Abstract
For the production of sound castings it is important to be able to predict the grade of microporosities formed in the center of the castings accompanied with V-segregation. Controlling parameters in computer calculation for the prediction were studied. Experimental work was first conducted where a total of six plate-shaped castings containing different grades of porosities were made by changing the mold taper. The grade of porosity in the castings was judged from radioactive non-destructive tests. The castings were then numerically analyzed and evaluated by means of temperature gradient at solidifying front. However, the critical values differed with the casting size and the grade of porosity could not be related to temperature gradient. The grade of porosity was next evaluated by the shape of the solidifying semi-solid region at the solidifying front. This was done by observing the U-shaped semi-solid region surrounded by iso-solid fraction lines fs=0.3 and fs=0.7. A new parameter L/H was proposed, where L was the central height of the U-shaped region and H was the width of the region at the height of 1/2L. Accordingly the parameter L/H was calculated by computer for each casting and compared with the observed grade of porosity. The region and grade of porosity were correlated well with L/H. The validity of the parameter was checked also on a more sophisticated shaped castings to find a good result. It is concluded that the parameter can be used for a wide variety of castings.
