scispace - formally typeset
Search or ask a question

Showing papers on "Electrical discharge machining published in 1999"


Journal ArticleDOI
TL;DR: In this paper, the machining characteristics of Ti-6A1-4V were investigated with kerosene and distilled water as the dielectrics, and the results showed that the material removal rate is greater and the relative electrode wear ratio is lower, when machining in distilled water rather than in keroene.

261 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used the finite element method to compute the temperature distribution which is post-processed for estimating material removal per spark, overcut obtained in the machined cavity, and attainable maximum penetration depth.
Abstract: The electrochemical spark machining (ECSM) process has been proved as a potential process for machining of low machinability high-strength electrically non-conducting materials, but the mechanism of material removal during the process, by and large, is not yet understood. In the present work, the electrochemical discharge is modelled as a phenomenon similar to that which occurs in arc discharge valves. This phenomenon is used to explain various experimental results, on the basis of circuit and arc discharge valve characteristics. The spark energy and the approximate order of hydrogen gas bubble diameter are computed by the proposed valve theory. Material removal rate is evaluated by modelling the problem as a 3-D unsteady state heat conduction problem. The problem is solved by the finite element method to compute the temperature distribution which is post-processed for estimating material removal per spark, overcut obtained in the machined cavity, and attainable maximum penetration depth. The conclusion drawn is that the application of valve theory to the ECSM process seems to be realistic. Estimated material removal rate, overcut and maximum penetration depth show a good agreement with experimental findings.

180 citations


Journal ArticleDOI
TL;DR: In this paper, the authors proposed a model to estimate the electrostatic forces acting on the metal surface and the stress distribution inside the metal due to this electrostatic force, and then the variation of the yield strength with depth inside a metal has also been found out.
Abstract: In Electro Discharge Machining (EDM), melting is the main process for metal removal. However, for short pulses (discharge duration 100 μs), this electrostatic force becomes very small and does not play a significant role in the removal of metal. In the model proposed, the electrostatic force acting on the metal surface and the stress distribution inside the metal due to this electrostatic force have been estimated. The variation of the yield strength with depth inside the metal has also been found out and finally the 'crater depth' due to this electrostatic force has been calculated.

159 citations


Journal ArticleDOI
TL;DR: In this paper, the influence of the machining parameters (pulse-on time, pulse-off time, table feed-rate, flushing pressure, distance between wire periphery and workpiece surface, and machining history) on the performance of wire electrical discharge machining (WEDM) in finish cutting operations was investigated.

140 citations


Journal ArticleDOI
TL;DR: In this paper, an attempt has been made to develop mathematical models for optimizing electric discharge machining (EDM) characteristics such as the metal removal rate (MRR), the tool wear rate (TWR), and the surface roughness (CLA value).

131 citations


Journal ArticleDOI
TL;DR: In this article, a high spark-resistive tool, ZrB2-Cu, was used for electrical discharge machining (EDM), where steel was used as the cathode workpiece and the MMC was employed as the anode tool.
Abstract: Frequent replacement of electrodes, due to their high wear rate, is an undesired feature of most thermal plasma processes. Hence, the discovery of a high spark-resistive tool, ZrB2-Cu, is of interest. Performance evaluation of this metal matrix ceramic (MMC) employed electrical discharge machining (EDM), where steel is used as the cathode workpiece and the MMC is used as the anode tool. Compared with the performance of copper and graphite tools, ZrB2-Cu yields the highest workpiece removal rate,; and the lowest tool wear rate at high plasma heat flux conditions, resulting in an extremely low wear ratio. Energy dispersive spectroscopy shows deposition of workpiece materials (Fe, Cr, Ni and S) on the ZrB2-Cu surface after EDM. This is due to the difference between the surface temperature of the tool and the workpiece. Scanning electron microscopy and elemental mapping analysis reveal that the composite electrode erodes by a combination of dominant evaporation and melting of the metal phase, negligible melting and thermal spalling in the ceramic phase, quick refreezing of the metal phase back to the surface, and deposition of the workpiece (steel) on the tool surface. Most of the heat is conducted through the Cu phase, reducing thermal stress in the ceramic phase. This causes lower surface temperatures for the molten ZrB2 matrix; hence, the Cu tends to refreeze quickly near the surrounding ceramic matrix.

112 citations


Journal ArticleDOI
TL;DR: In this article, an experimental analysis was carried out on a Cr, Mo, V steel for die casting by using both copper and graphite electrodes, and the observed results showed the importance of electrode material, injection flushing and geometry of cutting on removal rate, electrode wear and surface quality.

96 citations


Journal ArticleDOI
TL;DR: In this paper, the characteristics of the micro-hole of carbide by electric discharge machining with a copper tool electrode are described, and the effects of changing the polarity, the tool electrode shape and the rotational speed of the tool electrodes are studied.

83 citations


Journal ArticleDOI
TL;DR: In this article, the machinability of rotary electro-discharge machining with a tube electrode was evaluated in terms of material removal rate, electrode wear rate and surface roughness.

70 citations


Journal ArticleDOI
TL;DR: In this article, a 42 μm-wide micro slit with a depth of 1.02 mm was fabricated on a Ti-6Al-4V workpiece by using 25 μm thickness copper as the material of the rotating disk electrode and kerosene as the dielectric fluid.

70 citations


Journal ArticleDOI
TL;DR: In this paper, the problem of drilling small diameter cooling holes in electrically nonconductive ceramic coated nickel alloy using combined ultrasonic machining (USM) and electrical discharge machining was dealt with.

Journal ArticleDOI
TL;DR: In this paper, a method of introducing ultrasonic vibrations into MEDM processes was conceptualized and developed, which can produce a significant increase in the aspect ratios over the current methods of microhole drilling.
Abstract: This research concerns microhole machining capabilities by means of micro electro-discharge machining (MEDM). The limitations of this machining technology as well as the current attempts to improve microhole drilling in this field are investigated. The focus in this study was to develop a novel technique that enhances the capabilities of MEDM for realization of microholes with a high aspect ratio. Based on theories in fluidization engineering and ultrasonic degassing, a method of introducing ultrasonic vibrations into MEDM processes was conceptualized and developed. A comparative analysis has revealed that the new technique can produce a significant increase in the aspect ratios over the current methods of microhole drilling. The potential of the capabilities of ultrasonic vibrations in MEDM drilling is thus emphasized.

Journal ArticleDOI
TL;DR: In this article, the effect of current, voltage, pulse-on-time and duty factor on the grinding forces and material removal rate while machining high speed steel workpiece was investigated.
Abstract: A combination of two machining processes (i.e., a hybrid process) has a potential to improve process performance. This paper reports on experimental investigation of the electrical discharge diamond grinding process that combines mechanical grinding with electrical discharge machining. In this process, the workpiece is simultaneously subjected to heating, by electrical sparks bridging the gap between the metallic wheel bonding material and the work, and abrasion by diamond grains. The effect of current, voltage, pulse-on-time and duty factor on the grinding forces and the material removal rate while machining high speed steel workpiece, are investigated. The spark discharges facilitate grinding by thermally softening the work material in the grinding zone, and consequently decreasing the nromal force. It is observed that the material removal rate increases with an increase in current and pulse on-time, while it decreases with an increase in voltage and duty factor. These independent parameters ar...

Journal ArticleDOI
TL;DR: In this paper, the metal removal rate (MRR) in geometrical cutting is developed by considering wire deflection with transformed exponential trajectory of wire centre, and its mathematical expression is derived by analytical geometry.
Abstract: Fundamental geometry properties of wire electrical discharge machining (WEDM) process in corner cutting is studied. The concept of discharge-angle is introduced, and its mathematical expression is derived by analytical geometry. A model to estimate the metal removal rate (MRR) in geometrical cutting is developed by considering wire deflection with transformed exponential trajectory of wire centre. The computed MRR is compared with measured sparking frequency of the process since they are equivalent to each other for an iso-energy type machine. A very good agreement is obtained. Both of the discharge-angle and MRR drop drastically to a minimum value depending on the corner angle being cut as the guides arrive at the corner apex, and then recover to the same level of straight-path cutting sluggishly. Hence the observed phenomenon of increased gap-voltage and decreased sparking frequency in corner cutting can be physically interpreted. In addition, the variation of the machining load caused by the change of MRR, which was taken as unknown disturbance in the past, can be predicted and used for control purpose.

Journal ArticleDOI
TL;DR: In this article, a plane-stress model is used to describe the stress distribution, and the solutions are given as Airy's functions to reveal the influence of the loads and other parameters on wire yielding.

Journal ArticleDOI
TL;DR: In this article, the use of rapid prototype patterns, made by the stereolithography technique, for the manufacture of electric discharge machining (EDM) electrodes is discussed, and other techniques such as silicone rubber casting and electroforming in the making of the EDM electrode is also described.

Patent
15 Mar 1999
TL;DR: In this paper, the positionable driver assembly (4) houses a discharge electrode in the form of a continuous wire, exposing only a predetermined length, the working portion, of that wire for discharge machining.
Abstract: In a three dimensional generic electric discharge machining (EDM) apparatus the positionable driver assembly (4) houses a discharge electrode (1) that is in the form of a continuous wire, exposing only a predetermined length, the working portion, of that wire for discharge machining. Additional portions of that wire are incrementally advanced (5) from the housing as needed. In one embodiment, that need arises from electrode erosion, and, as an incremental portion of the electrode's working portion is eroded away, an additional increment of wire is advanced from the housing to restore the working portion to the desired length. For automatic control of the working portion's length, a novel sensor (48, 49, 38, 39, 34) monitors the virtual location of the discharge spark that occurs off the tip of the electrode during machining; and a significant shift in position of the spark, indicative of electrode wear, is detected and acted upon by the apparatus (8) to automatically replenish the spent electrode portion. In another embodiment (FIG. 16), wire (75) is automatically advanced (5, FIG. 1) under control of a computer (8, FIG. 1) programmed to predict the progress of workpiece cutting in which the electrode acts as a scoop. The continuous wire, in the form of a flat ribbon, is extruded (65) in increments to form continuous segments of semi-torroidal shape as the ribbon is automatically advanced over a period from the electrode housing for discharge machining that “scoops” material from the workpiece.

Journal ArticleDOI
Y Chen1, S.M. Mahdavian1
01 Dec 1999-Wear
TL;DR: Experiments with different values of discharge current, pulse duration time and interval time in electro-discharge machining were conducted to investigate their effects on material removal rate, surface quality and dimensional accuracy of the tool and product.

Proceedings ArticleDOI
01 Jan 1999
TL;DR: In this paper, a micro electro-discharge machining method based on patterned high-aspect-ratio machining electrodes fabricated by the LIGA process is described.
Abstract: This paper describes a new micromachining method which can produce ultrafine patterned high-aspect-ratio micro components from various kinds of materials that include those which cannot be used by silicon or the LIGA processes. This method, based on micro electro-discharge machining employs patterned high-aspect-ratio machining electrodes fabricated by the LIGA process. With this method patterned structures of several metals such as stainless steel and tungsten carbide super hard alloy have been successfully machined with short machining times. In this machining, copper electrodes electroplated via the LIGA process show good performance as far as wear resistance in the fine discharge energy region is concerned. Multiple structures have been also produced in parallel by using an electrode array. These results show that this method can be used to produce high-aspect-ratio micro components. It also shows that structures from materials which cannot be used by other micromachining techniques have become possible.

Patent
06 Aug 1999
TL;DR: In this article, a tooling process that integrates solid freeform fabrication (SFF) with electroforming to produce metal tools including molds, dies, and electrical discharge machining (EDM) electrodes is described.
Abstract: This invention describes a rapid tooling process that integrates solid freeform fabrication (SFF) with electroforming to produce metal tools including molds, dies, and electrical discharge machining (EDM) electrodes. An SFF part is metalized by electroless plating and then placed in an electroplating solution, where metal is deposited upon the part by electrolysis. When the desired thickness of metal has been reached, the SFF part is removed from the metal shell. The shell is then optionally backed with other materials to form a mold cavity, and EDM electrode, or other desired parts for tooling. Thermomechanical modeling and numerical simulation with finite element analysis (FEA) is used to determine the geometry of the SFF part and the electroform thickness for minimizing the manufacturing time and cost while satisfy the tooling requirement.

Journal ArticleDOI
TL;DR: In this paper, the possibility of high efficiency and high accuracy boring holes in silicon ingot by electrical discharge machining is experimentally investigated, and it is proved that even a high aspect ratio of about 200 boring is possible.
Abstract: This article deals with high efficiency and high accuracy fine boring in a monocrystalline silicon ingot by electrical discharge machining (EDM). In manufacturing process of integrated circuits, a plasma-etching process is used for removing oxidation films. This process has recently been examined for use of monocrystalline silicon as the electrode to minimize the contamination. However, it is difficult to machine silicon accurately by the conventional diamond drilling method, because the material removal is due to brittle fracture. The machining force in the EDM process is very small compared with that in conventional machining, therefore, the possibility of high efficiency and high accuracy boring holes in silicon ingot by EDM is experimentally investigated. The removal rate of monocrystalline silicon by EDM is much higher than that of steel, while the electrode wear is extremely small. The improvement method leads to a better hole without chipping at the exit of hole or sticking of the insulator on the wall of hole. Furthermore, it is proved that even a high aspect ratio of about 200 boring is possible.

Journal ArticleDOI
TL;DR: In this paper, a reverse simulation method for die-sinking EDM was developed to solve the inverse problem of obtaining the appropriate tool electrode shape for achieving the desired final workpiece shape.

Patent
05 Feb 1999
TL;DR: In this paper, a controller of a wire electric discharge machine monitors a change in thickness of a workpiece and a current density in real time, promoting a machining speed by preventing occurrence of disconnection of wire electrode even when the change in the thickness is caused in the workpiece.
Abstract: A controller of a wire electric discharge machine monitoring a change in thickness of a workpiece and a current density in real time, promoting a machining speed by preventing occurrence of disconnection of a wire electrode even when the change in the thickness is caused in the workpiece and improving a dispersion in a machining enlargement amount. A machining distance calculating device outputs a signal at each progress of machining by a predetermined distance Δx. A main pulse number storing device counts a main pulse number for discharge machining outputted from a main pulse generator during a time period of the signal. A thickness calculating device calculates the thickness from a reference main pulse number in machining a reference thickness, the main pulse number stored to the main pulse number storing device and the reference thickness at each reception of the signal. The calculated thickness, further, a machining current, the machining speed and a machining current density are displayed. A discharge pause time control device changes a pause time period of voltage applied to the wire electrode and the workpiece in accordance with a thickness change rate and adjusts the machining current density such that no change is caused before and after the change in the thickness.

Patent
29 Jan 1999
TL;DR: In this article, an electric discharge machining apparatus including a first power source for applying machining voltage to a machining gap to generate electric discharge, a second power source that applies voltage of equal to or lower than 20 V to the machining gaps, a transistor switching bridge connected to both the workpiece and the tool electrode, a switch for selectively connecting one of the first and second power sources to the transistor switch bridge, transistor controller for controlling on/off switching operation of the transistors, and a contact detector for electrically detecting the contact between the work piece and the
Abstract: An electric discharge machining apparatus including a first power source for applying machining voltage to a machining gap to generate an electric discharge, a second power source for applying voltage of equal to or lower than 20 V to the machining gap, a transistor switching bridge connected to both the workpiece and the tool electrode, a switch for selectively connecting one of the first and second power sources to the transistor switching bridge, a transistor controller for controlling on/off switching operation of the transistor switching bridge to alternatively change polarity of voltage being applied to the machining gap, a contact detector for electrically detecting the contact between the workpiece and the tool electrode when output of the second power source is applied across the machining gap, and an NC device which controls the switch so that the first power source is connected to the transistor switching bridge when the application of the machining power is required while the second power source is connected to the transistor switching bridge when detecting the contact by the contact detector is required.

Patent
16 Apr 1999
TL;DR: In this article, a hybrid two-actuator servo system for micro-EDM electrode positioning is presented. But the authors focus on the short stroke actuator and a slower actuator for the long stroke.
Abstract: The present invention relates to an improved servomechanism for regulating the spark gap in micro electrical discharge machining (micro-EDM). The present invention utilizes a hybrid two actuator servo system for positioning the micro-EDM electrode. The hybrid system comprises a fast, easily controllable, short stroke actuator (such as a piezoelectric actuator) for good instantaneous response, and a second, slower actuator for positioning the fast actuator and for providing the required long stroke. This allows the slower actuator to “feed” the electrode into the work-piece utilizing its long stroke, and the fast, short stroke actuator to respond quickly to instantaneous variations in the spark gap, such as short circuits.

Journal ArticleDOI
TL;DR: In this article, a detailed discussion of the design of a fuzzy controller for servo feed control in wire electrical discharge machining (WEDM) is presented from the viewpoint of industrial application and implementation.
Abstract: In this paper, a detailed discussion of the design of a fuzzy controller for servo feed control in wire electrical discharge machining (WEDM) is presented from the viewpoint of industrial application and implementation. The proposed controller contains two control loops. The main loop employs fuzzy logic as a rule-based control strategy for the gap voltage control. The output scaling factor of the fuzzy controller is on-line adjusted to obtain better control performance. A secondary loop is used to maintain machining stability by adjusting the reference voltage. The developed control system is tested under the conditions of approach machining, rough machining, and cutting a workpiece with a corner working path. Experimental results show the developed fuzzy control system is more feasible and effective for commercialised WEDM machines than a proportional controller.

Book ChapterDOI
01 Jan 1999
TL;DR: The most common machining operations rely on the relative motion between the workpiece and a cutting tool, which mechanically removes material in the form of chips as discussed by the authors, and the performance of these processes is influenced by the cutting tool geometry, workpiece properties, and cutting fluid.
Abstract: Publisher Summary The most common machining operations rely on the relative motion between the workpiece and a cutting tool, which mechanically removes material in the form of chips. These include the processes of turning, planing, shaping, drilling, milling, and grinding, which are discussed in this chapter. The performance of these processes is influenced by the cutting tool geometry, workpiece properties, and cutting fluid. The interrelationships between these factors make precise analysis of machining processes difficult. The repetitive nature of many of these operations makes automation desirable, and numerically controlled machines are widely used. Other less traditional means of removing metal include waterjet machining, electrochemical methods, electrical discharge machining, electron beam machining, and laser processes. Most mechanical machining operations are based on the generation of flat or cylindrical surfaces as these are the simplest to produce. The generation of new surfaces typically requires workpiece tool relative motion in two directions. The primary motion is the cutting speed; secondary motion is the cutting feed. These two motions, together with the cutting depth, produce a transient surface. These three parameters influence aspects of machining, including metal removal rate, machining time, tool wear, surface quality, and power requirements. Other machining operations utilize different combinations of relative motion, that is, tool motion only, workpiece motion only, or a combination.

Patent
Hidetaka Katougi1
20 Dec 1999
TL;DR: An electric discharge machining apparatus with a machining condition storage device and an input-output device has been described in this paper, where the machining shape characteristic is extracted from the shape data.
Abstract: An electric discharge machining apparatus having: a machining condition storage device ( 13 ) including a machining condition database in which machining condition data are stored; an input-output device ( 14 ) for reading either of shape data of a tool electrode ( 9 ) and machining shape data of a subject (W) for machining; a shape computing device ( 15 ) for extracting a plurality of sections from the shape data, mesh-dividing the sections into split elements, giving mesh data of solidness or hollowness and extracting machining shape characteristic from the mesh data; and a machining condition setting device ( 12 ) for selecting a machining condition while making the machining shape characteristic correspond to machining condition data in the machining condition database of the machining condition storage device ( 13 ). Even when the machining shape is complex, more efficient machining can be performed because an appropriate machining condition can be set.

01 Jan 1999
TL;DR: In this article, a high spark-resistive tool, ZrB2-Cu, was used for electrical discharge machining (EDM), where steel is used as the cathode workpiece and the MMC is used for anode tool.
Abstract: Frequent replacement of electrodes, due to their high wear rate, is an undesired feature of most thermal plasma processes. Hence, the discovery of a high spark-resistive tool, ZrB2-Cu, is of interest. Performance evaluation of this metal matrix ceramic (MMC) employed electrical discharge machining (EDM), where steel is used as the cathode workpiece and the MMC is used as the anode tool. Compared with the performance of copper and graphite tools, ZrB2-Cu yields the highest workpiece removal rate, and the lowest tool wear rate at high plasma heat flux conditions, resulting in an extremely low wear ratio. Energy dispersive spectroscopy shows deposition of workpiece materials (Fe, Cr, Ni and S) on the ZrB2-Cu surface after EDM. This is due to the difference between the surface temperature of the tool and the workpiece. Scanning electron microscopy and elemental mapping analysis reveal that the composite electrode erodes by a combination of dominant evaporation and melting of the metal phase, negligible melting and thermal spalling in the ceramic phase, quick refreezing of the metal phase back to the surface, and deposition of the workpiece (steel) on the tool surface. Most of the heat is conducted through the Cu phase, reducing thermal stress in the ceramic phase. This causes lower surface temperatures for the molten ZrB2 matrix; hence, the Cu tends to refreeze quickly near the surrounding ceramic matrix. C

Patent
27 Aug 1999
TL;DR: In this article, an energy evaluation data A is calculated by adding Pdk, Psk given the prescribed weight Kd, Ks to the counted normal discharge pulse number Pd and abnormal discharge pulse numbers Ps respectively.
Abstract: PROBLEM TO BE SOLVED: To carry out a wire electric discharge machining stably without dropping the machining speed unnecessarily by mostly suiting a pause time for contributing to the wire cut prevention of a wire electrode. SOLUTION: In this device, a normal discharge pulse number Pd and abnormal discharge pulse number Ps generated in the space G between a wire electrode 53 and a work W are counted respectively and an energy evaluation data A is calculated by adding Pdk, Psk given the prescribed weight Kd, Ks to the counted normal discharge pulse number Pd and abnormal discharge pulse number Ps respectively. The machining energy given to the space G between electrodes based on this energy evaluation data A is controlled.