Tips on how to design injection mold gate   

Gate is defined as an opening on the plastic wall through which the molten plastic is injected into the final part. Gate location can make or break your part design.  Therefore, it is very important to do a pre-analysis to decide the location, size, and shape of the gate as all these can greatly affect everything from the structural integrity to the visual appearance of a finished piece.

Yet most CAD designers give little thought as to where to and how to put the gate, or injection point, on the part they design. They simply leave that detail to the mold maker.This is a big mistake. Along with choosing the wrong gate size and type is the root cause of many molding difficulties such as welding line, shrinkage, warp and more. The gate has three critical components namely depth, width and land. Depth is the most important factor because it determines how fast gate solidifies.

Generally, gating system is composed of Sprue, Runner, Date and Vent.


In single cavity molds, the sprue usually enters directly in to the cavity, in which case the sprue diameter at the point of cavity entry should be approximately twice the wall thickness at that point.

Insufficient sprue gate diameter can cause excessive friction burning of the plastic at the gate area. Too large sprue diameter requires a prolonged cooling time. The cooling fountain should be installed directly opposite to the gate to avoid hot spot. The usual approach to solving sprue problem is to design a shorter sprue, use a hot sprue or eliminate the sprue altogether. The minimum sprue diameter of a conventional sprue should be approximately less than 20%of the nozzle orifice.


design injection mold gate
design injection mold gate

design injection mold gate

design injection mold gate
design injection mold gate

In conventional mold runner should be designed in order that


The runner is short.

Free from bends.

Equal runner length in multi cavities.

minimum cross section





The depth of the gate can be 40-90% of the wall thickness. When using an easy flow material it is best to use the lower percentage. Width of the gate should be two to three times the depth. Again for easy flow material it can be two times the depth. If a part is larger than 100mm think of adding another gate.


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