Research On The Active Blanking Vibration Reducing Based On Hydraulic Press

Blanking is one of the most important stamping processes. It can not only be the preparation for further stamping processes, but also get work pieces with a certain accuracy directly. There are lots of difficulties to study sheet metal blanking process since the deformation is limited in a tiny area of sheet metal and ends with fracture.Sheet metal blanking ends with the fracture, and thus the elastic energy accumulated in the press body and the oil releases suddenly.With the fracture, bringing severe vibration, great noise and damaging the die, equipments and hydraulic system.Generalized hydraulic presses can not be used for blanking.Up to now, passive damping, for example, adding vibration-reducing components between the working plate and the slider,has mainly been adopted.Though this method is effective to reduce the vibration and noise, but the structure is complex, with large space and energy wastes. The active vibration reducing method is put forward in this paper.The slider velocities would be controlled by adjusting the flow rate into or out the cylinder at some typical positions. The accumulated elastic energy could be completely released before the fracture so as to reduce the vibration maximally.This paper analyzes the plastic deformation, fracture process, mathematical model and the finite element method in blanking. Deform-2D was used to simulate blanking process of sheet metal with different thicknesses according to the Normal Cockroft & Latham fracture principle. The stress and strain distributions, blanking parameters' effects on the cracks and the force-stroke curves of the entire blanking processes were obtained, setting a foundation for reducing blanking vibration and noises. Simulation showed that low-carbon steels were different from hard steels in blanking. Hard steels had brittle fractures while low-carbon steels had ductile fractures. With the increasing in thickness and blanking clearance, punch strokes increased in cracks.On the basis of analyzing of the hydraulic system, several approaches were proposed, including meter-in control, meter-out control and bleed-off control ,etc.According to the structure of the model hydraulic press and the different approaches ,the mathematic models were set up. With the mathematics model, the simulation models based on MATLAB/Simulink software were set up and the simulations were carried out according to the prototypal experiment parameters of the model press.Blanking experiments were done, and the dynamic displacements of the slider were recorded. The press vibration can be judged based on the amplitudes. The results of the simulations experiments were indicated as following:1. The slider absolute vibration is the combination of rack vibration and the relative vibration, the latter is 3.5times of the former. Reducing the vibration caused by hydraulic oil compression is the key for vibration reducing.2. Reducing the volume of compression oil or increasing the die can reduces the vibration.3. Increasing the stiffness of press body can reduce the vibration of the rack, but has no significant effect to slider vibration.4. Meter-in control can control slider speeds. The releasing time of elastic energy accumulated during the blanking could be altered to guarantee part of the elastic energy to be released before the fracture , but it is ineffective.5.Meter-out control can control the slider speeds too. The releasing time of elastic energy accumulated during the blanking could be extended, reducing vibration. But the pressure in the low chamber might be too high and an accumulator would be needed.6.The suitable parameters of the accumulator for the simulated condition would be: volume is 5.5L, working pressure is 8MPa. The nominal pressure of throttling valve is 31.5MPa, the maximum constant flow is 80L/min.Rack vibration u can reduce to 56.17%, relative slider vibration x can be reduced to 45.31%, The absolute slider vibration X can be reduced to 44.31%.The research in this paper lay the foundation for the development of active vibration reducing and the new press.