Japanese Laid-open Patent Publication No. 51-129817 discloses a die-casting method in which the molten metal in a squeeze passage communicated with a die cavity at a portion other than the portion through which a runner is communicated with the die cavity is forcibly displaced by a squeeze plunger back into the die cavity. In the apparatus disclosed in Japanese Laid-open Patent Publication No. 51-129817, however, the squeeze passage has a shape as shown in FIG. 1 and the molten metal .alpha. in the squeeze passage displaced by the squeeze plunger 36 is restricted by a communication passage having a cross-sectional area smaller than that of the squeeze passage and, thereafter, is displaced back into the die cavity 30.
The present inventors conducted experiments with respect to this squeezing method. The test result showed that the force required for advancing the squeeze plunger was fluctuated over a wide range with a resultant difficulty to obtain a stably constant squeezing pressure. The present inventors considered that the fluctuation of the squeezing pressure encountered in the use of such an apparatus as shown in FIG. 1 was for the following reason. Namely, the moment at which the forward movement of the squeeze plunger 36 is started is inevitably delayed from the filling up of the squeeze passage 17 by a predetermined time period during which the surface of the molten metal .alpha. is solidified. Therefore, when the squeeze plunger 36 is advanced, the squeeze plunger 36 is required to displace also a solidified layer .beta. of the metal. It is considered that the solidified layer .beta. in the squeeze passage 17 is blocked by the communication passage 17a during the forward movement of the squeeze plunger 36 and is shorn in a quite complicated manner.
It is considered that the difficulty in obtaining a constant squeezing pressure acting on the molten metal .alpha. in the squeeze passage 17 is attributable to the fact that the resistance due to the shearing of the solidified layer .beta. during the forward movement of the squeeze plunger 36 is largely fluctuated.
USPTO Backgrounds
USPTO Backgrounds