Causes and Solutions of Cracking in Injection Molding

During the injection molding process, the injection molding products will have a variety of problems, and even have very serious problems, directly leading to unqualified product quality, and the crack in injection molding is one of the problems often encountered, how to do the crack in injection molding? Jiangsu Hengtai electronic plastic for everyone to share the causes of cracking and solutions.

First, what is injection molding crack

Cracking is a common defect in plastic products, which is mainly caused by stress deformation. There are mainly residual stress, external stress and stress deformation caused by external environment.

Second, the causes of cracking, and solutions

1. Cracking caused by residual stress

The residual stress is mainly caused by the following three conditions, namely, overfill, stripout and metal inserts. As a crack generated in the case of overfilling, its solution can mainly be started in the following aspects:

Because the pressure loss of the straight gate is reduced, if the crack is mainly generated near the straight gate, it can be considered to use the multi-point distribution gate, side gate and handle gate.

Under the premise of ensuring that the resin does not decompose and deteriorate, appropriately increasing the temperature of the resin can reduce the melting viscosity, improve the fluidity, and also reduce the injection pressure to reduce the stress.

Under normal circumstances, when the mold temperature is low, it is easy to produce stress, and the temperature should be appropriately increased. However, when the injection speed is higher, even if the mold temperature is lower, the stress can be reduced.

Injection and pressure holding time is too long will also produce stress, it is better to shorten it properly or carry out Th time pressure holding switch.

Non-crystalline resins, such AS AS resin, ABS resin, PMMA resin, etc. are more prone to residual stress than crystalline resins such as polyethylene, polyformaldehyde, etc., which should be paid attention to.

When the ejecting rod is pushed out, the ejecting force is too large, the stress is generated, and sometimes even whitening or cracking occurs around the ejecting rod because the ejecting inclination is small, the mold type glue and the punch are rough. The cause can be determined by carefully observing the location of the crack.

When inserting metal parts at the same time of injection molding, it is easy to produce stress, and it is easy to crack after a period of time, which is very harmful. This is mainly due to the difference in the coefficient of thermal expansion of the metal and the resin to produce stress, and over time, the stress exceeds the strength of the gradually deteriorating resin material and cracks. To prevent the resulting cracking, as an experience, wall thickness 7 "; Universal polystyrene with the outer diameter of embedded metal parts is basically not suitable for adding inserts, and inserts have less influence on nylon. Because the thermal expansion coefficient of glass fiber reinforced resin material is small, it is more suitable for embeddings.

In addition, preheating the metal insert before forming also has a good effect.

2. Cracking caused by external stress

The external stress here is mainly caused by unreasonable design and stress concentration, especially at sharp corners.

3. Cracks caused by external environment

Chemicals, moisture absorption caused by water degradation, and excessive use of recycled materials will cause physical deterioration, resulting in cracking.

During the injection molding process, from product design, mold manufacturing, plastic particle quality, operator operation and other aspects, we should always pay attention to and avoid the occurrence of such phenomena as cracking, after all, every detail is very important in the injection molding process.