What Influences Precision Mold Injection Molding?

Author: MULAN - Plastic Molding Manufacturer

Molds are the key to obtaining precision plastic products that meet quality requirements. Mold design, whether the mold design is reasonable or not will directly affect the quality of plastic products. Since the size of the mold cavity is obtained by adding the required size of the plastic product to the shrinkage rate of the material used, and the shrinkage rate is usually a value within a range recommended by the injection mold manufacturer or the engineering plastics manual, it is not only related to the gate of the mold The form, gate position and distribution are related, and are related to the crystal orientation (anisotropy) of engineering plastics, the shape and size of plastic products, the distance and position from the gate.

The main factors affecting plastic shrinkage include heat shrinkage, phase change shrinkage, orientation shrinkage, compression shrinkage and elastic recovery, etc., and these influencing factors are related to the molding conditions or operating conditions of precision injection molded products. Therefore, mold designers must have rich experience in design and injection molding, and must consider the relationship between these influencing factors and injection molding conditions and their appearance factors, such as injection pressure and cavity pressure and filling speed, injection melt temperature and mold temperature , mold structure and gate form and distribution, as well as gate cross-sectional area, product wall thickness, content of reinforcing filler in plastic material, crystallinity and orientation of plastic material and other factors. The influence of the above factors is also different due to different plastic materials, or other molding conditions such as temperature, humidity, continued crystallization, and changes in the injection molding machine after molding.

Since the injection molding process is the process of transforming plastic from solid (powder or pellets) to liquid (melt) to solid (product). From the pellets to the melt, and then from the melt to the product, there are temperature field, flow field and density field in the middle. Under the joint action of these fields, different plastics (thermosetting or thermoplastic, crystalline or non-crystalline, reinforced or non-reinforced, etc.) have different polymer structures and rheological properties.

All factors that affect the above "field" will definitely affect the physical and mechanical properties, size, shape, precision and appearance quality of plastic products. In this way, the intrinsic relationship between process factors and polymer performance, structural form and plastic products will be expressed through plastic products. Analyzing these internal connections is of great significance for rationally drawing up injection molding processing technology, rationally designing and manufacturing molds according to drawings, and even rationally selecting injection molding processing equipment.

Precision mold injection molding is also different from ordinary injection molding in terms of injection pressure and injection rate. Precision injection molding often uses high-pressure or ultra-high-pressure injection and high-speed injection to obtain a smaller molding shrinkage. Precision injection molding will be affected by many related factors and environmental conditions, but the most basic factors are plastic materials, injection molds, injection molding processes and injection molding equipment. In the early stage of designing plastic products, the engineering plastics that can be selected according to its environment are first selected.

Secondly, the selected plastic material, the dimensional accuracy of the finished product, the weight of the part, the quality requirements and the expected mold structure are used to select the appropriate injection molding machine.