Tips for filling in injection molding

2021-03-23 11:50:47 admin

Tips for filling in injection molding

Injection molding is a step that many molds need to go through. This step is divided into four stages, and filling is the first stage. This is not to say that filling is more important in the injection molding process. No one can do without the four stages. The following is mainly about filling.

First of all, we need to understand that filling is the first step of injection molding. It needs to work when the mold is closed. Generally, the filling is about 95%. There is also a saying that the shorter the filling time, the better the molding efficiency. It will be higher, but the injection molding time is affected by many factors. The filling is also divided into high-speed filling and low-speed filling, see below for specific differences.

(1) High speed: The shear rate is high during high-speed filling. Due to the effect of shear thinning, the viscosity of the plastic decreases, which reduces the overall flow resistance; the local viscous heating effect will also make the thickness of the solidified layer thinner. Therefore, in the flow control phase, the filling behavior often depends on the volume to be filled. That is, in the flow control stage, due to high-speed filling, the shear thinning effect of the melt is often very large, and the cooling effect of the thin wall is not obvious, so the effect of speed is the main factor.

(2) Low speed: When the low thermal conductivity filler, reduce the shear rate, relatively high local viscosity, large flow resistance. Since the thermoplastic replenishment speed is slow and the flow rate is slower, the effect of heat conduction is very good, and the heat is quickly taken away to cool the mold wall. Adding a smaller amount of viscous heating phenomenon and a thicker solidified layer further increase the flow resistance in the thin-walled part.

Generally, the strength of the weld line in the high temperature zone is better, because at high temperature, the polymer activity is more active and can be entangled with each other, and the melt temperature in the high temperature melting zone is similar, so the thermal properties are almost the same. It can increase the strength of the welding zone, if it is in the low temperature zone, the strength will be worse.