Polymer ammunition casing mold and manufacturing method

An injection mold configured for manufacturing an injection molded polymer casing for an ammunition cartridge, the injection molded polymer casing comprising a base having a primer retention feature and a flash hole, where a hollow cylindrical portion with an outside cylindrical surface opposite an inside cylindrical surface extends from the base along an axial centerline to an open end having an open end surface, the injection molding comprising five separate mold portions cooperatively delimiting a casing’s volume when cooperatively arranged into a molding state and configured to be movable away from one another to a release state to extract the injection molded polymer casing, the injection mold comprising:

• a base mold portion having an annularly shaped base cavity surface and a primer retention feature core extending from the base cavity surface;
• a first transverse mold portion having a first half cavity surface configured to form a first half of the outside cylindrical surface of the injection molded polymer casing;
• a second transverse mold portion having a second half cavity surface configured to form a second half of the outside cylindrical surface of the injection molded polymer casing;
• wherein the first transverse mold portion and the second transverse mold portion are configured to move away from one another in a direction perpendicular to the axial centerline of the injection molded polymer casing;
• a core pin mold portion having a frustoconical core configured for forming the inside cylindrical surface of the injection molded polymer casing;
• and
• a sleeve ejector mold portion having an annularly shaped top surface cavity surface configured for forming the open end surface of the injection molded polymer casing, the sleeve ejector mold portion having a through hole wherein the core pin mold portion is configured to be disposed through the through hole of the sleeve ejector mold portion;
• wherein the core pin mold portion is configured to move away from the base mold portion in a direction aligned along the axial centerline of the injection molded polymer casing;
• and
• wherein the sleeve ejector mold portion is configured to move away from the base mold portion in the direction aligned along the axial centerline of the injection molded polymer casing.

A method of manufacturing an injection molded polymer casing for an ammunition cartridge, the injection molded polymer casing comprising a base having a primer retention feature and a flash hole, where a hollow cylindrical portion with an outside cylindrical surface opposite an inside cylindrical surface extends from the base along an axial centerline to an open end having an open end surface, the method comprising the steps of:

• a) providing an injection mold consisting of five separate mold portions cooperatively delimiting a casing’s volume when cooperatively arranged into a molding state and configured to be movable away from one another to a release state to extract the injection molded polymer casing, the five separate mold portions being:
• a base mold portion having an annularly shaped base cavity surface, a primer retention feature core extending from the base cavity surface, and a flash hole core extending from the primer retention feature core;
• wherein an injection gate is fluidically connected to the base cavity surface, the injection gate configured to inject a melted polymer under pressure into the injection mold;
• wherein the injection gate is the only injection gate of the injection mold;
• a first transverse mold portion having a first half cavity surface configured to form a first half of the outside cylindrical surface of the injection molded polymer casing;
• a second transverse mold portion having a second half cavity surface configured to form a second half of the outside cylindrical surface of the injection molded polymer casing;
• wherein the first transverse mold portion and the second transverse mold portion are configured to move away from one another in a direction perpendicular to the axial centerline of the injection molded polymer casing;
• a core pin mold portion having a frustoconical core configured for forming the inside cylindrical surface of the injection molded polymer casing;
• wherein the frustoconical core has a cylindrically shaped narrowing draft angle configured to allow axial withdrawal that narrows starting from a frustoconical core proximal end and moving towards a frustoconical core distal end;
• and
• a sleeve ejector mold portion having an annularly shaped top surface cavity surface configured for forming the open end surface of the injection molded polymer casing, the sleeve ejector mold portion having a through hole wherein the core pin mold portion is configured to be disposed through the through hole of the sleeve ejector mold portion;
• wherein the core pin mold portion is configured to move away from the base mold portion in a direction aligned along the axial centerline of the injection molded polymer casing;
• wherein the sleeve ejector mold portion is configured to move away from the base mold portion in the direction aligned along the axial centerline of the injection molded polymer casing;
• wherein a flash hole core distal end is configured to be at least partially disposed within a frustoconical core distal end cavity;
• b) moving the five separate mold portions into the molding state;
• c) injecting the melted polymer under pressure through the injection gate into the injection mold;
• d) waiting a period of time for the melted polymer to harden through cooling;
• e) moving at least one of the five separate mold portions away from one another to the release state;
• and
• f) removing the casing from the injection mold.