Key Engineering Materials Vol. 625

Abstract: The ruled surface of impeller is widely used in the industry of automobile, shipbuilding, aerospace and aeronautics. Researches on the manufacture of blade possess general meaning. The importance of their performance in the certain field and the non-replace ability of their functions in the specified mechanical systems have resulted in that the technology of manufacturing and measurement for ruled surfaces has been a critical research project in the field of dimensional manufacturing and measurements. With the rapid development of the modern science and technology, complex ruled surfaces are employed more and more widely, but their tolerances become narrower and narrower. The common impeller surfaces represented by NURBS are given and then curve and surface interpolation algorithm represented by NURBS are presented. These provide theoretical foundation for NC machining programming of impeller surface. Principals of normal offset curve and inclined offset surface are used to simplify the model. The NC milling method of divide area is presented to raise machining efficiency and to improve quality of machined surface. The machining efficiency is important in line property of rule surface, flank milling rule surface with end-milling, improve surface quality and cutter efficiency. This paper presents a calculate method to generate five-axis flank milling NC code of divide area in the blade of compressor with Vericut simulating the five-axis flank milling NC code and measurement the result of processing that verification the precision of five-axis flank milling. This paper also simulates four-axis machining for comparing cutting efficiency between five-axis machining and four-axis machining and the status of both the great differences in processing efficiency.

Abstract: It is difficult to hand down magic-mirror fabrication technology, which has an extremely small satiny and continuous-curvature corrugated surface, due to downsizing of veteran engineers or even their successors. Therefore, the purpose of this study is to digitalize the magic-mirror fabrication technology using a CNC technology. A mirror finishing method is thus proposed that integrates ball end-milling and magnetic polishing it on the machining center. In addition, the workpiece is end-milled from the rear. Generation of the magic-mirror surface is also carried out.

Abstract: An orbital grinding system is developed for manufacturing high precision crankshafts for 5ton-5m class ship engines. Structural analysis is carried out by 3D modeling and FEM simulation using a commercial software. The grinding system can conduct high precision grinding process for crankshafts of ship engines as well as normal small crankshafts.

Abstract: The Fast Tool Servo (FTS) is widely used for the machining of micro-structures, especially for optical micro lens array. The working principle of FTS is that a voice coil motor or a piezoelectric (PZT) actuator is used as the driving elements, and the flexure hinges are developed as the guide mechanisms. In addition, an optical encoder is applied to measure the displacement. However, the existing design of FTS is too complicated and expensive. One reason is that the stroke of the FTS for the fabrication of optical micro lens array is only a few hundred micrometers, while its precision reaches to nanometric range, thus the optical encoder in not applicable. On the other hand, there exists sluggish and creep for piezoelectric materials, which makes the control of displacement difficult. This paper develops a displacement sensor embedded voice coil motor. In the design, the driving element is ampere force of the voice coil motor which is a linear ratio to the input current. Both the two covers are thin plates which serve as compliant mechanism by supporting the deformation at the Radial direction and provide linear stiffness in the axial direction. Therefore, the output displacement is proportional to the ampere force. The existence of external force affects the actual displacement, an embedded capacitor serves as displacement sensor will detects the real displacement, and the external force can be estimated by the current and measured displacement, which makes the motion control easy. At the same time, a multiphysics model of the developed FTS is built in this study by using finite element method and the displacement control under different cutting force is studied. The experimental results show that the developed FTS is efficient for achieving short stroke with high precision.

Abstract: In the respect of ultra-precision manufacturing of axisymmetric surface, the machine tool with tool swing feeding has less interpolation error sources compared to the conventional ultra-precision diamond turning machine tool. The installation errors of machine tool greatly affect the manufacturing accuracy of parts. Therefore, based on the multi-body dynamics theory , the structure characteristics of this machine tool, and the parts' relative positions of machine tool, in this paper we established the space geometric model and the integrated error model of machine tool integrated with the actual installation error of machine. The analysis results of the error model show that the relationship between the depth of axis (tool shaft and main shaft of machine) parallelism and the profile error is linear function; when the installation error of swing arm was lower than 150′′,the profile error of parts was less than λ/10.

Abstract: Off-axis aspheric surface is an indispensable optical device for the high precision measurement and manufacturing equipment, and the tool path generation is a very important factor for the manufacturing to obtain the surface with high precision form and nanometric surface finish. In this paper, the systemic description of tool path generation method about the off-axis parabolic surface with ultra-precision single point diamond turning is processed. Two effective methods of generating the accurate spiral tool path are proposed and compared. The proposed methods are mainly based on mathematical calculation directly from analytic surfaces, including the general process of tool path generation, cutting-tool compensation and avoiding tool interference. This work can provide the theoretical basis of choosing the cutting tool path for off-axis parabolic surface and can improve the efficiency and precision of machine. Finally, some cutting simulations are implemented to prove the proposed methods.

Abstract: Shaft and rotor deformation caused by the high pressure load, temperature and other external forces in the twin-screw compressor may produce flow leakage, tooth wear and bearing failure. A time-varying load analysis procedure is proposed in this paper to obtain the gas torques on rotors, bearing forces and the shaft deflections for the twin-screw compressor. Further, the calculated forces are compared with the existed well-known software to verify the correctness of the proposed method. Also, the forces on each bearings and the shaft deflection are predicted through KISSsoft modeling technique in this paper.

Abstract: In recent years, high-combustion-efficiency jet engines are required in the aircraft industry. Inconel 718, which has excellent mechanical and chemical characteristics. However, Inconel 718 is difficult to cut material because of its low-thermal conductivity. Consequently, Wet cutting is ordinarily adopted to reduce the heat on cutting heat edge in Inconel 718 cutting. Wet cutting which uses large amount of cutting fluid requires much cost and energy on maintenance or disposal of cutting fluid, and this method is environmentally-unfriendly. From the view point of reducing cost and environmental load, we examined the method of Near-Dry cutting which uses very small amount of cutting fluid for the cylindrical cutting of Inconel 718. However, this method has some problems, such as tool wear and cutting stock removal rate. In this report, we experimentally examined the relationship between cutting speed, tool materials, and tool fracture of near-dry cutting of Inconel 718. We compared these results with those of wet cutting, a method which is more expensive, requires significantly greater amounts of energy, and is less environment-friendly. The results indicate that when cutting speed is 100 m/min, tool fracture occurs at a cutting distance of 200 m. When cutting speed is 50 m/min, tool fracture does not occur and near-dry cutting distances can continue beyond 600 m. Moreover, tool wear could be reduced when S05 tool material, which has high bending strength, was used.

Abstract: Electrostatic film actuator is a thin, lightweight and flexible actuator composed of two plastic films with fine-pitched electrodes embedded in them. In this paper, we report a novel driving method for the actuator, in which the electrodes in one film (the slider film) are pre-charged with DC high voltages, and the slider film is driven by AC voltages applied to the electrodes in the other film (the stator film). Typically, the actuator has been driven by applying three-phase AC voltages to the electrodes in both films; in the driving method, the slider film required connections of feeding wires, whose tensions causing disturbance to its motion. The advantage of the pre-charging method is that the slider film is free from the feeding wires; in turn, it requires an additional step before driving: charging of the slider electrodes. To confirm the feasibility of the method, experiments were conducted using a pair of films fabricated by flexible printed circuit technology. Each of the films incorporate 475 strips of electrodes within their overlapping area; the electrodes are 18 mm in length and 40 μm in width, arranged at a constant pitch of 160 μm. DC voltages used for pre-charging the three-phase electrodes in the slider were 500 V, -500V and 0 V, respectively. After the pre-charging, 500 V three-phase voltage applied to the stator drove the slider with maximum thrust force of approximately 120 mN. We also found that the thrust force of the actuator decay with time after pre-charging, which indicate that further investigations are necessary to prolong its duration.

Abstract: Stereo matching is widely used in three-dimensional (3D) reconstruction, stereo machine vision and digital image correlation. The aim of stereo matching process is to solve the well-known correspondence problem, which tries to match points or features from one image with the same points or features in another image from the same 3D scene. There are two basic ways, correlation-based and feature-based, are used to find the correspondences between two images. The correlation-based way is to determine if one location in one image looks/seems like another in another image, and the feature-based way to find if a subset of features in one image is similar in the another image. In stereo matching, a simple algorithm is to compare small patches between two rectified images by correlation search. For the pair images acquired from two cameras inevitably exists some rotation transformation, the algorithm first runs a preprocessing step to rectify the images with the epipolar rectification to simplify the problem of finding matching points between images. The epipolar rectification is to determine a transformation of each image plane such that pairs of conjugate epipolar lines become collinear and parallel to one of the image axes. It will lead the loss of gray information of images. The effect is dependent on the amount of angle. When the angle is big enough, the correlation search may yield error results because of retrograded correlation effect. In order to solve the problem, the paper presents an improved stereo matching algorithm with differential evolution to solve the correspondence problem. Our method doesn’t need to runs the preprocessing step to rectify the images with the epipolar rectification. It uses a differential evolution algorithm to minimize the correlation function which contains the angle information after acquiring the epipoar geometry constraint of two image pairs. Then it utilizes a flood-fill algorithm to search correspondence sub-region in the area around the epipolar line. The flood-fill algorithm can overcome the problem of the traditional row-column scanning search method, which will encounter boundary barrier where exists concave polygons or cavities. The Experimental results show that the proposed method can be easily implemented in stereo matching without loss of information of image features with large rotation angle transformation. In the paper, we will introduce the stereo matching principle and its algorithms, including the differential evolution algorithm for finding the correspondences with large rotation transformation between stereo image pairs and the flood-fill traversal strategy for matching large area with complex concave polygons or cavities. In the end of the paper, some experimental results will be given to illustrate the method effectiveness. Keywords: digital image correlation, stereo matching algorithm, epipolar geometry, flood fill algorithm, differential evolution, rotation angle