How to Prevent Flash in Injection Molding

Even small errors or mistakes in plastic manufacturing can lead to molding defects that cost significant amounts of time and money. At Advanced Plastiform, Inc., we understand how important it is to avoid defects, and doing so requires experience, technical know-how, and attention to detail. During injection molding, one of the most common defects in a completed part is called "flash." To help you understand what to look for and how to avoid it, our injection molding company is sharing the steps you need to take to prevent flash in custom-made plastic components.

Understanding Injection Molding

Injection molding is a method of manufacturing plastics in which a thermoplastic is heated to a liquid state, then injected into a custom-made, double-sided mold. High pressure is used to ensure the plastic flows into the entire mold, coating and filling the cavities consistently, and when the plastic cools and hardens, the shaped component is ejected from the mold.

Injection molding is often used to produce high volumes of small or intricately designed parts and components. Thousands of items and parts are produced using this method including things like gears, knobs, bottle caps, and plastic syringes used in medical procedures.

What Is Flash in Injection Molded Parts?

"Flash" refers to thin, filmy plastic edges that are connected to the shaped plastic components. This defect occurs when a bit of liquid plastic seeps out or leaks from the mold cavity, then cools and hardens along with the rest of the component, creating a tab, flap, or similar protrusion. Flash is typically found around sealing faces, parting lines, ejectors, or venting channels.

Compared to other defects that can occur during the injection molding process, flash may not seem that serious. After all, the plastic isn't weakened or compromised in any way and the flash can often be trimmed away. While this is true, consider that trimming away flash requires more time and labor that had not been budgeted into the project. Also, additional trimming and removing flash can lead to inconsistency between parts and inaccuracy to the design.

How to Prevent Flash in Injection Molding

What causes melted plastic to leak from the mold cavity? The three most common causes are:

• Not clamping the mold together well enough to prevent leaking or seepage;
• Using a mold that has not been properly maintained or has worn out;
• Setting the injection pressure too high, forcing plastic out of the mold;
• Plastic viscosity is too low;

If flash is noticed during a production run, the situation can be fixed with the following remedies:

• Increasing the clamp pressure to force the mold parts shut and sealed.
• Testing conditions like injection speed and pressure or venting to prevent seepage.
• Cleaning and maintaining molds for multiple or long-term production runs, replacing them if needed.
• Increase viscosity of plastic.

To prevent flash in the first place, it's important to ensure your tooling is made from the proper materials with gates and venting in the proper location. Also, working with an experienced team who know how to perfect the settings on the first run will eliminate a majority of the concerns.

Contact Us for Injection Molding Services

Since 1988, companies across the Southeast and Mid-Atlantic have relied on us for injection molding and thermoforming because they know that we are dedicated to reducing costs and lead times for our customers without sacrificing quality. Our team of designers, engineers, and manufacturers are all dedicated to getting high-quality, consistent, accurate results that our clients can rely on to hold up to the job at hand. We work with companies in  North Carolina, South Carolina, Pennsylvania, Maryland,  Tennessee, Georgia, and Virginia. To get started, call us at  919-404-2080 or fill out the form below.