Advances in Science and Technology Vol. 139

Abstract: In machining of difficult-to-cut materials, increase of temperature in tool tip is one of the main reasons resulting in short tool life. Heat can promote adhesion wear and diffusion wear at rake face, accelerate thermal plastic deformation. Furthermore, heat could also accelerate flank wear and promote adhesion wear at flank face. As a result, machining precision of tool will become worse. The common method applied to reduce temperature of tool tip is cutting with coolant supply. Conventional coolant supply is only effective to cool down areas around cutting zone with low pressure when cutting speed is low. When higher cutting heat is generated, the fluid can be vaporized to form a high-temperature steam barrier and most of the fluid suppled does not penetrate in the area adjacent to cutting zone. However, high pressure coolant might overcome the disabilities of flood coolant in milling. Present relevant research focused on effect of ultra-high pressure coolant (UHPC) on rake face mainly. In this study, to improve the machining efficiency (processing time) by using end mill, a prototype of end mill with internal coolant nozzles (both rake side and flank side) was designed and CFD (Computational Fluid Dynamics) simulations were conducted to find out the relatively effective coolant supply method for coolant penetrating in cutting zone of flank face mainly. Beyond that, effects of UHPC on rake face were also examined. During the latest experiments, tool wears, cutting length and roughness of work material were measured under both dry and wet cutting conditions. For wet cutting, three kinds of coolant supply method were applied: flank face only, rake face only and both rake face and flank face. For each method, coolant was supplied under the pressure of 3MPa, 7MPa, 14MPa and 20MPa. Tool wear was significantly reduced, and roughness was improved by high pressure coolant supply.

Abstract: This study is aimed to estimate the fatigue damage ratio and to analyze the structural integrity for the monopile foundation of NREL 5-MW wind turbine. For simulating the uncertainty of environmental conditions, various random seeds, tide heights, and wave orientations are considered in the analyses. The Design Load Case 1.2 of IEC 61400-3 is applied in this study. A sequential approach is adopted to calculate the fatigue damage ratio. Firstly, the environmental conditions are implemented into the BLADED code. Secondly, ANSYS is employed to compute the stress/deformation using the output loading data from BLADED. Finally, the fatigue damage ratio is calculated by MATLAB using relevant fatigue theories. The results show that an increase in tide height causes a greater fatigue damage in the foundation. The maximum fatigue damage ratio is found in the case with a middle wind speed which is closer to the rated wind speed and is associated with the occurrence probability. The overall results demonstrate that the methodology developed in this study is applicable to the assessment of fatigue damage in the monopile foundation of OWT.

Abstract: In this paper, to confirm the effectiveness and validity of the open-source software Salome–Meca, we constructed and operated Salome–Meca in a design/development environment and performed basic problem solving and eigenvalue analysis, as well as structural analysis. A parametric study was then carried out in collaboration with the open-source software Dakota. Analysis results of Salome–Meca matched both theoretical values and analysis results of ANSYS. Furthermore, the parameter research in Dakota confirmed the eigenvalues and deformation behavior of a pump column pipe as each variable in Salome–Meca was changed; moreover, Salome–Meca and Dakota executed a series of analysis operations normally and automatically. Therefore, Salome–Meca and Dakota are expected to optimize the shape of a structure while avoiding resonance points at natural frequencies.

Abstract: Recently, the use of carbon fiber-reinforced plastic (CFRP) has been picking up in aerospace and automotive industries. However, machining of CFRP produces fine cutting chips, which disperse in the machining environment and can be hazardous to workers and machine tools. Therefore, a cutting-chip disposal technology is required to address this problem. This study investigated the chip dispersal behavior during the drilling of CFRP to identify the factors that affect the dispersal of cutting chips. The focus of this study was the airflow field generated by drill rotation. Therefore, a simulation analysis for around the drill edge was used. The results of the drill edge simulation and chip discharge behavior during CFRP drilling were validated experimentally. The results suggested that the airflow field around the drill edge caused by drill rotation did not significantly affected chip dispersal.

Abstract: A hydrostatic bearing using ionic liquid (IL) has been developed to float semiconductor wafers in a high vacuum chamber. In semiconductor manufacturing, it is important to suppress overheating of wafers and maintain a constant temperature distribution. This method aims to achieve uniform temperature distribution by supplying IL from the backside of the wafer to float it, thereby without mechanical contact. However, since there are no examples of wafers levitated by hydrostatic bearings using IL in a high-vacuum environment, the effect of circulating IL to the vacuum conditions such as vacuum pressure and outgassing were investigated in this study. Experimental results showed that the developed prototype machine was capable of maintaining a stable ultrahigh-vacuum of 10^-5 Pa and supplying sufficient pressure to levitate wafers even when 100 ml of IL was circulated.

Abstract: In general, high-precision machines, such as machine tools and measuring equipment, have employed moving tables with hydrostatic bearings. Hydrostatic bearings for these high-precision applications require high bearing stiffness and response speed. Various flow-control restrictors inserted in oil passages were proposed to improve bearing characteristics. However, the active control of conventional flow-control restrictors has some shortcomings because most flow-control restrictors employ voice coil motors (VCMs), which generally consume a large amount of electricity and raise the oil temperature. The increased oil temperature decreases the oil viscosity, which reduces bearing stiffness and damping. Although piezo actuators can solve the above problems and are suitable candidate alternatives to VCMs, their small range of travel has prevented their use in flow-control restrictors. In this paper, a novel flow-control restrictor using a bending beam in stroke expansion is proposed for the purpose of employing piezo actuators. In addition, the bearing characteristics of the hydrostatic bearing with the proposed flow-control restrictor were investigated numerically. In this investigation, the Rayleigh-Ritz method for solving the deformation equations of the bending beam and the divergence formulation method to obtain the pressure distribution in the hydrostatic bearing were adopted in the numerical calculations. The results showed that the hydrostatic thrust bearing with the proposed restrictor has higher stiffness compared with conventional hydrostatic bearings using a capillary restrictor.

Abstract: Recently, as workpieces have become increasingly fine, there has been growing demand for small-diameter hole drilling of 1 mm or less. Compared to general drills, small-diameter drills have lower tool rigidity and poor chip evacuation, making them prone to breakage. In actual machining operations, the workpiece may be wasted owing to unexpected tool breakage. Therefore, there is a growing expectation for "the development of prediction technology to avoid breakage" of small-diameter drills. In this study, we analyzed the mechanism of breakage for small diameter drill, which will help future research on the prediction and detection of tool breakage.

Abstract: The previous research confirms that the shape of measurement objects influences the measurement results, and the influences can be reduced by aligning the normal of the measurement object with the laser projection axis when using a laser displacement meter for 3D shape measurement [1]. but when the laser projection axis aligns with the normal of the measurement object, calculated based on the design value, the influence of the tilt of the measurement object is omitted if the measurement object has machining or mounting errors. This paper proposes a high-precision shape measurement method for on-machine measurement that considers machining errors and validated its effectiveness.

Abstract: In this paper, we propose a swing-up control law for the Pendubot, a type of two-joint, two-link, underactuated robot in which the shoulder joint is actuated and the elbow joint is unactuated, considering the restricted angular movement of the shoulder joint. The proposed control law is designed by the energy-based method. Using the phase plane trajectories obtained from the angular and angular velocity oscillatory motion of the forearm, a target trajectory of the shoulder joint is calculated such that the mechanical energy of the forearm motion increases. We design a tracking control law for the shoulder joint with respect to a target trajectory. The maximum amplitude of the target trajectory directly restricts the angular motion of the actuator. The effectiveness of the proposed method is verified by numerical simulation and actual experiments.