Basic Research On Sand Mold Performance Based On Gradient Printing

As a traditional casting process,sand casting plays a very important role in the foundry industry.When castings with complex shapes and high quality are manufactured by traditional casting methods,multiple sets or even more than ten sets of molds need to be turned over.This brings many problems such as difficulties in manufacturing the sand mold,long cycle time,and low precision.Additive manufacturing technology of sand mold provides a more convenient and flexible means for the rapid manufacture of sand mold.Compared to the traditional casting methods,the additive manufacturing technology does not require wood molds,and it has the advantages such as short manufacturing cycle,low cost,and integrated sand/core.Especially in the production of single and small batches of complex castings and the development of new products,there is a good prospect for additive manufacturing technology.This paper studies a sand-mold ink-jet printing forming method based on gradient printing.This method is based on the gray-scale printing technology.The sand mold's parts which required a higher strength has a higher gray level and a higher resin ejection amount;The sand mold's parts which required a lower gas generation has a lower gray level and a lower resin injection amount.Different parts of the sand mold have different resin injection amounts,thereby reducing the overall resin injection amount and improving the overall performance of the sand mold.The theoretical analysis of the sand-mold ink-jet printing forming process was carried out,including the establishment of sand particles accumulation model and the establishment of drop motion model.With a height ratio coefficient,a deposition model of sand particles and the calculation formula of porosity was established.The motion model of droplet dropping process was established,and the relationship between the velocity,displacement and the droplet falling time in the horizontal/vertical direction of the droplet was obtained.At the same time,the height of the nozzle,the scanning speed of the nozzle,and the volume of liquid were analyzed during the droplet dropping process.The effect of the sand laying process on the surface quality was studied.Based on the three-dimensional parameter characterization method,the surface quality of sand laying was quantified.By collecting the three-dimensional profile information of the sand laying surface,the datum plane is fitted and the calculation formula of the root mean square deviation of the surface profile was obtained.The surface quality of sand laying under different sand laying speed,curing agent content and size of sand was studied.The research shows that the effect of sand laying speed on the surface quality is small,and the sand laying efficiency can be improved by increasing the sand laying speed;The effect of curing agent content on the surface quality is more obvious,and the surface quality is good when curing agent content is?0.6%.When the curing agent content is too high,the sand laying surface is unstable and the wave phenomenon occurs.When the size of the sand is small,the surface quality is good and the accuracy is high.In order to solve the problem of low strength and high gas generation during the sand-mold ink-jet printing process,the effect of resin content and curing temperature on the strength and the gas generation of the sand mold was studied based on the independently developed sand-mold ink-jet printer.When the resin content is 5.2%,and the curing temperature is 80?,the sand mold strength is 1.71 MPa,and the gas generation is 11 mL/g(850? ± 10?).At the same time,the performance of sand mold based on gradient printing was studied.It was shown that the strength/gas generation of the sand mold is linearly related to the gradient content,and the gradient printing forming method is an effective method to reduce the overall gas generation volume of the sand mold.Through the printing experiments on a complex sand core,the rationality of the sand-mold ink-jet printing process in this paper was verified.At the same time,three types of methods:manual modeling,sand-mold ink-jet printing,and gradient-printing,were used to make typical sand molds and cast castings.By comparing the defect conditions of the castings,the feasibility of the gradient print forming method in reducing the overall gas generation of the sand mold was verified.