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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