Showing papers by "Naotake Mohri published in 1997"

Formation of Hard Layer on Metallic Material by EDM

Abstract: This paper describes a new method of surface modification by EDM to create a hard surface on the workpiece. When a metallic material that can make a hard carbide is used an electrode of EDM, hard layer can be made in a certain condition. The process begins with electrode wear by heat of EDM. Then worn electrode material is combineds with carbon which is a constituent of dielectric fluid and becomes hard carbide. The carbide is piled up on a workpiece and becomes a layer.In this paper, the relation between electrical conditions to form the layer and thickness of the layer is examined. When pulse duration is short, the workpiece tends to be machined and the layer is thin. While pulse furation is long, the workpiece does not tend to be machined and the layer becomes thick.It is found that this hard layer has high wear resistance. In a experiment to check wear resistance, the surface which is given a hard layer by EDM is found to be three times as resistant as the one without the layer, and it is more resistant than a surface with TiN layer with PVD.

Formation of Composite Layer Containing TiC Precipitates by Electrical Discharge Alloying

Abstract: In order to improve friction and wear characteristics, surface modification of aluminum matrix composites was carried out by applying a new method named Electrical Discharge Alloying, in which a conventional electrical discharge machine can be utilized. Titanium contained in a green compact electrode, and also carbon and silicon decomposed from a working fluid are transferred to the substrate surface through a single discharged arc. An increase in the gap voltage widens the gap distance. Since the pressure due to the evaporation of working fluid in the vicinity of a discharged arc decreases with a gap distance widened, it is hard to blow off the top layer of discharged craters with enriched titanium and carbon if the gap voltage is high. Consequently, the volume fraction of TiC in the modified surface increases with increasing gap voltage, and then the hardness of modified surfaces becomes high. The process, electrical discharge alloying, makes it possible not only to coat a composite layer containing TiC precipitates with a thickness of nearly 80 μm within a few minutes, but also to get different volume fractions of TiC by changing the gap voltage, which is one of the process parameters. Hardness of the modified surface can be controlled to have any value of 7-14 GPa by varying the volume fraction of TiC. It is also recognized that the process improves wear resistance of the modified surfaces.

Modal Analysis of Wire Electrode Vibration in Wire-EDM

Abstract: In wire electrical discharge machining (wire-EDM), it is very important to restrain the vibrations of a tool wire electrode for the improvement of machining accuracy. In this paper, we analyze the measured displacement of a wire electrode in the machining process for a thin plate with normal vibration modes. The fundamental characteristics of the vibration system are investigated through statistical analysis. 1st mode displacement behavior which is simulated under the external force caused by electrical discharge is compared with measured displacement.The force in real machining depends on the direction of the wire movement in vibration. The phase difference between the external force and the displacement is extremely important for the restraint of the wire vibration.

Incorporation of Alumina Particles with Different Shapes and Sizes into Molten Aluminum Alloy by Melt Stirring with Ultrasonic Vibration

Abstract: This paper presents the influence of particle shapes and sizes on the incorporation of Al 2 O 3 particles into molten Al-5 mass%Mg alloy by melt stirring with ultrasonic vibration. A new theoretical model of particle transfer into molten metal dealing with different shapes is proposed to estimate the difficulty in incorporation of spherical and massive particles. In the model, the particles are assumed to be spheroids with different major and minor axes. The difficulty depends on the maximum acceleration which originates from the interfacial tension: the incorporation of Al 2 O 3 particles into molten Al-Mg alloy becomes more difficult with the negative maximum acceleration increased. Four kinds of preheated A1 2 O 3 particles were added to a molten Al-5 mass%Mg alloy surface and stirred with ultrasonic vibration at 1023 K in a nitrogen atmosphere. The volume fraction of incorporated particles is related to the calculated maximum acceleration; that is, it is experimentally found to decrease as the negative maximum acceleration increased. According to the proposed model, the ultrasonic vibration makes the apparent contact angle of the A1 2 O 3 particle and the molten Al-Mg alloy improve from 1.78 to 0.87 rad. Gas defects, which are known to be a serious problem in metal matrix composites (MMC) produced by melt stirring, disappear in MMC samples formed with ultrasonic vibration. Moreover, the rotating torque for melt stirring decreases by applying ultrasonic vibration, because of the decomposition of agglomerate particles. Hence, the application of ultrasonic vibration to melt stirring is a novel candidate method of MMC production.

Three-dimensional shaping by dot-matrix electrical discharge machining

Abstract: This paper deals with a new prototyping method called dot-matrix electrical discharge machining (EDM) with scanning motion. The machining process by the dot-matrix method is similar to printing motion with a dot-impact printer. This method can be applied not only to EDM but also electrochemical machining and forming. A prototype of the machining unit for the dot-matrix method has six feeding devices for thin wire electrodes. The electrodes of 300 μm in diameter are arranged with the pitches of 760 μm. To obtain a smooth surface, a planetary motion in the x-y-plane is added to the feeding of the machining unit in the z-direction, the same area is machined repeatedly, or the machining unit is moved with fine feed. By compensating for the wear of the electrode during the scanning EDM, various shapes with the accuracy of micrometers order can be obtained without a formed tool electrode.

Self-running type electrical discharge machine using impact drive mechanism

Abstract: Summary form only given. Electrical discharge machining (EDM) is one of the best ways to machine fine structures because tools do not break, no burr is generated, and machinability does not depend on the hardness of a conductive workpiece. A self-running electrical discharge machine is developed to machine fine structures on a local area of a large workpiece. This electrical discharge machine consists of two parts: a 3-DOF mobile table and a 2-DOF electrode feeding device. The whole machine measures about /spl phi/140/spl times/140 mm and weighs 700 g. This machine moves on a workpiece with the impact drive mechanism which utilizes rapid deformations of piezoelectric elements. A control method of the table is introduced. The direction of the movement of the mobile table depends on the ratio of the applied voltage to each piezo driver. The machining performance is investigated experimentally. The steps of the mobile table is 0.5 /spl mu/m in the x and y directions 0.1 /spl mu/m in the z direction, and 20 /spl mu/rad in the /spl theta/ direction. The rate of the driving pulse is 90 Hz. The mobile table can move both on a dry and a wet surface. There is no interference of the movement among the axes in case of driving in the z or /spl theta/ directions. Machined holes and grooves with the electrical discharge machine of the self-running type are demonstrated. The motion accuracy without a guide is approximately 0.5 mm and 0.4 deg.

Machining Process of Insulating Ceramics by Electrical Discharge Machining.

Abstract: In this paper, a new electrical discharge machining (EDM) of insulating ceramics with an assisting electrode and its machining mechanism are described. The proposed method is available for machining a complex shape on insulating ceramics. In experiments, insulating Si3N4 ceramics is machined with an electrical conductive plate as the assisting electrode in working oil. The machining starts on the assisting electrode. When the tool electrode reaches at the interface between the assisting electrode and the insulating ceramics, the machining does not proceed for several minutes. In this period, discharge concentration or short circuit state occurs frequently, and an electrical conductive black layer generates on the ceramics surface. After complete formation of the black layer at the interface, machining of insulating ceramics progresses in stable; meanwhile, the black layer is continuously generated on the ceramics surface. This black layer consists of turbostratic carbon and α-SiC. The equilibrium phase diagram of carbon and silicon explains the formation of the black layer. Fundamental technology of machining insulating ceramics into complex shape by EDM has been established through the above consideration.

Transient Response of Wire Vibration System in Wire Electrical Discharge Machining.

Abstract: In this paper, a tool wire vibration system in wire electrical discharge machining (wire-EDM) is identified and primary factors of the wire vibration in real machining are investigated by considering transient response of the tool wire to exciting force caused by a single discharge. The influence of pressure caused by each discharge and the influence of an electrostatic force on wire displacement are investigated under a mechanical model in which the tool electrode is assumed to be a beam under a certain tensile force. The displacement of the wire induced by the electrostatic force was observed as the indicial response to applied stepwise voltage. This displacement by electrostatic force is considered as the initial condition for the impulse response to the following discharge. The wire responds to the impulsive pressure which is generated locally by a discharge. The response in the experiments is corresponding to the impulse response simulated with the beam model of the wire.

Dot-matrix electrical discharge machining for shaping fine structure

Abstract: In this paper, a new prototyping method called a dot-matrix electrical discharge machining (EDM) with scanning motion is proposed, and a prototype of a machining unit by the dot-matrix method is developed. The machining process by the dot-matrix method is similar to printing motion with a dot impact printer. This method can be applied to not only EDM but also electrochemical machining and forming. A prototype of the machining unit has six feeding devices for thin wire electrodes. The electrodes of 300 /spl mu/m in diameter are arranged with the pitches of 760 /spl mu/m. To obtain smooth surface, a planetary motion in the xy plane is added to the feeding of the machining unit in the z direction, the same area is machined repeatedly or the machining unit is moved with fine feed. By compensating the wear of the electrode during the scanning EDM, various shapes with the accuracy of micrometers order can be obtained without a formed tool electrode. The surface modification by EDM with thin wire electrodes is also investigated.

Self-running Electrical Discharge Machine by Using Impact Drive Mechanism.

Abstract: 本論文では大型工作物への局所的な精密加工法の一つとして,インパクト駆動機構を用いた自走式放電加工機を提案し,試作した加工機に関する実験を行った.結果をまとめると以下のようになる.(1)xy軸方向に移動しながら連続した穴を加工した.その穴を測定した結果,約5mmの移動に対して直線からのずれは0.05mm以下,角度の誤差は0.4°であった.(2)x軸方向にサーボをかけて電極側面を用いて溝加工を行った.z軸送り部だけでなくテーブル部も放電加工を行うのに十分な応答性を持つと考えられる.(3)電極送り機構の運動とテーブル部の運動の間では干渉は起こらなかった.今後は,本方式と立体を校正基準とする機上計測法を組み合わせ,小型形状測定機械を移動基準面の上で移動させることで,加工結果の形状や表面粗さ等の測定を行うシステムを構築することを検討する予定である.

Development of End Effector Utilizing Parallel Mechanism for EDM with a Scanning Motion.

Abstract: 本論文の結論は以下の通りである.(1) 3 自由度のパラレルマニピュレータを開発し, それを放電加工機の主軸に取り付けた走査放電加工システムを構築した.(2) 本マニピュレータにより, 溝の加工とシリコン電極による表面処理が可能であることを確認した.(3) リニアモードの周波数範囲は200Hzまでであり, 放電加工を行うには十分な応答周波数を持つ.今後は, ロボットなどを用いた他の加工システムに対してパラレルメカニズムの適用を検討していく予定である.