Precision injection molding plants are usually completed by injection molding machines and molds, and molds are the most important parts in between, which will directly affect the quality of the final product produced, so injection molding processing usually has extremely high precision for molds. High request.
The following is a more detailed answer to several aspects of precision injection molding factory mold precision requests.
1. The precision injection molding factory's request for scale is very well understood. There are large errors in the scale of the mold, and the scale errors of the products produced will naturally exist.
2. The request for the roughness of the appearance of the precision injection molding factory. If the appearance of the mold is not smooth and detailed, the output of the mold will be rough. The demand will be polished again or even scrapped directly, which directly affects the company's work efficiency.
3. The precision injection molding plant's request for density. Generally, the higher the density of the mold, the stronger the pressure bearing ability, and the less likely the injection molding plant is to deform. Therefore, the choice of mold density should be careful. .
When plastic molds are processed for precision injection molding, engineering plastic materials should be selected first, and engineering plastics that can be used for precision injection molding must select materials with high mechanical properties, stable dimensions, good creep resistance, and resistance to environmental stress cracking.
In the processing process, the factors that affect precision injection molded products mainly come from the temperature of the mold, the injection molding process control, as well as the changes in the ambient temperature and humidity of the production site and the acquired product annealing treatment.
Whether the injection mold is designed properly or not will directly affect the shrinkage rate of the plastic product, because the cavity size of the mold is obtained from the plastic product size plus the estimated shrinkage rate, and the shrinkage rate is determined by the plastic manufacturer or engineering plastic manual The recommended value in a range is not only related to the mold gate form, gate position and distribution, but also to the crystal orientation (anisotropy) of engineering plastics, the shape and size of plastic products, injection molding plants, to the pouring The distance and location of the mouth are closely related to the mold cooling distribution system.
The main factors affecting 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.
The program control of the injection speed is to divide the injection stroke of the screw into 3 to 4 stages, and use the appropriate injection speed in each stage.
For example: when the molten plastic just starts to pass through the gate, the injection speed is slowed down, high-speed injection is used during the filling process, and the speed is slowed down at the end of the filling process. This method can prevent flashing, eliminate flow marks and reduce products Residual stress, etc.
During low-speed mold filling, the flow rate is stable, the product size is relatively stable, the fluctuation is small, the internal stress of the product is low, and the internal and external stress of the product tends to be consistent (for example, a polycarbonate part is immersed in carbon tetrachloride, and the high-speed injection molding The parts are cracked and poured into the injection molding plant, and the low speed does not crack).
Under relatively slow mold filling conditions, the temperature difference of the material flow, especially the temperature difference between the material before and after the gate is large, helps to avoid the occurrence of shrinkage holes and depressions, but due to the longer filling time, it is easy to cause delamination of the parts Welding marks with poor bonding not only affect the appearance, but also greatly reduce the mechanical strength.
During high-speed injection, the material flow rate is fast. When the high-speed mold filling is successful, the molten material quickly fills the cavity, the material temperature drops less, and the viscosity drops less. You can use a lower injection pressure, which is a hot material filling Modality, high-speed mold filling can improve the gloss and smoothness of the part, eliminate the seam line phenomenon and delamination phenomenon, shrink shrinkage is small, the color is uniform, the larger part can be guaranteed to be full.
However, it is easy to produce fat and blistering products or yellow parts, or even burn zoom, or cause difficulty in demolding, or uneven filling. For high-viscosity plastics, it may cause melt rupture and cause cloud spots on the surface of the parts. .
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