Flash in Plastic injection molding

Flash- Plastic Injection Molding

Also known as burrs, it is a common defect in the plastic injection molding process and appears as thin layers of excess material on edges/ surface of molded parts.

Flash affects quality, functionality and product appearance. addressing flash helps in consistent, high production quality.

Flash occurs as a result of molten plastic that moves out from mold cavity during the injection process.

It forms a thin, unwanted material layer at the mold’s parting lines and appears on molded product edges where the two molded halves meet. It also forms around inserts, vents and ejector pins.

Flash appearance

Thin, sharp edges, protrusions. Thick material around ejector pins and molds.

• Aesthetic impact– It makes the product look inexpensive
• Functional Interference– On precision parts, it interferes with assembly, fitting, movement
• Safety concerns- Sharp/rough flash poses safety issues to end users
• Increased costs– Reduces efficiency and increases production costs if processes like trimming or machining are employed
• Quality control issues– Excessive flash leads to inconsistent product quality alongwith production delays.

Flash in injection molding- Causes

The causes of flash : mold design, process parameters, equipment condition, material properties

• Wear and Tear of the mold- Improperly aligned or imperfect parting line design
• Improper Clamping Force-Incorrect clamping pressure causes the mold halves to tilt slightly during injection process, creating a small gap causing leakout of material.
• Improper venting-It causes back pressure and excess material to squeeze out through small gaps.

Other causes leading to black spots are

• Low-viscosity materials
• Faulty material selection
• Contaminated materials
• High levels of regrind use
• Worn out components of the mold
• Damaged/ leaking nozzles

Addressing flash problems in injection molding

• Cryogenic Deflashing

• Laser Trimming