Deformation analysis and hole diameter error compensation for hybrid robot based helical milling

As an innovative machining process for hole-making, helical milling (also known as orbital drilling) presents great potential in machining aircraft structures due to temperature and cutting force reduction, flexible kinematics, and improved borehole quality. Meanwhile, the application of hybrid robot with their high accuracy and better stiffness are increased in aircraft assembly machining operations. Combining these two advanced technologies, this paper focuses primarily on the investigation of the TriMule hybrid robot elastic deformation during helical milling hole-making process and its influence on the diameter error of machined hole. The elastic deformation of series and parallel parts under cutting force condition was investigated by finite element simulation software SAMCEF. The TriMule robot helical milling experiments were also carried out to determine the variation of hole diameter error, and an offline compensation method with modifying the eccentricity at different hole depth was proposed based on the established diameter error model. From experimental verification results, it can be found that the hole diameter error of TriMule robot helical milling can be reduced and the consistency of hole diameter accuracy can be significantly improved by proposed error compensation method.