Method and Apparatus for Vent Purging in a Metal Molding Mold
Publication Date: 2003-Aug-26
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The present invention relates, in general, to an improved mold and process for metal molding, and is particularly applicable to a thixomolding injection molding process. The metal molding process typically includes the step of applying a release agent onto the faces of the mold halves for the purposes of preparing the molding surface for the next molding cycle. The application of the release agent may also function to cool the molding cavity. A sprayer that has been mounted onto an end-of-arm part-handling tool typically sprays the release agent onto the molding surface. A common problem encountered with the release agent is over-spray whereby the release agent is applied into areas where it is not intended. Of particular significance, the over-spray may deposit onto the surfaces of the mold venting vacuum ports and eventually cause the ports to clog shut; over-spray can clog the vacuum port in as few as 20 molding cycles. As a consequence of the partial or complete clogging of the vent port, the required function of providing a positive venting of the molding cavity during injection may be significantly reduced or completely arrested, thereby impeding the exhaust gas flow during injection that can impart defects into the molded part (e.g. voids, flashing, etc.). The improved method includes the clearing the vacuum ports with pressurized air during the spraying step. Advantageously, the mold venting is maintained at a high level ensuring that the injection gases are evacuated as quickly as possible and thereby avoid the production of short-shots. The new structure according to the present invention is to controllably and alternately connect the mold vacuum port to either a vacuum source or to a high flow fluid source, preferably shop (i.e. compressed) air. The controllable connection may be made through a two or three way solenoid valve as is commonly known. The improved method includes the step of venting high flow gas through the vacuum port during the step of applying the release agent thereby preventing the clogging of the vacuum port.