Study On The Precision And Performance Regulation Technology Of Multi-material Composite Sand Mold By 3D Printing

Sand 3D printing technology has become a research hotspot at home and abroad because it does not require mold making and has advantages of strong flexibility,high efficiency,high quality and raw material saving for small batch and single castings.The preparation of multi-material composite sand mold by 3D printing technology is studied in this paper.The multi-material composite sand has two or more kinds of sand materials,so that the sand has all of the performance of multiple materials.Therefore,on the basis of sand 3D printing forming materials mainly consisting of furan resin system and silica sand material,researching on 3D printing technology of multi-material sand mold to solve the problems of single forming materials,difficult control of sand shape and difficult high performance casting manufacturing.Research on the basic performance of multi-material composite sand mold materials,construct the multi-material composite sand mold printing system,study the inkjet principle of the nozzle,realize the efficient and stable operation of the printing system,and provide a good experimental basis for the subsequent research.The effects of basic physical and chemical properties of silica sand,chromite sand and zircon sand,such as particle size distribution,main composition,specific surface area and acid consumption value on tensile strength,air permeability and gas output of sand mold are investigated in order to improve the performance of multi-material composite sand mold.Under the condition of constant binder content,the tensile strength of zircon sand mold is the highest,silica sand mold is the second,and chromite sand mold is the lowest.The permeability of silica sand is better than that of chromite sand and zircon sand.The casting performance of multi-material composite sand material is the result of coupling effect of physical and chemical properties of sand material.Study on optimization and formulation of multi-material composite sand mold,establish geometric model and contact model of multi-material composite sand mold,and conduct numerical simulation of bonding between particles of multimaterial sand mold and mechanical analysis of contact of multi-material sand mold.By mixing silica sand with chromite sand and zircon sand in different proportions,the optimal multi-material composite sand material formula with excellent performance is obtained,so that the sand has a variety of functions,effectively improve its air permeability and strength,and at the same time have good thermal properties.The correlation between the air permeability and the pore structure and volume of the multi-material composite sand mold is established.The size and distribution of the pores of the multi-material composite sand mold have strong randomness and irregular distribution,and the sphericity,density and clearance are changed,thus affecting the performance of the sand.Multi-material composite sand mold can effectively adjust the sand mold performance,prepare high-quality casting,and the casting is not easy to produce casting defects.Research on 3D printing process of multi-material composite sand mold,put forward the multi-material composite sand mold forming method,improve the performance and forming accuracy of multi-material composite sand mold,and enhance the digital control ability of multi-material composite sand mold.The study on the properties of multi-material composite sand mold by interlaminar composite forming process are carried out.The mechanical properties of interlaminar composite sand mold are effectively improved when the transition area of interlaminar composite sand mold is the optimal composite sand mold material.Among them,when the mass ratio of silica sand and chromite sand in the transition area of multi-material composite sand is 9:1,the strength mechanical properties and air permeability of interlayer composite sand are increased by 34.5%and 33.0%compared with the two single-material sand mold.The effect of sand layer thickness and resin content on the forming accuracy of multi-material composite sand mold printing is studied,the thickness of sand layer has a great influence on the forming accuracy of sand mold.With the decrease of layer thickness,the forming accuracy of silica sand and chromite sand gradually increases.The study on the precision control of multi-material composite sand mold laying by the in-layer composite forming process is carried out.When the curing agent content of silica sand and chromite sand is 2.0wt.‰～2.5wt.‰ and 3.0wt.‰～3.5wt.‰,the sand laying width,sand laying track and sand laying amount all meet the requirements of precise manufacturing of multi-material composite sand mold.Research on the macro and micro properties of multi-material composite sand mold castings,carry out the casting of multi-material composite sand alloy,analyze the macro and micro properties of castings,establish the mapping relationship of cast mold,and realize the shape control of multi-material composite sand mold.The optimization of multi-material composite sand mold can effectively inhibit element segregation,refine grain size,and improve the macroscopic mechanical properties of castings.When the wall thickness is the same,the grain size of zircon sand casting is the smallest.The grain size of castings increases with the increase of wall thickness.Zircon and chromite sand have good cooling effect on castings,and have good solid solubility,fine microstructure and great improvement in mechanical properties.At the same temperature,the multi-material composite sand mold has different thermal conductivity of different gradients,and is higher than the silica sand,speeding up the casting solidification rate,refining the microstructure,improving the casting performance,and preparing high-quality castings.The main innovations in this paper are as follows:(1)A digital 3D printing forming method of multi-material composite sand mold is proposed.The multimaterial composite sand mold is prepared by mixing silica sand,chromite sand and zircon sand in different proportions.The optimized composite sand mold has the characteristics of high strength,good air permeability and low gas generation,which can enrich the manufacturing method of multi-material sand mold and effectively improve the casting performance.(2)A digital multi-material composite sand mold paving method and its precise sand laying device are proposed,which can lay two or more kinds of sand materials at the same time.The interface bonding performance and its influence rule of multi-material composite sand mold overall printing are revealed,and the correlation relationship between the size,trajectory,area,paving sand amount with curing agent content,paving sand speed,paving sand thickness,paving sand mouth size and cylinder force of multi-material composite sand overall printing is established,which improve the accuracy and quality of multi-material composite sand mold overall printing.(3)The mapping relationship between the multi-material composite sand mold and the casting properties is established,and the influence law of the multi-material composite sand mold with different wall thickness on the macro and micro properties of the casting is studied.The composite sand mold can effectively refine the grain structure of the casting and realize the precise control of the macro and micro properties of the casting.In this paper,the process of multi-material composite sand mold forming based on sand 3D printing technology and the optimization of digital sand laying device and the performance regulation of sand mold castings are studied systematacially.It has important theoretical research significance and engineering application value for promoting the development of 3D printing multi-material composite sand mold forming technology and preparing the high-end complex castings.