Research On Electrohydraulic System For Powder Compacting Press

Powder metallurgy technology is recognized as a resource-efficient and environmentally friendly process,with the development trend of global green manufacturing,which attracted more and more attention.It is a near net shape metal forming process for components with special properties and requirements for a wide range of critical and demanding applications in machinery manufacturing,automotive,aerospace and defense industry and other fields,which has been widely used and rapidly developed in the last few years.Powder compaction press is one of the most important equipment in powder metallurgy parts forming.Powder compaction forming is a process in which powders held in a die are subjected to an external force in order to densify them and produce a compact with prescribed shape and dimensions.In powder densification process,the pressing force load mechanism need to have a strong linear transmission stiffness,with the high energy density.As a result,most of the powder compaction press equipment is driven and controlled by the electro-hydraulic system.During the powder compaction forming,the electro-hydraulic control system which drives the punches works with the following features:(1)The strength of the compaction load force is high,and it is non-linear time-varying.What's more,due to special complex powder mechanical properties,it's difficult to model the powder compaction process.(2)Accroding to different process characteristics,the time-sharing system needs to complete both the high-precision motion control and the force control in the pressing process.(3)Aside from the nonlinear nature of hydraulic dynamics,the electro-hydraulic system also has large extent of model uncertainties.(4)For the multi-punch die-set tool system in multi-step powder parts forming process,the forces by every punch are coupled,they must ensure that the movement of the compression process to follow each step of filling coefficient,compression ratio,consistent with the principle of suppression rate.In summary,research on a high performance electro-hydraulic control system for powder compation press with good process adaptability is not only of academic value,but also has important practical significance and necessity.The thesis mainly talks about the electro-hydraulic system for powder compaction press,by means of theoretical mechanics,nonlinear control,simulation analysis and experimental research.Taking full account of the dynamics of the system,the powder mechanical properties in the complex shaped green compacting process,relevant control technology is studied.Command-filtered-based Adaptive Robust Control(CF-ARC)is designed for the punches motion.collaborative estimation algorithm is proposed for limit of the model parameters.Disturbance-observer-based Robust Control(DOB-RC)is also designed for the compaction force control.The compound control method combined CF-ARC motion control with DOB-RC force control is proposed.The multi-punches cooperative control with trajectory planning is put forward in the paper.Modeling techniques and control method of the above effect on powder compaction press prototype platforms and its performance has been verified.While developing the application in the powder compaction hydraulic press made by Nantong Metalforming Equipment Co.LTD.The contents of the thesis including six chapters are summarized as below:In Chapter1,the background of the technique for powder compaction press equipment electro-hydraulic control is presented.The specific difficulties and challenges which the technique faces are summarized based on the intensive literature survey.After a detailed introduction of the current research status and progress,the research contents and the significance of the thesis are dissertated.In Chapter2,the powder compaction force with pressing displacement model on the basis of theoretical analysis integrated with experimental data is presented.The method for the model parameters fitting,the optimization of the nominal parameters and the scoping range range of parameters uncertainty is summarized.The method for the verification of the pressing velocity in the compaction process with the proposed model is demonstrated.The applicability of the model is analyzed by comparison.The controller with the compaction force compensation model is designed.In addition,the validity of the proposed model is verified by the experiments.In Chapter3,the dynamic model for the punch driven by electro-hydraulic system is proposed.Command filter adaptive robust control(CF-ARC)for the punch motion is designed,with the parameters limits and estimation cooperative optimizinig algorithm of the model.Robust control based on disturbance observer combined powder compaction force model metioned herein.Motion-force control method with CF-ARC combined into DOB-RC following the absolute minimum principle is presented.This method ensures the smoothness and the stability of the motion-force control switching.From the control precision and process control requirement of designing the composite entry point,process-oriented control strategy is proposed.Experimental results show that the proposed motion-force compound control method can rechieved a higher precision and have a good process adaptability.In Chapter4,the dynamic model of the multiple punches driven by the electro-hydraulic system is builded through the subapace state-space partitions.Multi-punch cooperative control is achieved by the multiple punches trajectory planning.The plannd trajectory follows the principle of the filling factor,consistent with the compression ratio and the pressing velocity,taking into account the smoothes,the continuty and the ability of electro-hydraulic driven system.Equivalent simplified pressure estimation methods are put forward to decouple compensation control of die-stamping force model.system control design is simplified as the extensive application of the motion-force combined control methods in every punch space.The controllers and parameters adaptation can be individually designed.Simulation results show the effectiveness of the multi-punches cooperative control methodIn Chapter5,based on the multi-punches cooperative control method for powder pressing,case study for the multistep powder parts pressing with a floating die is carried out in the powder compaction press experimental propotype.The results show that t the multi-punches cooperative control method can simplify the multistep parts compaction process,under the control,it can realize the multistep compact densification forming strictly follow the principle of the same pressing rate.This method can be applied in complex shape and high precision powder compacting process.In Chapter6,the research of the thesis is summarized,the major innovation of the research and further-prospect has been done.