What is Jetting?

Jetting is a common defect in plastic injection molding, appearing as wavy lines, serpentine trails, or irregular streaks on the surface of a part—typically near the injection point. This issue occurs when molten plastic enters the mold cavity at excessively high speed and fails to fill the walls uniformly, causing the material to advance in thin, jet-like streams before fully merging together.

This defect not only affects the visual appearance of the part but can also lead to weak zones in the structure, since the polymer layers do not properly fuse during filling. Therefore, jetting is both an aesthetic and functional concern, especially in technical components or visible end-use parts.

The most common causes of jetting include:

• Injection speed that is too high at the beginning of the cycle.

• Poor gate or injection point design (too narrow or incorrectly positioned).

• Mold or material temperature that is too low, increasing plastic viscosity.

• Part geometry that allows unrestricted flow before the material contacts the mold walls.

To prevent jetting, it is important to fine-tune the injection parameters. This may involve lowering the initial injection speed (using a staged or multi-phase injection), increasing mold or melt temperature, or redesigning the gate to enable smoother, more controlled flow. Changing the gate location or adding flow deflectors can also help distribute the material more evenly.

At Plásticos Lezo, we closely monitor all injection parameters to prevent defects like jetting, particularly in parts where surface quality or mechanical strength is critical. We perform flow simulations and analyze mold and part design to detect potential flow problems early, optimizing the process from design through to final validation.

We also have extensive experience adjusting gate dimensions, refining injection profiles, and selecting materials with specific flow characteristics to minimize defects without compromising cycle times or product performance.

In short, jetting is a technical molding issue that can affect both the appearance and functionality of plastic parts. At Plásticos Lezo, we address it through an integrated approach that combines material expertise, mold design know-how, and precision injection control—ensuring high-quality, visually clean, and structurally sound components.