Force Control Of Robotic Grinding For The Aeroengine Blisk

The blisk is the core part of aeroengine.Its machining accuracy and surface quality directly affect the working efficiency and service life of aeroengine.At present,manual grinding are mostly used in the finishing of the blisk.But there are some problems in manual grinding,such as low efficiency and precision,poor surface consistency,difficult to ensure the processing requirements,dust pollution endangers workers’ health and so on.With the development of robot machining technology,it provides a new idea for the finishing of blisk.However,the traditional scheme of robot holding single DOF end effector has the problem of slow response speed,which makes the machining efficiency difficult to guarantee.Therefore,this paper has carried out the research of force controlled grinding of Blisk robot,which aim at the problem of low machining efficiency and poor precision.In order to improve the robotic machining accuracy and efficiency of the blisk.In this paper,the robot is used to hold the two DOFs end effector with force control,It focuses on the establishment of grinding system,material removal model,the planning of grinding contact force and the design of two degree of freedom force control algorithm.Firstly,a material removal model for cylindrical grinding tool is established,and the model is verified by multiple single factor and multi factor grinding experiments.Then the contact force planning method is studied,Finally,the method of force control based on two degree of freedom end effector is studied.The grinding platform was built and the blisk grinding experiment was carried out,and the grinding methods proposed were verified one by one.The main research contents and achievements of this paper are as follows:1.Design and fabrication of a robotic blisk grinding system.A robotic grinding system which contains a two degrees of freedom active force controlled end effector is proposed and fabricated for robotic grinding of medium size complex blisks.The developed robotic grinding system can significantly improve the machining efficiency and reduce the harm to the workers,compared to the traditional manually grinding process.The cost for a robotic grinding system can be much less than using a multi-axis machine tool.Comparing to the existing robotic grinding system which has only one degree of freedom motion in the contact force control device,the proposed system can achieve a better adaptively and machining efficiency while maintaining the same surface finish quality.2.Material removal model.Based on the existing material removal models,a new material removal model was established which mainly aimed at cylindrical grinding tool.In the model,the second power of contact force,reciprocal of contact velocity and spindle speed are directly proportional to material removal per unit area.The other uncontrollable factors were modeled as material removal coefficient.A series of single factor experiments were carried out on the cylinder bar which considering the effect of grinding process parameters on material removal per unit area.Then the material removal coefficient was calibrated according to the experimental data.Finally,the material removal model was validated by a series of multi-factor experiments.3.Planning of grinding contact force.In order to achieve controllable material removal,a contact force planning method for grinding is proposed.Based on the contact force model,the contact force required for each point of the workpiece is calculated according to the machining allowance.Then the contact force and contact direction angle of each point of the workpiece are mapped with the arc length of the tool center point,and then the contact force planning is completed.4.Design of two degree of freedom adaptive contact force control algorithm.In view of the great change of curvature at different positions on the blisk,we designed the adaptive contact force control algorithm on the basis of the proposed two DOFs end effector.The proposed algorithm can adjust the contact force direction in real time according to the different contact points on the surface,so that the normal direction of the contact force is consistent with that of the workpiece contact point,and the control contact force is consistent with the expected contact force.The results show that the proposed algorithm can well control the contact force of grinding,and the force error is within±1.5N.The grinding effect of blisk is better than the traditional constant force grinding method,and the roughness of blisk is 0.298μm.