Injection moulding of thermosetting plastics is a process that physical and chemical changes and it is irreversible. Because the material is frictionally heated by screw shear mixing, the temperature will be higher, so that the parts can be treated quickly. However, there are still some defects in the process, which need to be solved in time.

1. The investment cost of equipment and mould is high. The investment cost of thermosetting injection machines and thermosetting injection moulds is 5 to 10 times that of compression moulding process. This is one of the main reasons that affect the popularization and application of injection technology.

2. The utilization rate of injection material is poor. For small injection parts, the waste rate of multi-cavity injection moulds can reach 50%, generally 15% to 20%, so the raw materials waste is very large. Nowadays, all countries in the world are developing runner-free and gate-free injection technology to overcome this defect.

3. Injection parts with more inserts are not suitable. Because the injection moulding process of thermosetting plastics is rapid prototyping production, the embedded parts cannot be automated. It is bound to take up more time, so that the rapid automatic injection machines cannot produce high-speed.

4. Limited by the type of filler. If the injection material is not made of soft filler, the reinforcing fibre injection material is damaged due to the shearing action of screw, which is difficult to meet the strength requirements of the product, and the wear of the barrel and screw is serious, affecting the service life.

5. Injection parts have orientation. When molten injection material passes through nozzles and runners at high speed, wood flour and fibrous fillers will rank in the direction of flow. The mechanical strength and physical properties of injection parts are directional, which can easily cause warpage deformation of injection parts.