Key Engineering Materials Vols. 656-657

Abstract: In surface grinding, the shape error is occurred by the thermal deformation of a ground workpiece. To finish the workpiece with high accuracy, it is necessary to understand the temperature distribution of the workpiece during grinding process. However there is no study to analyze the temperature distribution of a large workpiece during surface grinding process. In this study, an advanced simulation analysis method of the temperature distribution for a large workpiece was developed. In the developed simulation analysis method, the temperature distribution was calculated from the power consumption of the wheel motor. The power consumption can be obtained easily without any specialized equipment. To evaluate the developed simulation analysis method, in-process measurement of the temperature distribution of a large workpiece was also carried out. A large workpiece ground in this study weights about 1.3 tons. The temperature distribution was measured with thermistors mounted in many places of the ground workpiece. At the area close to the grinding surface, it was found that temperature rises immediately after the passage of grinding wheel with measuring the developed in-process measurement system. On the other hand, at the area far from the grinding point, temperature does not change quickly. The in-process measured temperature distribution agreed well with the simulated results.

Abstract: Ni based heat-resistant alloys have high strength at high temperature. In addition, they have low thermal conductivity and work-hardening properties. Therefore, Ni based heat-resistant alloys are known as a difficult-to-cut material. The final goal of our study is to develop a cutting method for extending the life of cutting tools for Ni based heat-resistant alloys. As a first step, this study investigated the size effect in machining on initial tool wear in Ni based heat-resistant alloys cutting. Using two types of Ni based heat-resistant alloys with different average grain size, orthogonal cutting tests were performed under changing uncut chip thickness from 12.5 to 200 μm. The cutting speed and width of cut were 30 m/min and 1 mm, respectively. As a result, it was found that when the uncut chip thickness is less than the average grain size, the initial tool wear strongly depends on the average grain size. In contrast, when the uncut chip thickness is sufficiently larger than the average grain size, the initial tool wear does not depend on the average grain size. These results indicate that the ratio of the uncut chip thickness to the average grain size is an important factor to extend the life of cutting tools for Ni based heat-resistant alloys.

Abstract: Behavior of the material adhered to the cutting edge of a cermet insert was evaluated based on the profile of the machined surface in continuous turning of an austenite stainless steel SUS304. Height of the adhesion material decreased rapidly with increase of the cutting speed from 10m/min to 20m/min. The behavior of the adhered material was more stable than we expected. The adhered layer near the cutting edge was very stable, while the growth or breakage of the adhered material happened on the surface of the stable layer.

Abstract: In a large-area electron beam (EB) irradiation method developed recently, high energy EB can be obtained without focusing the beam, and large-area EB with almost uniform energy density distribution of 60mm in diameter can be used for instantly melting and evaporating metal surface. Then, the surface smoothing and surface modification of metal molds made of steel, cemented carbide and ceramics can be performed efficiently. When the large-area EB is irradiated to a sharp edge, the material removal remarkably progresses at the edge due to the heat accumulation and EB concentration there, which leads to the edge rounding. Our previous study clarified that micro-deburring was also possible by using this phenomenon. Moreover, this method would be effective for removal of discontinuous micro burrs generated by thermal machining processes, such as EDM and laser cutting. In this study, the possibility to completely remove micro burrs generated in EDM was experimentally investigated. The difference in micro-deburring characteristics with the type of workpiece material was also investigated. As a result, the EDM micro burrs with a height of about up to 50μm could be completely removed by this method. Furthermore, it was made clear that the magnetic property of workpiece materials greatly influenced the deburring characteristics, and the thermal property such as melting point and thermal conductivity also did.

Abstract: EDM finishing technology has progressed recently, and very small surface roughness can be obtained by controlling the electrical discharge conditions. Also, EDM using powder mixed fluids can improve the surface characteristics. Therefore, the EDM finished surface is highly expected to be applied as a final metal mold surface. In that case, the characteristics of EDMed surface influence the molding performance and the life of metal molds. As a new surface finishing method by EDM, the characteristics of EDMed surface using a nickel powder mixed fluid was experimentally discussed in this study, since nickel coatings have been widely applied to improve the corrosion resistance and the mold releasability of metal molds. Experimental analysis clarified that the resolidified layer containing nickel content could be formed on the surface by EDM in nickel powder mixed fluid. Also, the water repellency and the releasability of molded resin from the EDM finished surface could be improved.

Abstract: Micro-channel chips used in micro total analysis systems are attracting attention in medicine. In generally the photolithography technology used in semiconductor manufacturing is used to manufacture micro-channel chip Si-dies. However, this technology requires many processes, such as mask fabrication and the application of photoresist to a substrate as well as expensive clean room facilities. A micro-channel chip has a micro-groove 30–100 μm wide. This study examined how to form a fine groove by cutting with a micro-endmill, with the aim of shortening the window time and reducing the cost. This steel die requires high accuracy, for example, a burr area ratio of not more than 5% of the groove bottom area, a surface roughness of the side and bottom faces of less than 1μmRz, and a change in the sectional area of less than 1%. So, this study examines micro-endmill’s cutting conditions, for example cutting speed, feed per tooth, and axial depth of cut. In MQL (minimum quantity of lubricant) cutting, the early fracture occurs when cutting was began. The cause has bad removing of the chips in MQL cutting, it is considered that the chips of hardened work have been re-cut as the result. Therefore, this study applied ultrasonic cavitation to milling, in order to solve this subject. This report experimentally examined the cutting performance of ultrasonic cavitation-assisted milling. We obtained the following results. In cutting distance of 20 m, the burr of MQL cutting is generated more than 5%, on the other hand, the burr of ultrasonic cavitation-assisted milling is less than that. In ultrasonic cavitation-assisted milling, a tool wear and fracture can be decreased by improvement of removing chips and lubrication.

Abstract: An attempt is made here to join 2024 aluminum alloy plate by friction stir joining (FSJ) using tools with different eccentricity. Joint surface morphology was observed, and the sizes of both arc line spacing and flash were measured. Furthermore, study the effect of eccentricity of the tool on the surface topography of FSJ joint and analyze the formation of the joint surface topography. It is found that, the space trajectory of long axis of shoulder which formed by the eccentricity of the tool determine the morphology of the arc lines; the ratio between the feed speed and the rotation speed determine the arc line spacing; length of time that long axis of shoulder squeeze the edge of the joint line in the advancing side and the retreating side determines the size of flash in both sides of the joint line. Arc lines were regularly distributed in the joint lines and there are also regular texture structure distributed in the flash of each side. The flash in the advancing side is less than the retreating side. Increasing the amount of eccentricity, it has litter effect on the arc line spacing but will destroy the arc lines morphology in the joint surface and promote the formation of filamentous flash structure in the both sides of the joint.

Abstract: Recently, carbon fiber reinforced plastics (CFRP) are expected to be used more in the aerospace and automotive industries, because of their outstanding lightweight material characteristics and tensile strength [1][2]. Underlying this are problems closely related to improvement of the earth’s environment. However, a mechanical property is influenced by the difference in the distribution state of the carbon fiber, and the adhesion intensity of the binding material. Moreover, they have the characteristic of intense anisotropy, strength wise depending on the orientation of the carbon fibers [3][4]. Therefore, CFRPs are considered difficult-to-machine materials [5], because the surface finish deteriorates according to the carbon fiber orientation. Establishing the optimal cutting conditions to solve such problems also from an economical viewpoint is essential. In our study, end milling operations of different carbon fiber orientation CFRP composite material were investigated with three kinds of different helix angle end mills. Evaluations were based on the surface finish, cutting force and cutting temperature. Moreover, the relationships between the carbon fiber orientation and the machining operations were determined. We earlier evaluated the machinability from the relationship between carbon fiber orientation and tool helix angle by down-cut milling to solve these problems [6]. In this study, machining operations of different carbon fiber orientation CFRP composite material were investigated with three kinds of different helix angle end mills by up-cut milling. Evaluations were based on the surface finish, cutting force and cutting temperature. Moreover, the results of this experiment were compared with the results of down-cut milling.

Abstract: During micro electrochemical machining process, the gap between tooling and workpiece is dynamically and mutually influenced by multiple machining parameters, which include machining voltage, feed rate, electrolyte flow rate and others. Once inter-electrode gap could not be kept easily with a stable distance due to spark or short-circuit situation maybe happened to damage the cathode. Hence, it is needed to have a real-time protection function embedded within the μECM machining controller. The study of the short-circuit protection module for electrochemical machining is based on field programmable gate array (FPGA) system architecture. The advantages of the digital logic FPGA chips are programmable, high-response and stable operation, custom development and combination of multiple functions with Silicon Intellectual Property. It can achieve special process control or operation analysis logic to meet specific application requirements process equipment control, logic processing and signal analysis. Through the design and application technology of the digital logic FPGA chip, we can develop customized and combine of multiple functions with Silicon Intellectual Property. These silicon intellectual properties combined with the soft-core embedded processors can form the system on programmable chip control module. With a variety of Silicon Intellectual Properties restructuring integration and use of FPGA programmable features that can programmable short-circuit protection logic for electrochemical machining. This module combines power signal capture circuit device, and continuing to capture current signals during electrochemical machining process. The current signals via analog to digital converters and digital filtering, and based on the selection of the short-circuit logic electrochemical determine whether the establishment of short-circuit conditions. When a short circuit occurs, the module can react immediately turn off the power supply, to protect the machining electrode and enhance precision machining.

Abstract: Recently, high-combustion-efficiency jet engines have become required in the aircraft industry. High burning temperatures are necessary to maximize the combustion efficiency of jet engines. Inconel 718, which has excellent mechanical and chemical properties, has been selected for use in many jet engine parts. However, Inconel 718 is a difficult material to cut because of its low thermal conductivity. Consequently, wet cutting is typically used to reduce the heat generated in cutting Inconel 718. Wet cutting, which uses a large amount of cutting fluid, is costly and requires considerable energy for maintenance and disposal of the cutting fluid, making this cutting method environmentally unfriendly. To reduce the associated cost and environmental load, the near-dry cutting method, which uses a very small amount of cutting fluid, may be preferable for cylindrical cutting of Inconel 718. However, this method has some drawbacks, such as the cutting stock removal rate and the wear on cemented carbide tools. For example, the cutting stock removal rate is lower than with wet cutting because cutting edge fracture occurs easily in near-dry cutting. In this study, we conducted experiments to examine the relationships between the tool materials, cutting speed and tool fracture in near-dry cutting and wet cutting, and we compared the results obtained using the two cutting methods. We found that an S05-type cemented carbide coating can reduce tool wear. We also found that in the early stages of cutting, between cutting speeds of V = 50 and 90 m/min, the tool wear can be comparatively reduced.