Injection molding flash is one of most seen injection moulding defects in plastic manufacturing industry. Flash in injection molding is a thin film of plastic escapes from the mold cavity. Flashing injection moulding is mostly happened at the parting line of the mold or between inserts and ejector pin locations. The plastic flashing should be removed by the plastic injection molding manufacturer before packing or turn to next treatment process.
How Plastic Injection Molding Flash Occur?
As all we known, a plastic part is made by two parts of injection mold. This plastic injection mold have a male cavity and female cavity. The empty part between these two parts molded the plastic part. And there is a parking line between these two half mold. The molten plastic resin material may escape along the parting line during injection molding if the mold is not closed tights enough or too big gap along the parking line. And it may be happened near the ejector pins and the insert blocks if the assemble tolerance is unscientific and too big. Of cause there many different reasons makes injection molding flash happened in different conditions. Blow table list some of the plastic flash trouble shooting and remedies for your checking and reference:
| Injection Molding Flash Occur Causes | Injection Molding Flash Remedies |
|---|---|
| Clamp tonnage / High pressure is too low | 1. Reduce injection pressure or hold pressure 2. Set a higher clamping presure 3. Try to run the mold on a bigger tonnage injection machine |
| Clamp pressure too high | Reduce clamp tonnage to help balancing venting |
| Parting line mismatch | Check the mould surfaces, slides and cavity for whether any obstruction clamp closing. Clean the mold surface to avoid any unwanted material stick on the mold. Use pressure-sensitive paper to check pressure on parting line in flash area and non flash area while the tool is in the press. |
| Plastic injection mold is damage | 1. Check whether any damage around the plastic flash position. 2. Check whether the air venting gap is too big or not. |
| Injection Speed too fast | Slow down the injection rate step by step |
| Injection Pressure is too high | Lower the injection pressure step by step |
| Holding Pressure is too high | Lower the holding pressure step by step |
| Holding Pressure is too low | Do a first stage short shot test, and then increase the clamp tonnage step by step. |
| Sprue bushing too long | 1. Check thermal expansion of sprue bushing under production conditions. Shorter bushing may be needed. 2. Adjust the sprue bushing length: |
| Overfilling | 1. Adjust first-stage cut-off position or reduce shot weight. 2. Check machine response on switchover from filling to pack/hold stage. 3. Reduce the feed setting (stroke length) 4. If the total cycle time is too long, material is likely overheating in the barrel. Reduce the cycle time during the cooling phase. 5. Use a material that has the stiffest flow possible without causing non-fill. 6. Use the flow rate formulations provided by resin manufacturers. Thin-walled products may require an easy-flow resin while thick-walled products can use a resin that has a stiffer consistency. |
| Viscosity too low | 1.Double check whether the running plastic is with right melting flow rate. 2. Check for whether the plastic is over melt. Set a melting temperature between the resins supplier recommend. 3. Excessive residence time, which causes degradation 4. Presence of moisture from improper drying 5. Excessive amount of colorant that contains a lubricating vehicle |
| Mold temperature to high | Lower the mold temperature step by step if you are runing a hot runner system plastic injection mold. |
If you still can`t fix the problem of flash plastic, please check the planeness of the fixed platen and the moveable platen of your injection molding maker. Because it maybe not in the good situation after long time running and the bolts may got loosed.
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