Analysis Of Unloading Accuracy For Hydraulic Overload Protection System Of Mechanical Press

Hydraulic overload protection system is one kind of the overload protection system that have been widely used in large four-point mechanical press. It is characterized by high working accuracy, working pressure adjustable, automatic resetting after overload. But sometimes the overload protection system will unload under the pressure of nominal pressure during use. Many engineers often try to solve the problem by experience or experiments, but the method not only has certain blindness but also takes a lot of time. So it is very important to analyze the problem and find calculation methods to solve the problem. This paper deals with one kind of widely used hydraulic overload protection system which has a relief valve, and put forward the technical proposal and the calculation methods. The main contents are as follows:The operational principle of the hydraulic overload protection system is analyzed, the existence of the shoulder force of the hydraulic overload protection system is found, and the influence of the shoulder force on hydraulic overload protection system is studied. Three schemes are adopted:reducing the pre-pressure, adding the extension pipe and changing the structure of the connector.The connector of hydraulic overload protection system is simplified and analyzed based on the finite element method. The equivalent stiffness scheme is proposed and worked out based on curve fitting in order to realize the combined simulation. The dynamic model of press machine impacting mechanism is constructed in ADAMS and the constraints is added into the model, meanwhile, the simulation model of the hydraulic protective system of the mechanical press is constructed in AMESim. Finally, the combined simulation of the hydraulic and mechanical system is realized.The hydraulic overload protection system is studied in view of combined simulation, the simulation result is very close to the experiment result and the error is only6%, so the method of combined simulation is very accurate. The pre-pressure of mechanical press of2000ton and the extension pipe length under different pre-pressure is worked out; the result of calculation is valuable to the company.The response characteristics of the pilot unloading valve is analyzed in view of AMESim and the factors which can influence the response characteristics of the pilot unloading valve is found out. The essence and effects that solve the unloading problem through changing the structure of the pilot unloading valve is researched. The structural changes can reduce the sensitivity of the pilot.The optimizing pre-pressures of mechanical press of2000ton and the length of the extension pipe under different pre-pressure are calculated from the research. The research results of hydraulic overload protection system which used in large four-point mechanical press has an important significance in providing a series of useful data and a method to solve the problem, and this research method can also be used in other hydraulic overload protection system of large four-point mechanical press.