Study On Pneumatic Extruding Metal Direct-writing Deposition Shaping Technology

In the past thirty years,“additive manufacturing” has received extensive attention and researches,Hitherto,multiple mature additive manufacturing technologies(AMTs)have been developed,but they still face some problems such as high cost,poor performance of the parts,and so on.In order to contribute to solving these problems,this thesis presents a technology called pneumatic extruding metal direct-writing deposition(PEMDWD),which combines the advantage of constant pressure driving and direct-writing deposition shaping(DWDS).PEMDWD is a direct manufacturing technology for metal parts,its working principle is: after the metal material is heated and melted,the molten metal is extruded continuously and uniformly under the driving of constant pressure,meanwhile,the substrate moves along the track controlled by the numerical control program,the molten metal is deposited onto the substrate to form metal parts.In the process of DWDS,the thermal transfer is controlled by thermal management strategy,this makes the interlayer bonding to be metallurgical bonding,which can increase the strength of the final metal parts.PEMDWD is a low-cost technology with potential application,and the prototyping materials used by PEMDWD can be various.This thesis makes exploration and research on the basic scientific issues of PEMDWD,and the main research contents and achievements are listed as follows:This thesis first expounds in detail the working principle of PEMDWD and the general frame of the DWDS system,and the experimental device of PEMDWD was build.The directwriting deposition system mainly consists of three subsystems: motion control and execution,pressure monitoring and control,temperature control.The technical details of each subsystem are described,the key points of the design and manufacture for the key components and structure of the DWDS system are discussed,including the selection of the method for machining holes,the selection of sealing materials and the design of sealing structure.Using the PEMDWD device,the DWDS of the molten metal was achieved,this provided reliable hardware foundation for the following research work.The influence of nozzle structure on the flow of molten metal is analyzed using the related theories of fluid mechanics.Theoretical analysis results show that a throttling channel that is added to the nozzle structure can reduce the flow of molten metal in the process of the DWDS.A physical model for the flowing of molten metal in the nozzle was established to analyze the influence of throttling channel on the flow behavior of molten metal,and the flow behavior of molten metal in the nozzle was simulated numerically using ANSYS CFX.The simulation results show that the kinetic energy of the fluid is lost when the molten metal flows through the throttle channel,the final result is that the flow of the molten metal decrease about 28%.In order to test the reliability of the physical model,the simulation results are compared with the experimental results,the results show that the physical model established in this thesis and numerical simulation are effective tools for theoretical analysisBased on the related theories of heat transfer,a physical model for the cooling of molten metal in the process of DWDS was established in this thesis,the mathematical expression that describes the temperature distribution of the metal line was derived,and according to the mathematical expression,the changing curves of the temperature of the metal line with path were drawn.Using these curves,the solidification time of metal liquid is analyzed.Based on the experiments and the inspection or testing of the samples,the influence of substrate velocity,distance between substrate and nozzle,molten metal temperature and substrate temperature on the shape,microstructure and microhardness of the metal lines are discussed respectively.By means of experiments and tensile tests,the influence of ironing press on the mechanical properties of metal line is preliminarily analyzed,but the working mechanism of the influence of ironing press on the mechanical properties of metal material still awaits more research.Based on the study of the control of shape and property,the mechanism of interlayer bonding is investigated,and how the experimental parameters affect the interlayer bonding is discussed and analyzed.On the basis of the previous chapters,reasonable experimental parameters were set up,two-dimensional pattern and three-dimensional entity of metal materials were successfully fabricated using the above-mentioned DWDS device,which indicates that the principle of PEMDWD is feasible.The three-dimensional entities includes three kinds: thin-walled objects,inclined thin-walled objects and thick-walled objects,the key problems appeared in the process of DWDS are investigated.