| Following a great prosperity in the domestic electrical and aviation engines industries, the application of aircraft engine, steam turbine, gas turbine and compressor has increased dramatically in recent decades. The industrial demands for blades have also greatly increased because they are the vital components in the above-mentioned equipments. There exist a great variety of different types of blades with various complex surfaces, which are very difficult to machine. The designing level and manufacturing quality of blade surfaces have great influences on the working efficiency and serve life of the above equipments.The blades are firstly machined by casting or precision forging, then by CNC milling, and at last by finishing process. The finishing process is mainly focused on the removal of the residual milling marks and the improvement of the surface form accuracy. In domestic blade machining industries, the finishing process is still mainly completed by manual grinding/polishing. The manual grinding/polishing have to be done at very poor working conditions and thus the health of the workers is seriously affected. The finishing efficiency and the finishing accuracy are also very low. In our country, the special machine tool for finishing blade surface is very few, which has become a bottleneck restricting the industrial developments. Therefore, this thesis has strived to develop new machine tools to improve the finishing quality as well as the finishing efficiency for complex blade surfaces.In this thesis, detailed investigations were firstly carried out on the machine tools and finishing methods. The thesis work is financially supported by the project named Key Project of Science and Technology Development Plan of Jilin Province. The objective of this thesis is to develop one kind of special machine tool equipment for blade surface finishing. This thesis has also contributed a new designing method that is featured by designing the machine tool from the consideration of bionic principles. Innovative machine tool structure for finishing blade surface was proposed by the new designing method. The innovative work in this thesis include machine tool structure design, grinding/polishing mechanisms, solution algorithm and simulation verification of machine tool kinematics, machine tool dynamics analysis, and the development of control system.The basic DOFs required in the finishing process were analyzed according to the blade surface. After a comparison of these DOF combinations, a 4-1 type was chosen as the machine tool structure. In the tool side, the hybrid structure that is composed of rotatable fixture, parallel mechanism and single-direction moving slide provides four moving DOFs. In the workpiece side, a single-direction DOF was designed. The working platform of the proposed machine tool is composed of a three-limb parallel mechanism, where the blade is fixed by a rotatable fixture. In the grinding/polishing process, the parallel mechanism imitates the polishing motion of human hands, thus adjusting the finishing pose in real-time. As a result, the currently finishing point keeps in touch with the grinding/polishing tool. By using a pressure sensor, pressure force in the grinding/polishing process is obtained and based on which, the movements of the parallel mechanism can be adjusted. Thus, the pressure adjustment in the grinding/polishing process can be realized. In the developed machine tool, the X and Y slides are connected with the parallel mechanism to realize the grinding/polishing movements on different points of the blade surface. This hybrid configuration not only expands the working space in the proposed machine tools, but also effectively makes up for the serious variations of parallel mechanism stiffness in different positions, which is realized by the humanoid finishing process and the elastic grinding characteristics.In order to adapt well with the curvature variations of the blade surface in the finishing process, a narrow abrasive belt was used in the grinding/polishing tool system. A horizontal spacing method was used in the grinding/polishing process. In this thesis, a completely new tool system that has the self-adaptability of the curve surface was proposed. In this tool system, a rotatable contact wheel holder was designed to realize the exchange of contact wheels according to the surface curvature variations. The grinding/polishing mechanisms of abrasive belt finishing process were studied. The relationship between the finishing parameters and the finished surface quality was analyzed from a large number of experimental data in the literatures.The stiffness of the machine tool is an important indicator that influences its working space, carrying capacity, load capacity, and so on. A static stiffness model for 3RPS parallel mechanism was built up, which was used to study the static stiffness characteristics of the proposed machined tool. This work has made a foundation for optimization of the overall performance and the machining precision of the proposed machine tool.The finishing precision of blade surface should be very high because the blade surface must be very smooth. In finishing process, the interference between the blade and tool system always occurs because of the complex curved surface of blade. For realizing the high-quality, high efficiency finishing process, this thesis proposed a kinematic algorithm oriented on the blade finishing process. According to the given finishing methods, the kinematics model was built and based on which, the finishing movements for each axis were also calculated. In this calculation, the cloud data that was used to describe the blade surface information acted as input. In addition, the kinematics algorithm of the proposed machine tool was also verified by the simulation work.The vibration resistance and machining stability are two important factors affecting the machining quality and machining efficiency. Dynamic analysis of the machine tool is a key work to improve the performance of the machine tool system. In this thesis, the dynamic model of the machine tool has been built based on the Cartesian coordinates. The mathematical relationship between the constraint reaction forces from hinges of machine tool and the motion parameters was built. Simulation work on the grinding/polishing forces in the finishing process, the acceleration and deceleration movements, and the influence of blade surface curvature variations on the driving force of each limb, were carried out. Simulation results showed that the dynamic performance of the proposed machine tools is able to meet the finishing requirements of complex blade surfaces.According to the characteristics of the proposed machine tool structure, the control system was developed based on the idea of modularization. The control system consists of two parts: axis motion control system and grinding/polishing process control system. Axis motion control system consists of host PC machine, Turbo PMAC2 multi-axis motion control card, interface board and the AC servo motor. The axis motion control system is responsible for the realization of the blade grinding/polishing movements according to the planning path. The multi-axis motion control of the machine tool was realized by connecting the PMAC2 with a number of AC servo motors. The grinding/polishing process control system was used to control the grinding/polishing tool system to realize the choice of contact wheel. The relative motion between grinding/polishing tools and the blades need to be realized by the resultant movements of each parallel limb and series axis. Path planning was done in Cartesian space, while the control needs to be done in joint space. They have a relationship of nonlinear mapping. Therefore, the proposed machine tool has used a double-precision interpolation strategy, namely crude interpolation that based on the Cartesian space and the dedicate interpolation that based on the joint space.This thesis analyzed the major factors that affect the finishing efficiency and accuracy of the developed machine tool. The relationship between the limb-length error of the 3RPS parallel mechanism and the moving error of the platform center was calculated. The results showed that the limb-length driving error is the main factor that affects the movement error of the parallel mechanism. Furthermore, the limb-length driving error also affects the accuracy of blade pose adjustment in the finishing process. Therefore, the limb-length is very important for achieving the control accuracy demands of the machine tool. In this thesis, the mathematical model of the control system for a single limb was built. The motion control and motion simulation were also performed by using the PID control algorithms.The research results show that the developed machine tool in this thesis is practical and reasonable. By using the proposed machine tool, the finishing automation of complex blade surfaces can be achieved, and the finishing efficiency and finishing quality can be significantly improved. The research work has made a contribution for breaking the bottlenecks in the blade surface finishing process, and thus provided another effective solution for high-quality, high-efficiency finishing of complex blade surface.
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