Investigation Of The Formability And Collapsibility Characteristics On Slender-Complex Sand Core

With the rapid development of the aerospace industry, there have been increasing demands for the complex thin-walled magnesium alloy castings, The structures of casting parts are developed towards to integration, hollow thin-walled, complication and precision. Complex thin-walled magnesium alloy casting is often accompanied by sophisticated cavity and slender holes, so that it makes the casting parts and the foundry sand cores to be very complex, and it’s difficult to shape sand core precisely, the performance of the foundry sand cores becomes very harsh. Others, the intracavity pores of casting parts are also difficult to be clean. All these are greatly hindered the development of horizontal for our air magnesium alloy complex casting parts. Therefore, the study of the formability and collapsibility on the slender-complex sand core can lay the foundation for the preparation of complex sand core, and it has important theoretical and practical significance to improve the manufacturing level for the casting of complex magnesium alloys.Based on the structural characteristics of complex magnesium alloy castings, this paper designed a box mold for characterization researching of slender-complex sand cores, used the method of sand shooting to shape sand core, and carried out the research of the formability and collapsibility of slender-complex sand core and obtained some valuable results.(1) The paper uses the complete molding, filling density and bending strength as the evaluation index of formability, studied how these factors(the sand core shape, core shooting pressure, raw sand, binder and it’s addition) influent the forming properties of slender-complex core, analysised the regression equation of the filling volume and bending strength with these impact factors.When the sand core is slender and has corner, it’s easy to produce defects at the corner, and difficult to tight which portion far away from the shooting port. Because the corner can change the sand flow direction in the filling process greatly and make the kinetic energy of the sand has a big partial loss; the large length makes the pressure away from the sand shooting port is too small, and the loss along the way of the kinetic energy is large. Therefore, with the increasing of the sand shooting pressure, the sand have more kinetic energy, the complete molding of sand core is better, the filling density and the strength are both increased.With the increasing of the addition amount of the resin binder, the strength of the sand core increased. When the binder addition is less than 2%, the filling density of the sand core increased with the increasing of the addition amount of the resin binder; when the binder amount is greater than 2%, the filling density decreased, because a small amount of binder addition can increase the mobility of the sand, which can make the sand fill the molding easier; and when the binder addition is too large, the sand bonded together which makes it difficult to flow. The formability of the sodium silicate sand core has also been researched and it shows that sodium silicate sand core is easily broken and it is too brittle to take out from the molding after hardening. It’s not suit for forming slender-complex sand core.The type of the raw sand has the greatest impact on the formability of the sand core. Due to the high roundness, good mobility, and small resistance in sand shooting process of the ceramsite, the sand core has little defects, the filling density and the strength were higher; the formability of Dalin sand core followed and Duchang sand core is the third.(2)This paper uses the residual strength and the shakeout amount after heating of the sand core as the evaluation index of the collapsibility, studied how these factors(the heating temperature, raw sand, addition of the binder) influence the collapsing properties of slender-complex core, analysised the regression equation of the residual strength and shakeout amount with these impact factors.With the increasing of the heating temperature, the adhesive bond between sand is destroyed; the residual strength of the sand core is gradually reduced; the shakeout amount is increased. With the increasing of the addition amount of the resin binder, the adhesive force between the sand becomes greater and the residual strength increases, sand core is difficult to collapse.The type of the raw sand has the greatest impact on the shakeout amount of the sand core. The adhesion between Duchang sand is insufficient because of its large angular coefficient, after being heated, the sand core is easy to scattered in the external force, The addition amount of resin binder has the greatest impact on the residual strength of the sand core. The more the addition amount of the binder, the higher the residual strength, so the more difficult to collapse.