In vacuum casting, it is necessary to accurately account for the effects of energy reflection and absorption by bodies. The 'Radiation' module can solve complex tasks of heat exchange by radiation, considering re-radiation and shading.
PoligonSoft can simulate all processes related to vacuum casting and obtain results that allow for predicting and preventing the occurrence of defects.
Macro and microporosity
Residual stresses
Deformations and warping
Cracks (hot and cold)
Directional solidification
Radiation
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Save significant costs in materials and labor, in addition to reducing product development time.
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Prevent and correct casting defects, such as porosity, air inclusions, or solidification issues.
Experiment with different variables of the casting process to find the most efficient configuration.
Nickel Alloy - CHS70
Vacuum Casting Equipment - UPPF-3M
Mold - Ceramic mold with thermal insulation
Mold Preheating - 1050°C
Pouring Temperature - 1500°C
Vacuum Exposure Time - 180 sec.
Air Cooling
The initial castings were subjected to luminescence and radiographic control, which revealed the presence of both macro and micro porosity with individual pore sizes of more than 0.2 mm.
The geometry of the blade is such that hot spots almost always form at the transition points from the blade to the platform. Additionally, the central part of the blade is also prone to the formation of shrinkage defects.
PoligonSoft solves the differential equations of heat and mass transfer in the crystallizing casting using the finite element method (FEM).
For its implementation, it is necessary to construct a mesh model of the calculation region. In this case, the calculation region consists of the metal, the ceramic shell, and the thermal insulation.
The shell generator allows for the automatic creation, without prior constructions, of a mesh model of the ceramic shape and the insulating layer with a specified thickness, based on the 3D model of the part.
Thermal
insulation
Ceramic
mold
Asbestos
Refractory
brick
Reflective
chamber
Mathematical model of the foundry furnace
A model of the technological process was formulated with the following sequence of calculations:
Calculation of the cooling of the empty mold from the moment of its extraction from the preheating furnace to the metal pouring.
Modeling of the crystallization process from the moment of mold filling to the admission of air.
Modeling of the crystallization process from the moment of air admission to complete solidification in the open air in the workshop.
Heating + Transfer + Vacuuming
Pouring + Vacuum Holding + Cooling
Mold temperature fields at the start of pouring.
Temperature and porosity of the cast at the moment of air admission.
Calculated porosity of the blade after cooling compared to the results of the metallographic study of the actual piece.
With the aim of eliminating defects, PoligonSoft modeling of the solidification process of castings with different sizes of the feeding part was carried out.
The adopted criterion was that a casting is considered suitable if, according to the modeling results, the porosity in the casting is non-existent in problematic sections.
Based on the calculations, it was concluded that it is not possible to eliminate the porosity in the blade by increasing the mass of the feeding part or changing the insulation scheme of the casting block.
Therefore, it was decided to modify the design to allow the installation of additional feeders in the problematic area.
Seeds
Ceramic Mold
Bath with Liquid Metal Coolant
Lower Heater
Upper Heater
Nickel Alloy - Inconel 625
Liquid Metal Coolant - Aluminum
Initial Mold Temperature - 20°C
Pouring Temperature - 1510°C
Upper Heater Temperature - 1560°C
Lower Heater Temperature - 1640°C
Coolant Temperature - 840°C
The molten metal is lowered from the hot zone of the furnace to the cold part with the liquid metal coolant.
By changing the cooling rate, the desired macrostructure can be achieved.
Heat is transferred to the mold through radiation from the heaters and from the bath with liquid aluminum.
When the surface temperature of the mold rises, aluminum begins to function as a coolant.
The mold will not reach a uniform temperature due to this factor; therefore, it is necessary to obtain the temperature distribution before pouring.
The mold filling occurs very quickly, in about 3 seconds.
Despite the short time required for pouring, the temperature of the molten metal decreased significantly upon contact with the colder seeds, with a difference of about two hundred degrees.
The calculation allows obtaining the temperature field of the molten metal at the end of filling.
The most complex stage of thermal calculation is the dragging of the filled mold with its immersion in the bath of liquid aluminum because the conditions change continuously throughout the calculation.
The conditions of heat exchange by radiation between the moving mold, the heaters, the liquid metal coolant, and the furnace walls change.
PoligonSoft automatically resolves this task without the need for additional actions by the user.
In the final stage, we use the Macrostructure module to calculate the resulting macrostructure of the casting, based on the obtained temperature fields and the physical characteristics of the alloy.
The necessity of changing the design of the casting block can be considered, as it does not provide a uniform heating of the mold before pouring nor a uniform distribution of the two-phase zone through the sample section, which in turn affects its structure.
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