In plastic injection molded products, the cause of short shots in the ribs is that the air in the mold is trapped in the ribs, and the air cannot escape from the mold, so the molten resin is not completely filled and short shots occur. Occurs. The cause of the trapped air is related to the flow direction of the molten resin and the direction of the ribs. If the way the molten resin enters the ribs flows along the rib grooves, the air inside the mold also escapes along the rib grooves. However, if it flows in a direction perpendicular to the ribs, it becomes difficult for air to escape, and short shots may occur.
Direct engraving on the mold can reduce the processing cost of the mold, but to allow air to escape, processing that is not direct engraving is required.
As a processing method for it, there are methods that processing the rib into a split mold to release air from a minute gap and forming a gas vent part by providing a protruding pin or a dummy pin at the part where a short shot occurs.