Gradient Material Freeze-form Extrusion System Analysis And Control

Functionally graded materials have been increasingly used in the aerospace field due to unique physical properties.Currently,many studies of the preparation of gradient materials combine with rapid prototyping to fabricate gradient parts.However,the existing method produces the parts that has much more organic objects,and the fabrication is complicated,and environment unfriendly.This thesis proposes a kind of Freeze-form Extrusion Fabrication process,which can form the higher accurate three-dimensional solid parts by extruding aqueous pastes below the paste freezing temperature.During the deposition process of three dimensional components,the release of the bubble or breakdown of material agglomeration which can change the extrusion force of nozzle,which can make the material uncontimues to extrude and affect the surface quality of parts,even leading parts to failure.This thesis presents a dual extrusion device,using the adaptive control strategy regulate the extrusion force to meet the processing requirements of steady force.For fabricating gradient material testing,unilateral extrusion system of dual extrusion device can be described as a single-input single-output process.AIC method is used to determine the order of extrusion systems based on the input and output data after making the system fully responsive.A mathematical model is developed for extrusion process by forgetting factor recursive least squares method,and minimum variance adaptive control is used to design the adaptive extrusion force controller.The simulation algorithm for adaptive control and different extrusion force signal tracking,to verify the reliability of the controller and indicate that the method can achieve the desired control objectives.This thesis designs a closed loop control system,builds the experimental test platform and programs the PC control interface to achieve adaptive control algorithm and effectively control dual-extrusion device.Experimental results show that the adaptive controller based on the minimum variance has certain anti-disarrangement capability,through the square wave signals,triangular wave signals and sine wave test signal indicate that controller can accurately tracking extrusion force,and meet the molding requirements of the extrusion force constant and improve the part quality.