Resolving injection molding flash defects

Introduction Flashing is a common defect in plastic injection molding industry. It typically occurs due to low melt viscosity or inefficient mold locking, resulting in material overflow on the mold surface, presenting as excess plastic beyond parting lines or flowing into gaps in mold inserts or core pins. Failure to address this flashing phenomenon can severely damage the mold. Our goal is for operators to produce flash-free products, eliminating the need for trimming. Trimming not only consumes significant inspection time but can also result in improperly trimmed parts being delivered to customers. Furthermore, the longer a mold operates with Injection molding flash defects issues, the higher the maintenance costs become.

Injection molding flash defects – Types of Flashing

Feather-like injection molding flash defects indicates high-temperature conditions. Verify temperature settings of the barrel and mold; Thicker flashing is often caused by excessive clamp force, low machine tonnage, or mold damage; If multiple molds on the same machine exhibit flashing, verify that the platen parallelism meets the requirements of the injection molding machine manufacturer.

Identifying the Cause of Flashing

Tracing the entire mold process backward is always our last resort; we must first take measures to identify the cause of flashing. Here are the procedures to follow before making any process changes:

Injection molding flash defects – Clean the Mold

Dirty molds can sometimes be the cause of flashing. When cleaning the mold, check for flashing or other debris buildup, blockages, or damage to moving slider components.

Verify the Process

Have there been any changes to processes that could lead to flashing? Settings to review may include barrel/mold temperature, tonnage, shot size, decompression, injection speed, pack, and hold pressures.

Check the Material

Are the correct materials being used? Are different batches of materials being used? Is the percentage of recycled material higher than the established percentage? Insufficient drying leading to higher moisture content in the product or excessive use of recycled material can improve material flow, thereby increasing the risk of flashing.

Check Hold Switching Conditions

With mold closed, set hold time and pressure as low as possible – most injection molding machines can be set to zero, with some as low as 1 psi. The product should only partially fill to 95% to 98%, leaving small gaps or dimples. If the part is fully filled, adjustments should be made to achieve the correct partially filled state. If the partially filled condition is correct, there may be partial mold damage.

Check Mold Closure

If there is suspicion of mold closure damage, apply blue dye to parting lines and/or closing areas in the mold’s fixed half where flashing exists. Close the mold and apply a certain tonnage, then open the mold and verify if the blue dye has clearly transferred to the movable half. If the transfer is light or nonexistent, the mold needs repair.

Injection molding flash defects – Historical Data

Key historical data used for troubleshooting are fill time or peak pressure. If the fill rate is too fast, slow down the injection speed while verifying that the peak pressure variation remains within the process control window. If the peak pressure is too high, change the V/P switching position, while also confirming that the fill time variation remains within the established process control limits. Also, verify that the temperature settings of the barrel and mold are within the verified process control limit values.

Conclusion

Assessing flashing conditions may be straightforward when appropriate inspection procedures are followed to clearly identify the cause of this defect. It is important to remember that the first step in troubleshooting most process failures is to clean the mold and verify if any defects exist in the injection molding process. Quickly addressing flashing issues can prolong mold life and prevent defective products from being sent to customers. Product quality is the key to our success and profitability.