Plastic injection molding process mainly includes filling -
The holding -
Demoulding four phases, such as the four phase directly decides the forming quality of products, and the four phase is a complete process continuously.
1, filling stage filling is the first step in the process of the injection molding cycle, time starts from mold closing injection, into the mold cavity filling to about 95%.
Theoretically, filling, the shorter the time, forming efficiency is higher, but in practice, the molding time or injection speed should be restricted by many conditions.
High speed filling.
As shown in figure 1 -
2, high shear rate during high speed filling, plastic exist due to the effect of shear thinned viscosity drop situation, reduce the overall flow resistance;
Local viscous heating effect will also make the solidified layer thickness thinning.
So in flow control stage, filling behavior often depends on the size to fill.
In flow control stage, because of the high speed filling, the melt shear thinned effect often big 2, the function of the holding stage pressure maintaining phase is continuous pressure, compaction melt, increase the density of the plastic (
Increases the secret)
, to compensate for the shrinkage of the plastic behavior.
In the process of pressure, because in the injection mould cavity filled with plastic, high back pressure.
In the process of compaction pressure, injection molding machine
screw can only make tiny movement forward slowly, the plastic flow speed is relatively slow, then the current called the holding current.
Because in the holding stage, plastic mold cooling solidification is accelerated, the melt viscosity increase quickly, so the resistance within the mold cavity is very large.
In the late stage of pressure, material density increased continuously, also gradually forming, plastic pressure maintaining phase will continue until gate seal curing, at this time the holding stage, the cavity pressure peak.
Cooling phase in injection mold, the design of the cooling system is very important.
This is because the only cooling solidification molding plastic products to a certain rigidity, stripping to avoid plastic deformation caused by external forces.
Due to the cooling time of the molding cycle is about 70% ~ 80%, thus well designed cooling system can greatly shorten the molding time, improve the injection molding productivity, reduce the cost.
Improper design of the cooling system can make the molding time stretched, increased cost;
Uneven cooling will further cause plastic buckling deformation.
Injection molding machine by clamping molding cycle time, the fill time, the holding time, cooling time and stripping time.
With cooling time proportion is the largest, is about 70% ~ 80%.
So the cooling time will directly affect molding cycle length and the size of the production of plastic products.
Stripping stage plastic temperature should be cool to below the heat distortion temperature of the plastic products, in order to prevent the plastic products caused by residual stress relaxation phenomenon or release the warping and deformation caused by the force.
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