding of blades with an uneven machining allowance distribution, it is hard to obtain the preferable profile accuracy and surface quality to meet the high-performance requirements of aero-engine. To solve this problem, a novel trajectory planning method is proposed in this paper by considering the developed interpolation algorithm and the machining allowance threshold. The residual height error obtained from grinding e...     

高纯钨磨削加工试验研究

为探究适用于高纯钨磨削加工的砂轮,使用80~#绿碳化硅砂轮和金刚石砂轮开展磨削对比试验,从工件表面粗糙度角度评价上述两种砂料对高纯钨磨削加工表面的影响。试验结果表明,绿碳化硅砂轮对应的工件得到了更理想的表面粗糙度。使用绿碳化硅砂轮开展工艺试验,分析在不同磨削参数下加工表面粗糙度的变化趋势,以此为依据对高纯钨磨削加工工艺参数进行评价与优化。综合考虑加工表面粗糙度以及加工效率,得出适合于钨磨削加工的参数为砂轮线速度v_s=23m/s、磨削深度a_p=8μm、工作台进给速度v_w=10m/min,该参数下得到的表面粗糙度均值为0.336μm。     

一种机器人砂带磨削的路径规划方法(英文)

机器人砂带磨削系统具有弹性接触和宽行加工两个显著优点,被广泛应用在具有复杂工件的终加工领域,提高表面质量和加工效率。有关在曲率约束下的磨削路径规划研究较为少见。由于工件与接触轮之间存在复杂的弹性接触,因此,机器人磨削路径可以利用接触运动学的一般方法来求解。机器人砂带磨削过程且需要满足一般的砂带磨削工艺要求,其中最重要的是保证接触轮与工件的局部几何特征贴合。在曲率较小的局部,相邻刀位点的弧长加大,以保证加工效率。相反地,在曲率较大的局部,相邻刀位点的弧长较小,以保证加工精度。利用一系列平面与目标曲面相截,得到相应的截平面的轮廓曲线。对于任意一条轮廓线,优化相邻刀位点之间的弧长,在曲率较大的局部增加一个中间刀位点。本文提出了一种包含弧长优化和主曲率匹配的磨削路径生产方法,通过离线仿真验证了有效性,并利用该方法提高了曲面的磨削质量。该路径规划方法为生成光顺且精确的机器人曲面磨削路径提供了理论依据。     

碳化硼材料动压气浮轴承零件精密加工

针对高精度、高硬度、高脆性碳化硼材料的动压气浮轴承零件精密加工存在加工合格率低和效率低的问题,进行了加工流程、精密磨削与精密研磨的技术改进。首先,采用电火花套切方法去除大部分加工余量、小余量精密磨削和精密研磨加工的工艺方法,提高了轴承零件加工效率。其次,通过设计制作专用高精度定位磨削夹具和金刚石砂轮修整装置,解决了轴承零件磨削加工形位精度不高和砂轮无法进行在位修整的问题。最后,通过研制圆柱面精密研磨机,解决由于原有研磨设备精度差造成的加工质量和效率低的问题。通过采取技术改进措施,实现了碳化硼轴承零件亚微米级形位精度的磨削加工,提高了轴承零件的加工精度、合格率和加工效率。     

钛合金TC4电火花诱导可控烧蚀高效磨削技术研究

利用大部分金属尤其是难加工金属的可燃特性,开发一种针对难加工金属材料的新加工工艺——电火花(EDM)诱导可控烧蚀高效磨削技术。采用开槽导电砂轮进行磨削加工,首先利用导电区域与加工材料产生电火花诱导放电并通入助燃氧气,使材料表面产生电火花引燃烧蚀并软化,然后将已烧蚀和软化的材料磨除,对钛合金TC4进行烧蚀磨削试验,并与常规电火花磨削和机械磨削进行对比,分析了材料去除率(RMM)、表面质量和机床主轴电机功率变化等指标。结果表明,在试验条件下,烧蚀磨削在放电利用率提高的同时可获得表面粗糙度为0.59 μm的加工表面,与机械磨削的表面粗糙度值相近,而相同条件下电火花磨削的表面粗糙度为1.29 μm。由于烧蚀后产生了软化层,在切深小于软化层厚度的条件下,相对于电火花磨削和机械磨削状况,烧蚀磨削主轴电机功率相比空载时的增加值分别降低了95.2%和96.8%。此工艺方法可大大提高难加工材料的可磨削性能。     

镍基高温合金GH4169磨削参数对表面完整性影响

研究了用单晶刚玉砂轮磨削镍基高温合金GH4169时,磨削参数对表面完整性中的表面特征(表面粗糙度、表面形貌、表面显微硬度和表面残余应力)的影响,以期优化磨削参数.砂轮速度依次选择15,20,25m/s,磨削深度分别选择50,100,150μm,工件速度分别选择5,10,15m/min.研究结果表明:表面粗糙度对工件速度的变化最敏感,表面显微硬度对砂轮速度变化最敏感,表面残余应力对砂轮速度变化最敏感;同时表明了磨削参数对磨削表面形貌、显微硬度梯度、微观组织、残余应力梯度的影响,揭示了表面完整性中的变质层形成规律.其塑性变形层在5～10μm,显微硬度变化影响层为80～100μm,残余应力影响层厚度为80～200μm,其为磨削镍基高温合金表面完整性控制研究提供相关的实验数据基础.      

Improving profile accuracy and surface quality of blisk by electrochemical machining with a micro inter-electrode gap

Electrochemical machining (ECM) has emerged as an important option for manufacturing the blisk. The inter-electrode gap (IEG) distribution is an essential parameter for the blisk precise shaping process in ECM, as it affects the process stability, profile accuracy and surface quality. Larger IEG leads to a poor localization effect and has an adverse influence on the machining accuracy and surface quality of blisk. To achieve micro-IEG (<50 μm) blisk finishing machining, this work puts forward a novel variable-parameters blisk ECM strategy based on the synchronous coupling mode of micro-vibration amplitude and small pulse duration. The modelling and simulation of the blisk micro-IEG machining have been carried out. Exploratory experiments of variable-parameters blisk ECM were carried out. The results illustrated that the IEG width reduced with the progress of variable parameter process. The IEG width of the blade’s concave part and convex part could be successfully controlled to within 30 μm and 21 μm, respectively. The profile deviation for the blade’s concave surface and convex surface are 49 μm and 35 μm, while the surface roughness reaches R_a = 0.149 μm and R_a = 0.196 μm, respectively. The profile accuracy of the blisk leading/trailing edges was limited to within 91 μm. Compared with the currently-established process, the profile accuracy of the blade’s concave and convex profiles was improved by 50.5 % and 53.3 %, respectively. The surface quality was improved by 53.2 % and 50.9 %, respectively. Additionally, the machined surface was covered with small corrosion pits and weak attacks of the grain boundary due to selective dissolution. Some electrolytic products were dispersed on the machined surface, and their components were mainly composed of the carbide and oxide products of Ti and Nb elements. The results indicate that the variable-parameters strategy is effective for achieving a tiny IEG in blisk ECM, which can be used in engineering practice.     

Feasibility study of creep feed grinding of 300M steel with zirconium corundum wheel

The ultrahigh strength 300M steel has been commonly used in the manufacture of aircraft landing gear and rotor shaft parts due to its excellent mechanical properties. Creep feed grinding is one of the essential operations during the whole component manufacturing processes. In this work, the feasibility of creep feed grinding of 300M steel by using the hard zirconium corundum wheel was theoretically and experimentally evaluated. A variety of responses including grinding forces, temperature fields...     

面向型面精度一致性的整体叶盘砂带磨削新方法及实验研究

由于整体叶盘由多个叶片组成,根据"木桶定律",整体叶盘的性能和寿命取决于型面精度(型线精度和表面质量)最差的叶片。因此,在满足整体叶盘型面精度的前提下,提高各叶片型面精度一致性对其性能和寿命具有重要的影响。提出一种面向型面精度一致性的砂带磨削新方法,一方面通过砂带周期性的往复运动结合自锐式磨削原理,实现型面铣削残差层的高效去除;另一方面通过砂带周期性的自动更新,保证各叶片的型面精度在同一截面具有高一致性。阐述并建立了面向型面精度一致性的砂带磨削新方法及其磨削控制方程。在此基础上,对某航空发动机整体叶盘的11个叶片进行了砂带磨削实验,并且运用标准差对整体叶盘型面精度一致性进行定量分析。研究结果表明:整体叶盘磨削后,表面粗糙度小于0.25 μm,型线精度小于0.05 mm,同时型面精度一致性显著提高,证明了该方法的有效性。     

航空发动机叶片前后缘自由式砂带抛光技术

由于叶片前后缘(LTE)的轮廓形状和表面质量将对航空发动机的气动性能和叶片的疲劳性能产生直接影响,因此为提高前后缘的轮廓度和表面质量,通过对目前航空发动机叶片前后缘抛光所存在的问题进行分析,结合叶片前后缘抛光工艺要求,并基于自由式砂带抛光的工艺特点,提出了叶片前后缘自由式砂带抛光工艺方法;针对该抛光工艺方法,建立其砂带张紧力控制系统,确定了抛光加工中的砂带走刀步长计算公式及抛光轨迹规划方法;最后以某型号叶片的前后缘作为加工对象进行抛光实验研究。检测结果显示:叶片前后缘轮廓度误差小于0.01mm,其表面粗糙度小于0.4μm,证实了该抛光工艺方法对提高叶片前后缘的轮廓度和表面质量的有效性。     

Development of a new high-shear and low-pressure grinding wheel and its grinding characteristics for Inconel718 alloy

Nickel-based alloy has been widely used due to its outstanding mechanical properties.However, Nickel-based alloy is a typical difficult-to-machine material, which is a great constrain for its application in the manufacturing field. To improve the surface quality of the ground workpiece, a new high-shear and low-pressure grinding wheel, with high ratio of tangential grinding force to normal grinding force, was fabricated for the grinding of selective laser melting(SLM) manufactured Inconel718 all...     

基于碟形砂轮磨齿的面齿轮包络残差研究

介绍了采用碟形砂轮磨削面齿轮的原理及过程,研究了齿廓包络和齿宽包络两种包络方式产生包络残差的机理.分别建立了两种加工方式下包络残差的计算模型和方法,并研究了所产生包络残差的特点.通过数值算例分析了包络过程中刀具周向进给角度、齿宽方向进给量以及碟形砂轮外径对齿面包络残差的影响规律.计算结果表明:齿宽包络比齿廓包络具有更高的效率.进行了以齿廓包络方式的面齿轮磨齿加工实验,当刀具周向进给角度分别取为2°,1°,0.5°及0.2°时,齿面表面粗糙度逐渐明显提高,齿面磨削加工印痕的数目和方向与包络仿真计算结果一致.初步证明根据包络残差计算结果选取合适的进给量参数,可以保证面齿轮磨齿加工的表面粗糙度水平并能提高加工效率.