How to Avoid Flash in Injection Molding

When creating prototypes, it is crucial to pay attention to cosmetic flaws because even small mistakes can lead to defects that waste valuable resources. Therefore, it’s essential to collaborate with a specialist who understands the significance of producing high-quality injection molded parts. These experts often implement the best quality control measures to prevent defects like “flash.”

What is flash, and how does it occur?

Flash is the most common flaw found in parts manufactured through injection molding. It appears as thin, film-like plastic edges attached to the molded components. Flash occurs when molten plastic leaks from the mold cavity and then cools and hardens with the main component. This results in protrusions like flaps or tabs around ejectors, parting lines, venting channels, and sealing faces, causing aesthetic imperfections.

Is flash a serious issue?

While flash might not seem as critical as defects that could impact the function and safety of injection molded parts, it still matters. Although flash generally does not compromise the strength of the plastic, it requires additional post-processing to remove it, leading to higher production costs. Furthermore, trimming and removal can potentially introduce inconsistencies in the design and overall part quality.

Ways to prevent flash in injection molding

To avoid flash during injection molding, it is important to understand how molten plastic can leak from the mold. Common causes include improper mold clamping to prevent seepage and worn-out molds. Extremely high injection pressure or very minimal plastic viscosity can also lead to leaks.

Experienced injection molding technicians can address flash during production in the following ways:

  • Increase the clamp pressure to achieve a proper seal on the mold.
  • Adjust injection pressure and speed or utilize venting to prevent leakage.
  • Maintain and clean molds for long-term and repeated production, replacing them when necessary.
  • Improve plastic viscosity to reduce the likelihood of flash.

Choosing the right materials and utilizing appropriate tools like valve gates and venting in the correct locations can also help prevent flash. Working with an experienced injection molding partner who knows the best practices for preventing flaws is a wise decision.

HLH Proto specializes in injection molding and ensures defect-free parts. If you need high-quality injection molded parts delivered quickly and cost-effectively, contact their team for reliable service.


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