Vacuum-Assisted Investment Casting of Al-Ni-Bronze

摘要

This study was conducted to identify some of the major process parameters of vacuum-assisted investment casting of Al-Ni-bronze that needed to be optimized to ensure proper quality and desirable mechanical properties of cast parts for disposable surgical tools. Two series of experiments have been conducted to establish, quantitatively, the relationships between the vacuuming parameters and mold filling, shrinkage and tensile strength in test samples and real castings. It was found and that, in addition to the gravity, vacuum force, as well as 45 deg angle of attachment casting to the sprue, provides significantly higher filling rate. This is particularly true in the castings located near the pouring cup, at the top of the cluster, in the areas of lower value of hydrostatic pressure. Experiments revealed mold permeability as an additional factor that, besides vacuuming parameters, also influences mold degree of vacuuming and, eventually, mold filling. Developed information illustrates how the quality and properties of vacuum-assisted investment castings may be regulated by proper selection of vacuuming parameters and cluster design. Finally, a method and formula for gate calculation in vacuum-assisted investment casting has been developed to optimize hydrodynamic conditions for proper mold filling and feeding of the castings during solidification. This gating method takes into consideration the impact of an angle of the part's attachment to the sprue, vacuum pump efficiency, gravity and vacuum forces applied during pouring and, finally, casting solidification. The obtained data has been used for development of optimal process parameters and recommendations on vacuum-assisted investment casting of disposable surgical tools made of Al-Ni-bronze.