Research And Development Of CNC System For Large Thin-walled Parts Mirror Milling Equipment

The Large Dimension Thin-wall Workpieces are the key components of the high-end equipment in the field of aerospace engineering,such as missile,large aircraft,and heavy lift launch vehicle.Considering the characteristics including large size,small thickness,low stiffness,irregular shape,and high material removal rate,for The Large Dimension Thin-wall Workpieces,it is easy to cause deformation and flutter under the influence of heat/force in cutting,residual stress,clamping force and so on.Hence,it is difficult to meet the requirements of high quality,high efficiency and green processing by using conventional techniques.To solve this problem,the mirror milling technology has been adopted and the CNC system for the large dimension thin-wall workpiece has been developed.In this paper,we focus on the improvements of the developed CNC system for the large dimension thin-wall workpiece and the problem of the support and machining synchronous motion in the system.In this paper,the general structure of the hardware and software system has been established according to the requirements of the mirror processing equipment.In addition,based on the idea of "IPC+UMAC motion controller",the hardware and software system is developed with the modular design method.In our work,the electrical control system and the servo control system have been designed;the motion program for the upper system and the PLC program were developed;the hardware and software platform for the CNC system of the mirror processing equipment is built.The mirror milling process is used for large thin-walled parts processing equipment,which requires strict synchronous motion between the machining side and the symmetrical axis of the supporting side.In this paper,the synchronous control between the symmetrical axes is simplified as a dual axis synchronous control.On the basis of analyzing classical position control strategy and geometrical relationship between synchronization error and tracking error of linear biaxial synchronous motion,this paper introduces the coupling error variable to design a cross-coupled synchronous controller with position loop nonlinear PID.And the experimental results based on X-Y motion platform demonstrate that compared with traditional PID control of cross coupling synchronization,single axis tracking errors under the effect of nonlinear PID control of cross coupling synchronization have decreased by 50% and 62.5% in maximum and RMS values and the maximum value and RMS value of synchronization errors between axis have decreased by 60% and 63.64% respectively.The good dynamic and static characteristics of CNC system for large thin-walled mirror milling equipment and the high positioning accuracy of each axis are the prerequisites for ensuring machining accuracy.Based on the servo control principle of UMAC controller,the dynamic and static characteristics of the CNC system are improved by PID feedback and speed/acceleration feedforward feedback through Pewin32Pro2 software,and the two-way error complement technology is used to further improve the positioning accuracy and repeat positioning accuracy.The positioning error of each axis of machine tool is detected by laser interferometer.The results show that the positioning accuracy of the servo axes of the CNC system is less than 0.008 mm,and the repeatable positioning accuracy is less than 0.005 mm,which meets the requirements of the design index.