Advanced Materials Research Vol. 1017

Abstract: Electrically conductive PCD (EC-PCD), which was made of electrically conductive diamond particles, was applied to an electrode for EDM. In this study, properties of EC-PCD electrode in the EDM of cemented carbide were investigated and the results were compared with those of copper-tungsten (Cu-W) electrode and standard PCD (S-PCD) electrode. In terms of EDM speed, 35μm/min with Cu-W electrode, 15μm/min with S-PCD electrode and 22μm/min with EC-PCD were recorded. As for the electrode wear rate, though Cu-W electrode wore by 20-30%, S-PCD and EC-PCD did not wear at all and even the electrode length became longer by several micro meters. Roughness value of the EDMed surface was Rz=8μm with both Cu-W and S-PCD, while it was Rz=3μm in the case of EC-PCD. From the above, it was found that EC-PCD showed excellent performance in the electrode wear rate and the roughness of the EDMed surface, though EDM speed was 0.7 times of Cu-W electrode.

Abstract: In order to achieve a high efficient and high quality EDM of PCD, the authors have developed a new PCD having superior electrical conductivity by using boron diamond as a source material. On the other hand they applied a method to give ultrasonic vibrations to the electrode, and have made it clear that even the standard PCD could be machined at the similar level of efficiency to the cases of EDMing die steels and cemented carbides. With a purpose to obtain a good surface roughness on the PCD at high efficiency, various EDM conditions and methods were compared in this paper. Firstly, influence of discharge duration time was examined, and it was found that a shorter pulse duration time as t_e=0.5μs showed high efficiency and smaller electrode wear rate. Secondary, influence of bipolar pulse current method was examined, and it was found that the method effected higher efficiency but rather large amount of electrode wear resulted. Thirdly, ultrasonic assisted EDM was conducted, and it was found that the method showed superior result regarding efficiency and wear rate on both standard PCD and EC-PCD. A combination use of ultrasonic assisted and bipolar pulse current EDM methods was also attempted in this research. On the contrary to the expectation, efficiency and electrode wear rate became worse in EDM of standard and EC-PCD in comparison with other methods tested before.

Abstract: Laser forming is a technology which can form sheet material such as steel and plastic by irradiating a laser beam on the surfaces of material. In the forming, it does not need costly dies and molds, and forming degrees of freedom are high. However, since the forming mechanisms are complex, complete forming technology for practical use has not been developed. The objectives of this paper are to explain phenomena of laser forming by experiments and FEM analysis and to develop a forming method of curved surfaces by laser forming. The phenomena are explained by the temperature change, stress change, and plastic strain change at a laser irradiation point which was obtained by FEM analysis. Line energy is proposed for explanation of laser forming phenomena to classify the forming mechanisms, and a method is proposed in order to form curved surfaces of sheet material by irradiating a laser beam on maximum and minimum curvature lines. The effectiveness of the method was verified by a basic experiment.

Abstract: Recently, the demand for long life to industrial products has risen. The high strength alloy coating on necessary part can decrease a manufacturing cost for life prolongation. This study proposes a laser surface alloying method to form an Fe-Al alloy coating on a carbon steel. By laser heating to an Al foil stuck on the steel, the mutual diffusion proceeds and the Fe-Al alloy grows. The material property of the generated alloy is greatly different according to a heat treatment temperature. For example, Fe₃Al grows at 950 °C or more, and it has high toughness. A furnace heating effects the properties of inside of base material negatively. A high-frequency heating is not suitable for a local surface reforming. The laser processing is suitable for a local surface reforming. A defocused CO₂ laser was irradiated to the Al foil stuck on the steel block by the shot lining in various processing conditions. The metal structures of the laser irradiated area was observed, to search for the suitable processing conditions for alloy coating. It was clarified that a local Fe-Al alloy coat was able to be formed without change of the properties of base material by high speed laser scanning.

Abstract: Dental zirconia ceramics have been widely used in dental restorations due to their superior aesthetical and mechanical properties. Ultrasonic vibration assisted grinding (UVAG), as a novel effective machining process for hard and brittle materials, is introduced into directly machining sintered dental zirconia ceramics. This study is dedicated to investigating the influence of input variables (spindle speed, feedrate and cutting depth) on surface roughness during UVAG of sintered dental zirconia ceramics. The experiment is conducted through single-factor method, and the experimental results are statistically analyzed by One-Way ANOVA. Besides, the influence tendency of input variables on surface roughness is also obtained. The results indicate that the influence of spindle speed on surface roughness is highly significant. The value of surface roughness rises with the increase of spindle speed, feedrate, and cutting depth. Therefore, a better surface quality will be achieved with the combination of lower spindle speed, cutting depth and feedrate.

Abstract: The effect of changes in the magnetic field on the magnetic flux density during the electrical discharge machining (EDM) of a permanent magnet is reported. During EDM of the permanent magnet, a second magnet for the external magnetic field was set up, and the internal temperature and surface magnetic flux density on the opposite surface of the permanent magnet during machining were evaluated. It was found that even though the internal temperature of the magnet remained unchanged, the surface magnetic flux density changed when the external magnetic field was varied. In addition, the magnetic field generated by the magnet changed when a plate with high permeability was pressed onto the surface of the permanent magnet.

Abstract: Lapping is widely applied to hole surface finishing. However, for small holes of high hardness material, low efficiency and unstable hole surface quality of traditional lapping cannot be ignored. In this paper, the ultrasonic transducer and horn–tool were designed by the analytical method and the finite element method (FEM). An equipment of ultrasonic lapping for small holes was developed. Vibration performance tests of developed equipment were conducted by using microscope and laser displacement sensor. The result showed that the amplitude of ultrasonic lapping equipment can meet manufacturing demand. The machining performance of the developed ultrasonic lapping equipment was also investigated by comparing the surface quality and material removal rate with traditional lapping. The result showed that the higher material removal rate and better hole surface quality can be obtained by ultrasonic lapping.

Abstract: Copper-tungsten alloy which is widely used in the field of EDM has high melting temperature and excellent electrical and thermal conductivity. Copper tungsten electrodes for electrical discharge dressing of metal-bond wheel were studied, and experiments were conducted to observe their wear performance in this paper. Orthogonal experiment was designed to explore the wear at the edge of and the bottom of electrode with the machining of holes. Thickness of the carbon layer, micro topography and experimental results were analyzed. Low current and big pulse duration can reduce the electrode wear rate. Although carbon on the electrode surface can be wiped out easily, wear rate of copper-tungsten electrode decreases with the increasing in thickness of the carbon at the initial phase. There are fewer cracks and residue presented on the machined surface by microscope.

Abstract: In general, the form generation theorem of laser removal processes has not yet been established. The cause of this is that laser is a light source and has no tool shape as conventional machining tools. Therefore, its transcription characteristics could not be determined. In this paper, the application of the form generation theorem to laser removal process is examined experimentally. In order to establish the form generation theorem, first the “equivalent tool shape” of the focused beam is determined. To determine the equivalent tool shape, a groove is machined with the laser intensity just above the removal threshold of the work piece material. From the machining result, the cross-section of the groove is machined in to a V-shape. The V-shape is peculiar to the workpiece material, thus can be determined as equivalent tool shape of laser machining. The groove shape can be simulated numerically by considering the removal threshold and dependence of absorption characteristics to incidence angle. The numerical simulation and the experimental result were in good agreement. Based on the equivalent tool shape and the form generation theorem, a rectangular cross-section groove is experimented. As a result the groove was finished with a flat bottom having ruggedness like a saw-blade. This result indicates that the laser shaping based on the form generation theorem can be possible by laser irradiation with properly suppressed intensity.