Research On Double-sided Grinding And Polishing System And Path Planning For Blade Finishing

Blade is one of the important components in the power plants, such as aero-engine, turbine, and wind generators. The blade surface is not only complex, but also often work in the harsh conditions. The material of the blades is alloy considering the complexity of the blade surface and the working condition of the blades. The quality of the blades has big influence on the performance of the power plants. Under the conditions above, this paper developed a double-sided grinding and polishing machine tool. A lot of attention is paid to the structural design of machine, the motion control, the classification of processing trajectory and analysis of kinematics according to the surface characteristic of the blade.The machine body is composed by the bed, double X-oriented tables, double Z-oriented tables, Y-oriented table, rotary table C and flip table B. Grinding and polishing tool system units fixed to the Z-oriented table. In the process of machining, double X-oriented tables and double Z-oriented tables move together and drive the grinding and polishing tools according to the region divided for machining. The tools move along their trajectory polishing the arc convex and concave arc synchronously.Combining the features of the machine configuration, on the basis of analysis on several numerical control systems, based on modularization thinking, an open CNC system was developed using the PC machine plus the PMAC. The CNC system consists of the host computer, the low computer and the actuator module. The host computer is mainly composed of PC-based machine, including path planning module, the movement solving module, process simulation module, sports debug module, the information displaying module and the pressure control module. The lower computer is mainly the PMAC, which is used to receive the information data launched by the host computer and to control the seven movements of machine grinding and polishing tool system axis and to control the motor commands sent to the actuator module final motion.According to the existing blade solid model, three-coordinate measuring machine is used to collect the data points on the blade and obtain the scattered data of different regions. Then reverse engineering software is used to select the data points, and repair the blade model which can finally develop the three-dimensional solid model. On the basis of layered principle, the paper proposed a new algorithm to obtain the contour lines of the blade.The processing trajectory is generated by fitting the data points using three non-uniform B-spline curves, beginning at the intersection of the contour lines. On the basis of the analysis of different processing methods, the process of machining blades can divide to double-sided machining process and the axis machining, and the machining trajectories are not the same. According to structural characteristics of the specific tools used for grinding and polishing, the corners of the contact roller is calculated and the angle between reference vector of the corners at the critical point and the axis of the section is consider as a basis for processing trajectory. Then the angles between vector of the calculated points on the fitting curve and the reference axis is calculated. If the two angles mentioned above of the point are the same, it will be the point on the fitting curve as processing path segment point. The curve generated by fitting the points mentioned can divide the blade to two region, one is the region can be directly machining by double-sided process, and another region which may lead to wheel interference should be grinding and polishing by multi-axis processing.In the process of double-sided machining, the angle of rotary table C should be adjusted considering the needs of the blade surface, in order to ensure the good contact between the wheel of the polishing tool and the blade surface. The value of the angle of the rotary table is calculated according to the relationship between the intersection of the normal vector of the plane and the average angle of the cutting plane. The selection of the machining width of the belt is quite difficult, considering many factors such as the angle difference of two trajectories under the turntable and the allowances. A new method of width optimization for machining is proposed and the process to solve working width of the belt is given.Based on the analysis of the configuration of the machine, the coordinate system is developed and the kinematics of the machine is studied. According to two motion modes of grinding machine, respectively, the kinematic model of the double-sided grinding and polishing and multi-axis simultaneous grinding and polishing process are established, and gives the inverse kinematics algorithm. Choosing one of the trajectories as a processing example for computing the inverse kinematics solution, the calculated results is mapped to the movement of the relevant sports of the machine axis for movement of each axis. Finally, the virtual prototype simulation model of the machine is developed, and based on the results of inverse kinematics, the simulation exercises on the process. The simulation results showed that the trajectories obtain from the simulation is consistent with the given trajectories, which proves the model and the inverse kinematics algorithm.Finally, the machining experimental studies are carried out. There are three factors having an effect on the surface quality, feeding speed, belt granularity and rotate speed of the belt. The result of the experiments shows that the belt granularity has the most apparent influence comparing to the other two factors. After optimizing the process parameters, surface roughness of the blade is up to 0.735μm.