Determining dynamically active abrasive particles in the media used in centrifugal force assisted abrasive flow machining process

Abrasive flow machining (AFM) is a relatively new non-traditional process in which a semisolid media consisting of abrasive particles and a flexible polymer carrier is extruded through or across the component to be machine finished. This process is capable of providing excellent surface finishes on a wide range of simple as well as intricated shaped components. Low material removal rate happens to be one major limitation of this process, because during machining not all the abrasive particles participate in removing material from the work piece. Limited efforts have hitherto been directed towards improving the efficiency of the process so as to achieve higher material removal rates. An effort has been made towards the performance improvement of this process by applying centrifugal force on the abrasive media with the use of a rotating centrifugal force generating (CFG) rod introduced in the work piece passage. The modified process is termed as centrifugal force assisted abrasive flow machining (CFAAFM). This paper presents a mathematical model developed to calculate the number of dynamics active abrasive particles participating in the finishing operation in the AFM and CFAAFM process. The analysis of results show that there is great enhancement of number of dynamic active abrasive particles in CFAAFM as compared to the AFM process, which seems to be the contributing factor for the increase in material removal and % improvement in surface roughness for a given number of cycles in CFAAFM. The results of experiments conducted to validate the model show a close agreement between the analytical and experimental results.     

ABRASIVE FLOW MACHINING WITH ADDITIONAL CENTRIFUGAL FORCE APPLIED TO THE MEDIA

Abrasive flow machining (AFM) is one of the important non-traditional metal finishing technologies which was introduced during the late 1960s. The process has found applications in a wide range of fields such as aerospace, defence, surgical and tool manufacturing industries. Recently, an effort has been made towards the performance improvement of this process by applying centrifugal force on the abrasive media with the use of a rotating centrifugal force generating (CFG) rod introduced in the workpiece passage. The results have been encouraging. The present paper discusses the results of changing the parameters like shape and rotational speed of CFG rod, extrusion pressure, number of process cycles and abrasive grit size. The results indicate that all the input variables have significant effect on the response parameters, which for the present study were taken as material removal and surface roughness. An analytical model is proposed for the velocity and the angle at which abrasive particles attack the workpiece surface in the process.     

ABRASIVE FLOW MACHINING WITH ADDITIONAL CENTRIFUGAL FORCE APPLIED TO THE MEDIA

Abrasive flow machining (AFM) is one of the important non-traditional metal finishing technologies which was introduced during the late 1960s. The process has found applications in a wide range of fields such as aerospace, defence, surgical and tool manufacturing industries. Recently, an effort has been made towards the performance improvement of this process by applying centrifugal force on the abrasive media with the use of a rotating centrifugal force generating (CFG) rod introduced in the workpiece passage. The results have been encouraging. The present paper discusses the results of changing the parameters like shape and rotational speed of CFG rod, extrusion pressure, number of process cycles and abrasive grit size. The results indicate that all the input variables have significant effect on the response parameters, which for the present study were taken as material removal and surface roughness. An analytical model is proposed for the velocity and the angle at which abrasive particles attack the workpiece surface in the process.     

Enhancing AFM process productivity through improved fixturing

Abrasive flow machining (AFM) is a non-conventional finishing process that deburrs and polishes by forcing an abrasive laden media across the workpiece surface. The process embraces a wide range of applications from critical aerospace and medical components to high-production volumes of parts. One serious limitation of this process is its low productivity in terms of rate of improvement in surface roughness. Limited efforts have hitherto been directed towards enhancing the productivity of this process with regard to better quality of workpiece surface. This paper discusses improved fixturing as a technique for productivity enhancement in terms of surface roughness (R _a). A rotating centrifugal-force-generating (CFG) rod is used inside the cylindrical workpiece which provides the centrifugal force to the abrasive particles normal to the axis of workpiece. The effect of the key parameters on the performance of process has been studied. The results shows that for a given improvement in R _a value, the processing time can be reduced by as much as 70–80%. It is seen that the significant process parameters are revolutions per minute of CFG rod, extrusion pressure and abrasive mesh size.     

Influence of Cavitation on Unsteady Vortical Flows in a Side Channel Pump

Double-sided lapping is an precision machining method capable of obtaining high-precision surface. However, during the lapping process of thin pure copper substrate, the workpiece will be warped due to the influence of residual stress, including the machining stress and initial residual stress, which will deteriorate the flatness of the workpiece and ultimately affect the performance of components. In this study, finite element method (FEM) was adopted to study the effect of residual stress-related on the deformation of pure copper substrate during double-sided lapping. Considering the initial residual stress of the workpiece, the stress caused by the lapping and their distribution characteristics, a prediction model was proposed for simulating workpiece machining deformation in lapping process by measuring the material removal rate of the upper and lower surfaces of the workpiece under the corresponding parameters. The results showed that the primary cause of the warping deformation of the workpiece in the double-sided lapping is the redistribution of initial residual stress caused by uneven material removal on the both surfaces. The finite element simulation results were in good agreement with the experimental results.     

A study on the application of newly developed magneto-elastic abrasive to improving the surface roughness of the bore

Spiral polishing mechanism refers to the technology of applying a high-speed turning screw rod in the process of workpiece surface polishing. For the purpose of increasing the machining effect, a powerful ring magnet was installed around the workpiece. In this study, the new self-developed magneto-elastic abrasive would be used to polish the inner wall of the bore, the so-called workpiece surface, under the attraction of the surrounding magnet and the drive of the turning rod. The new magneto-elastic abrasive not only eased the polishing force by its flexibility but also avoided deep scratches on the workpiece surface. The control of machining parameters on surface roughness and material removal were discussed to look for the best combination of the parameters; at the same time, the effects of each parameter on the workpiece surface topography after the polishing were also examined. The results of the experiment indicated that magnetic flux density and magneto-elastic abrasive concentration affected the surface roughness the most. In addition, the newly developed magneto-elastic abrasive significantly improved the polishing effect of the workpiece surface, at the rate of 94 %.     

超声磁力复合研磨钛合金锥孔的试验研究

为了提高钛合金锥孔的研磨质量和研磨效率,提出了采用超声波振动辅助磁力研磨的复合加工方案。加工时,磨粒在磁场束缚下切削锥孔表面,并对其进行不断撞击,且因为磁场力、超声振动力和离心力等综合影响的原因,磨粒的切削轨迹呈现明显的多向性。针对钛合金锥孔,与传统磁力研磨法进行试验对比,并分析研磨后试件的材料去除量、表面粗糙度和表面形貌等来验证超声磁力复合研磨的效果。结果表明：超声磁力复合研磨加工效率得到提高;锥孔的材料去除量增加至1.6倍;研磨后锥孔平均表面粗糙度由原始的R_a1.23 μm降至R_a0.25 μm,下降率是传统工艺的1.3倍;试件表面的微波峰、凹坑和加工纹理均被去除,锥孔表面质量得到显著提高,且试件形状精度得到改善。     

钛合金曲面磨粒流加工扰流流道仿真与试验研究

针对具有复杂曲面的钛合金工件磨粒流抛光后表面粗糙度Ra不均匀问题,提出一种具有扰流结构的仿型约束加工流道。借助计算流体动力学（CFD）分析软件,结合SST k-ω湍流模型、离散相模型（DPM）和Oka冲蚀模型,仿真分析原始流道和5种不同扰流角度的扰流流道内磨粒流动力学特性。数值模拟结果表明：扰流流场中的磨粒流相较于原始流场在工件表面具有更大的湍流动能、动压力和冲蚀速率,其中扰流角度为30°时冲蚀均匀性较好。基于仿真条件搭建了磨粒流加工试验平台,使用原始流道和30°扰流流道分别进行了加工试验。试验结果表明：使用原始流道加工5 h后,工件表面曲率不同区域的表面粗糙度Ra值分散,加工效果均匀性较差;使用扰流流道加工5 h后,工件表面各区域表面粗糙度Ra的均匀性明显优于无扰流流场的加工均匀性。     

Experiment research on grind-hardening of AISI5140 steel based on thermal compensation

The grind-hardening process utilizes the heat generated to induce martensitic phase transformation. However, the maximum achievable harden layer depth is limited due to high grinding forces, and the tensile residual stress appears on the ground surface in the grind-hardening process. This paper proposes a new grind-hardening technology using thermal compensation. The workpiece of AISI5140 steel is preheated by electric resistance heating, and ground under the condition of the workpiece temperature 25°C, 120°C, 180°C and 240°C. The grinding force, harden layer depth and surface quality including residual stress on ground surface, surface roughness and micro-hardness are investigated. The experimental results show that a deep harden layer with a fine grain martensite can be obtained with the thermal compensation. The ground workpiece surface produces a certain compressive residual stress, and the residual compressive stress value increases with preheating temperature. As the preheating temperature increases, grinding force slightly decreases, while there is slightly increment of surface roughness. Compared with the conventional grind-hardening process, both the harden layer depth and residual stress distribution are significantly improved.

     

超声滚压工艺对TC4钛合金表面残余应力的影响

钛合金关节轴承是航空发动机的重要部件之一,但由于其润滑条件较差,极易产生磨损从而导致失效事故。采用超声滚压工艺对钛合金试件表面进行强化试验,以有效增强试件表面耐磨性能和抗疲劳特性,并着重研究静压力、滚压次数和主轴转速等超声滚压强化工艺参数对钛合金表面残余压应力与剪切应力的影响规律。试验结果与理论分析结果表明,残余压应力随着静压力、滚压次数和主轴转速的提高而增大,剪切应力随着静压力、滚压次数和主轴转速的提高而总体减小;滚压后试件表面可获得-2 000～-500 MPa的残余压应力和-600～-300 MPa的剪切应力。超声滚压技术可以有效提高钛合金材料表面的残余压应力,并有效降低表面的剪切应力。     

Investigating the Tribological Characteristics of Burnished Polyoxymethylene—ANFIS and FE Modeling

ABSTRACT

Polymers are utilized in numerous tribological applications because of their excellent characteristics; for example, accommodating shock loading and shaft misalignment. A high surface finish is required to ensure consistently good performance and extended service life of manufactured polymeric components. Burnishing is the best choice as a finishing process for this study due to its ability to increase hardness, fatigue strength, and wear resistance and also introduce compressive residual stress on the burnished workpiece. Due to the complexity and uncertainty of the machining processes, soft computing techniques are preferred for anticipating the performance of the machining processes. In this study, ANFIS as an adaptive neuro-fuzzy inference system was applied to anticipate the workpiece hardness and surface roughness after the roller burnishing process. Five burnishing variables, including burnishing depth, feed rate, speed, roller width, and lubrication mode, were analyzed. A Gauss membership function was used for the training process in this study. The predicted surface roughness and hardness data were compared with experimental results and indicated that the Gauss membership function in ANFIS has satisfying accuracy as high as 97% for surface roughness and 96% for hardness. Furthermore, the generated compressive residual stress on the burnished surface was studied by a 2D finite element model (FEM). The simulated results of residual stress were validated with the experimental results obtained from X-ray diffraction (XRD) tests.     

ON THE PERFORMANCE ANALYSIS OF FLEXIBLE MAGNETIC ABRASIVE BRUSH

Magnetic abrasive finishing (MAF) of alloy steel workpiece with unbounded magnetic abrasive particles (UMAPs) indicates that the surface finish in the range of nanometer can be achieved. Important controllable four process parameters have been identified which are as current to the electromagnet, machining gap, abrasive size (mesh number), and number of cycles. Experiments have been planned using design of experiments technique. Based upon the results of response surface methodology and analysis of variance (ANOVA), it is concluded that magnetic flux density that depends on current to the electromagnet and machining gap, is most influencing parameter followed by grain size and number of cycles. The surface roughness profile generated during the MAF process has been discussed. To understand the cutting mechanism of magnetic abrasive finishing process, scanning electron microscopy (SEM) and atomic force microscopy (AFM) of the machined surfaces have been carried out. The correlation between surface finish and material removal has also been established.     

H13淬硬模具钢精车过程的数值模拟

采用热力学耦合有限元方法研究了淬硬钢精车过程中切屑形成规律。运用H13 淬硬模具钢流动应力模型进行数值模拟,考查了H13淬硬模具钢精车过程中工艺参数对工件性能和刀具的影响。结果表明:切削速度愈高,进给量愈小,刀具刀尖半径愈大,则工件加工层上的静水拉应力愈小,表面质量愈好; 淬硬钢精车时径向力起主要作用,大于切削力;切削速度愈大,切削力和径向力则愈小,愈有助于改善工件加工层上的表面质量;切削速度、进给量和刀具刀尖圆角半径愈大,工件和刀具温度愈高,愈易导致刀具前刀面扩散磨损和刀具后刀面磨损。研究结论有助于优化H13淬硬模具钢精车过程中工艺参数选择和改进刀具镶片设计。     

ON THE PERFORMANCE ANALYSIS OF FLEXIBLE MAGNETIC ABRASIVE BRUSH

ABSTRACT

Magnetic abrasive finishing (MAF) of alloy steel workpiece with unbounded magnetic abrasive particles (UMAPs) indicates that the surface finish in the range of nanometer can be achieved. Important controllable four process parameters have been identified which are as current to the electromagnet, machining gap, abrasive size (mesh number), and number of cycles. Experiments have been planned using design of experiments technique. Based upon the results of response surface methodology and analysis of variance (ANOVA), it is concluded that magnetic flux density that depends on current to the electromagnet and machining gap, is most influencing parameter followed by grain size and number of cycles. The surface roughness profile generated during the MAF process has been discussed. To understand the cutting mechanism of magnetic abrasive finishing process, scanning electron microscopy (SEM) and atomic force microscopy (AFM) of the machined surfaces have been carried out. The correlation between surface finish and material removal has also been established.     

The use of ultrasonic cavitation peening to improve micro-burr-free surfaces

Advances in machining technology, particularly in the field of micro-machining, have led to the design and creation of miniature components suitable for use in the precision engineering industry. However, the need to contain ubiquitous burrs still exists and has to be addressed. Previous studies on deburring have mostly focused on the parametric investigations of orientation, temperature, type of liquid media and abrasives, frequency, deburring time and power. It is hypothesized that by inducing compressive residual stresses on a pre-machined workpiece surface, the resulting burrs caused by machining can be minimized or even eliminated. The paper presents the findings of an investigative study into the possibility of inducing compressive residual stresses on machined surfaces by the use of ultrasonic cavitation, with the aim of reducing or eliminating burr formation. The paper also briefly reviews the development of ultrasonic cavitation and covers published work on deburring by ultrasonic cavitation. Experimental results are presented on the performance of ultrasonic cavitation peening on the residual stress in Stavax stainless steels and on micro-burr formation.     

基于ANSYS的磨削残余应力场仿真研究

作为影响工件表面完整性的关键因素之一,残余应力影响工件强度,在制造时会导致产生变形和开裂等工艺缺陷,同时在制造后的自然释放过程中也会导致材料的疲劳强度、应力腐蚀等力学性能降低。本文借助有限元分析软件ANSYS,采用热—力顺序耦合方法,建立了平面磨削残余应力场的有限元模型。该模型能够动态反映磨削加工过程中工件表层残余应力的变化情况。在此基础上,分析了不同磨削参数对工件表层残余应力的影响,从计算机仿真角度对磨削加工工艺参数进行了优化。仿真结果表明,在磨削过程中,工件表层同时存在着残余拉应力和残余压应力,与其他磨削参数相比,磨削深度对残余应力的影响最为显著。     

磨料流微去除力学分析与可控因素影响

研究了磨料流抛光中磨粒微去除力学建模方法以及可控因素影响抛光效果的问题。以力为纽带,提出磨粒去除工件表面微凸材料的动力来源于三个方面--介质作用力、磨粒挤压载荷和磨粒冲击载荷。利用建立的力学模型,分析了磨料流加工的内在因素,其中可控因素包括：加工温度、加工压力、活塞的移动速度、磨料黏度、磨粒物理性质（如尺寸、硬度）等;研究了各可控影响因素与工件表面抛光质量及效率的关系;量化了可控因素的大小对磨粒作用在工件表面的力的影响程度;将磨粒作用在工件表面的力合成并分解为与活塞运动方向相同的轴向力和垂直于工件壁面的切向力,指出微去除效果随轴向力与径向力的比值改变而发生变化,设计出简易的测量轴向力和径向力的方案。用试验验证了所建模型和可控因素对抛光效果影响,以及工件表面的加工纹理方向直接影响工件表面粗糙度的减小率和材料去除率的正确性。     

微晶玻璃超光滑表面残余应力的对比分析研究

通过对微晶玻璃、陶瓷、金属3个试件进行超精密加工,使试件表面粗糙度值达到纳米级,采用非破坏性的X射线衍射sin2ψ法测量原理对不同试件的残余应力进行了测试研究。结果表明：在试验条件下,3个试件都只存在残余压应力,并且陶瓷的残余压应力最大,金属残余压应力最小。超光滑表面残余应力的研究对提高表面完整性,改善加工工艺具有重要的意义。     

砂轮约束磨粒喷射加工外圆表面创成机理及三维形貌

磨粒喷射精密光整加工是重要零件在磨削后进行去除表面缺陷层、降低粗糙度和波纹度为目的光整加工新工艺。试验在MB1332A外圆磨床上完成,加工试样为表面粗糙度0.6 m左右的45钢。加工表面形貌和微观几何参数分别用扫描电子显微镜和Micromesvre2表面轮廓仪测量。应用自相关函数对磨削加工表面和光整加工表面进行分析,并研究材料去除机理和微观表面形貌的创成机理。在楔形区游离磨粒获得能量对工件进行抛磨、滑擦、和微切削是材料去除机理的核心因素,磨料流体侧向挤出是均化和降低表面波纹度的主要因素。试验结果表明,试样表面从连续的方向一致的沟槽被随机不连续的微坑所代替,表面粗糙度明显得到改善。随着加工循环的增加,工件表面的粗糙度值由0.6 m下降到0.2 m左右。此外,光整加工可以获得各向同性网纹交错的表面,表面轮廓的支撑长度率提高,对工件的耐磨性有利。     

Experimental study on grinding-induced residual stress in C-250 maraging steel

Residual stress plays a significant role in the performance of a part, while the residual stress in the ground maraging steel, which is often used in the manufacture of precision parts, is rarely mentioned. In order to understand the variations of residual stress in ground maraging steel and provide insight into the controlled-stress grinding process of the steel, the surface and subsurface residual stress distributions in ground C-250 maraging steel (3J33) were studied. The results show that the mechanical effects dominate the thermal effects in the dry grinding process, indicated by only compressive residual stress generated in the ground workpiece. Furthermore, more insights into the residual stress distribution were provided by proposing four residual stress distribution parameters including surface residual stress, peak compressive residual stress, the depth of peak compressive residual stress, and residual stress penetration depth. The variations of these parameters were comprehensively studied. Results show that the surface residual stress and peak compressive residual stress depend greatly on the grinding speed and higher grinding speed generates larger compressive residual stress, while the depth of peak compressive residual stress varies slightly with the grinding parameters. The residual stress penetration depth increases with the increase of the grinding speed and grinding depth, and decreases with the increase of the workpiece speed. The results in this study can be used to assist in controlled-stress grinding applications for high performance critical parts of maraging steel.