Injection compression molding is an advanced form of conventional injection molding. It can increase the injection length/wall thickness ratio of injection parts; use smaller clamping force and injection pressure; reduce the internal stress of the material; and improve processing productivity.
Injection compression molding is applicable to various thermoplastic engineering plastic products, such as: Large-sized curved parts, thin-walled, miniaturized parts, optical lenses, and parts with good anti-attack characteristics.
The main features of injection compression molding compared with the traditional injection molding process, the injection compression molding is a significant feature is that its mold cavity space can be automatically adjusted according to different requirements.
For example, it can close the mold guide portion before the material is injected into the cavity, and the cavity space can be expanded to twice the finished wall thickness of the part. In addition, it can also be used during material injection or according to different modes of operation. After the completion of the injection, the size of the cavity is controlled accordingly to match the injection process, so that the polymer can maintain the appropriate pressure state and achieve the effect of compensating the material shrinkage.
Depending on the geometry of the injection-molded parts, the surface quality requirements, and the different conditions of the injection molding equipment, there are four injection shrinkage protection divisions to choose from. They are: sequential, co-actuated, respiration and local pressurization.
Sequential icm(seq-icm)
In the sequential injection compression molding process, the injection operation and the engagement of the mold cavity are performed sequentially. At the beginning, the mold guide portion is slightly closed and there is a cavity space approximately twice the wall thickness of the part. After the resin is injected into the mold cavity, it pushes the movable part of the mold until it is completely closed, and the polymer is compressed in the cavity.
During this process, since there is a moment when the polymer flow pauses and stops from the completion of the injection to the start of compression, it may form a streamline on the surface of the part, the visibility of which depends on the color of the polymer material, and the shaping of the part. When the texture structure and material type. The method of operation. Can use crankshaft type equipment to carry out this icm.
Cooperative icm (sim-icm)
Like the sequential icm, the co-acting icm starts, and the die guide is also slightly closed. The difference is that the material starts to inject pressure while the material starts to inject into the cavity. The extrusion screw and the die are During the common movement of the cavity, there may be a delay of s2 or s2.
Since the polymer flow always maintains a stable flow state in front of it, it will not appear as a pause of the seq-icm process and a surface streamline.
Since both of the above methods leave a large cavity space at the beginning of the operation, when the molten polymer injection cavity has not yet encountered the directional pressure, it may first flow into the lower side of the cavity due to gravity. , And may appear to be undesired due to temporary unstressed foam.
Moreover, the larger the wall thickness of the part, the larger the cavity space, and the length of the streamer length will increase the time period when the mold is fully closed, which may increase the above phenomenon.
Breathing icm (breath-icm)
With the respiratory icm, the mold is completely closed at the beginning of the injection. Therefore, the polymer will remain in compression as soon as it is injected. This overcomes the potential problems that may arise with the aforementioned two methods. In the polymer to the cavity When injecting, the mold gradually pulls apart and forms a larger cavity space, and the polymer in the cavity is always kept under a certain pressure.
When the material is close to the full cavity, the mold has begun to push back until it is completely closed, so that the polymer is further compressed and reaches the required finished thickness of the part. The above mold expands the movement between the cavities by means of the injection type. The injection pressure of the polymer in the chamber or the preset injection machine motion program to achieve.