Study On Preparation And Properties Of The Coated Sand For Selective Laser Sintering

In contrast to the long cycle and difficulty in the conventional process to make large-scale complex sand?core?molding,the selective laser sintering?hereinafter referred to as SLS?rapid forming technology,because of its velocity,precision and no limitation in shape,is applied widely in more and more fields.It provides a good solution in the sand core development and consequently in the complex thin-walled castings,avoiding problems like high cost and long period etc.However,there are still some problems,such as the expensive price,higher gas evolution and poor casting performance.because the SLS coated sand?also named 3D printing coated sand?is developed only a few years in our country.It is difficult to meet the actual industrial requirements due to the improved strength being always in the accompany with higher gas emission.Therefore,it is not only have a high scientific value but also a practical utility of rapid prototyping technology to design a kind of cheap,high-intensity and low gas emission SLS coated sand.In this paper,the main raw material for SLS coated sand were studied by analyzing the properties and microstructure between silica sand?SiO₂-based?and pearl sand?Al₂O₃-based?,based on the main raw material types,formula and particle size of selective sandblasting.At the same time,the particle size composition was determined to be 70/140 mesh according to the study of the relationship among the particle size composition,the properties of the coated sand and quality of the sintered parts,and it is also combined with the actual requirements of the tutor team to develop the product.Finally,the influence of process parameters on the performance of various sands and the mixing mechanism of coated sand were analyzed through changing the preparation process parameters and composition ratio,designing the orthogonal experiment to prepare the coated sand and testing the performance,including the tensile strength test,the bending strength test,the gas volume test,burning reduction test,SEM test,melting point test,etc.The results show that:With the increasing of the temperature when the resin was added,the tensile strength,bending strength,gas volume and the reduction burning of coated sand initial increased and subsequent decreased.With the increasing of resin mixing time,the tensile strength and bending strength increased first and then decreased,and the amount of gas volume increased slowly.With the increasing of the temperature of the addition of urotropine,the tensile strength and bending strength increased first and then decreased,and the gas volume and burning reduction slightly reduced and then increased and then decreased.With the increase of urotropine mixing time,the tensile strength and bending strength increased first and then decreased,and gas volume and burning reduction almost keep no change.With the increase of calcium stearate,the tensile strength and bending strength increased first and then decreased,and the gas volume and burning reduction were almost unchanged.With the increasing of resin content,the tensile strength,bending strength,gas volume and burning reduction of coated sand all increased evidently.With the increasing of the content of coupling agent,the strength was featured by initial increased and subsequent decreased,and the gas volume and burning reduction increased slightly.The tensile strength and bending strength increased rapidly with the increasing of the content of urotropine,until it reached maximum,and then it increased slowly as the further rising of urotropine content,and the gas volume and burning reduction increased gradually.With the increase of calcium stearate content,the tensile strength and bending strength of the coated sand increased slowly,and the gas volume and burning reduction decreased slowly.At last,the optimum coating process was obtained through analyzing the relationship between the technological parameters and various component contents of the coated sand.The coated sand was prepared under the optimum composition ratio and the coating process parameters.Then,the sand cores and the cylinder head molding were printed by the rapid prototyping system.And the achievement of qualified cylinder head in aluminum alloy verified the success of the SLS coated sand studied in this work.