Research On Cutting Stability Of Marine Propeller Blade Industrial Robot

The use of industrial robots for milling can effectively control the cost of expensive equipment and achieve low-cost manufacturing of marine propellers compared to dedicated machine tools for the machining of marine propeller blades.However,due to the poor rigidity of industrial robots,chatter is generally avoided by adopting more conservative process parameters,and conservative process parameters will lead to la a low material removal rate.Therefore,to improve processing efficiency,large process parameters need to be used.But blindly changing process parameters not only causes robot chatter but also aggravates tool wear and increases the frequency of tool change,which reduces machining efficiency conversely.In this thesis,to address the complex and contradictory relationship between material removal rate,tool wear,and cutting stability,the process parameters are optimized with the objectives of stable cutting condition,slower tool wear,and optimal machining efficiency,which provides the basis for efficient machining of marine propeller blades by industrial robots.(1)The model of wear overlap distribution per tooth based on tool runout and the inclination angle is proposed.The wear overlap distribution model is established through probability density function,linear transformation,linear superposition,and inverse transformation.The worn cutting edge trajectory model is developed using tool geometry model,cutting edge wear pattern,and homogeneous transformation of coordinate system.The actual cutting depth and contact point of each flute model are established by the effect of the milling mechanism per tooth.The model of wear overlap distribution per tooth is proposed using the combined the actual cutting depth and contact point of each flute model and the worn cutting edge trajectory model.The proposed wear overlap distribution per tooth model is validated through a case study,and the wear overlap geometry distribution and the wear overlap distribution values of each flute are analyzed.(2)The model of cutting force based on wear overlap distribution per tooth is proposed.The model of cutting edge sweeping surface based on wear overlap distribution per tooth is established by tool path with the parallel axis runout and tool wear model.The solving equation for the instantaneous un-deformed chip thickness with wear overlap distribution per tooth is developed by the definition of the instantaneous un-deformed chip thickness.The Z_T-axial upper and lower boundaries of the cutter-workpiece engagement area are established by analyzing the cutting depth of the cutting edge in different regions.The model of cutting force based on wear overlap distribution per tooth is developed using the combined instantaneous un-deformed chip thickness with wear overlap distribution per tooth and the boundaries of the cutter-workpiece engagement area.The proposed cutting force model based on wear overlap distribution per tooth is validated by comparing the experimental data in the literature,and the influence of wear overlap distribution per tooth on cutting force is analyzed.(3)The cutting stability model of the industrial robot is established.The homogeneous transformation matrixes of the adjacent joint coordinate system are determined by establishing the coordinate system of each joint of the robot and using the D-H method.The velocity Jacobian matrix is established using the combined homogeneous transformation matrix and the vector product method.The stiffness model of the industrial robot is developed by the reciprocal relationship between flexibility matrix and stiffness matrix,the relationship between robot end deformation and external force,and the velocity Jacobian matrix.The dynamic model with three degrees of freedom is determined by the established cutting force model and robot stiffness model.The dynamic model with three degrees of freedom is solved by the method of the frequency domain,and the stability lobe diagram is drawn.The dynamic model with three degrees of freedom is validated by comparing the experimental data in the literature,and the influence of cutting parameters on the stability lobe diagram is analyzed.(4)The process parameter optimization model is proposed with material removal rate and wear overlap distribution per tooth as the objective functions and robot cutting stability as the constraint condition.The artificial bee colony algorithm is used to optimize the process parameters by the material removal rate model,the wear overlap distribution per tooth model,and the industrial robot cutting stability model,and the optimal cutting parameters are obtained:the cutting depth is 1mm,the step over depth of cut is 18mm,the feed rate is 2002mm/min,and the spindle speed is 4293r/min.the material removal rate increased by nearly 29%is found by comparing the cutting parameters with parameters in the literature.