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How to Avoid Flash in Injection molding



When plastic injection molding is performed, injection molding flash is a common defect that can occur. This defect will not only affect the quality of the parts, but also may cause damage to the mold. Therefore, it is important to understand the causes of injection molding flash, the appropriate repair methods, and how to prevent this defect.

All relevant information about plastic injection molding flash edges is discussed in detail below to help you solve or avoid this problem.

What Is Flash In Injection Molding?

Flash is an injection molding defect characterized by the presence of excess material extending beyond the intended parting line of the mold. It occurs when molten plastic escapes from the mold cavity and solidifies outside of the designated part boundaries.Although the precision of mold production is high and high-pressure clamping is used during molding, there are actually very small gaps left due to the high filling pressure of TPE during injection molding.

Flash can negatively impact the appearance and functionality of the final product.The type of defect needs to be determined based on product design. For products with higher requirements, the flash should not exceed 0.05mm, while for products with lower requirements, the flash should not exceed 0.1mm. Acceptance standards can be established based on the actual use of the product.

What Causes Injection Molding Flash?

 plastic injection molding flash

Inadequate Clamping

Insufficient mold clamping is a primary cause of flash. When the mold halves are not securely clamped together, molten plastic can seep out through the gaps, resulting in flash formation.

Excessive Injection Pressure

Overly high injection pressures can force molten plastic to escape from the mold cavities. This excessive pressure can lead to flash, particularly in areas where the mold sealing is not sufficient.

Worn Mold

The wear and tear on the mold over time can also contribute to flash formation. As molds age, they may develop imperfections or gaps that allow plastic to escape and create flash.

Ways To Fix Flash In Injection Molding Process

Maintain Mold

Regular mold maintenance is crucial for preventing flash. Inspect molds regularly to identify and address any signs of wear or damage. Proper maintenance ensures that the mold remains in optimal condition, reducing the risk of flash.

Optimize Clamping

Ensuring proper mold clamping is essential to prevent material escape and flash formation. Properly secured mold halves create a tight seal, preventing plastic from leaking out. Regularly check and adjust clamping mechanisms to maintain effective sealing.

Reduce Injection Pressure

Adjusting injection pressure within recommended limits is another effective measure to mitigate flash. Excessive pressure can force plastic to escape, so optimizing injection parameters helps maintain control and prevent flash.

By understanding the common causes of flash and implementing these solutions, you can minimize the occurrence of this injection molding defect. A well-maintained mold, proper clamping, and controlled injection pressure contribute to producing high-quality, flash-free parts, improving both aesthetics and functionality.


Mold flash is a defect that seriously reduces product quality and may cause damage to the mold. It usually occurs during the injection molding process and is caused by various reasons. If you need further information about rapid injection molding, we are willing to provide assistance to ensure the smooth progress of your manufacturing process and excellent product quality.


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