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How to optimize the weld line on the surface of injection molded parts—New energy power equipment

 Tuesday, 31 August 2021

In injection molding, when the plastic melt fills the mold cavity, if the temperature of the front melt of two or more melts is not exactly the same when they meet, these melts cannot be fully fused, and linear grooves are generated at the confluence to form fusion marks .

The causes and solutions of weld lines in injection molding are as follows:

1.The melt temperature is too low ,Low temperature melt has poor shunting and confluence performance and is easy to form weld lines. When the inner and outer surfaces of plastic parts produce welding fine lines at the same part, it is often due to poor welding caused by too low material temperature. In this regard, the temperature of the barrel and nozzle can be appropriately increased, or the injection cycle can be prolonged to promote the rise of the material temperature. At the same time, the passing amount of cooling water in the mold shall be controlled and the mold temperature shall be appropriately increased. In general, the strength of the plastic part at the melting mark is poor. If the corresponding part where the welding mark occurs in the mold is locally heated and the local temperature of the welding part of the formed part is increased, the strength of the plastic part welding part can often be improved. If the low-temperature molding process must be adopted due to special needs, the injection speed and injection pressure can be appropriately increased to improve the confluence performance of the melt, or a small amount of lubricant can be appropriately used in the raw material formula to improve the flow performance of the melt.
2.The gate position is unreasonable , The gate form with less diversion shall be adopted and the gate position shall be reasonably selected to avoid inconsistent mold filling rate and interruption of mold filling material flow as far as possible. Single point feeding shall be selected when possible. In order to prevent low-temperature melt from injecting into the mold cavity to produce fusion marks, a cold material cavity can be set in the mold while increasing the mold temperature.

3.Poor mold exhaust , At this time, first check whether the mold exhaust hole is blocked by the solidified product of the melt or other objects, and whether there is foreign matter at the gate. If the carbonization point still appears after the blockage is removed, an exhaust hole shall be added at the material collection point of the die, or the material collection can be accelerated by repositioning the gate, appropriately reducing the clamping force and increasing the exhaust gap. In terms of injection molding process, auxiliary measures such as reducing material temperature and mold temperature, shortening high-pressure injection time and reducing injection pressure can be taken.

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