Most plastic electronic components are injection molded. Due to the high design accuracy of these plastic parts, special engineering plastics are used for processing. Conventional injection molding cannot be used for these plastic parts, but precision injection molding technology must be adopted. In order to ensure the performance, quality, reliability, and long-term stability of these precision plastic parts, injection molding produces high-quality plastic products that meet product design requirements. It is necessary to improve the plastic materials, injection molding equipment, mold design, injection molding process, and injection site management.

The commonly referred to precision injection molding refers to the requirement that the shape accuracy of injection molded products should meet strict dimensional tolerances, positional tolerances, and surface roughness. To carry out precision injection molding, there are many related conditions, and the most essential ones are plastic materials, injection molds, injection processes, and injection equipment.

(1) Plastic materials

When designing plastic products, engineering plastic materials should be selected first, and engineering plastics that can be precision injected must be selected with materials that have high mechanical properties, stable dimensions, good creep resistance, and environmental stress cracking resistance; Secondly, suitable injection molding machines should be selected based on the selected plastic material, finished product size accuracy, part weight, quality requirements, and expected mold structure.

The factors that affect precision injection molded products during the molding process mainly come from mold temperature, injection molding process control, changes in production site environmental temperature and humidity, and subsequent annealing treatment of the products.

(2) Injection mold

In terms of precision injection molding, molds are one of the key components used to obtain precision plastic products that meet quality requirements. The molds used for precision injection molding should meet the requirements of product size, accuracy, and shape, and the mold materials should be strictly selected. However, even if the precision and size of the mold are consistent, the actual size of the molded plastic product will still vary due to differences in shrinkage. Therefore, effectively controlling the shrinkage rate of plastic products is crucial in precision injection molding technology.

The rationality of injection mold design directly affects the shrinkage rate of plastic products. Due to the fact that the size of the mold cavity is calculated by adding the estimated shrinkage rate to the size of the plastic product, and the shrinkage rate is a value recommended by the plastic manufacturer or engineering plastic manual within a range, it is not only related to the gate form, gate position, and distribution of the mold, but also to the crystal orientation (anisotropy) of the engineering plastic, the shape, size, distance, and position to the gate of the plastic product. At the same time, it is closely related to the cooling distribution system of the mold.

The main factors affecting the shrinkage rate of plastics include thermal shrinkage, phase change shrinkage, orientation shrinkage, compression shrinkage, and elastic recovery, which are related to the molding or operating conditions of precision injection molded products.

Therefore, when designing injection molds, it is necessary to consider the relationship between these influencing factors and injection conditions, as well as their apparent factors, such as injection pressure, mold cavity pressure, filling speed, injection melt temperature, mold temperature, mold structure and gate form and distribution, as well as the influence of gate cross-sectional area, product wall thickness, content of reinforcing fillers in plastic materials, crystallinity and orientation of plastic materials. The influence of the above factors also varies due to different plastic materials, other molding conditions such as temperature, humidity, continued crystallization, internal stress after molding, and changes in injection molding machines.

(3) Injection molding process

The injection molding process is the process of transforming plastic from a solid state (powder or pellet) to a liquid state (melt) and then to a solid state (product). From pellets to melt, and then from melt to product, the process involves the interaction of temperature field, stress field, flow field, and density field. Under the combined action of these fields, different plastics (thermosetting or thermoplastic, crystalline or amorphous, reinforced or non reinforced, etc.) have different polymer structure forms and rheological properties. Any factors that affect the above-mentioned "field" will inevitably affect the physical and mechanical properties, size, shape, accuracy, and appearance quality of plastic products.

In this way, the inherent connections between process factors, polymer properties, structural morphology, and plastic products will be manifested through plastic products. Analyzing these internal connections is of great significance for the rational formulation of injection molding processing technology, the rational design and manufacturing of molds, and even the rational selection of injection molding equipment.

Precision injection molding differs from regular injection molding in terms of injection pressure and injection rate. High pressure or ultra-high pressure injection, as well as high-speed injection, are commonly used in precision injection molding to achieve smaller molding shrinkage.

Taking into account the various reasons mentioned above, when designing precision injection molds, in addition to considering the design elements of general molds, the following points must also be taken into account:

① Adopt appropriate mold size tolerances;

② Prevent errors in molding shrinkage rate;

③ Prevent injection molding deformation;

④ Prevent demolding deformation from occurring;

⑤ Minimize mold manufacturing errors;

⑥ Prevent errors in mold accuracy;

⑦ Maintain mold accuracy.