The remote control mold manufacturer said that, in general, the injection molding process includes four stages: filling, holding pressure, cooling, and demolding, which directly determines the molding quality of the product and is a complete continuous process.

1. Filling stage of mold injection molding process

(1) Filling is the first step of the entire injection molding cycle. The time is from the start of injection molding when the mold is closed to the filling of the mold cavity to about 95%. In theory, the shorter the filling time, the higher the molding efficiency, but in practice, the molding time or injection speed is limited by many conditions.

(2) high-speed filling. When filling at high speed, the shear rate is high, and the viscosity of the plastic decreases due to shear thinning, which reduces the overall flow resistance. The effect of local viscous heating also causes the thickness of the cured layer to be thinned. Therefore, in the flow control phase, the filling behavior usually depends on the volume to be filled. In other words, in the flow control stage, due to high-speed filling, the shear thinning effect of the melt is often great, but the cooling effect of the thin wall is not obvious, so the speed efficiency is dominant.

(3) low speed filling. When low-speed filling is controlled by heat conduction, the shear rate is low, the local viscosity is high, and the flow resistance is large. Due to the slow replenishment speed and slow flow of thermoplastics, the heat conduction effect is obvious, and the heat is quickly taken away by the cold mold wall. In the case of a small amount of viscous heating, the thickness of the solidified layer is thicker, which further increases the flow resistance at the thinner walls.

The remote mold said that due to the fountain flow, the plastic polymer chains of the flow wave front are aligned with the almost parallel flow wave front. Therefore, when two plastic melts meet, the polymer chains on the contact surface are parallel to each other; in addition, the two melts have different properties (different residence times in the mold cavity, different temperatures and pressures).

As a result, the structural strength of the melt-adhesive intersection area is poor at the micro level. Put the parts in the light of the appropriate angle, with the naked eye observation, you can find a clear weld, this is the formation mechanism of the weld. Welding marks not only affect the appearance of plastic parts, but also cause stress concentration due to loose microstructure, which reduces the strength of the parts and causes fracture.

Generally speaking, the weld line strength is better in the high temperature region, because at high temperature, the polymer chains are more mobile and can interpenetrate and entangle. In addition, the temperature of the two melts in the high temperature zone is similar, and the thermal properties of the melts are almost the same, which increases the strength of the welding zone. On the contrary, in the low temperature region, the welding strength is poor.

2. The mold injection molding process pressure holding stage

The remote control mold said that the function of the holding stage is to continuously apply pressure, compact the melt and increase the density of the plastic (densification) to compensate for the shrinkage behavior of the plastic. During the pressure holding process, the back pressure is high because the mold cavity is filled with plastic. In the process of pressure holding and compaction, the screw of the injection molding machine can only move forward slightly slowly, and the flow speed of the plastic is also very slow, which is called pressure holding flow. In the holding stage, the plastic is cooled and solidified by the mold wall faster, and the melt viscosity increases rapidly, so the resistance in the mold cavity is very large.

In the later stage of pressure keeping, the material density continues to increase and the plastic parts are gradually formed. The pressure holding stage should continue until the gate solidification seal, when the pressure holding stage of the cavity pressure reaches a high value.

In the holding phase, the plastic exhibits partial compressibility due to the rather high pressure. In areas of higher pressure, the plastic becomes denser. In the low pressure area, the plastic is loose and the density is low, which causes the density distribution to change with location and time.

During the pressure holding process, the plastic flow is extremely low, and the flow no longer plays a leading role; pressure is the main factor affecting the pressure holding process. In the holding process, the plastic has filled the mold cavity, and the gradually solidified melt is used as the pressure transmission medium. The pressure in the mold cavity is transmitted through the plastic to the surface of the mold wall, which helps to open the mold, so proper clamping force is required to clamp the mold.

Under normal circumstances, the expansion force of the mold will slightly open the mold, which is helpful for the exhaust of the mold; but if the expansion force is too large, it is easy to cause burrs, flash and even mold opening. Therefore, when choosing an injection molding machine, it is necessary to choose an injection molding machine with sufficient clamping force to prevent the mold from expanding and effectively maintain the pressure.