Research On Multi-cylinder Hydraulic System Control And Forming Surface Of Pushing-cylinder Stretch Forming Equipment

Stretch forming is a flexible forming method of sheet metal.Compared with other forming methods,the quality of workpieces produced by stretch forming is better and the mechanical strength is higher.The application of the pulling-cylinder stretch forming equipment is restricted by its complicated structure,low efficiency and low utilization rate of sheet metal.Therefore,it is of great significance for the research of new stretch forming equipment.The pushing-cylinder stretch forming technology is a new kind of flexible sheet forming technology.The pushing-cylinder stretch forming equipment mainly converts the load of the pulling hydraulic cylinder of the pulling-cylinder stretch forming equipment to the pushing hydraulic cylinder.By using the characteristics of the large thrust of the rod-less cavity of the hydraulic cylinder,the output force of the pushingcylinder stretch forming equipment is increased.The same diameter of the hydraulic cylinder is used to achieve large output,thus realizing flexible stretch forming of sheet metal.The pushing hydraulic cylinder is referred to as the pushing-cylinder,which used as the main hydraulic cylinder.And the pulling hydraulic cylinder is called as the pulling-cylinder,which is the direction control hydraulic cylinder.Through the selfcoordinated movement of the pushing and the pulling cylinders,a series of discrete clamps are driven to exert tensile force and flexural torque-moment of flexion on sheet metal resulting in plastic deformation.In this paper,the numerical simulation method is used to simulate the pushingcylinder stretch forming process.The stress and strain distribution of sheet metal are analyzed to predict the defects that may occur during the stretch forming process,thus optimizing the pushing-cylinder stretch forming process The performance of hydraulic control system of the pushing-cylinder stretch forming equipment is analyzed,which lays a theoretical foundation for the application of the pushing-cylinder stretch forming process.The main research contents of this paper are as follows:(1)A pushing-cylinder stretch forming equipment is designed,and the movement range of the clamping mechanism of the pushing-cylinder stretch forming equipment is compared with that of the pulling-cylinder stretch forming equipment.the process of pushing-cylinder stretch forming and the mechanical behavior of sheet metal during stretching are analyzed.the loading trajectory of the clamp during pushing-cylinder stretch forming process is derived,and the principle of selecting the blank size of sheet metal during stretch forming is explained.(2)Based on the working principle and structural characteristics of the pushingcylinder stretch forming equipment,a hydraulic servo control system for pushingcylinder stretch forming equipment is designed.The working principle of the hydraulic servo control system is briefly explained,and the mathematical model and transfer function of the hydraulic servo control system are derived.Through the zero-pole diagram,Nyquist curve,Bode curve and unit step response curve,the time-domain and frequency-domain characteristics of the hydraulic servo control system of the pushingcylinder stretch forming equipment is studied.The stability,sinusoidal tracking performance and dynamic response characteristics of the hydraulic servo control system of the pushing-cylinder stretch forming equipment are analyzed.(3)In the hydraulic control system of the pushing-cylinder stretch forming equipment,PID control and fuzzy PID control are imported.The effects of PID control and fuzzy PID control on the dynamic response characteristics,tracking performance and anti-interference ability of the hydraulic control system of the pushing-cylinder stretch forming equipment are analyzed by numerical simulation.Under the fuzzy PID control,the kinematic performance of single cylinder and multi cylinder of the pushingcylinder stretch forming equipment is studied.(4)The multi-body dynamics model and hydraulic control system model of the pushing-cylinder stretch forming equipment are established.The equivalent stress,equivalent strain of spherical parts and saddle parts,and the output force of the pushing-cylinder stretch forming equipment are analyzed.(5)The stretch forming test of saddle part is carried out on the pushing-cylinder stretch forming equipment,and the surface quality and dimensional accuracy of saddle part are analyzed.