Two plate mold

Two plate mold is the easiest injection mold structure and has many advantages. It’s consist with A side and B side 2 main parts, when it is load in ejection machine to do molding, A side is fixed and held still, B side is movable. See below figure to get the details of the 2 plate mold.

Some of the term explanation:
Location ring: location the filling hole between injection nozzle and sprue, usually made of S55C
Return pin: ensure the ejector pin pull back before the mold close, it protects the injection mold from damage, it’s usually made of SKD61.
Guide pin/ guide bushing: GP and GB are designed for precision guiding so the GP and GB have to be precise themselves.
Ejector guide pin: during ejection, EGP works as guiding to ensure the ejection is correct.
Support pillar: support the B side plate to avoid deformation under high injection pressure.
Spure: allow the melt flow into the cavity.

Three plate mold

3 plate mold is also named as small gate mold, comparing with 2 plate mold, one of the differences is additional mold plate is required between top clamp plate and cavity plate, which called runner plate, it allows the runner scrap and plastic molded parts released separately, see below figure of three plate mold structure.

Another difference is 3 plate mold require 3 times opening.
The first time opening, see below figure.

The second time opening is to release the molded parts, see below figure.

The third time opening is to release the runner automatically.

Three plate mold is usually employed when the part is too big and need multiple injection points. Three plate mold design has more advantages to locate the gate.

But usually 3 plate mold is not recommended as there are some disadvantages, it’s not just because of a much more complex structure but much higher scrap rate, it’s also lack of stability because of complex mechanism. It’s random to use for high volume production because it required longer cycle time and bigger injection molding machine as the run distance is longer comparing with 2 plate mold.