Approach for Polishing Diamond Coated Complicated Cutting Tool: Abrasive Flow Machining(AFM)

Lower surface roughness and sharper cutting edge are beneficial for improving the machining quality of the cut?ting tool, while coatings often deteriorate them. Focusing on the diamond coated WC?Co milling cutter, the abrasive flow machining(AFM) is selected for reducing the surface roughness and sharpening the cutting edge. Comparative cutting tests are conducted on di erent types of coated cutters before and after AFM, as well as uncoated WC?Co one, demonstrating that the boron?doped microcrystalline and undoped fine?grained composite diamond coated cutter after the AFM(AFM?BDM?UFGCD) is a good choice for the finish milling of the 6063 Al alloy in the present case, because it shows favorable machining quality close to the uncoated one, but much prolonged tool lifetime. Besides, compared with the micro?sized diamond films, it is much more convenient and e cient to finish the BDM?UFGCD coated cutter covered by nano?sized diamond grains, and resharpen its cutting edge by the AFM, owing to the lower initial surface roughness and hardness. Moreover, the boron incorporation and micro?sized grains in the underly?ing layer can enhance the film?substrate adhesion, avoid the rapid film removal in the machining process, and thus maximize the tool life(1040 m, four times more than the uncoated one). In general, the AFM is firstly proposed and discussed for post?processing the diamond coated complicated cutting tools, which is proved to be feasible for improving the cutting performance

Uniform surface polished method of complex holes in abrasive flow machining

Abrasive flow machining(AFM) is an effective method that can remove the recasting layer produced by wire electrical discharge machining(WEDM). However, the surface roughness will not be easily uniform when a complex hole is polished by this method. CFD numerical method is aided to design good passageways to find the smooth roughness on the complex hole in AFM. Through the present method, it reveals that the shear forces in the polishing process and the flow properties of the medium in AFM play the roles in controlling the roughness on the entire surface. A power law model was firstly set up by utilizing the effect of shear rates on the medium viscosities, and the coefficients of the power law would be found by solving the algebraic equation from the relations between the shear rates and viscosities. Then the velocities, strain rates and shear forces of the medium acting on the surface would be obtained in the constant pressure by CFD software. Finally, the optimal mold core put into the complex hole could be designed after these simulations. The results show that the shear forces and strain rates change sharply on the entire surface if no mold core is inserted into the complex hole, whereas they hardly make any difference when the core shape is similar to the complex hole. Three experimental types of mold core were used. The results demonstrate that the similar shape of the mold core inserted into the hole could find the uniform roughness on the surface.

Abrasive Waterjet Machining Simulation by Coupling Smoothed Particle Hydrodynamics /Finite Element Method

In dealing with abrasive waterjet machining（AWJM） simulation,most literatures apply finite element method（FEM） to build pure waterjet models or single abrasive particle erosion models.To overcome the mesh distortion caused by large deformation using FEM and to consider the effects of both water and abrasive,the smoothed particle hydrodynamics（SPH） coupled FEM modeling for AWJM simulation is presented,in which the abrasive waterjet is modeled by SPH particles and the target material is modeled by FEM.The two parts interact through contact algorithm.Utilizing this model,abrasive waterjet with high velocity penetrating the target materials is simulated and the mechanism of erosion is depicted.The relationships between the depth of penetration and jet parameters,including water pressure and traverse speed,etc,are analyzed based on the simulation.The simulation results agree well with the existed experimental data.The mixing multi-materials SPH particles,which contain abrasive and water,are adopted by means of the randomized algorithm and material model for the abrasive is presented.The study will not only provide a new powerful tool for the simulation of abrasive waterjet machining,but also be beneficial to understand its cutting mechanism and optimize the operating parameters.

Machining performance on hybrid process of abrasive jet machining and electrical discharge machining

To develop a hybrid process of abrasive jet machining (AJM) and electrical discharge machining (EDM),the effects of the hybrid process parameters on machining performance were comprehensively investigated to confirm the benefits of this hybrid process.The appropriate abrasives delivered by high speed gas media were incorporated with an EDM in gas system to construct the hybrid process of AJM and EDM,and then the high speed abrasives could impinge on the machined surface to remove the recast layer caused by EDM process to increase the efficiency of material removal and reduce the surface roughness.In this study,the benefits of the hybrid process were determined as the machining performance of hybrid process was compared with that of the EDM in gas system.The main process parameters were varied to explore their effects on material removal rate,surface roughness and surface integrities.The experimental results show that the hybrid process of AJM and EDM can enhance the machining efficiency and improve the surface quality.Consequently,the developed hybrid process can fit the requirements of modern manufacturing applications.

A review on the erosion mechanisms in abrasive waterjet micromachining of brittle materials

The fabrication of miniature structures on components with high-integrity surface quality represents one of the cutting edge technologies in the 21st century.The materials used to construct such small structures are often difficult-to-machine.Many other readily available technologies either cannot realise necessary precision or are costly.Abrasive waterjet(AWJ)is a favourable technology for the machining of difficult-to-machine materials.However,this technology is generally aimed at large stock removal.A reduction in the scale of this technology is an attractive avenue for meeting the pressing need of industry in the production of damage-free micro features.This paper reviews some of the work that has been undertaken at UNSW Sydney about the development of such an AWJ technology,focusing on the system design currently employed to generate a micro abrasive jet,the erosion mechanisms associated with processing some typical brittle materials of both single-and two-phased.Processing models based on the findings are also presented.The review concludes on the viability of the technology and the prevailing trend in its development.

Machining of the Flat Surfaces with Abrasive-metallic Lapping Tools

The constructional principle of abrasion metal disc is that abrasive insertions are spread uniformly on the working surface of a metal base. During lapping by means of such tools only the machining fluid is dosed and that by drop. Abrasive elements of circular shape pellets are produced by mixing boron carbide BC400 micrograins with electrographite components, the pellets were pressed with a load of about 12 kN. Next they were heated in furnace at about 520K for hours, then cooled together with the furnace. Tests were carried out on the making of circular abrasive insertions of which the main components were born carbide and micrograins of electric copper mixed the epoxide resins.

THE EROSIVE PROCESS IN ABRASIVE WATERJET CUTTING OF POLYMER MATRIX COMPOSITES

A study is carried out which analyzes the machinability of polymer matrix composites under an abrasive waterjet (AWJ) and the associated erosive process or mechanism. It shows that AWJ cutting can produce good quality kerf at high production rate if the cutting parameters are properly selected. A scanning electron microscopy (SEM) analysis of the cut surfaces reveals that the erosive process for the matrix material (resin) involves shearing and ploughing as well as intergranular cracking, while shearing is a dominant process for cutting the fibres in the upper cutting region but the fibers are mostly pulled out in the lower region.

High Speed Lapping of SiC Ceramic Material with Solid (Fixed) Abrasives

An experimental investigation is carried out to machine SiC ceramic material through the method of high speed plane lapping with solid(fixed) abrasives after the critical condition of brittle-ductile transition is theoretically analyzed. The results show that the material removal mechanism and the surface roughness are chiefly related to the granularity of abrasives for brittle materials such as SiC ceramic. It is easily realized to machine SiC ceramic in the ductile mode using W3.5 grit and a high efficiency, low cost and smooth surface with a surface roughness of R_a 2.4?nm can be achieved.

FORMING AND PRECISION MACHINING TO NANOMATERIALS LUMP

The technology of forming and machining lump nano-materials has beeninvestigated. Grinding, abrasive machining test has been conducted to Fe, Co, Ni and Al lumpnano-materials. Experiments have been done to measure grinding force, grinding thermal, machiningroughness and micro-hardness. Image analysis is carried out by metallographic and scanning tunnelmicroscopic microscope. Researches provide the basis data for forming and machining lumpnano-materials.

THE EFFECT OF, ABRASION ON LOW STRESS MECHANICAL PROPERTIES OF FABRIC

The low stress mechanical properties of a pure wool and a wool / polyester blend twill fab-rics which were abraded at various abrasion cycles were measured using the KES-F system andthe Instron tensile machine. The surface change of fabrics before and after abrasion was stu-died by means of scanning electron microscope. With the increasing number of cycles, the re-covery behavior of the fabrics studied in tensile, shear and bending deformation decrease, theantibuckling ability lowers, the friction coefficient increases. The geometric roughness de-creases during the first step of abrasion then enhances with further abrasion. The influence ofabrasion on mechanical properties of the pure wool fabric are larger than that of blend fabric.

Research on the abrasive wear resistance of YDCrMoV coating produced by CO_2 shielded flux-cored wire surfacing

Caterpillar construction machines play an important part in many fields such as hydraulic and electric engineering, the construction of highway, for its particular of structure. The walking system of caterpillar construction machines is always under the condition of three-body abrasive wear. The abrasive wear of walking system is very severe, which always results in damages of components or structures of walking system of caterpillar construction machines. It is very important to repair the walking system by cladding technique. The abrasive wear properties of four kinds coatings produced by the shielded flux-cored wire surfacing for the repair of the damaged components of walking system of caterpillar construction machines have been studied experimentally on an MLS-23 type wet sand rubber wheel abrasive tester. The surfaces morphologies of the abrasively worn specimens and their microstructures are investigated by transmitting electron microscopy (TEM) after wear testing. Results show that the wear mechanism of cladding metals of the flux-cored wire No.1 and the No.2 is micro-cutting while that of the No.3 and the No.4 is micro-ploughing. The four kinds of flux-cored wire coatings present great potential applications for the repairing of caterpillar construction machines in the Three Gorges Engineering.

Experimental Investigation on Constrained Abrasive Fluid Polishing for Optical Glass

To find a cost effective,high-precision and environmental friendly way of polishing for optical glass,a series of experiments were focused on about constrained abrasive fluid polishing. Since abrasive particles can repeatedly impact the workpiece in a multidirectional way with high energy, the constrained abrasive fluid polishing method for optical glass has been proposed based on the abrasive fluid machining theory and elastic emission machining theory. A constrained abrasive fluid polishing system was designed and developed to polish K9 glass samples. Results show that K9 glass obtains a high accuracy with less fluid. Experiments indicate that,in a more effective,high-precision and environmental friendly way,constrained abrasive fluid polishing is possible to improve the quality of workpiece surface compared with free abrasive fluid polishing. In the process of removing materials of constrained abrasive fluid polishing,it gives priority to removing the materials of high spot and the high frequency error of smooth local zone can be modified. The abrasive particles can repeatedly impact the workpiece in a multidirectional way,and there are certain relationship among surface quality,material removal rate, and parameters such as speed,clearance, angle, time and particle size. In the process of constrained abrasive fluid polishing, it shows a high material removal rate,and it needn't to clamp workpieces. As a result,it could improve the processing efficiency significantly. The research on constrained abrasive fluid polishing has a practical significance and practical value in industrial production.

Experimental study of free abrasive wire sawing by using multi-strands wire

Grains in the slurry can be brought into cutting zone by steel wire with a certain speed to achieve the purpose of removing the workpiece material in the free abrasive wire sawing machining. Because its own of multistrands characteristics,we use it to replace the steel wire to do slicing experiment. In this paper,multi- strands wire is made by seven metal wires and has many grooves on its surface. Compared with steel wire,it can carry more grains into cutting zone which is conducive to improving the slicing efficiency. We do some comparative slicing experiments by applying multi-strands wire( 0.25 mm) and steel wire( 0.25 mm) to cut optical glass(K9). The results show that slicing efficiency and the surface roughness of the workpiece sliced by using multi-strands wire are better than that by using steel wire,but the kerf width of the former is wider than that of the latter in the same experimental conditions.

Clarification of abrasive jet precision finishing with wheel as restraint mechanisms and experimental verification

According to the critical size ratio for the characteristic particle size to film thickness between grinding wheel and work, the machining mechanisms in abrasive jet precision finishing with grinding wheel as restraint can be categorized into four states, namely, two-body lapping, three-body polishing, abrasive jet machining and fluid hydrodynamic shear stress machining. The critical transition condition of two-body lapping to three-body polishing was analyzed. The single abrasive material removal models of two-body lapping, three-body polishing, abrasive jet finishing and fluid hydrodynamic shear stress machining were proposed. Experiments were performed in the refited plane grinding machine for theoretical modes verification. It was found that experimental results agreed with academic modes and the modes validity was verified.

Characteristics of force chains in frictional interface during abrasive flow machining based on discrete element method

Abrading is a very important sub-technology of the surface treatment tech no logy with vast applications in the industry. This study aims at analyzing the inherent laws of friction systems during abrading. In particle flow code modeling, the abrading process can be simplified to the movement of particles in a parallel-plate shear friction system. In this study, the PFC2D software is used to construct the particle flow friction system with the set of parallel plates and the model parameters according to the abrading processing equipment and processing materials, control the simulation of a single variable, and compare the output data to estimate the impact of change of parameters on the force chain. The simulation results show that the shear dilatancy can be divided into three stages: plastic strain, macroscopic failure, and granular recombination stages. The distribution and load rates of the weak force chains depend on the load, velocity, friction coefficient between granules, granular diameter, and number of granular layers. The number of granular layers and the load increase cause the direction of the force chain to be oriented with the vertical direction, and the force chains move toward the horizontal direction as the velocity increases. The increase in load does not cause the shear dilatancy stage to occur;the velocity, friction coefficient between granules, and granular diameter increase cause the shear dilatancy to occur gradually.

Research on the underlying mechanism behind abrasive flow machining on micro-slit structures and simulation of viscoelastic media

In this study,the machining mechanism of abrasive flow machining(AFM)microstructures was analyzed in depth according to the transmission morphology and rheological behaviors of the abrasive media.The transmission morphology demonstrated the excellent combination of the polymer melt with abrasive grains at the interface,indicating that the polymer melt,combined with the uniform distribution of the polymer chains,could exert a harmonious axial force on the abrasive grains.Based on the rheological behavior analysis of the abrasive media,for example,the stress relaxation and moduli of storage and loss,a machining mechanism model was established incorporating the effect of microplastic deformation and continuous viscous flow,which was further verified by the grooves along the flow direction.In addition,the PhanThien-Tanner(PTT)model combined with a wall slipping model was employed to simulate the machining process for the first time here.The value of the simulated pressure(1.3 MPa)was similar to the measured pressure(1.45 MPa),as well as the simulated volumetric rate(0.0114 mL/s)to the measured volumetric rate(0.067 mL/s),which further proved the validity of the simulation results.The flow duration(21 s)derived from a velocity of 1.2 mm/s further confirmed the residual stretched state of the polymer chains,which favored the elasticity of the abrasive media on the grains.Meanwhile,the roughly uniform distribution of the shear rate at the main machining region exhibited the advantages of evenly spread storage and loss moduli,contributing to the even extension of indentation caused by the grains on the target surface,which agreed with the mechanism model and machined surface morphology.

微磨料气射流加工技术研究现状与展望

微磨料射流加工技术是一种基于高能流体的磨粒冲蚀磨损加工技术,已广泛应用于难加工材料、复杂三维型面、光滑表面的加工。为进一步提高磨料射流加工过程中的精准控形控性能力,国内外学者开展了诸多基础加工理论与工艺探索等方面的研究工作。本文在概述磨料射流加工技术发展的基础上,全面总结了国内外学者在微磨料气射流加工(MAJM)技术中的微磨料气射流束发散效应及其抑制策略、材料力学性能对材料冲蚀去除模式的影响、材料冲蚀加工过程磨料嵌入抑制策略、微结构冲蚀加工几何特征等方面的主要研究成果,并对微磨料射流加工技术的难点与发展趋势进行了展望。

Simulation of abrasive flow machining process for 2D and 3D mixture models

Improvement of surface finish and material removal has been quite a challenge in a finishing operation such as abrasive flow machining （AFM）. Factors that affect the surface finish and material removal are media viscosity, extrusion pressure, piston velocity, and particle size in abrasive flow machining process. Performing experiments for all the parameters and accurately obtaining an optimized parameter in a short time are difficult to accomplish because the operation requires a precise finish. Computational fluid dynamics （CFD） simulation was employed to accurately determine optimum parameters. In the current work, a 2D model was designed, and the flow analysis, force calculation, and material removal prediction were performed and compared with the available experi- mental data. Another 3D model for a swaging die finishing using AFM was simulated at different viscosities of the media to study the effects on the controlling parameters. A CFD simulation was performed by using commercially available ANSYS FLUENT. Two phases were considered for the flow analysis, and multiphase mixture model was taken into account. The fluid was considered to be a Newtonian fluid and the flow laminar with no wall slip.

Effect of back pressure on the grinding performance of abrasive suspension flow machining

Abrasive suspension flow machining(ASFM)is an advanced finishing method that uses an abrasive suspension slurry for grinding and chamfering as well as the finishing of inaccessible components.This study examines the effect of back pressure on the grinding characteristics of an abrasive suspension flow during the grinding of slender holes.A numerical model was developed to simulate the abrasive suspension flow in a slender hole and was verified experimentally using injector nozzle grinding equipment under different grinding pressures and back pressures.It is shown that the ASFM with back pressure not only eliminates the cavitation flow in the spray hole,but also increases the number of effective abrasive particles and the flow coefficient.Increasing the back pressure during the grinding process can increase the Reynolds number of the abrasive suspension flow and reduce the thickness of the boundary layer in the slender hole.Moreover,increasing the back pressure can improve the flow rate of the injector nozzle and its grinding performance.

小孔内表面磁力研磨加工技术研究进展

磁力研磨加工是提高小孔内表面质量的一种重要光整技术,利用该技术能高效提升小孔类零部件在极端环境下的使役性能。针对小孔内表面的磁力研磨光整加工,按其发展历程对磁力研磨加工技术进行总结,归纳了磁性磨粒研磨、磁针磁力研磨、液体磁性磨具研磨、超声辅助磁力研磨和电解磁力复合研磨等加工方法的技术特点,并分析评述了其局限性。对磁力研磨加工过程中材料去除机理进行了研究,材料主要以微量切削与挤压、塑性变形磨损、腐蚀磨损、电化学磨损等方式去除,材料种类不同,去除机理也不同。其中,硬脆性材料主要以脆性断裂、塑性变形和粉末化的形式去除;塑性材料在经历滑擦阶段、耕犁阶段和材料去除阶段后主要以切屑的形式去除。此外,还对磁力研磨加工过程中的材料去除模型进行了研究,对单颗磁性磨粒材料去除模型和“磁力刷”材料去除模型进行了分析讨论。最后,对磁力研磨加工技术今后的研究发展给出了建议并进行了展望。