Design of rib plate of electrode in electrochemical smoothing and electrobrightening of large hole

This study discusses the improvement of surface finish of medium or large holes beyond traditional drilling, boring, rough turning, or extruding by electrochemical smoothing using inserted rib-plate electrodes. High electrical current is not required when the rib plate is used to reduce the engaged area for large hole. Traditionally, the hole polishing requires a sequence of complicated premachining or scarce manual skill. In the current experiment, six types of electrode are completely inserted and connected to both continuous and pulsed direct currents. The controlled factors include the chemical composition and the concentration of the electrolyte, and the diameter of the electrode. The experimental parameters are the current density, on/off period of pulsed current, rotational speed of electrode, and the electrode geometry. For the inserted electrodes, a thin rib plate with small wedge angle towards the root of the plate provides more sufficient discharge space, which is advantageous for polishing. The electrode of single plate performs better than the double-plate electrode. The electrode of a single plate with slant discharge flute performs the best polishing effect. Pulsed direct current can slightly improve the polishing effect at the expense of increased machining time and cost. It was also found that electrobrightening after reaming or precise turning uses quite a short time to make the hole bright, and the electrochemical smoothing saves the need for reaming or precise turning, making the total process time less than the electrobrightening.     

<Emphasis Type="Italic">Continuous Secondary Ultrasonic Electropolishing of an SKD61 Cylindrical Part</Emphasis>

An effective ultrasonic-aided electropolishing system using low-cost electrodes for polishing cylindrical parts is developed. The process can be integrated with the primary processes of traditional turning, drawing, form rolling, or extrusion to achieve a good surface finish for moulds. Ultrasonic energy is applied to the electrolyte for residue discharge during electropolishing. Both continuous and pulsed direct current are tested in the study. The controlled factors include the chemical composition and concentration of the electrolyte, the electrolyte temperature, the flowrate of electrolyte, the initial gap width, and the rotational speed of the workpiece. The experimental parameters are the frequency and power of the ultrasonic vibration, electrical current density, pulse period, rotational speed of the electrode, the electrode feedrate, and the electrode geometry. The incorporation of ultrasonics is found to be more effective than the use of pulsed current, without sacrificing the polishing time. An average surface roughness of 0.3 μm can be obtained by this method. ID="A1"Correspondance and offprint requests to: Professor H. Hocheng, Department of Power Mechanical Engineering, National Tsing Hua University, Hsinchu, Taiwan. E-mail: hocheng@pme.nthu.edu.tw     

Design of effective plate-shape electrode in ultrasonic electrochemical finishing

This research provides a process of ultrasonic aided electrochemical finishing using a low-cost electrode with high efficiency. It requires no expensive special-purpose equipment or high material removal as the conventional ECM does. It offers fast improvement of the surface roughness of the workpiece and is a new area in ECM. In the current study, the electrochemical finishing is classified into electrochemical smoothing and electrobrightening, higher electrical current is not required when an effective plate-shape electrode is used to reduce the response area. This process can be used for various turning operations including profiling, form turning, and flute and thread cutting. Through simple equipment attachment, electrochemical smoothing and electrobrightening can follow the cutting on the same machine and chuck. The controlled factors include the chemical composition and concentration of the electrolyte, the initial gap width, and the flow rate of electrolyte. The experimental parameters are the current density, rotational speed of the workpiece, on/off period of pulsed current, frequency and power level of ultrasonics, and the electrode geometry. Smaller end radius and smaller angle of declination are associated with higher current density and provides larger discharge space and better polishing effect. The electrode of inclined plane with slant discharge flute performs the best. The average effect of the ultrasonics is better than the pulsed current while the machining time needs not to be prolonged by the off-time. It was also found that electrobrightening after precise turning needs quite a short time to make the workpiece smoothing and bright, and the electrochemical smoothing saves the need for precise turning, making the total process time less than the electrobrightening.     

Design of ECM tool electrode with controlled conductive area ratio for holes with complex internal features

The design method of electrochemical machining (ECM) tool electrode with controlled conductive area for the machining of holes with given complex internal features was presented in this paper. Such holes were difficult to machine with traditional mechanical machining methods. In authors’ previous work, it has been proved that electrochemical machining (ECM) using tool electrode with controlled conductive area ratio was effective to machine many kinds of complex holes. However, it is considered that the inverse problem, i.e., designing of suitable tool electrode for given internal feature is of great importance for practical application. Therefore, in this work, the proposed ECM process was modeled to investigate the electric potential and current distribution in the electrolyte and on the electrodes’ surface, and the evolution of inner hole profile. Then, the relationship between conductive area ratio and the machining depth was investigated by a set of fundamental simulation experiments. Simulation result showed that suitable tool electrode with specific helical conductive area can be designed for the machining of hole with given internal feature. A prototype tool electrode with non-uniform conductive area ratio from its tip to the root was fabricated and used in the verification experiment. The machining result showed that a free-formed hole was successfully shaped and the inner hole profile is in well accordance with the given internal feature.     

Synchronous finishing processes using a combination of grinding and electrochemical smoothing on end-turning surfaces

A new finishing mode has been utilized as an effective finishing tool design with an electrode and a nonconductive grindstone to execute grinding and electrochemical smoothing synchronously. This mode can be used for various end-turning operations. Through simple equipment attachment, grinding and electrochemical smoothing can follow the cutting process on the same machine. Among the factors affecting electrochemical smoothing, grinding performance combined with electrochemical smoothing, is primarily discussed. In the experiment, different types of electrodes are used with continuous and pulsed direct current. The control factors include die material, chemical composition, and concentration of the electrolyte. The experimental parameters are finish tool and workpiece rotational speed, flow rate of electrolytes, gap width between electrode and workpiece, electrical current density and pulsed period, and finishing tool geometry. High workpiece and electrode rotational speed produces a better finish. A thin electrode is associated with higher current density and provides larger discharge space for a better finish. Pulsed direct current can promote the effect of electrochemical finishing. Decreasing the height of the finish tool to a partial-form tool is associated with less restricted electrolyte flow and more discharge space, which creates better finishes than the full-form tools. The grindstone, with an adequately convex shape, also appeared to have an adequate initial gap width between the electrode and workpiece, which matches enough current density and obtains a better finish. The most effective geometric design for the finishing tool and the advantage of the low-cost equipment in electrochemical smoothing, following end-turning, is investigated in this study.     

公差弥补法在极坐标钻铰齿孔量具中的应用

根据钻铰齿孔极坐标检具的具体情况和生产现状 ,通过对该检具的综合误差分析提出的公差弥补法可有效地应用于钻铰齿孔工序的检测中。推出的检具综合误差计算 ,对实施公差弥补法提供了量化的计算依据。该方法在生产中应用 ,解决了长期困扰生产的一个大难题     

Electrical discharge machining of submicron holes using ultrasmall-diameter electrodes

We have carried out the electrical discharge machining (EDM) of submicron holes using ultrasmall-diameter electrodes. Two types of electrode were used: tungsten electrodes fabricated by the combination of wire electrodischarge grinding and electrochemical machining, and silicon electrodes originally designed as probes for scanning probe microscopes. The diameters of the former and latter were 1 μm or less, and less than 0.15 μm, respectively. Holes were drilled using a relaxation-type pulse generator at an open-circuit voltage of less than or equal to 20 V with the machine's stray capacitance as the only capacitance. Using tungsten electrodes, holes of less than 1 μm in diameter and more than 1 μm in depth were successfully drilled. A 1.3-μm-wide slot was also fabricated by drilling many holes with a small pitch. It was possible to drill holes of approximately 0.5 μm diameter using silicon electrodes because the electrode diameter was less than those of the tungsten electrodes. These holes have the smallest reported diameter for holes drilled by EDM, indicating the possibility of submicron- and nanoscale machining by EDM.     

Proposal of ECM method for holes with complex internal features by controlling conductive area ratio along tool electrode

Holes with complex internal features are difficult to machine with traditional mechanical machining methods. In this paper, a novel electrochemical machining (ECM) method using a tool electrode with controlled conductive area ratio to shape the complex inner surface of the hole was presented. The machining process was modeled to investigate the electric potential and current density distribution on the electrodes’ surface and in the electrolyte, and the evolution of the shape of inner surface of the hole. Simulation results showed that the proposed ECM method has the potential to create holes with various complex internal features. A prototype tool electrode with gradually decreased conductive area from its tip to the root was fabricated and used in the verification experiment. The machining result showed that a reverse-tapered hole was successfully shaped and the inner hole profile is in well accordance with the simulation result.     

Design of freeform surface finish using burnishing assistance following electrochemical finishing

This study discusses the performance assessment of the continuous burnishing processes following electrochemical finishing using a design, which incorporates a finish-tool that includes an electrode and a nonconductive burnishing-tool. One can expect to make an effective evaluation on the processing features and set up the complete data for processing parameters. In the future, it is also expected to spread a freeform surface finish instead of the conventional hand or machine polishing. In the experiment, a model toy missile is taken as a workpiece. The electrode is used with the continuous and pulsed direct current application. The burnishing-tool uses ceramic material and is connected with the electrode and axial feed. It was found that the finished effect of the finish-tool with convex features is better than mat of the concave features. Pulsing direct current can slightly improve the effect of electrochemical finishing. High rotational speeds produce a better finish for workpieces. This presents an effective and low-cost finishing process that includes the design of a finish-tool, which uses burnishing assistance, and follows electrochemical finishing after traditional machining makes the freeform surface of a workpiece smooth and bright.     

Electron backscattered diffraction characterization technique for analysis of a Ti2AlNb intermetallic alloy

This investigation was conducted to ascertain the benefits of electropolishing after mechanical polishing for electron backscattered diffraction of a Ti₂AlNb intermetallic Ti−21Al−29Nb (at.%) alloy containing the orthorhombic (O) and body-centered-cubic (BCC) phases. Electropolishing was performed at −40 °C in 6% H₂SO₄ methanol solution. Atomic force microscopy was used to measure the surface topography in attempt to correlate nano-scale surface roughness with electron backscatter diffraction pattern quality. The results suggest that mechanically polishing with colloidal silica (SiO₂) or alumina followed by electropolishing is a sufficient surface preparatory technique for producing quality electron backscattered diffraction patterns for O + BCC microstructures. However, poor pattern quality results after mechanically polishing without electropolishing. High-quality orientation maps for O-dominated O + BCC microstructures were only possible through mechanical polishing followed by electropolishing. The data also suggest that surface roughness, on the order of 50 nm, has less effect on pattern quality than subsurface deformation. Overall, removing the near-surface damage was more critical than reduction of topography.     

数控钻床多功能自动刀架设计

由于在实际加工中有好多垂直面上的孔需要加工,而夹具又很难去夹持,因此这就给刀架设计提出了新的要求。文章所设计的自动刀架主要实现两个面上孔的加工,同时也解决了垂直面上孔难加工的问题。所设计的刀架不仅可以实现钻孔加工,也可以实现扩孔、铰、攻丝和切削等加工。     

Precision machining of micro tool electrodes in micro EDM for drilling array micro holes

Micro electro discharge machining (micro EDM) is suitable for machining micro holes on metal alloy materials, and the micro holes can be machined even to several microns by use of wire electro discharge grinding (WEDG) of micro electrodes. However, considering practicability of micro holes <Φ100 μm in batch processing, the controllable accuracy of holes’ diameter, the consistency accuracy of repeated machining and the processing efficiency are required to be systematically improved. On the basis of conventional WEDG method, a tangential feed WEDG (TF-WEDG) method combined with on-line measurement using a charge coupled device (CCD) was proposed for improving on-line machining accuracy of micro electrodes. In TF-WEDG, removal resolution of micro-electrode diameter (the minimum thickness to be removed from micro electrode) is greatly improved by feeding the electrode along the tangential direction of wire-guide arc, and the resolution is further improved by employing negative polarity machining. Taking advantage of the high removal resolution, the precise diameter of micro-electrode can be achieved by the tangential feed of electrode to a certain position after diameter feedback of on-line measurement. Furthermore, a hybrid process was presented by combining the TF-WEDG method and a self-drilled holes method to improve the machining efficiency of micro electrodes. A cyclic alternating process of micro-electrode repeated machining and micro holes’ drilling was implemented for array micro holes with high consistency accuracy. Micro-EDM experiments were carried out for verifying the proposed methods and processes, and the experimental results show that the repeated machining accuracy of micro electrodes was less than 2 μm and the consistency accuracy of array micro holes was ±1.1 μm.     

Experimental Investigation on Electrical Discharge Drilling of Ti-6Al-4V Alloy

This article describes the experimental investigation related to creation of holes in aerospace titanium alloy workpiece using static electrode machining and electrical discharge drilling (EDD) process. Special attachment for holding and rotating the tool electrode was developed and installed on electrical discharge machining (EDM) machine by replacing the original conventional tool holder provided on die sinking EDM. The effect of input parameters such as gap current, pulse on-time, duty factor and RPM of tool electrode on output parameters for average hole circularity (C_a) and average surface roughness (R_a) have been studied. It is observed that the effect of rotating electrode machining has considerable influence on the output parameters over stationary electrode machining. The micro-graphs and photographs of few selected samples were taken by SEM and metallurgical microscope, which also commensurate with the findings of the study.     

Design of continuity processes of electrochemical finishing and grinding following turning

A newly designed finishing process utilizing an effective electrode and a grinding tool to execute the continuous electrochemical finishing and grinding processes following turning is described in this paper. The proposed process can be used for a variety of turning operations. Electrochemical finishing and grinding can be performed following the finishing process on the same machine by using a simple attachment. The factors affecting electrochemical finishing, grinding performance, and electrochemical finishing are discussed. The electrode was tested with both continuous and pulsed direct current. A higher work piece rotational speed produced a better finish. Changing the electrode design from a semicircle to a wedge form with a small end radius caused the electrolytic products and heat to dissipate more rapidly and provided the best finishing. Pulsed direct current finishing was slightly better than using continuous direct current finishing. However, the use of pulsed current would increase machining time and cost. This paper was recommended for publication in revised form by Associate Editor Dae-Eun Kim Dr. P.S. Pa obtained his doctorate at National Tsing Hua University, Taiwan. Presently he is an Associate Professor at Graduate School of Toy and Game Design of National Taipei University of Education. His fields of interest are innovative design and manufacturing processes. His current research includes ECM process for mould and die materials, precision finishing, toy design, and electro-optical engineering.     

Experimental study on micro EDM-drilling of Ti6Al4V using helical electrode

There is a growing interest in the machining of micro-holes with high aspect-ratio in difficult-to-machine alloys for the aerospace industry. Processes based on electro discharge machining (EDM) and developed for the manufacture of both micro-electrode and micro-hole are actually used, but most of them involve micro-EDM machines. In this work, the influence of EDM parameters on material removal rate, electrode wear, machining time and micro-hole quality when machining Ti6Al4V is studied. Due to an inefficient removal of debris when increasing hole depth, a new strategy based on the use of helical-shaped electrodes has been proposed. The influence of helix angle and flute depth with respect to process performance has been addressed. Main results include 37% reduction in machining times (hole diameter 800 μm) when using electrode helix angle of 45° and flute-depth of 50 μm, and an additional 19% with flute-depth of 150 μm. Holes of 661 μm diameter and as much as 6.81 mm depth, which yields in aspect ratio of 10:1, have successfully been machined in Ti6Al4V.     

五轴电火花机床加工空间斜孔的电极定位参数研究

空间斜孔的加工实质上是电火花机床电极沿孔的轴线的运动。对于由3个坐标轴旋转变换得到的空间斜孔,可通过五轴电火花机床沿3个坐标轴方向上的平移运动和绕两个坐标轴方向的旋转运动,使机床电极轴线与空间斜孔轴线重合,为此需要求解加工空间斜孔的电极定位参数。分析了通过坐标系旋转平移变换得到空间斜孔轴线的过程。根据空间斜孔的空间角度和几何参数求解空间斜孔轴线矢量的坐标变换矩阵,以建立空间斜孔轴线的矢量模型。得到了五轴数控电火花机床加工空间斜孔的电极摆角和电极定位坐标,使电极轴线与空间斜孔轴线重合。并制作了根据空间斜孔几何参数自动求解数控电火花机床的电极摆角和电极坐标的计算软件。     

Hollow target magnetron-sputter-type solid material ion source

A thin-walled aluminum (Al) hollow electrode has been inserted into an ion source to serve as an electrode for a radio frequency magnetron discharge. The produced plasma stabilized by argon (Ar) gas sputters the Al electrode to form a beam of Al(+) and Ar(+) ions. The total beam current extracted through a 3 mm diameter extraction hole has been 50 μA, with the Al(+) ion beam occupying 30% of the total beam current.     

L-Shaped Curved Hole Creation by Means of Electrical Discharge Machining and an Electrode Curved Motion Generator

The study deals with the manufacture of curved holes for water channels in moulds, which are difficult to machine. As holes are generally formed by drilling operations, curved holes are formed approximately as a combination of straight holes, which leads to interference with the smooth stream of coolant and also the low efficiency and unstable performance of cooling of the mould. To solve the problem and to create a curved hole, we devised a simple mechanism, which consists of a helical compression spring, wires, pulleys, and an electrode for electrical discharge machining, which is installed on an electrical discharge machine (EDM). The device allows the electrode to move along a curved line. From experimental results, it is found that the device enables the machining of a curved hole. In addition, the device can make an L-shaped curved hole by connecting two curved holes machined from two perpendicular directions.     

电火花加工多材质电极制备方法及试验研究

随着电火花加工技术的不断发展,利用多材质电极来实现微小复杂曲面的电火花成形加工,具有加工速度快、一次成形等特点而被广泛应用.针对多材质电极的制备,以黄铜、紫铜、铁、钼及铜钨合金等材质电极在模具钢上进行了加工试验,以研究的电极损耗及形状变化规律为基础,根据复杂曲面加工需求设计多材质电极,运用热镀法制备多材质电极,通过扫描...