In-Mold Cutting System Design: A Classic UG Mold Engineering Case Study

In-Mold Cutting System Design: A Classic UG Mold Engineering Case Study

In-mold cutting (also known as in-mold gate severing) is a sophisticated yet highly effective solution for achieving clean, automatic gate separation—especially in high-precision or high-volume plastic part production. Today, I’d like to share a classic mold design case built in UG (Siemens NX) that demonstrates key engineering considerations for a reliable in-mold cutting system.

1. Cutting Blade Design

· The cutting mechanism is positioned directly beneath the overlap gate.

· During operation:

o Retracting the blade forms the gate during filling.

o Advancing the blade shears the gate post-cooling for clean separation.

· Notably, the blade tip profile conforms precisely to the product’s surface geometry, eliminating the need for a traditional sharp edge—reducing wear and preventing damage to delicate features.

2. Actuation Method: Ejector Plate vs. Mini Hydraulic Cylinder

· While an ejector plate system can drive the cutter, it requires coordination with the molding machine’s pre-ejection sequence.

· Alternatively, a mini hydraulic cylinder offers greater flexibility:

o Cylinder bore can be selected based on required force.

o Enables precise, point-to-point actuation without relying on machine ejector timing.

3. In-Cavity Pressure Measurement for System Sizing

To correctly size the hydraulic actuator, we embedded pressure sensors inside the cavity to capture real-time peak pressure during the entire injection cycle.

Measured maximum cavity pressure: 535 bar

This data ensured the selected cylinder delivers sufficient force to reliably cut the gate—even under worst-case process conditions.