Research on cracking mechanism of the thin shell mould in expendable pattern shell casting during pattern removal process

Aiming at the cracking phenomenon of the thin shell mould in the expendable pattern shell casting during the pattern removing process, some systemic researches are presented.The influence of the pattern removing method and temperature on the pattern removing were investigated.The shell mould cracking mechanism was analyzed by using thermo-gravimetric analysis (TGA), and combining the temperature field and the volume change of the expanded polystyrene (EPS) foam pattern being tested.The results indicated that the shell mould was not easily cracked when the pattern removing process was carried out with the furnace being heated little by little because of the shell slowly shrinking with dehydration and shell strength gradually increasing.The shell mould was soon destroyed when it was set directly into the furnace at above 400 oC because of the thin shell mould rapidly shrinking and the foam pattern hindering.However, the shell mould had no cracking when it had been preheated for a long time even if the furnace temperature was above 400 oC and the shell was put into the furnace directly.Moreover, when the shell mould was directly set into the furnace at lower temperatures, 250 to 300 ℃, the shell would shrink slowly and the foam pattern would stay at the maximum expansion stage temperature of 100 to 110 ℃ for a long time; and the shell mould would experience an expansion force from the foam pattern for a long time.The expansion force is related to the pattern removing temperature, holding time, foam pattern thickness and density.Therefore, the foam pattern with higher density could make the shell crack.

Numerical simulation and optimization of shell mould casting process for leaf spring bracket

Although the shell mould casting process has a wide range of application in many fields,the prediction of casting defects is still a problem.In the present work,a typical leaf spring bracket casting of ZG310-570 was fabricated by shell mold casting.The finite element model and ProCAST software were utilized for simulating the filling and solidification processes of the casting;and the formation mechanism of the gas pore,and shrinkage porosity defects were analyzed.The results indicate that the gas pore and shrinkage porosity defects are formed due to air entrapment,insufficient feeding and non-sequential solidification.Subsequently,through changing the position of risers,adding a connecting channel between the risers,and setting blind risers at the U-shaped brackets,an optimized gating and feeding system was established to improve the quality of the casting.After optimization,the gas pore and shrinkage porosity defects of the leaf spring bracket casting are effectively eliminated.The experiment results with the optimized casting process are in good agreement with the numerical simulation,which verifies the validity of the finite element model in the shell mould casting.

Microstructure and mechanical properties of AZ91D magnesium alloy by expendable pattern shell casting with different mechanical vibration amplitudes and pouring temperatures

To refine the microstructure and improve the mechanical properties of AZ91 D alloy by expendable pattern shell casting(EPSC),the mechanical vibration method was applied in the solidification process of the alloy.The effects of amplitude and pouring temperature on microstructure and mechanical properties of AZ91 D magnesium alloy were studied.The results indicated that the mechanical vibration remarkably improved the sizes,morphologies and distributions of the primaryα-Mg phase andβ-Mg17 Al12 phase,and the densification and tensile properties of the AZ91 D alloy.With an increase in amplitude,the microstructures were gradually refined,resulting in a continuous increase in mechanical properties of the AZ91 D alloy.While,with the increase of pouring temperature,the microstructures were continuously coarsened,leading to an obvious decrease of the mechanical properties.The tensile strength and yield strength of the AZ91 D alloy with a vibration amplitude of 1.0 mm and a pouring temperature of 730℃were 60%and 38%higher than those of the alloy without vibration,respectively.

Experimental study on separation of valuable refractory aggregate from investment casting ceramic shell waste

In the present study, a processing technique for recycling investment casting ceramic shell waste was proposed to separate valuable refractory aggregate zircon sand. The microstructure and phase constituents of the shell waste and separation process were investigated. The results show that the characteristics of microstructure and phase constituents of the shell waste can meet the conditions for preferential y separating zircon sand, and zircon sand can be separated by gravity separation on a shaking table. The separated zircon sand has good shape and high purity, and can be used for the production of castings and other applications.

Formation mechanism and criterion of linear segregation in ZL205A alloy

The experiments and numerical simulation were conducted for ZL205A aluminum alloy cylindrical shell casting. The formation mechanism of the linear segregation produced by the low pressure die casting (LPDC) process was investigated. And the heat transfer of the casting during solidification process was analyzed by simulation technique, resulting from the information of linear segregation obtained by plenty of experiments. The new linear segregation criterion was proposed through the simulation and experimental results. It was found that the melting metal with high Cu contents was feeding the crack shrinkage formed by the tearing under the effect of feeding pressure during the later solidification, which led to the formation of linear segregation. The control methods for the linear segregation were suggested based on the proposed mechanism. Finally, the criterion of linear segregation was confirmed by the production of the actual castings.