Shenzhen Alu Rapid Prototype Precision Co., Ltd.

Decompression, also known as suckback, is a key process control feature in injection molding machines. It involves retracting the screw slightly (typically 0.1 inches or 1-2 mm) without rotation at the end of the injection phase, just before transitioning to the packing/holding stage or screw recovery. This action relieves built-up pressure in front of the screw tip and nozzle, creating a small void or gap that helps manage material flow and pressure dynamics.

How It Works

1.Timing and Initiation: Decompression can occur pre-rotation (before the screw rotates to recover material for the next shot) or post-rotation (after recovery). It's often triggered by time (e.g., a 50 ms delay after injection) or position (based on screw travel setpoint for precision).

2.Mechanics: As the screw retracts, it pulls back from the nozzle, reducing hydraulic pressure on the molten plastic (or other material) ahead of it. This gap is later filled during screw rotation, which doses material for the next cycle. In position-based systems, it's tied to the check ring's travel to ensure proper seating.

3.Impact on Shot Size: Pre-rotation decompression effectively increases the shot volume by allowing the screw to extrude more material as it retracts (similar to an extruder action). Post-rotation decompression can push slightly more material into the mold via compressed air in the barrel but doesn't add net material without rotation.

Tuning typically starts with no decompression to establish a baseline shot weight and process stability, then incrementally adds distance (e.g., starting at 1 mm) while monitoring metrics like cushion consistency, pressures, and defects over multiple runs.