磨料射流铣削工艺参数优化

目的对表面粗糙度和材料去除率作为输出参数的磨料水射流铣削45#钢过程进行研究,旨在寻找最优加工参数。方法对射流去除材料机理进行了分析,设计并进行了以磨料粒度、射流压力、横向进给距离、靶距为加工工艺参数的田氏正交实验。采用Minitab对不同实验参数组合下磨料水射流加工45#钢的表面粗糙度、材料去除效率进行了数据分析,并从材料去除机理方面,对4种加工工艺参数对于铣削表面质量和材料去除效率的影响程度和影响趋势,以及各因素之间的交互作用进行了分析。结果对射流铣削面表面粗糙度影响较显著的因素是横向进给距离,射流压力次之;对于材料去除效率,磨料粒径的影响最显著,横向进给距离次之。结论综合材料去除效率和表面粗糙度值,选出最优加工参数:磨料粒径2000目,射流压力120~160 MPa,喷嘴横移距离1.0~1.5 mm,靶距约30 mm。     

Surface modification by electrical discharge machining: A review

The last decade has seen an increasing interest in the novel applications of electrical discharge machining (EDM) process, with particular emphasis on the potential of this process for surface modification. Besides erosion of work material during machining, the intrinsic nature of the process results in removal of some tool material also. Formation of the plasma channel consisting of material vapours from the eroding work material and tool electrode; and pyrolysis of the dielectric affect the surface composition after machining and consequently, its properties. Deliberate material transfer may be carried out under specific machining conditions by using either composite electrodes or by dispersing metallic powders in the dielectric or both. This paper presents a review on the phenomenon of surface modification by electric discharge machining and future trends of its applications.     

短电弧加工不同直径电极间隙流场研究

在短电弧加工过程中,利用流体软件Fluent对不同的电极直径加工间隙流场进行仿真,通过极间流场中的压力场与速度场间接得出加工屑排除的变化规律,并通过实验进行验证。结果发现:电极直径的增大可以促进加工屑从加工间隙排出,减少因间隙颗粒的堆积而产生的短路现象,从而避免“二次放电”;当加工深度不变时,电极直径的大小与工件材料的去除率呈正相关,证明短电弧加工过程中存在“面积效应”;电极直径的相对变化对工件表面质量没有明显的改善,即对表面粗糙度的影响不大。     

Effects of pulsating electrolyte flow in electrochemical machining

Electrochemical machining (ECM) is a promising and low-cost process for yielding various components of difficult-to-machine materials, and has been well established in diverse applications. Distributions of gas and temperature affect the electrolyte electrical conductivity and determine the machining accuracy in ECM. Attempts have been made to generate the pulsating flow via a servo-valve in the electrolytic supply pipe, which is introduced to improve the heat transfer, material removal rate and surface profile in ECM. A multi-physics model coupling of electric, heat, transport of diluted species and fluid flow is presented. Simulation results indicate that pulsating flow has a significant impact on the distributions of velocity, gas fraction, and temperature near the workpiece surface along the flow direction. Experiments are conducted to verify the feasibility of the proposed process and study the effects of pulsating flow on material removal rate. The experimental results agree well with the simulations. Using optimal pulsating parameters, the material removal rate and surface profile are enhanced.     

高体积分数SiCp/Al复合材料超声辅助划切微观去除机理

目的 揭示高体积分数SiC_p/Al复合材料在超声辅助加工条件下的材料去除机理。方法 采用SiC_p/Al复合材料的超声辅助划切试验,探究划切参数变化对超声振幅、划切力及摩擦因数的影响规律,并通过扫描电子显微镜和激光共聚焦显微镜对划痕表面微观形貌进行观察,分析单点金刚石磨粒工具超声辅助划切材料去除的特点。结果 随着划切深度从0.01 mm增加到0.05 mm,电流值逐渐降低,电流值变化量从12 mA增加到25m A,超声振幅逐渐衰减,金刚石压头的轴向冲击作用减弱。划切深度和划切速度的增加使切向挤压切削作用增强,划切力和摩擦因数增大。在材料去除过程中,碳化硅颗粒存在破碎成小颗粒、剪切断裂破碎和拔出等多种去除形式,铝基体出现明显的塑性流动和涂覆现象,并形成切削沟槽外侧堆积。结论 当切削深度和进给速度较小时,材料去除主要是在轴向的高频振动冲击作用下完成,材料表面加工质量较好;当切削深度和进给速度逐渐增大时,材料去除是在轴向冲击破碎和切向挤压切削共同作用下完成,材料表面加工质量逐渐降低。     

On the mechanism and mechanics of material removal in ultrasonic machining

Precision abrasive machining processes such as ultrasonic machining are commonly employed to machine glasses, single crystals and ceramic materials for various industrial applications. Until now, precision machining of hard and brittle materials are poorly investigated from the fundamental and applied point of views. Taking into account the major technological importance of this subject to the production of functional and structural components used in high performance systems, it is often desired to estimate the machining rate for productivity while maintaining the desired surface integrity. The success of this approach, however, requires not only the fundamental understanding of the material removal on the microstructural scale but also the relationship between the machining characteristics and material removal rate in ultrasonic machining. In this study, the ultrasonic machining of glass was investigated with respect to mechanism of material removal and material removal rate (with basic machining parameters) with a mild steel tool using boron carbide abrasive in water as slurry. The analysis indicates that the material removal was primarily due to the micro-brittle fracture caused on the surface of the workpiece. For micro-brittle fracture mode, the relationship for the material removal rate, considering direct impact of abrasive grains on the workpiece, based on a simple fracture mechanics analysis has been established. The effect of machining conditions on material removal rate has been discussed. This research provides valuable insights into the material removal mechanism and the dependence of material removal rate on machining conditions and mechanical properties of workpiece material in ultrasonic machining.     

Analytical model to determine the critical conditions for the modes of material removal in the milling process of brittle material

Brittle materials are prone to cleavage-based fracture during machining. In conventional scale machining of brittle material, crack-propagation is the dominant mechanism of material removal which results in a degraded machined surface. The challenge is to perform machining of brittle material such that the material removal occurs predominantly by chip formation rather than the characteristic brittle fracture. In this case, a high quality finish is achieved on the machined surface. Ductile-mode machining has emerged as a promising technique to finish a crack-free machined surface on macroscopically brittle materials. In the past, ductile-mode machining has mostly been performed by single-edge cutting process. This paper outlines an analytical model to determine the critical conditions for finishing a crack-free surface on brittle material by milling process. Four distinct modes of machining have been identified in the milling process of brittle material. In this model, the critical conditions for different modes of machining have been determined with respect to the relationship between the radial depth of cut and the depth of subsurface damage caused by the brittle fracture during machining. Verification tests were performed on tungsten carbide workpiece and the experimental results have validated the proposed machining model. It has been established that if the radial depth of cut is greater than the subsurface-damage depth in the milling process of brittle material, it is possible to finish a crack-free machined surface by removal of material through a combination of plastic deformation and brittle fracture. However, if the radial depth of cut is less than the subsurface damage depth, brittle fracture must be prevented in ductile-mode milling to finish a crack-free machined surface.     

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.     

基于轴承毛坯表面分析的磨削材料去除率模型与应用实验

目的 在轴承套圈磨削加工中,传统基于动力学模型建立的磨削材料去除率模型仅考虑了磨削工件-砂轮-机床三者的弹性变形,未考虑毛坯零件表面不规则变形对模型的影响,导致传统理论模型在实际磨削应用中的效果不佳。针对此问题,基于轴承套圈毛坯表面形状分析建立了新的磨削材料去除率模型,并进行了应用实验。方法 基于轴承套圈毛坯零件表面形状的工艺研究,针对粗磨阶段毛坯零件表面不规则形状和弹性变形对磨削加工及产品质量的影响,建立不同偏心圆数量的轴承套圈结构分析方法,并提出一种以分段函数形式的磨削材料去除率模型,该模型充分考虑了轴承套圈毛坯零件表面不规则变形和偏心圆形状对磨削材料去除的影响,可有效反映轴承套圈实际材料磨削去除过程。最后,通过大量实验对所建的分段函数形式的磨削材料去除率模型进行应用实验研究。结果 与传统磨削材料去除率模型GPSM相比,所建的以分段函数形式的磨削材料去除率模型MMRG的准确率提高了96%以上,该模型可有效在线量化分析毛坯表面不规则大小及偏心圆结构。结论 该模型对指导毛坯零件制造,保证磨削加工质量和磨削加工效率有着重要的理论指导意义。     

随机网格结构固结磨料磨盘平面磨削性能研究

针对超精密磨削加工过程对工件材料去除效率、表面质量、亚表面损伤等指标的复合需求,提出一种基于泰勒多边形设计的随机网格结构固结磨料磨盘（textured-fixed abrasive plate, T-FAP）,并以光固化树脂作为结合剂基体材料混合微米级氧化铝磨料制备磨盘,使用MATLAB图像分析和磨抛轨迹仿真方法研究磨盘磨削过程中表面磨损时变图案特征对其加工性能的影响,并通过铝制工件的平面磨削实验对磨盘磨削过程中的材料去除率及工件表面粗糙度进行分析。实验结果表明：相比传统固结磨料磨盘,采用随机网格结构磨盘加工的工件表面粗糙度为0.84μm,材料去除率为3.21μm/min,能够在保证材料去除率的同时获得较高的表面精度。     

基于LS-DYNA3D的超声加工机理分析

超声加工过程中,材料的去除率直接影响加工效率.对加工过程中材料所受应力进行了数值分析,用LS-DYNA软件模拟材料在磨粒的冲击下内部应力的产生和材料被去除的过程.     

Lightweight semi-actively damped high performance milling tool

Long cantilevered high performance milling tools tend to vibrate during machining operation due to process excitation. This impairs the quality of the workpiece surface and limits the achievable material removal rate. An optimisation of the dynamic properties of these tools enables an increased machining performance. This paper introduces a lightweight design of a shell end milling tool with an integrated semi-active damping system based on magnetorheological fluids. The investigations show that this approach allows an adjustment of the dynamic behaviour of the tool. In machining experiments a significant increase of the material removal rates and improved surface quality are achieved.     

Milling error prediction and compensation in machining of low-rigidity parts

The paper reports on a new integrated methodology for modelling and prediction of surface errors caused by deflection during machining of low-rigidity components. The proposed approach is based on identifying and modelling key processing characteristics that influence part deflection, predicting the workpiece deflection through an adaptive flexible theoretical force-FEA deflection model and providing an input for downstream decision making on error compensation. A new analytical flexible force model suitable for static machining error prediction of low-rigidity components is proposed. The model is based on an extended perfect plastic layer model integrated with a FE model for prediction of part deflection. At each computational step, the flexible force is calculated by taking into account the changes of the immersion angles of the engaged teeth. The material removal process at any infinitesimal segment of the milling cutter teeth is considered as oblique cutting, for which the cutting force is calculated using an orthogonal–oblique transformation. This study aims to increase the understanding of the causes of poor geometric accuracy by considering the impact of the machining forces on the deflection of thin-wall structures. The reported work is a part of an ongoing research for developing an adaptive machining planning environment for surface error modelling and prediction and selection of process and tool path parameters for rapid machining of complex low-rigidity high-accuracy parts.     

Effects of mixed abrasive grits in slurries on free abrasive machining (FAM) processes

Effects of mixed abrasive grits in slurries on free abrasive machining (FAM) processes are studied using a single-sided lapping machine. Impacts of mixing abrasives on various parameters such as amount of material removed, material removal rate, surface roughness, particle size distribution and relative angular velocity are studied. The material removed is monitored as a function of time. The experimental results suggest that (i) mixing abrasive grits can increase the amount of material removed, (ii) smaller abrasives can directly or indirectly affect the material removal process, (iii) slurries undergo severe grain size transition during lapping, and (iv) the surface roughness did not change significantly under different loading. The results of this study may have profound implication on the FAM processes that practitioners use today because the mixed abrasive grits increase material removal rate and reduce the grain size transition, while rendering similar surface roughness.     

Disturbance of material removal in laser-chemical machining by emerging gas

Using laser-chemical machining allows a localized and precise processing of metallic work pieces. The temperature distribution on the surface is the primary factor of this selective and gentle machining method. Investigations regarding temperature and material removal related surface effects like locally induced gas bubbles and reduced material removal are shown. It is shown that the processing feed rates only have a negligible impact on the resulting temperature field and thus the width of the cavity, while laser intensity appears to be the dominant parameter. Furthermore, it is shown that emerging gas bubbles caused reduced material removal resulting in irregular cavities.     

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.     

Experimental investigation of the process behaviour in Mechano-Electrochemical Milling

The increasing demand for high-performance materials, in for example aerospace and biomedical industries, calls for more efficient and capable technologies. This paper describes a new technology, namely Mechano-Electrochemical Milling (MECM), which combines electrochemical machining (ECM) with a mechanical cutting process. The process behaviour has been investigated experimentally based on the machining of two Titanium alloys, Titanium grade 2 and Titanium grade 5. The material removal mechanism was investigated through analysis of the machined surface and removed material. Besides the slightly higher material removal rate in MECM compared to ECM, the MECM process results in more stable process conditions.     

Modeling of material removal in mechanical type advanced machining processes: a state-of-art review

Performance of any machining process is evaluated in terms of machining rate and surface finish produced. Higher machining rate and better surface finish are desirable for better performance of any machining process. Comprehensive qualitative and quantitative analysis of the material removal mechanism and subsequently the development of analytical model(s) of material removal (MR) are necessary for a better understanding and to achieve the optimum process performance. Analytical MR models are also necessary for simulation, optimization and planning (i.e. operation and process planning) of the process, prediction of process performance indicators, verification and improvements of experimental results, selection of appropriate models for specific type of work material and machining conditions, etc. Since the inception of different unconventional machining processes, various investigators have proposed different analytical models of material removal as functions of controllable process variables. A continual need for a comprehensive and exhaustive review of various analytical material removal models for different advanced machining processes is being felt. This paper is intended to fulfil this need in the area of advanced machining. Various analytical and some semi-empirical/empirical material removal models (approximately 40) for different mechanical type advanced machining processes have been comprehensively and exhaustively reviewed, and have been presented in a format suitable for quick reference.     

State of the art electrical discharge machining (EDM)

Electrical discharge machining (EDM) is a well-established machining option for manufacturing geometrically complex or hard material parts that are extremely difficult-to-machine by conventional machining processes. The non-contact machining technique has been continuously evolving from a mere tool and die making process to a micro-scale application machining alternative attracting a significant amount of research interests.In recent years, EDM researchers have explored a number of ways to improve the sparking efficiency including some unique experimental concepts that depart from the EDM traditional sparking phenomenon. Despite a range of different approaches, this new research shares the same objectives of achieving more efficient metal removal coupled with a reduction in tool wear and improved surface quality.This paper reviews the research work carried out from the inception to the development of die-sinking EDM within the past decade. It reports on the EDM research relating to improving performance measures, optimising the process variables, monitoring and control the sparking process, simplifying the electrode design and manufacture. A range of EDM applications are highlighted together with the development of hybrid machining processes. The final part of the paper discusses these developments and outlines the trends for future EDM research.     

基于等效阻抗的蓝宝石超声研磨工艺试验

由力电类比可知:超声研磨加工系统的等效阻抗可反映加工力,且二者呈正相关关系。加工系统的等效阻抗随着加工间隙的增加而减小,该加工间隙为串联谐振频率下工具平衡位置与工件之间的间隙。基于上述理论,采用等效阻抗的控制方法对蓝宝石进行超声研磨工艺试验,探索不同研磨参数对蓝宝石材料去除率及表面质量的影响,并简单对比了超声研磨与普通研磨的区别。结果表明:无论在材料去除率或表面质量方面,超声研磨均优于普通研磨。随着输出电流、阻抗阈值、研磨速度及研磨时间的增加,材料去除率均呈先增大、后减小的趋势,但增大的速度各不相同;表面质量呈先减小、后增大的趋势,且在某处存在最佳值。