Substrate pre-treatment of cemented carbides using abrasive flow machining and laser beam ablation

A significant driver in research activities of manufacturers and university institutions is the improvement of tool life for cutting tools. Recent publications have shown that the substrate pre-treatment prior to coating as well as defined rounding of cutting edges are key factors for cutting tool life. Different technologies are used for substrate pre-treatment, depending on the machining task, flexibility of the process and economic aspects. However regarding the surface quality two opposing requirements come into conflict. While high surface quality supports the chip removal during machining, the film adhesion between substrate and coating is greater on rough surfaces. This paper presents a comparison of the abrasive flow machining (AFM) and laser ablation technologies as pre-treatment processes for cemented carbides. With respect to the relevant processing parameters, the effects of a pre-treatment using AFM and laser ablation on roughness, surface topography, mechanical activation and chemical composition have been determined.     

Tool grinding of end mill cutting tools made from high performance ceramics and cemented carbides

The paper presents different approaches to improve the process knowledge in tool grinding with a focus on ceramic shank-type end mills. The flute grinding operation was analyzed using a kinematical simulation to acquire an insight into the local distribution of the material removal rate or the microscopic chip parameters. Further investigations cover the cutting edge quality emerging in characteristic tool grinding operations on end mills with helical flutes made from advanced ceramics. Final machining test prove a reliable cutting behaviour without catastrophic failure and a gentle abrasive and adhesive wear observed on the ground cutting tools.     

Effect of machining fluid on the process performance of electric discharge milling of insulating Al2O3 ceramic

Wire electric discharge machining (WEDM) and electrical discharge machining (EDM) promise to be effective and economical techniques for the production of tools and parts from conducting ceramic blanks. However, the manufacturing of insulating ceramic blanks with these processes is a long and costly process. This paper presents a new process of machining insulating ceramics using electrical discharge (ED) milling. ED milling uses a thin copper sheet fed to the tool electrode along the surface of the workpiece as the assisting electrode and uses a water-based emulsion as the machining fluid. This process is able to effectively machine a large surface area on insulating ceramics. Machining fluid is a primary factor that affects the material removal rate and surface quality of the ED milling. The effects of emulsion concentration, NaNO₃ concentration, polyvinyl alcohol concentration and flow velocity of the machining fluid on the process performance have been investigated.     

改进的单向磨料流加工效果及轴向力测量研究

由合金材料制成的结构复杂工件内通道及相交部位的毛刺难以有效去除,而采用磨料流(AFM)加工工艺可以有效抛光零件复杂表面、提高工件加工质量。基于此,对不同工作压力的单向磨料流作用下,工件的表面粗糙度和扩展直径进行研究,介绍一种适用于单向AFM轴向力在线测量的装置,分析了不同加工压力和流体通道长度对轴向力和体积流量的影响。研究结果表明:4.0 MPa加工压力下的AFM加工可以有效降低工件表面粗糙度,同时使工件获得更均匀的表面粗糙度,但是4.0 MPa条件下的加工时长远大于7.0 MPa;流体通道长度越短,体积流量相对于轴向力来说随着加工压力的增加而明显增加;而对于最长的流体通道,加工压力的增加导致轴向力的增加更为显著。     

磨料流加工中夹具设计的研究

磨料流加工(AFM)是光整加工领域的一项新技术。磨料流加工由磨料流加工机床,夹具和流体磨料三部分组成。当用磨料流加工形状较复杂的零件时,夹具设计的好坏对表面加工质量和加工效率有重要的影响。本文分析了磨料通过工件孔道的特性。介绍了用于研究材料去除量与加工距离和形状关系的实验。材料去除量在通道两端比中间小是磨料流加工的一基本特性。本文讨论了如何避免因此而产生的工件变形以及如何利用这一特性来获取某种特殊效果。最后,给出了一个用于加工某不锈钢三通体的夹具。     

On ultrasonic assisted abrasive flow finishing of bevel gears

Finishing of bevel gears is an important requirement in many machining shop floors. Variants of abrasive flow machining (AFM) could be plausible solutions for finishing such parts with intricate geometries. In the present work, a relatively new variant of AFM called ultrasonically assisted abrasive flow machining (UAAFM) technique was employed to finish bevel gears made of EN8 steel. An analysis of the process has been presented with suitable illustrations. A finite element simulation of the behavior of the medium during finishing of bevel gears using the UAAFM process has been presented. A 3D model was constructed to simulate the flow of medium through the outer wall of the gear tooth surface using computational fluid dynamics (CFD) approach. The velocity, pressure and temperature values along the length of the workpiece were computed for both UAAFM and the conventional AFM processes. Further, the effectiveness of the process was investigated through experimental trials by conducting a comparison study between classical AFM and UAAFM. Ultrasonic frequency, extrusion pressure, processing time and the media flow rate were considered as the input variables while improvements in surface finish and material removal were considered as the monitored outputs. Results confirm that improvements in surface roughness and material removal are significantly higher than those obtained with conventional abrasive flow machining. The study further reveals that, the applied high frequency (ultrasonic) vibration to the workpiece has the maximum influence on the process responses among the variables considered.     

Experimental investigations into abrasive flow machining (AFM)

A new non-traditional finishing process known as abrasive flow machining (AFM) is used to deburr, radius, polish and remove recast layer of components in a wide range of applications. The process is relatively new, although around 2000 machines are in use worldwide. Material is removed from the workpiece by flowing a semisolid visco-elastic/visco-plastic abrasive-laden medium across the surface to be finished. Areas inaccessible to traditional methods, and complex passages, can be finished to high quality by this process. The process embraces a wide range of feasible applications including aerospace, dies and moulds, automotive parts, medical components, etc.In the present work, the effects of different process parameters, such as number of cycles, concentration of abrasive, abrasive mesh size and media flow speed, on material removal and surface finish are studied. The dominant process parameter found is concentration of abrasive, followed by abrasive mesh size, number of cycles, and media flow speed. Experiments are performed with brass and aluminum as work materials. Experimental and theoretical results are compared. The machined surface texture is studied using scanning electron microscopy.     

Modeling of material removal and surface roughness in abrasive flow machining process

Abrasive flow machining process provides a high level of surface finish and close tolerances with an economically acceptable rate of surface generation for a wide range of industrial components. This paper deals with the theoretical investigations into the mechanism of abrasive flow machining (AFM) process. A finite element model is developed for the flow of media during AFM and the same is used to evaluate the stresses and forces developed during the process. Theoretical analysis to estimate the material removal and surface roughness obtained during AFM is also proposed. The theoretical results are compared with the experimental data available in the literature, and they are found to agree well.     

碟轮修整单层钎焊金刚石砂轮的试验研究

单层钎焊金刚石砂轮在制作完成之初由于砂轮基体加工存在误差以及磨粒粒径大小不一等原因造成磨粒等高性不一致,这使其难以在硬脆材料的精密磨削中得到广泛的应用。采用自制的钎焊碟轮对80/100#单层钎焊金刚石砂轮进行了修整试验研究。在修整试验前后跟踪了砂轮磨粒等高性的变化,进行了SiC陶瓷的磨削试验,并观测了工件表面质量的变化情况。试验结果表明:采用此方法能够实现单层钎焊金刚石砂轮的高效精密修整。修整试验结束后砂轮磨粒等高性较好,磨削SiC陶瓷的表面质量得到明显改善,表面粗糙度Ra值达到了0.1μm以下。     

磨粒流抛光阀块内孔道的数值模拟与试验研究

针对液压阀块孔道内部结构复杂难以进行精密加工的问题,提出利用磨粒流精密抛光技术来实现加工工艺。使用流体仿真软件Fluent进行数值模拟,研究进口压力、磨料浓度、磨粒粒度等对磨粒流加工效果的影响。以液压阀块内的孔道为研究对象,对不同的进口压力、磨料浓度、磨粒粒度下内孔道磨粒流的速度、湍流动能、静压、壁面剪切力进行仿真,得出结论：当入口压力为8 MPa、磨料浓度为0.1、磨粒粒度为200目时,阀块内孔道的抛光效果较好。以该参数进行相应的磨粒流加工实验,结果表明：阀块孔道内壁面的表面粗糙度明显降低,提高了孔道内壁面的表面质量。     

An investigation of laser-assisted machining of Al2O3 ceramics planing

Laser-assisted machining (LAM), an alternative method of fabricating difficult-to-machine materials, uses primarily laser power to heat the local area (without necessarily evaporating or melting any material) before the material is removed. It not only efficiently reduces the cutting force during the manufacturing process but also improves the machining characteristics and geography with regard to difficult-to-machine materials, especially structural ceramics.This study on the application of laser-assisted machining to Al₂O₃ ceramics examines the measurements of cutting force and workpiece surface temperature as well as surface integrity and tool wear. Specifically, it uses the lattice Boltzmann method (LBM) to calculate the temperature distribution inside the ceramic workpiece during the LAM process and ensure that the laser energy causes no subsurface damage. The experimental results reveal that the LAM process efficiently reduces the cutting force by 22% (feed force) and 20% (thrust force) and produces better workpiece surface quality than conventional planing.     

Fluid flow analysis of magnetorheological abrasive flow finishing (MRAFF) process

A new precision finishing process called magnetorheological abrasive flow finishing (MRAFF), which is basically a combination of abrasive flow machining (AFM) and magnetorheological finishing (MRF), has been developed for nano-finishing of parts even with complicated geometry for a wide range of industrial applications. This paper deals with the theoretical investigations into the mechanism of MRAFF process to study the effects of various process parameters. In the present work, an attempt has been made to analyze the medium flow through the fixture by finite difference method by assuming the medium as Bingham plastic to evaluate the stresses developed during the process. A capillary viscometer has been designed and fabricated to study the effect of magnetic field on the rheological properties of the medium. Microstructure of the mixture of ferromagnetic and abrasive particles in magnetorheological polishing fluid (MRPF) has been proposed, and normal force on the abrasive particles is calculated from the applied magnetic field. A model for the prediction of material removal and surface roughness has also been presented. Theoretical results compare well with the experimental data available in the literature.     

应用ELID技术进行微晶玻璃超精密磨削

由于微晶玻璃具有优良的物理、机械性能，在光学等领域得到了越来越多的应用。ELID磨削利用在线．电解的方法修整超细粒度的金刚石砂轮，可以有效地实现硬脆材料的超精密加工。本文将ELID磨削技术应用于微晶玻璃的超精密加工，通过改进ELID磨削的关键技术，包括砂轮电火花整形、电解修整电源和ELID磨削液的改进，实现了微晶玻璃的超精密磨削加工，同时通过采用原子力显微镜对不同磨削参数下的工件表面进行分析，以保证在塑性状态下对微晶玻璃进行磨削。因此提高了ELID磨削的质量。获得了Ra2．308nm的较好表面质量。     

基于磨料流加工技术叶片泵转子去毛刺试验研究

针对叶片泵转子叶片槽两侧面及槽底孔内毛刺不能被彻底去除的问题,提出基于磨料流加工技术的方法,建立磨料流体三维模型,利用Fluent软件模拟分析槽底孔中心及槽道边沿压力分布,设计装夹方案并进行现场试验。加工后的槽道内壁光滑,无毛刺,表面粗糙度值未显著变化,尺寸精度未受影响,表明磨料流加工技术可有效去除转子槽内的毛刺。     

Behavior of the magnetic abrasive tool for cutting edge preparation of cemented carbide end mills

Magnetic abrasive processes combine characteristics of grinding and lapping. Due to deformable tool behavior, complex surface shapes and edges can be machined. Therefore, this process is predestined for preparation of drilled cutting tools. High quality finishing results require in depth process expertise. This paper focuses on the behavior of the magnetic abrasive tool taking Magnetfinish^® kinematics into account. Main characteristics of the magnetic abrasive tool behavior during finishing end mills of 12 mm diameter are reshaping and in-process densification of magnetic abrasive layer. Consequently, flute surface modifications occur only in the cutting edge surrounding area. Furthermore, in-process displacements of magnetic abrasive cause non-uniform cutting edge rounding. SEM images indicate abrasive motion along the cutting edge as the best method to obtain smooth cutting edge surface.     

Material removal analysis in abrasive waterjet cutting of ceramic plates

Fine ceramics have been recognized increasingly in structural and functional applications on account of their merits of hardness, corrosion resistance, electromagnetic response and bio-compatibility. Due to the need for dimensional control or production optimization, post-sintering machining can be required. Cutting by conventional means is most often practiced, but the associated heavy tool wear is hard to overcome. A waterjet at transonic speed carrying abrasive particles provides an effective means for hard-material removal. Undesired material fracture at entrance and exit can be reduced significantly by sequential abrasive micro-machining.

The present paper discusses the kerf formation of a ceramic plate cut by an abrasive waterjet. The mechanism and the effectiveness of material removal are studied first. Different materials are found to possess different removal rates in machining and there also exists a critical combination of hydraulic pressure, abrasive flow rate and traverse speed, below which through-cut for a certain thickness cannot be achieved. The wall finish achieved is determined by the mesh size of the abrasives: sufficient hydraulic pressure with fine abrasives will produce a smooth surface comparable to that from grinding. The kerf is slightly tapered with wider entry due to decreased cutting energy with kerf depth. A high-power input per unit length produces a small taper but a wide slot.     

Fixed abrasive diamond wire machining—part I: process monitoring and wire tension force

The process monitoring and mechanics of fixed abrasive diamond wire saw machining are investigated in this study. New techniques to affix diamond particles to a steel wire core have advanced to make this process feasible for the machining of ceramics, wood, and foam materials. Developments in fixed abrasive diamond wire machining are first reviewed. Advantages of using fixed abrasive diamond wire machining are then introduced. The process monitoring and signal processing techniques for measuring the cutting forces, wire speed, down feed rate, and wire bow angle in diamond wire saw machining are developed. The application of a capacitance sensor to measure the wire bow and a procedure to convert the wire bow to vertical cutting force in a rocking motion wire saw machine are developed. The tension force of the wire during cutting is also derived and discussed.     

磨料水射流切割工程陶瓷机理分析

高压磨料水射流切割工程陶瓷时，切割破碎物料机理极其复杂。本文以流体力学和材料断裂力学为理论基础，结合试验对工程陶瓷的切割加工进行了研究，为磨料水射流技术在脆性材料加工领域中进一步推广应用提出理论假没。     

Edge-chipping reduction in rotary ultrasonic machining of ceramics: Finite element analysis and experimental verification

Rotary ultrasonic machining (RUM) is one of the machining processes for advanced ceramics. Edge chipping (or chamfer), commonly observed in RUM of ceramic materials, not only compromises geometric accuracy but also possibly causes an increase in machining cost. In this paper, a three-dimensional finite element analysis (FEA) model is developed to study the effects of three parameters (cutting depth, support length, and pretightening load) on the maximum normal stress and von Mises stress in the region where the edge chipping initiates. Two failure criteria (the maximum normal stress criterion and von Mises stress criterion) were used to predict the relation between the edge chipping thickness and the support length. Furthermore, a solution to reduce the edge chipping is proposed based upon the FEA simulations and verified by experiments.     

Fixed abrasive machining of non-metallic materials

This paper summaries advancements in fixed abrasive machining of non-metallic materials, which include reinforced concretes, stones, rocks, carbon fiber reinforced plastic, metal and ceramic matrix composites, wood, wood-fiber plastic composite, biomaterials (bone, plaque, and enamel), and structural and electronic ceramics. The broad impacts, diverse applications, and innovations of fixed abrasive machining processes are presented. Benefits of the engineered deterministic distribution of abrasive grain grinding tools are demonstrated. Industrial perspectives and future research on innovative fixed abrasive machining technologies that enable new processes and improve the productivity are highlighted.