Research On Process Optimization And Performance Of Forming Sand Mold (Core) By Three Dimensional Printing

As one of the main process methods of additive manufacturing,Three-dimensional Printing(3DP)possesses a sea of advantages in terms of various forming materials,low running cost,simple operation,etc.,especially when it is applied to complex casting sand for a quick printout.However,there still exist drawbacks,such as poor stability,low strength and heavy gas emission,in forming sand molds(cores)by 3DP.The paper conducts research on properties of 3DP sand mold(core),including its strength,gas volume and size accuracy,effected by 3DP parameters containing post-processing technology,spray volume,layer thickness,etc.and material characteristics regarding the angular coefficient and particle size of the raw sand,etc.in order to provide certain technical support for the industrial application of 3DP-printing sand molds.The main content and results are summarized as followsThe effects of post-processing and printing parameters on the performance of 3DP printing sand molds(cores)were studied.The curing mechanism of the phenol-based adhesive is analyzed based on the curing performance of the resin,and the posttreatment curing process is formulated by the adhesive TG-DSC curve.The phenolic hydroxyl group or alcoholic hydroxyl group of the phenol resin and the epoxy group in the epoxy resin undergo a ring opening reaction by heating in 190? with 6-hour heat preservation,and the bead sand type obtained after the final curing has a high tensile strength of 2.05±0.15 MPa.If the amount of liquid sprayed increases,the strength,gas volume and dimensional deviation of the sand mold all increase,and the dimensional deviation in the height direction is larger than that of the forming surface.Whereas,if the thickness of the layer increases,the above deviations all decrease.When the spray volume is set to 60% and the layer thickness is 0.2mm,the cured sample has a tensile strength of 2.48 MPa and an outgassing volume of 7.4 m L / g after curing at 190 ? for 6 hours,which meet the requirements of sand casting.Study includes the influence of the type and size of the raw sand on the forming quality of the 3DP-printing sand mold(core).The lower the angular coefficient of the raw sand,the better the quality of the sand mold,the tighter the sand mold,the less powder loss on the surface,the higher the surface smoothness,the greater the strength,which reaches 2.67±0.16 MPa.Under the same condition,the strength of the sand mold is 0.69±0.03 MPa with cerabeads in the size of 788.0?m.By comparison,printed with cerabeads in an average particle size of 72.9 ?m,The air permeability is 43.07 and the size deviation of the shaped surface is 3.33±0.08%.As the average particle size of the sand decreases,the sand porosity decreases,whereas the density and the strength gradually increases.The sand mold printed with 72.9 ?m cerabeads has a porosity of 44.03% and a strength of 2.6±0.09 MPa.Based on the above results,the logic valve sand core with complex structure and conformal air holes is successfully printed by making use of the 72.9 ?m cerabead,phenolic resin adhesive coupled with 0.2 mm print layer and 70% spray volume,which is scanned three times,in 3h.The clear and compact overall outline and the surface without powder dropping fulfill the required criteria for sand casting.