Extrusion-forming Process Control And Experimental Study Of Functionally Gradient Material

Functionally Gradient Material(FGM),a specific composite material,is designed on the basis of computer-aided design combining new material design concept,the chemical composition and atomic arrangement of which vary gradiently.Owning to its unique composition,functionally gradient material has high strength,high wear resistance and high temperature resistance and is widely used in aerospace,biological engineering,nuclear industry as well as other fields.At present,researchers apply the principle of rapid prototyping to the preparation of FGM.The FGM parts formed by this means contain a larger sum of organics,which post-processing degreasing is complicated and not environmental-friendly.This dissertation uses low-temperature extrusion free forming technology to manufacture FGM,principle of which is to mix water-based paste of two different materials in different proportions to carry out stacking molding and finally process a three-dimensional part with a certain gradient.However,bubbles,agglomerates,and liquid phase migration are unavoidable during the paste-extrusion process,which will affect the molding process and even result in rough surface quality of the final molded parts.This paper focuses on the instability of the extrusion process,builds a FGM forming platform,and strives to find a controllable FGM manufacturing method.In accordance with the established FGM experimental platform,preparation method of the paste material during the FGM molding process is defined and the interference factors in the molding process are analyzed.The effects of air bubbles,agglomeration and liquid phase migration in the paste materials during the FGM molding process are analyzed in detail;the speed matching formula in the FGM molding process is deduced and verified,at the same time,the optimum paste concentration suitable for FGM molding is found through the experiment.The experimental results demonstrate that under the condition of speed matching,FGM parts shaped with the appropriate paste concentration has higher accuracy,which has paved the way for the further modeling and control of the FGM system.System identification method is used to establish a stable FGM control model.In accordance with the method of system identification,the FGM system identification experiment is designed.The voltage signal of the servo extrusion cylinder is used as input signal as the extrusion force was output one.The residual error variance analysis method is used to identify the order of input and output data.The results illustrate that the obtained model of the system is second-order;the least-squares recursive algorithm is used to identify the parameters of the system model,the parameter estimates of the FGM system model are obtained,and the established off-line model is checked and analyzed to verify the model effectiveness.An adaptive controller is designed to study the real-time control method of the FGM molding process.A minimum-variance adaptive controller is designed to adaptively control and simulate the established FGM system model.The simulation results show that the designed adaptive controller is feasible and practicable.In accordance with the simulation results of adaptive controller,the output extrusion force expected value of the FGM system is adjusted and the FGM gradient experiment is designed.The experimental results indicate that this method can be used to obtain FGM materials with an arbitrary ratio gradient,the feasibility of which is also verified.In conclusion,the designed adaptive controller can effectively control the FGM molding process online.