Research On Key Technology Of 3D Sand Printing Mold

Casting is a liquid metal forming process with a long history.And sand casting accounts for about 70% of the total industry.However,sand casting has the problems of long production cycle,high mold manufacturing cost,low process flexibility,large environmental pollution,and high labor costs,especially in the areas of cleaner production and intelligent casting.Three Dimensional Sand Printing(3DSP)is one of the effective ways to bring the foundry industry into the smart direction.3DSP can directly manufacture sand molds without molds,has short production cycles,and simplifies the design and production mode of casting.However,3DSP also has problems such as unclear relationship between process parameters and sand mold performance,low sand mold accuracy and strength,and unclear material systems.These problems severely limit the application of 3DSP.Therefore,the research on sand technology of 3DSP is very important.First,the paper systematically studies the effects of parameters such as print layer thickness,curing agent addition amount,powder feed coefficient,powder spreading speed,and resin addition amount of 3DSP furan resin sand mold on the performance of the sand mold.The results show that the density of the sand mold has a significant positive correlation with the powder spreading speed,a significant negative correlation with the amount of curing agent added,and no significant correlation with the print layer thickness.The mechanical properties of the sand mold(tensile strength at normal temperature,compressive strength at high temperature,duration of high temperature,limited thermal expansion force)are inversely proportional to the thickness of the print layer;the permeability of the sand mold is directly proportional to the thickness of the print layer.The tensile strength,high temperature performance of the sand mold is inversely proportional to the amount of the curing agent added,and the permeability of the sand mold is proportional to the amount of the curing agent added;the tensile strength,high temperature performance,and gas generation of the sand mold are proportional to the amount of resin added,and the permeability of the sand mold Inversely proportional to the amount of resin added.Based on the above trends,a better combination of process parameters is as follows: the amount of curing agent added is 0.4%(accounting for the mass fraction of raw sand),the thickness of the print layer is 0.30 mm,and the amount of resin added is 2.18%(accounting for the mass fraction of raw sand).The performance is: the average normal temperature tensile strength is 2.21 MPa,the average drying tensile strength is 2.64 MPa,the average high temperature compressive strength is 182.43 KPa,the average air permeability of the sand mold is 304.61,and the average gas output is 14.60 m L/g.Secondly,the anisotropy of the performance and dimensional accuracy of the sand mold in different directions in space is studied.The results show that the tensile strength,flexural strength,and shear strength of the sand mold are anisotropic in different directions.The main reason is that the bond strength in the printing ink channel> the bond strength between the ink channel and the ink channel> the thickness of the printing layer and Adhesive strength between printed layer thicknesses.The average tensile strength in the X direction is 2.48 ± 0.10 MPa,the average tensile strength in the Y direction is 2.35 ± 0.08MPa(a drop of about 5%),and the average tensile strength in the Z direction is 2.21 ± 0.11Mpa(a drop of about 10%);in the X direction The average bending strength is 6.59 ± 0.27 MPa,the average bending strength in the Y direction is 5.76 ± 0.31MPa(a decrease of about 12%),and the average bending strength in the Z direction is 5.08 ± 0.27MPa(a decrease of about 22%).The shear strength is 3.67 ± 0.18 MPa,the average shear strength in the X direction is 3.38 ± 0.08MPa(a decrease of about 8%),and the average shear strength in the Y direction is 3.41 ± 0.11MPa(about 7%).Relative error in X direction> Relative error in Y direction> Relative error in Z direction.The average relative error in the X direction is 2.70%,the average relative error in the Y direction is 2.63%,and the average relative error in the Z direction is 2.10%.The air permeability of the sand mold is not large,but the air permeability in the Z direction is smaller than the air permeability in the X and Y directions,and the air permeability in the X direction and the Y direction are not significantly different.Finally,the effect of the size of raw sand on the performance of 3DSP was studied.The results show that fine sand can be embedded in the pores of coarse sand through appropriate particle size grading,which can increase the sand density and reduce the porosity.The setting effect of fine sand can increase the contact point of the sand particles,increase the number of bonding bridges,and improve the tensile strength of the sand mold.The molding sand with relatively concentrated particle size distribution has high limited thermal expansion force at high temperature,and the continuous distribution of particle size has different expansion times due to different particle sizes,which can reduce the limited thermal expansion force.The particle size gradation will affect the density of the powder bed,and the density of the powder bed will affect the penetration behavior of the binder.A high density of the powder bed will cause the binder to penetrate more easily in the X and Y directions,resulting in dimensional errors in the X and Y directions.Increased,the dimensional error in the Z direction is mainly related to the particle size,and the larger the particle size,the larger the dimensional error.Through experimental research on medium carbon steel automotive molds,a complete and qualified 3DSP complex furan resin sand mold was obtained using appropriate printing parameters.The average tensile strength of the sand mold was measured to be 2.6 MPa,and the gas generation was 14 m L/g.Brush the sand surface,and cast the qualified medium carbon alloy steel castings.The moldless rapid casting of complex medium carbon steel automobile molds has been realized.The surface is smooth,the characters are clear,and the cost is low,making it possible for the 3DSP new technology to be used in production.