Analysis And Optimization Of Process Parameters And Nozzle Structure For FDM Type Metal Composite 3D Printing

3D printing technology uses additive manufacturing methods,which can be quickly integrated,more and more widely used in various fields.Based on fused deposition modeling（FDM）technology and powder injection molding technology,316L composite material was used as FDM metal 3D printing raw material,the printing process parameters and the structure of the printing nozzle were designed and optimized respectively.An experimental platform for FDM-type metal 3D printing and a gradient heating printing nozzle were set up,the printing process parameters were optimized by orthogonal experiments,and the temperature field of the nozzle was simulated and analyzed,the structure and material of the nozzle were optimized.When the optimized printing parameters and the new structure nozzle are used for printing,the printing nozzle is smooth,the model accuracy is high,and the interlayer bonding performance of the formed sample is impressive.Using the powder injection molding process for reference,the printed green body was catalytically degreased and sintered at high temperature,and stainless steel samples were obtained.The main contents and conclusions of this paper are as follows:（1）Designed and optimized the printing experiment platform.The nozzle of the modified FDM plastic 3D printer is a printing nozzle of gradient heating bar stock,and the drive control circuit and control program are upgraded,which is compared with the built Delta 3D printer.The results show that the deposition process of the modified printer wire is smooth,and the formed samples with higher surface accuracy can be obtained.（2）The heating phase change process of printing raw material was studied by designed experiments.The results show that the heating characteristics of the composite material are:softening temperature is 155±2℃,melting extrusion temperature is 190～200℃when used as FDM consumables,and when the heating temperature reached 205±2℃,the thermoplastic of the material will produce permanent loss.（3）Optimized the printing process parameters.By analyzing the influence of FDM 3D printing process parameters on the printing molding sample,the height error and offset of the printing sample were selected as evaluation indicators,and the orthogonal optimization experiment was carried out using the printing layer height,extruder temperature,and wire extrusion speed as the influence factors.The parameter optimization results are as follows:when the printing layer height is 0.25 mm,the nozzle temperature is 195℃,and the wire extrusion speed is 70 mm/min,higher surface quality specimens can be obtained.（4）Established the simulation and analysis model of gradient heating of printing nozzle.The main heat transfer methods and mathematical theories in the nozzle structure were analyzed,and the steady-state thermal analysis simulation model and runner simulation model were established for the nozzle structure,and based on the Maxwell theoretical model and the Bruggeman theoretical model,the thermal conductivity of metal composites was solved.（5）The heating structure of the printing nozzle was optimized and the supporting material was changed.The thermal analysis and simulation of the nozzle structure model were carried out,and obtained different steady-state gradient temperature profiles of the nozzle,which confirmed with the experimental results of the printed samples,it is found that the connection between the aluminum alloy support frame and the nozzle material pipe plays a role of"heat dissipation",resulting in the phenomenon of material blocking of the extrusion wire.The material of the support board is changed,and the composite fiber board with good heat insulation performance is used as the nozzle support board.Under the same heating temperature gradient,the temperature distribution of the material pipe is improved,the minimum temperature in the"heat dissipation area"is increased about 4℃.The analysis also found that the heat dissipation effect of the nozzle support structure on the material pipe could shorten the temperature width of the melting area.The optimized nozzle structure is as follows:the supporting structure is connected with the material pipe between the heating blocks T1 and T2,three heating blocks are heated and the temperature gradient of heating blocks T1-T3 is 195,185 and 155℃,the length of the material pipe is about110mm.The steady-state thermal analysis and runner analysis of the optimized structure were carried out.It was found that the heating and melting area of the nozzle tube was concentrated near the extruder,and the temperature gradient transition in the heating and softening area was better.With this structure nozzle,there is no material blocking and sample delamination during actual printing.（6）The printed samples were subjected to catalytic degreasing and high temperature sintering.The degreasing process parameters are as follows:degreasing temperature 120～130℃,HNO₃steam feeding rate is 0.03～0.06 m L/min,N₂ flow rate is 100～200 m L/min.Under this process,the shape of the sample is kept intact,the degreasing rate can reach 1 mm/h,and the degreasing weight loss rate is 7.0～7.9%.The sintering process parameters are as follows:the pressure in the furnace is+0.04 MPa during sintering,the thermal degreasing temperature is 350℃,450℃,the sintering temperature is 1380℃,and the sintering temperature node is kept for 30 min.After sintering,the sample produces densification shrinkage with a shrinkage ratio of about 10%.