injection molding flash

Definition
molding flash occurs when a thin layer of material is forced out of the mold cavity at the parting line or ejector pins location. This excess material remains attached to the molded article, and normally has to be manually removed.

Causes
Worn or poorly fitting cavity/mold plates
Including, mold plate deformations and obstructions (grease, dirt, debris)

Insufficient clamp force
The machine clamp force must be greater than the pressure in the cavity (that is, clamp opening force), to sufficiently hold the mold plates shut.

Overpacking
Overpacked sections cause increased localized pressure.

Non-optimal molding conditions
Including, material viscosity, injection rate, and runner system. For example, high melt temperature, which makes a less viscous melt.

Improper venting
An improperly designed venting system, a very poor venting system, or a venting system that is too deep.

Remedies
Ensure correctly fitting mold plates
Set up the mold to seal properly. Clean the machine from any obstructions. Add pillar support or thicken the mold plates if there is any deformation of the mold plate during the molding process.

Avoid overpacking

Select machine with higher clamp force

Vent appropriately
Use the material supplier recommended venting size.

Optimize processing conditions
Reduce pressures and shot size to the minimum required.

Solving one problem can often introduce other problems to the injection molding process. Each option hence requires consideration of all relevant aspects of the mold design specification.

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