Research On Machining Path Planning And Collision Detection Technology Of Large Marine Propeller Root Hub

As a key component of the ship's power system,the propeller's processing quality directly affects the normal operation and performance of ship.In general,the processing of large fixed-pitch propeller is to manufacture the blank with casting forming method,and then to process the blade,hub face and inner hole with CNC machining.Due to the complex structure of the propeller,the narrow flow channel between adjacent blades,and poor openness,the root and hub is still processed by manual grinding that not only has a long processing cycle,the quality of the processing is difficult to guarantee,but also the working environment of the employees is extremely harsh.In order to solve the machining problems of large-scale marine propeller root hub,this paper proposes a machining plan for the propeller root hub based on the overall analysis of the company's specific needs,propeller structure characteristics and propeller root hub machining process.In addition,a series of study of the working space,tool path planning and collision detection technology in CNC are conducted based on the designed machine tool scheme.The specific contents are as follows:(1)In order to determine the propeller root hub area that can be processed by the machine tool,based on the analysis of the machine tool kinematic model,the Monte Carlo random point method and the Matlab robot toolbox simulation are used to obtain the machine tool workspace cloud map;and the two methods of fitting the propeller to the cloud map of the workspace,Boolean operation of three-dimensional model of the workspace and the propeller are used to analyze the relative position of the workspace and propeller.(2)For the tool path of the propeller root hub fixed axis machining,this paper completes the derivation of the relationship between the machine tool linkage axis and the semi-linkage axis with the machine tool kinematics,which analyzes the tool maximum value,the tool step length,and the machining line spacing.According to the characteristics of the machining surface,compares the impact of different cutting methods on the processing time to shorten the hollow cutting time in the processing as much as possible on the premise of satisfying the working conditions of the machine tool and the processing quality of the parts.Finally,the tool path is obtained according to the calculated value.(3)Aiming at the problem of interference and collision during the machining of the propeller root hub,a bounding box collision detection algorithm with the separation axis theory is used in this paper.Firstly,the interference between the OBB bounding box of the machine tool's key components and the tool with the octree node of the workpiece is analyzed;and then,for the bounding box of the collision,the collision between thebounding box and the triangular face of the part is predicted.Finally,the cutter axis vector is optimized to avoid the location of collision.(4)The pre-generated tool trajectory is used to generate a CNC machining program through a dedicated post-processor.After that,a machining simulation platform is built via the Vericut software to simulate and verify the blade root hub machining program within collision detection.