Flow phenomenon known as “jetting”

Jetting also known as free jet formation occurs when molten plastic enters the cavity at high speed in an uncontrolled, narrow jet rather than filling it evenly. This can result in surface defects such as wavy lines, and can also lead to internal weaknesses due to poor bonding between material layers.

Moldex3D provides powerful tools for detecting and remedying free-jet issues, and is continuously improving the detection of this phenomenon through solver updates. The molten plastic appears as a narrow, often snake-like stream. This irregular flow pattern can be observed using Moldex3D.

Free jet typically occurs when the plastic is not injected against an obstacle. Moldex3D’s flow simulation shows velocity distributions across the entire part and provides detailed information on temperature, shear rate and other factors. Users can influence the flow path and reduce the velocity at entry points by adjusting the gate design or its placement, leading to a more uniform and better-controlled filling process.

From Moldex3D version 2025 R2 onwards, the Viscoelastic F Solver can be used to visualise jetting without a VE Solver licence. However, for the Flow-VE coupling effect, a VE_SOLVER licence is still required. Simulation accuracy also depends on mesh resolution, solver precision and time steps.

Please do not hesitate to contact us if you require assistance or are interested in precise settings.