No abstract

No abstract

Molten metal flow behavior during fast shot injection with 500 to 1650 ton commercial die casting machines was studied in the filling portion of the die cavity in the shape of disc, box and plate. The velocity of the molten metal is as high as 15 to 20m/s at the gate of a die cavity, but it decreases abruptly within a passage of 20 to 25cm and reaches 2 to 3m/s at the final filling portion, irrespectively of the tested cavity shapes. The gas pressure in the cavity shows a maximum value when the flow reaches the probe. The gage pressure increases from 0.1 to 0.2kgf/cm2 at the gate to 1 to 2kgf/cm2 at the final filling portion. The velocity of metal decreases with increase in the gas pressure at the final filling portion. Its abrupt decrease in practical aluminum casting is attributable to the pressure rise in the cavity. Provision of an appropriate gas vent in the final filling portion increases the velocity of the molten metal.

The casting defects are reduced by increasing the molten metal velocity near the defects. When the linear runner, where flowout volume through the lower runner gate was greater than the volume through the upper one, was used, the molten metal unequally filled up the cavity and the molten metal velocity suddenly decreased at a final filling portion.Therefore, the casting defects frequently occurred at the final filling portion. On the other hand, when the stair shaped runner was used, the molten metal equally filled up the cavity without a turbulent flow, and the molten metal velocity did not decrease at the final filling portion. Therefore, the molten metal filled up the cavity with inconsiderable casting defects in a short time.

The flash formation times in four types of casting processed by four types of pressure die casting machines (500-1650 tons) were studied by measuring the metal flow behavior in the die cavity and the plunger stopping time. The flash in the product area and near the overflow area was formed only when molten metal was filling in the cavity. The flash near the biscuit and runner area, however, occurred after the molten metal had filled in the cavity, as well as occurring while the molten metal was filling in the cavity. This result has also been demonstrated by the cross section structure of the flash.