Research On Additive Manufacturing Of Bauxite Shell Based On Slurry Extrusion

The traditional casting process generally needs pattern or mold,which has long production cycle and high cost,so it is difficult to meet the future market demand for personalized,diversified and flexible manufacturing of single or small batch castings.Additive manufacturing process adopts the principle of discrete accumulation forming,which has the characteristics of high flexibility and short cycle.The development of new mold manufacturing technology based on additive manufacturing technology has become a research hotspot in recent years.SLS(Selective Laser Sintering)?SLA(Stereolithography)?3DP(Three Diamensional Printing)and other additive manufacturing technologies have the problems of large amount of organic binder,complex process,large investment and high cost in mold preparation.How to reduce the influence of organic binder and obtain high quality mold has become a difficult problem for these processes.In this paper,a kind of additive manufacturing process of casting shell based on slurry extrusion is proposed.Through the extrusion and stacking of bauxite slurry,the casting blank is formed.The silica sol is mainly used as binder.The gas generated during sintering is less and the pollution is lower,which greatly reduces the influence of organic binder on the quality of casting shell.The additive manufacturing process is simple and easy,and the casting shell with excellent performance can be obtained It expands the development and application of additive manufacturing technology in foundry industry.In this paper,firstly,the additive manufacturing equipment of casting shell based on slurry extrusion is designed and manufactured,and the manufacturing process are debugged and optimized.The precision oriented shell design is studied through orthogonal experiment,and the key parameters of shell design and manufacturing,such as shell thickness,filling mode and shell height,are optimized The feasibility of the developed additive manufacturing equipment and shell design scheme is verified by practice.The main conclusions are as follows(1)The additive manufacturing equipment based on slurry extrusion consists of delta motion system,screw extrusion head,push rod feeding device as the main mechanism,and computer as the upper computer.It has the characteristics of large printing space and continuous feeding.The operation software is simplify3 d,which has the functions of data processing and system control.After debugging and extrusion experiments,the recommended extrusion speed is less than 100 mm / min,the recommended ratio of feed speed and extrusion speed is 1,and the recommended layer height is 80% of nozzle diameter.(2)Taking the shell height,shell thickness and filling method as the factors affecting the dimensional accuracy of the shell,the orthogonal experiment is designed.The analysis results show that the shell thickness has the greatest influence on the dimensional accuracy of the X and Z directions,which is determined by the proportion of the filling part and the contour part in the shell.The thicker the shell is,the larger the proportion of the filling part is The results show that the best accuracy level can be achieved when the thickness is 10 mm;the filling method has the greatest influence on the dimensional accuracy of Y direction,which is determined by the gap inside the shell;the smaller the gap in the thickness direction,the higher the accuracy;the smaller the gap in the length and height direction,the higher the accuracy;the linear filling method has the highest accuracy;the effect of the shell is small.Through the verification experiment,the actual error of the standard test piece in the direction of length,width and height is0.328 mm,0.436 mm and 0.281 mm respectively.The results are similar to those of Taguchi method.(3)According to the best level combination of orthogonal experiment,the casting shell samples were designed.The bauxite shell samples were prepared by the developed additive manufacturing equipment for casting shell.The shell samples were obtained by freeze-drying and high-temperature sintering.The results show that: the screw extrusion process of additive guiding equipment is smooth and the extrusion wire is uniform;due to the use of the integrated design of shell and core,the positioning of each part of the shell is accurate,and the reasonable filling method and printing size make the dimensional accuracy of the shell good;the fracture analysis shows that the microstructure of the shell is reasonable and the sintering is good;the surface roughness of the shell in the plane direction(RA)The three-point bending strength of the shell is 6.27 MPa to 8.22 MPa.The results show that the shape of the castings with different shapes,such as nut,shell and shaft,is complete without deformation,and the surface has slight stripes;the surface roughness of the castings in the plane direction is 1.6?m,and the surface roughness in the height direction is 7.1?m.