Low pressure lost foam process for casting magnesium alloys

Abstract

The lost foam process is capable of making castings with extremely complicated shapes at high soundness levels and with low manufacturing costs. However, there are several challenges to produce magnesium castings using the conventional lost foam process because of the low heat content of magnesium alloys. Therefore, a novel low pressure lost foam process has been developed especially for magnesium castings, in which the melt is filled under counter gravity conditions at low pressure. This paper introduces the low pressure lost foam process. The measurement of flow profiles in the plate shape and the L shape EPS patterns under different conditions reveals that the process can offer unique advantages for achieving laminar flow and fully controlled flow during melt filling. The dimensional accuracy with the specially designed castings shows that CT4-8 is achievable for magnesium castings produced by the low pressure lost foam process, according to the dimensional tolerance grading given in ISO8062-1994. A comparison and Weibull statistics analysis of the mechanical properties of AZ91E alloy confirms that the low pressure lost foam process gives comparable yield strength, ultimate tensile strength, and elongation to the conventional precision sand process.

Experimental and numerical study of section restriction effects on filling behavior in low-pressure aluminum casting

“…Simulating the tube and mold geometries, they revealed that a section change induces oscillations that increase in amplitude when increasing the pressure ramp. Fan et al (Fan and Ji, 2005) used similar hydrodynamics hypothesis to estimate the filling velocity in low pressure casting of a lost foam mold with sudden section reduction by a factor 0.76. The comparison showed a good correlation between experiment and analytical model without showing clear oscillations.…”

Influence of process parameters on filling ability of A356 aluminium alloy in expendable pattern shell casting with vacuum and low pressure

“…It is evident that the relation between filling length and gas flowrate is apparently linear, and it is in agreement with the previous study. 17 Meanwhile, it can be seen that the filling length of the thick section is also bigger than that of the thin section under the same conditions, as shown in Fig. 4.…”

Geometrical effects on filling dynamics in low pressure casting of light alloys

“…They measured a filling height delay in comparison with this simple model in the case of a magnesium automotive part, that they explained by pressure losses. A more developed model based on Bernouilli's equation was proposed to link the pressure ramp and the system geometry to the metal gate velocity [11]. Considering the filling of a lost-foam casting with a sudden section restriction, the experimental results were in good agreement with the proposed model [11].…”

“…A more developed model based on Bernouilli's equation was proposed to link the pressure ramp and the system geometry to the metal gate velocity [11]. Considering the filling of a lost-foam casting with a sudden section restriction, the experimental results were in good agreement with the proposed model [11]. However, in the case of a plate-shape casting of aluminum alloy, some filling oscillations were experimentally identified, while they could not be explained based only on this analytical model [8].…”