Gradient Material Freeze-form Extrusion Process Analysis And Control

The chemical composition,microstructure and atomic arrangement of the Functionally Gradient Material(FGM)vary continuously from one side to the other,resulting in a gradual change in the properties and functions of the material.Because of the unique performance of functionally graded materials,it is widely used in aerospace,bioengineering,and nuclear industry.At present,many studies have applied the Rapid Prototyping Manufacturing(RPM)principle to the preparation of FGM,but these methods have high organic content in FGM,post-treatment degreasing complex and unfriendly environment.In this thesis,two different water-based paste materials were extruded and mixed at a temperature below their freezing proposes using the Freeze-form Extrusion Fabrication(FEF)process and finally worked out a three-dimensional solid part with a certain gradient.However,in the process of extrusion of the paste,the release of the bubble or breakdown of material agglomeration,which can change the extrusion force of nozzle,result in the formation process is not continuous or the emergence of parts in some places too much accumulation and affect the surface quality of parts,even leading parts to failure.Therefore,this paper designs a set of double-extrusion mixing device for the principle and process of gradient part forming,the extrusion speed control and squeezing force adaptive control strategy are used to control the extrusion speed and the extrusion force at any time,so that the two kinds of different materials are mixed in any proportion and continuously and uniformly extruded from the nozzle.Aiming at the squeezing force control in the FGM extrusion process,the unilateral extrusion process can be described by a single input single output process by the classical identification method.The parameters of the established process model are estimated by the recursive least squares method,and the squeeze force adaptive controller is designed according to the minimum variance adaptive control strategy and the reliability of the controller is verified by Matlab simulation.For the material to be any proportion of extrusion and mixing,the calculation formula of the control voltage required for the extrusion speed control is obtained by reasoning and calculation.Finally,the conditional proportional control strategy for FGM extrusion process control is developed by combining the extrusion speed control and the squeezing force adaptive control.The double-squeezing device is designed as closed-loop control system,FGM extrusion molding experiment platform is designed,and composed the human-computer interaction software to realize the intuitive and convenient experiment and data acquisition.FGM molding experiments show that FGM low-temperature extrusion can quickly and directly form FGM parts,the conditional proportional control strategy can effectively control the extrusion process of extrusion speed and extrusion force,and meet the continuous molding requirements of FGM parts.