The CNC bending machine is mainly an upper piston press. Its main working feature is that a vertical downward pressure is formed by two working hydraulic cylinders moving in parallel to drive the mold on the bending beam to perform the bending work. Its CNC Dipma hydraulic control system mainly controls the synchronous operation of the bending process and the positioning of the hydraulic cylinder at the bottom dead center when the machine is working at full load.
Stages 1#: Stationary state
The rest position of the plate bending machine is the upper bending beam at the top dead center. To prevent uncontrolled downward movement, the system seals off the rod chamber of the hydraulic cylinder with a leak-free back pressure valve.
Stages 2#: Downward movement
Most of the downward fast closing motion of ordinary bending machines adopts the form of free landing, that is, the movement is generated by the dead weight of the bending machine beam and various accessories. During this process, the rodless cavity of the hydraulic cylinder is filled with oil through a filling valve, and the rod cavity will generate back pressure at this time. Fast forward speed up to 250mm/s) is controlled by a proportional directional valve open loop or closed loop.
The fast-forward motion starts from the top dead center and ends at a maximum distance of 6mm from the bent sheet after a short braking phase. Various press brakes require different fast-forward end positions.
Stages 3#: Stamping/Bending
The punching/bending phase begins with the build-up of the rodless cavity. On the one hand, the stamping speed is limited by the amount of oil supplied by the oil pump, and on the other hand, it can be adjusted by the proportional valve directional valve. At the same time, the directional valve also controls the synchronous operation of the bending beam and the positioning of the bottom dead center.
The limitation of the rush pressure is accomplished by the proportional relief valve limiting the pressure of the pump. The corresponding speed, synchronization, positioning, and pressure setpoints come from the numerical control.
Stages 4#: Stress Reliever
The decompression of the rodless cavity starts either when it reaches the bottom dead center, or after a short holding time, so that the deformed material flows for a certain period of time, thus further improving the dimensional accuracy of the part.
The pressure maintenance and decompression are completed by the proportional directional valve according to the instructions of the numerical controller. Depending on the required operating cycle time, the decompression time must be kept as short as possible; however, it must be sufficiently long to avoid unloading shocks in the entire system.
In short, the decompression curve is not allowed to be too steep and needs to be smooth. The optimization of the entire process is achieved through proportional directional valves.
Stages 5#: Return trip
The flow rate of the pump and the bearing area of the rod cavity of the hydraulic cylinder determine the maximum return speed, which in most cases is close to fast speed. The return stroke starts from the decompression of the rod chamber and ends at the top dead center. The backhaul also requires a synchronous operation.