The basis for determining the carrier tape injection molding is the accuracy of the injection molded products, that is, the dimensional tolerance, geometric tolerance and surface roughness of the products. There must be many related conditions for precision injection molding, and the most essential are the four basic factors: plastic material, injection mold, injection process and injection equipment.

When designing plastic products, engineering plastic materials should be selected first, and engineering plastics that can carry out precision injection molding must choose those materials with high mechanical properties, stable size, good creep resistance and environmental stress cracking resistance. Secondly, the applicable injection molding machine shall be selected according to the selected plastic materials, dimensional accuracy of finished products, piece weight, quality requirements and expected mold structure. In the processing process, the factors affecting precision injection molding products mainly come from the accuracy of mold, injection shrinkage, and the variation range of ambient temperature and humidity of products.

In carrier tape injection molding, the mold is one of the keys to obtain belt plastic products that meet the quality requirements. The mold for belt injection molding should meet the requirements of product size, accuracy and shape. However, even if the accuracy and size of the mold are consistent, the actual size of the molded plastic products will be inconsistent due to the difference of shrinkage. Therefore, it is very important to effectively control the shrinkage of plastic products in precision injection molding technology.

Whether the mold design is reasonable or not will directly affect the shrinkage rate of plastic products. Because the mold cavity size is obtained from the size of plastic products plus the estimated shrinkage rate, and the shrinkage rate is a value within a range recommended by the plastic manufacturer or the engineering plastics manual. It is not only related to the gate form, gate position and distribution of the mold, It is also related to the crystal orientation (anisotropy) of engineering plastics, the shape and size of plastic products, and the distance and position from the gate.

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

Therefore, the relationship between these influencing factors and injection conditions and their apparent factors must be considered when designing the mold, such as injection pressure and cavity pressure and filling speed, injection melt temperature and mold temperature, mold structure and gate form and distribution, gate cross-sectional area, product wall thickness, content of reinforcing filler in plastic materials The crystallinity and orientation of plastic materials. The effects of the above factors are also different due to different plastic materials, other molding conditions such as temperature, humidity, continuous crystallization, internal stress after molding, and changes of injection molding machine.

Because the injection molding process is the process of transforming plastics from solid (powder or granular) to liquid (melt) and to solid (product). From granular material to melt, and then from melt to product, it needs to go through the action of temperature field, stress field, flow field and density field. Under the joint action of these fields, different plastics (thermosetting or thermoplastic, crystalline or amorphous, reinforced or non reinforced, etc.) have different polymer structure, morphology and rheological properties. All factors affecting the above “field” will affect the physical and mechanical properties, size, shape, accuracy and appearance quality of plastic products.

In this way, the internal relationship between process factors and polymer properties, structural morphology and plastic products will be shown through plastic products. Analyzing these internal relations is of great significance to reasonably formulate the injection molding process, reasonably design and manufacture the mold according to the drawing, and even reasonably select the injection molding equipment. Precision injection molding is also different from ordinary injection molding in injection pressure and injection rate. Precision injection molding often adopts high-pressure or ultra-high-pressure injection and high-speed injection to obtain small molding shrinkage.

Based on the above reasons, in addition to the design elements of general molds, the following points must be considered when designing precision injection molds:

① Adopt appropriate die dimensional tolerance;

② Prevent forming shrinkage error;

③ Prevent injection molding deformation;

④ Prevent demoulding deformation;

⑤ Minimize die manufacturing error;

⑥ Prevent the error of die accuracy;

⑦ Maintain mold accuracy.