what affects failure of precision injection molding

The basis for judging precision txhaj tshuaj molding is the accuracy of injection molded products, yog, the dimensional tolerances, geometric tolerances and surface roughness of the products.

To carry out precision injection molding, there must be many relevant conditions, and the most essential are the four basic factors of plastic materials, injection molds, injection molding process and injection molding equipment.

When designing plastic products, engineering plastic materials should be selected first, and engineering plastics that can be precision injection molded must choose those materials with high mechanical properties, dimensional stability, good creep resistance, and environmental stress cracking resistance.

Thib ob, the appropriate china injection molding machine should be selected according to the selected plastic material, finished product dimensional accuracy, part weight, quality requirements and expected mold structure.

In the process of processing, the factors that affect precision injection molded products mainly come from the accuracy of the mold, injection shrinkage, and the range of changes in the environmental temperature and humidity of the product.

In precision txhaj tshuaj molding, the mold is one of the keys to obtain precision plastic products that meet the quality requirements. The mold used for precision injection molding should truly meet the requirements of product size, accuracy and shape.

But even if the precision and size of the mold are the same, the actual size of the molded plastic products will be inconsistent due to the difference in shrinkage. Yog li ntawd, it is very important to effectively control the shrinkage rate of plastic products in precision injection molding technology.

Whether the mold design is reasonable or not will directly affect the shrinkage rate of the plastic product. Because the size of the mold cavity is calculated by adding the estimated shrinkage rate to the size of the plastic product, the shrinkage rate is 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, but also to the crystal orientation (anisotropy) of engineering plastics, the shape and size of plastic products, the distance to the gate and Location related.
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The main factors that affect plastic shrinkage are thermal shrinkage, phase change shrinkage, orientation shrinkage, compression shrinkage, and elastic recovery. These influencing factors are related to the molding conditions or operating conditions of precision injection molded products.

Yog li ntawd, the relationship between these influencing factors and injection conditions and their appearance 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 , And the influence of factors such as gate cross-sectional area, product wall thickness, reinforcing filler content in plastic materials, crystallinity and orientation of plastic materials.

The influence of the above factors is also different due to different plastic materials, other molding conditions such as temperature, humidity, continued crystallization, internal stress after molding, and changes in the injection molding machine. Rau

Because the injection molding process is a process of transforming plastic from solid (powder or pellets) to liquid (melt) to solid (khoom). From pellets to melt, and then from melt to product, the temperature field, stress field, flow field, and density field are in the middle.

Under the combined action of these fields, different plastics (thermosetting or thermoplasticity, crystallinity) Or non-crystalline, reinforced or non-reinforced, lwm yam.) have different polymer structural morphology and rheological properties.
All the factors that affect the above-mentioned “field” will definitely affect the physical and mechanical properties, size, shape, precision and appearance quality of plastic products.

Ua li no, the internal connection between process factors thiab polymer properties, structural morphology and plastic products will be manifested through plastic products. A clear analysis of these internal connections is of great significance to rationally formulating the injection molding process, rationally designing and manufacturing molds according to drawings, and even rationally selecting injection molding equipment.

Precision injection molding and ordinary injection molding are also different in 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 mold shrinkage rate.
Rau
Based on the above reasons, in addition to the general mold design elements, the following points must be considered when designing precision injection mold:
① Use appropriate mold size tolerance;
②Prevent molding shrinkage errors;
③Prevent injection deformation;
④Prevent demoulding deformation;
⑤ Minimize the mold manufacturing error;
⑥ Prevent errors in mold accuracy;
⑦Keep the precision of the mould.

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