Towards the effective tool wear control in micro-EDM milling

The electrode wear in micro-electrical discharge milling (micro-EDM milling) is one of the main problems to be solved in order to improve machining accuracy. This paper presents an investigation on wear and material removal in micro-EDM milling for selected process parameter combinations typical of rough and finish machining of micro-features in steel. The experiments were performed on state-of-the-art micro-EDM equipment. Based on discharge counting and volume measurements, electrode wear per discharge and material removal per discharge were measured for several energy levels. The influence of the accuracy of volume measurements on the electrode wear per discharge and on the material removal per discharge are discussed, and the issues limiting the applicability of real time wear sensing in micro-EDM milling are presented.     

In-situ process monitoring and adaptive control for precision micro-EDM cavity milling

The linear tool wear compensation method (LCM) is commonly applied in micro-EDM 3-D milling to compensate the tool length wear in order to achieve high machining accuracy. Traditional LCMs mainly rely on empirical models and off-line wear measurements, whereas the process dynamics are not taken into account. When machining complex 3D cavities, an increasing number of tool wear compensation cycles have usually to be performed in order to maintain the targeted machining accuracy. This negatively affects the duration of the overall machining cycle. To realize efficient precision micro-EDM cavity milling, without the necessity to predefine Z-axis tool feed in the NC trajectory before machining, an in-situ process control system is developed to adaptively control the tool wear compensation factor based on the discharge pulse behavior. Experiments have shown that the change of the compensation factor can be detected and also a continuous increase of the factor (over compensation) leads to the saturation of the mean effective pulse frequency. Pulse monitoring therefore provides valuable information for understanding the process dynamics and for selecting the machining parameters towards better machining efficiency. Furthermore, the information gathered in-situ can be utilized to predict the tool wear and perform in-situ tool wear prediction. To implement this on machine-level, a combined off-line and in-line adaptive control of the tool wear compensation factor is proposed and experimentally validated by milling different 3D cavities. The off-line adaptive control is only necessary when the predicted machining depth error exceeds a certain limit. In this way, more than 80% of the off-line adaptive control cycles can be eliminated, whereby a total save of cycle time up to 18% has been reached, while still maintaining the desired dimensional and form accuracy.     

A new interpolation method of variable period and step size in micro-EDM milling based on square constraint

In certain applications of statistical process control, it is possible to model quality of a product or process using a multiple linear regression profile. Some methods exist in the literature which could be used for monitoring multiple linear regression profiles. However, the performance of most of these methods deteriorates as the number of regression parameters increases. In this paper, we specifically concentrate on phase II monitoring of multiple linear regression profiles and propose a new dimension reduction method to overcome the dimensionality problem of some of the existing methods. The robustness, effectiveness, and limitations of the proposed method are also discussed. Simulation results show that in term of average run length criterion, the proposed method outperforms the traditional methods and has comparable performance with another dimension reduction method in the literature.     

管坯无芯推压缩口机的研究

用主应力法分析推导了管坯无芯推压缩口成形力的计算公式,设计了液压管坯缩口机,实现了预定的功能。     

Investigate on effect of cryogenic cooling on oxidation wear of WC-Co carbide tool milling titanium alloy

Abstract

For titanium alloy at high cutting speed, the severe tool wear will ineluctably take place diminishing the available tool life because of the high instantaneous temperature rise. Especially the WC-Co material in carbide tool will be reacted with the oxygen element in the air and generate oxide, and the tool oxidation wear is inevitable. In milling Ti–6Al–4V alloy operations, this article presents the first comprehensive investigation on the oxidation wear effect of cryogenic cooling on carbide tool compared with the conventional cooling. Based on the Gibbs free energy of the chemical reaction, the machining characteristics of the oxidation reactions were analyzed in detail. A series of machining testes were executed adopting controllable cryogenic cooling milling system. The surface and cross-section morphology and phase composition characteristics of tool were measured by SEM and XRD measuring equipments, as well as the oxidation wear mechanism of tool in cryogenic cooling. The results show that the thermal oxidation degree of the elements of WC-Co is higher in the conventional cooling processing. After cryogenic cooling intervention, oxidation reactions in tool are reduced significantly. Even the most probable reaction is disappeared, and the oxidation degree is decreased. When the temperature drops to 180 K, it has the best cooling effect. In cryogenic, the effective binding of WC crystal particle to the adhesive phase Co is a major factor for inhabiting oxidation wear of tool. The investigations indicate that the cryogenic cooling method can effectively inhibit the oxidation effect of carbide tool in milling titanium alloy process, and it improves the resist oxidation ability of tool.     

高效干式切法盘形齿轮铣刀铣削力的研究

利用干式盘形成形齿轮铣刀在铣齿机上加工齿轮是提高齿轮加工效率有效途径。铣削力是其中的关键因素。研究了齿轮铣削中的顺铣和逆铣两种工艺方法,推导了铣削力计算公式。实验验证,计算的铣削力与实际铣削力基本吻合,该铣削力计算公式可以为铣削工艺选择提供参考。     

真空熔烧钴基合金-碳化钨复合涂层的研究

采用真空熔烧法制作与钢基体牢固结合的钴基合金—碳化钨复合涂层 ,利用扫描电子显微镜 (SEM)及 X射线衍射仪对涂层的组织结构和表面形貌进行观察与分析 ;采用法向拉伸法测出复合涂层与母材的界面结合强度 ;应用盘销式摩擦磨损试验机对复合涂层材料和淬火态 45钢进行了磨损对比试验。结果表明 ,采用真空熔烧方法制得的复合涂层结构致密 ,界面结合强度高 (3 70～ 40 0 MPa) ,耐磨性能好。     

轮槽加工中铣削力与铣削温度分布规律研究

轮槽铣刀的改进往往是推动轮槽加工技术进步的最直接动力,而轮槽铣刀不同点的切削用量不同,很难测量出刀具不同点的力和温度。基于微元思想并利用标准盘铣刀和等效方法进行了铣削试验,得到了轮槽铣刀相应型线上铣削力与铣削温度的分布曲线并关注了危险点。     

Study on burr formation in micro-machining using micro-tools fabricated by micro-EDM

The purpose of this study is to study burr formation in micro-machining using micro-tools. The micro-tools employed are fabricated by micro-EDM using the wire electro-discharge grinding (WEDG) method in the micro-EDM/milling machine we had already developed. Micro tungsten-carbide tool with a minimum of 31-μm in diameter had been fabricated. The simple-shaped micro-tool fabricated is able to perform the micro-machining operation which is a combination of micro-milling and grinding processes. Micro-slot and micro thin-walled structure had been produced on Al 6061-T6 materials successfully. Burr formation in micro-machining is investigated experimentally and classified into four types: primary burr, needle-like burr, feathery burr and minor burr. Formation mechanisms of these burrs and the relationship between their existence and the machining condition are discussed.     

激光熔覆WC/Ni60B涂层磨损析出强化研究

采用激光熔覆的方法,以45#钢为基体,Ni60B自熔性合金粉末为基体相,微米和纳米WC-12%Co为增强相,研究制备了WC-12%Co颗粒增强金属基复合涂层.采用MM-200环块磨损试验机,对熔覆涂层在干摩擦滑动磨损条件下进行相同载荷不同磨损距离的磨损试验,分析了涂层在干摩擦磨损中的析出现象.试验结果表明:磨损后,2种熔覆涂层的表面显微硬度均比磨损前有所提高;磨损过程中,熔覆涂层中有析出现象;析出相有望改善涂层的磨损性能.     

立式加工中心圆孔铣削工艺研究

在立式加工中心上利用铣刀直接铣削圆孔,如二维铣削圆孔、螺旋式铣削圆孔和高速铣削圆孔等.采用FUNAC0iMA系统的MVC400机床进行试验,证明直接铣削圆孔比传统的钻、铰和镗工艺能获得更好的加工效益.     

A comparative experimental investigation of deep-hole micro-EDM drilling capability for cemented carbide (WC-Co) against austenitic stainless steel (SUS 304)

Microelectro-discharge machining (micro-EDM) has become a widely accepted non-traditional material removal process for machining difficult-to-cut but conductive materials effectively and economically. The present study aims to investigate the feasibility of machining deep microholes in two difficult-to-cut materials: cemented carbide (WC-Co) and austenitic stainless steel (SUS 304) using the micro-EDM drilling. The effect of discharge energy and electro-thermal material properties on the performance of the two work materials during the micro-EDM drilling has also been investigated. The micro-EDM drilling performance of two materials has been assessed based on the quality and accuracy of the produced microholes, machining stability, material removal rate (MRR), and electrode wear ratio. The results show that deep-hole micro-EDM drilling is technically more feasible in WC-Co as it offers microholes with smooth and burr-free surfaces at the rim in addition to improved circularity and lower overcut than those provided by SUS 304. Moreover, WC-Co exhibits better machinability during the deep-hole micro-EDM drilling, providing relatively higher MRR and stable machining.     

高速面铣加工的动态铣削力和刀具振动研究

基于力学式切削力预测方法建立了面铣刀动态铣削模型,该模型充分考虑切削厚度、刀具前角和刀具后刀面磨损对铣削力的影响.在Matlab/Simulink环境下,进行了动态铣削力和刀具振动仿真及其频谱分析,并根据仿真结果对转速、齿数、刀具磨损量等影响因素进行了分析验证,该模型有利于揭示各切削参数对动态铣削力和刀具振动的影响规律,从而为实现切削加工参数优化提供理论支持.     

Workpiece and electrode influence on micro-EDM drilling performance

In recent years, the need for products containing micro-features has shown a pronounced and steady growth in several fields of application. For the development of micro-holed devices, one of the most important technologies is micro-EDM (Electro Discharge Machining). Micro-EDM can be considered as an ideal process to obtain burr-free micron-size features with high aspect ratios. In particular, micro-EDM is a non-contact material removal process in which rapid electric spark discharges remove the material composing the workpiece by means of melting and vaporizing phenomena. The present work deals with the fabrication of micro holes using micro-EDM technology. The investigation focuses on the influence of different electrodes and workpiece materials on the process performance, expressed in terms of tool wear ratio. In particular, the influence of four different workpiece materials (stainless steel, titanium, magnesium and brass), three electrode materials (copper, brass and tungsten carbide) and two different electrode shapes (cylindrical and tubular) was investigated. Moreover, an analysis of the geometrical characteristics of the micro holes in terms of conicity and diametrical overcut was carried out. An influence of electrode geometries, electrode material and workpiece material on the final output was found.     

三维微细电火花加工伺服控制系统设计及实验研究

针对微细电火花加工伺服控制系统的要求,进行了微细电火花加工伺服控制系统总体设计.伺服控制系统特点是执行机构采用步进电机+压电陶瓷的宏微细合式驱动机构,实现了大行程和小步距的有机结合,能够提高电火花加工机床的加工性能.同时Z轴增加一个振动源,实现自动排屑和微调加工间隙.通过实验验证,证明系统运行良好,运动平台能够达到较高的精度,并实现了简单的极微细电火花加工.     

薄壁结构件铣削加工动态特性研究

分析了国内外有关薄壁件铣削加工力学模型、动态特性及加工变形的研究现状;在已有文献基础上建立了侧壁铣削加工动力学分析有限元模型,并通过试验对模型进行了验证;以建立的模型为基础,进行了大量有限元模拟分析,并对结果进行了讨论.结果表明,在一定范围内提高转速有利于减小薄壁件加工变形,提高加工精度.     

精密数控机床铣刀故障监测方法的研究

刀具在加工过程中不可避免的存在着磨损和破损现象,刀具的消耗直接导致工件精度下降和生产成本增加。开展了一系列实验,深入研究刀具状态监测方法,构建了新型铣削过程刀具磨损监测试验系统。通过振动传感器和声发射传感器对铣削过程中不同磨损程度刀具的信号进行检测、采集、分析。选择对刀具磨损状态反映敏感的特征量。采用BP神经网络,建立刀具磨损特征向量与刀具磨损状态之间的非线性映射关系。     

纳米WC-Co硬质合金研究现状

综述纳米硬质合金的研究开发概况及应用。重点介绍纳米WC和WC-Co粉体的制备方法和烧结工艺,指出要成功地制备纳米硬质合金,关键在于抑制烧结过程中WC晶粒的长大。简要介绍纳米硬质合金的应用前景。     

高速铣削高锰钢的铣削力模拟与试验研究

基于正交自由切削的切削力解析法原理,采用大变形有限元法及热弹塑性本构方程建立了高速铣削加工的有限元模型,对难加工材料高锰钢ZGMn13进行了高速铣削加工过程的模拟研究,模拟了切屑的形成过程及探讨铣削力的分布.并结合大量的铣削试验,分析了高速铣削高锰钢过程中铣削力受切削参数的影响及其变化规律.仿真结果与试验数据吻合,验证了所建立的有限元模型的正确性,可对铣削力随进给速度的变化规律进行有效地预测.     

多齿圆周铣削残留面积高度研究

提出了一种非简化的多齿圆周铣削几何运动模型,该模型考虑进给速度对刀齿运动轨迹的影响,发现在多齿圆周铣削中存在残留面积的现象,并推导出计算残留面积高度的公式,公式表明多齿圆周铣削的残留面积高度与刀具齿数、每齿进给量和刀具半径有关;然后以残留面积高度公式为基础,利用Visual C++(MFC)为平台开发出计算和辅助分析残留面积高度的系统;最后采用Matlab仿真软件验证非简化模型的合理性和在多齿圆周铣削中存在残留面积.