Die casting machine and method

Abstract

The die casting machine comprises a mold closing actuator capable of selectively inducing a closing pressure on first and second platens for forcing them towards a closed position in which their mold portions are pressed against each other along a parting line. An injection sleeve is movable relative to the mold portions between a distal position in which the injection sleeve and the mold portions are spaced apart; and an injection position in which the injection sleeve engages the mold portions at an inlet opening when the first and second platens are in their closed position. The injection sleeve applies a transverse contact pressure when it engages the mold portions. The closing pressure is unevenly distributed on the platens so as to compensate the transverse contact pressure to have a resulting effective molding pressure on the mold portions that is substantially evenly distributed across the parting line.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This application is a Continuation Patent Application of U.S. patent application Ser. No. 13 / 976,575 filed Jun. 27, 2013 which is a U.S. National Phase Patent Application of PCT Patent Application No, PCT / CA2010 / 002069 filed on Dec. 29, 2010, the disclosure of which is incorporated herein by reference in its entirety.FIELD OF THE INVENTION[0002]The present invention relates to die casting machines.BACKGROUND OF THE INVENTION[0003]Die casting machines are used to mold metallic articles. To do so, liquid metal is fed into the inner cavity of a mold where the metal hardens as it is cooled before the article is ejected from the mold. The process is repeated in a cycle to create numerous articles.[0004]Molds typically comprise two mold portions that join at a so-called parting line that is in fact a plane along which mold surfaces of each mold portion engage one another. The mold portions both have recesses on these flat mold surfaces that form...

AI Technical Summary

Benefits of technology

The patent is about a device that can push the platen and injection sleeve together to force them into their injection position. This makes it easier to create precise and consistent injections.

Problems solved by technology

It will be noted that principles that are applicable for hot chamber die casting machines are often not applicable for cold chamber die casting machines, and vice versa, due to differences in these operation characteristic.

One problem with prior art cold chamber die casting machines is linked to the feeding of liquid metal into the injection sleeve.

A problem with this configuration is that the horizontal disposition of the injection sleeve allows air to remain present in very significant proportion in the injection sleeve when the injection sleeve filling operation is completed but before the injection step starts.

Consequently, a significant volume of air is often injected into the mold cavity concurrently with liquid metal, resulting in air bubbles being entrapped in the liquid metal in the mold.

Although some known techniques exist to exhaust the entrapped air within the mold cavity, some air will often remain trapped, resulting in the metallic article comprising weakness zones once the metal is hardened where air bubbles are present.

However, this injection sleeve design suffers from at least one problem: the injection sleeve liquid metal port is located within the mold itself, forcing the feeding of the metal to be accomplished in an area between the two mold halves that is not easily accessible for a robotised arm.

Positioning the injecting sleeve outside of the mold entirely and injecting the liquid metal at the parting line instead of between the two mold halves, has up to now not been seen as an operable or viable option in cold chamber die casting machines.

However, in cold chamber die casting machines where injection forces are more important, this design with injection at the parting line is considered non-functional or non-practical and is not used in prior art devices to the knowledge of the present inventors.

Since this sleeve-mold sealing pressure would be applied transversely of the mold, parallel to the parting line, this is likely to result in the mold being deformed by curving transversely unless the mold closing pressure is so important that it would counteract this deformation.

Such a mold deformation would be undesirable since it would contribute to allowing the liquid metal to flash within the mold during the injection as a result of unevenly distributed pressure on the mold portions; while increasing the mold closing pressure significantly to counteract this deformation means that the die casting machine needs to be equipped with more expensive components in addition to more energy being expended to operate the die casting machine.

In any event, by increasing the sleeve-mold sealing pressure, the mold is likely to wear down under the repeated pressured engagement of the sleeve on the mold.

The mold wearing down at the junction area with the injection sleeve means that it might become uneven, resulting in the sleeve-mold sealing pressure being applied unevenly, in turn resulting in the metal seeping out between the injection sleeve and the mold during injection.

Air bubbles in the liquid metal also appear during the liquid metal pouring operation from the ladle into the injection sleeve, as a result of turbulence from the liquid metal inflow.

Another problem related to prior art die casting machines relates to liquid metal seeping outside of the inner mold cavity, between the mold portions.

Reasons why the liquid metal flashes is because the pressure applied to keep the two mold portions pressed against each other is not important enough or is not well distributed along the parting line.

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