Dual-robot Mirror Milling Collaborative Machining Of Large Thin-walled Parts

To achieve the green and efficient processing of large thin-walled aerospace parts,mirror milling is replacing other traditional processing methods as the mainstream processing method.Based on the new five degree-of-freedom(DOF)hybrid robot TriMule developed by the research group,a novel dual-robot mirror milling system is proposed in this study.The mechanical structure of the system is mainly composed of a processing hybrid robot,a supporting hybrid robot and a fixture.The cutter and the flexible supporting head are installed at the end of the machining robot and the supporting robot respectively.Because the deformation and vibration of the workpiece are directly affected by the collaborative performance of the cutter and the supporting head,the key problem is how to achieve collaborative machining by the cutter and the flexible supporting head in equal wall thickness machining.The collaborative machining of the tool and the supporting head is essentially the pose collaborative between the machining robot and the supporting robot.Therefore,kinematic modeling of the five DOF hybrid robot TriMule is established.The vector method is used to solve the kinematic position positive and inverse solutions.The correctness of the kinematics model is illustrated by simulation.A collaborative machining method is proposed by establishing a relative pose relationship between the cutter and the supporting head.In this method,the tool trajectory of the machining robot is generated in real time according to the end trajectory of the off-line planning supporting robot and the preset machining parameters.Next,the control parameters of each driving motor are obtained by the kinematics for the machining robot.A dual-robot endmost geometrical pose is used to obtain the machining wall thickness via contact-type online measurement for replacing ultrasonic thickness measurement systems.The error of wall thickness is compensated by the machining robot.In order to reduce the influence of forced vibration on the machining quality,the tool-workpiece-support structure are jointly modeled,and the system model is solved by the finite element method.The hammering experiment is carried out on the thin-walled system with or without local multi-point support.The vibration suppression characteristics of the local multi-point aerodynamic support are analyzed.In the dual-robot mirror milling processing platform,the triangle grille commonly used in aerospace fuel tanks is taken as an example to carry out the dual-robot collaborative machining and the comparison processing experiment with or without local multi-point support.The effectiveness of the dual-robot collaborative machining strategy is proved by dual-robot collaborative machining experiments.The comparison of the experimental results show that the local multi-point support can effectively suppress the forcing vibration in the milling process of large thin-walled parts.