Design of gating system is an important factor in obtaining defect-free casting. One of the casting defects is a porosity caused by internal
shrinkage in solidification process. Prediction of the internal shrinkage porosity in the femoral stem of commercially pure titanium (CP-Ti)
is investigated based on the gating system design. The objective of this research is to get the best gating system between three gating
system designs. Three gating system designs of the femoral stem were simulated in an investment casting method. The internal shrinkage
porosity occurs on the largest part and near the ingate of the femoral stem. The gating system design that has ingates cross section area:
78.5; 157; and 128.5 mm2
has the least of the internal shrinkage porosity. This design has the most uniform solidification in the entire of
the femoral stem. An experiment is conducted to validate the simulation data. The results of internal shrinkage porosity in the three gating
system designs in the simulation were compared with the experiment. Based on the comparison, the trend of internal shrinkage porosity at
the three gating system designs in the simulation agrees with the experiment. The results of this study will aid in the elimination of casting
defect.
In order to predict the distribution of shrinkage porosity in steel ingot efficiently and accurately, a criterion R√L and a method to obtain its
threshold value were proposed. The criterion R√L was derived based on the solidification characteristics of steel ingot and pressure
gradient in the mushy zone, in which the physical properties, the thermal parameters, the structure of the mushy zone and the secondary
dendrite arm spacing were all taken into consideration. The threshold value of the criterion R√L was obtained with combination of
numerical simulation of ingot solidification and total solidification shrinkage rate. Prediction of the shrinkage porosity in a 5.5 ton ingot of
2Cr13 steel with criterion R√L>0.21 m・℃1/2・s
-3/2 agreed well with the results of experimental sectioning. Based on this criterion,
optimization of the ingot was carried out by decreasing the height-to-diameter ratio and increasing the taper, which successfully eliminated
the centreline porosity and further proved the applicability of this criterion.
Turbine blades have complex geometries with free form surface. Blades have different thickness at the trailing and leading edges as well
as sharp bends at the chord-tip shroud junction and sharp fins at the tip shroud. In investment casting of blades, shrinkage at the tip-shroud
and cord junction is a common casting problem. Because of high temperature applications, grain structure is also critical in these castings
in order to avoid creep. The aim of this work is to evaluate the effect of different process parameters, such as, shell thickness, insulation
and casting temperature on shrinkage porosity and grain size. The test geometry used in this study was a thin-walled air-foil structure
which is representative of a typical hot-gas-path rotating turbine component. It was observed that, in thin sections, increased shell
thickness helps to increase the feeding distance and thus avoid interdendritic shrinkage. It was also observed that grain size is not
significantly affected by shell thickness in thin sections. Slower cooling rate due to the added insulation and steeper thermal gradient at
metal mold interface induced by the thicker shell not only helps to avoid shrinkage porosity but also increases fill-ability in thinner
sections.
The paper concerns the problem of discontinuity in high pressure die castings (HPDC). The compactness of their structure is not perfect, as
it is sometimes believed. The discontinuities present in these castings are the porosity as follow: shrinkage and gas (hydrogen and gas-air
occlusions) origin. The mixed gas and shrinkage nature of porosity makes it difficult to identify and indicate the dominant source. The
selected parameters of metallurgical quality of AlSi9Cu3 alloy before and after refining and the gravity castings samples (as DI - density
index method), were tested and evaluated. This alloy was served to cast the test casting by HPDC method. The penetrating testing (PT) and
metallographic study of both kinds of castings were realized. The application of the NF&S simulation system allowed virtually to indicate
the porosity zones at risk of a particular type in gravity and high-pressure-die-castings. The comparing of these results with the experiment
allowed to conclude about NF&S models validation. The validity of hypotheses concerning the mechanisms of formation and development
of porosity in HPDC casting were also analyzed.