Machined Surface Topography Simulation And Experimental Study Of Controllable Pitch Propeller Milling

One of the key parts in manufacturing azimuth thrusters of a dynamic positioning system is the large scale controllable-pitch propeller blade,which is consist of complex surface contour. Subject to time-variant thrust and torque loading, there are strict design and manufacturing requirements on the geometric accuracy and thickness distribution of the blade profile.CNC milling processing are widely adopted in the machining of propeller blade,The surface topography has a significant impact on the surface integrity and material removal allowance in subsequent polishing process,the research on milling parameters and milling planing strategies plays an important role in obtaining uniform cutting allowance and improving process quality. The present work is carried out on simulating and experimental study of model propeller milling fabricating by selecting different milling parameters and tool path for controllable-pitch propeller blade.A surface topography simulation algorithm is presented to simulate the relations between milling parameters and surface topography. For ball end tools and toroidal tools,which are widely used for milling, a mathematical model has been established to uniformly describe its geometric characteristic. Considering of the relative motion relationship between the tool and workpiece, a quaternion transformation model is established to describe the translation and rotation motion of tool coordinate system and the workpiece coordinate system. Then,the tool trajectory, tool position and tool posture can be effectively described based on the transformation model. A computing method is presented to extract the discrete point on the milling cutting edge based on the instantaneous tool coordinate and posture in trajectory and describe them relative to the workpiece coordinate system. Those discrete points on the milling cutting edge are compared to the corresponding points on the workpiece surface at each tool position point in trajectory, the height of the discrete points on the workpiece are updated based on the Z-map algorithm, therefore the geometry information of the workpiece surface topography is achieved. Based on the whole process, a simulation system is developed to describe the surface topography geometry in workpiece milling process.To demonstrate the effectiveness of the machined surface topography simulation system, machining experiments were conducted on scale shrink model propeller blade, and ball end milling cutters are used in the scale model propeller processing experiments,Considering variables process parameters such as spindle speed, feed rate, cutter incline angle and tool path spacing, we study the different milling strategies with four types of tool path and their impaction on the machined surface topography of blade and analyzed their advantages and disadvantages. In conclusion, this work provides an alternative evaluation criterion for choosing the appropriate machining parameter.