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Design Principles of Injection Molding Molds' Sprue System and Ejection Mechanism

Principles of injection molding mold pouring system design

Good exhaust design

Injection molding supplies should have a well-designed exhaust system that allows the molten material to smoothly fill all parts of the mold cavity and allows gas in the mold cavity to be smoothly discharged.

Reduce the distance of molten material flow

Molten material should be directed to the mold cavity of the injection molding mold using the shortest distance possible, while meeting the requirements of molding and exhaust. Doing so can shorten the molding cycle, improve the quality of plastic products, and reduce raw material consumption.

Prevent deformation of the core and inserts

When common injection molding materials quickly enters the mold cavity, it should be directed away from the core and inserts to avoid deformation. For large or high precision plastic parts, a multi-gate feeding system can be used.

Prevent thickness disparity

It is difficult to accommodate different geometries with varying thicknesses in the same injection molding mold. Therefore, be mindful of this requirement in the injection mould design process.

Heat and pressure loss should be minimized

The pouring system should be as short in length as possible to minimize pressure and temperature losses during injection molding. Pouring system design should also be easy to modify and remove residual materials.

Principles of ejection mechanism design for injection molding mould

The ejection mechanism, also known as the demolding mechanism or extraction mechanism, is the final motion in the injection molding process. The mechanism removes the molded items from the mold cavity of the injection molding mould. When designing the ejection mechanism, the following principles must be followed:

The direction of ejection motion should be accurate and reliable without being stuck in place. Adequate strength and rigidity are required to withstand the resistance to demolding. To prevent deformation of the molded item, the ejection force must be applied to the core area, wherever possible, to minimize the risk of the molded item becoming deformed or damaged. The ejection force is typically applied to areas such as rib reinforcements, flanges, and thick walls. During the design process, the adhesion of the molded parts to the injection molding mould, as well as the shape and surface roughness of the molded part, should be considered.

Generally, a good injection mould design should ensure that the molded parts remain on the side of the moving mold after the mold is opened. This simplifies the ejection mechanism. If the ejection mechanism needs to be placed on the surface of the molded part that is used or assembled, it is preferable for the contact point of the push rod to be recessed slightly to avoid affecting the dimensions and uses of the molded part. The end face of the push rod should be higher than the reference surface; otherwise, the surface of the molded part will protrude, which affects the smoothness and appearance of its reference surface.

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