How to reduce the sharp angle effect when making plastic molds
Sharp corner effects often occur when mold manufacturers design molds. The so-called mid-point angle effect mainly means that when the angle formed by two or three faces is less than 120°, a concentration of stress is generated at the sharp corner. When the stress reaches a certain degree, the sharp angle It is the place where cracks are most likely to occur. Under a continuous stress, the cracks continue to expand and eventually cause the product to break or crack. How to avoid the crack effect in the mold design?
Under the premise of ensuring the normal mold exit of the mold, the injection molding process should be as simple as possible and easy to demould. Try to avoid or reduce various core-pulling mechanisms around the mold. This not only greatly simplifies the mold structure, but also facilitates mold injection molding. Can improve production efficiency.
When doing the mold, avoid the concentration of the fillet stress as much as possible, and increase the strength of the part to ensure the stress concentration generated at the corner of the part, and reduce the crack that will occur when the product is stressed or impacted. Improper molding conditions or unreasonable part structure can cause large internal stresses, which are particularly prone to stress cracking. When the corner radius of the center is less than 0.3 times the wall thickness of the part, the stress concentration increases sharply. When the wall thickness is greater than 0.8 times, the stress concentration becomes significantly smaller.
Rounded corners are good for the manufacture of various molds. The parts are designed with various rounded corners to improve the strength of the mold. The corresponding parts of the mold should also be rounded, which increases the firmness of the mold. The mold will not be quenched or used. The cracking due to the concentration of stress also increases the strength of demolding of the mold.
Only the use of rounded corners can be easily filled and demolded. For some plastics with poor fluidity or plastics with fillers, it is especially important to design various rounded corners to improve the filling performance and improve the parts. Use performance.
How to avoid the sharp corner effect when the mold manufacturer designs the mold, rounding is one of the best methods.
To meet the different physical and mechanical properties of the machine when used. The main requirement is that the product is dense, the welding is firm, the strength is high, and the internal stress is small. However, in our daily injection molding or try-out process, even if the process parameters are adjusted, the products often have various phenomena such as insufficient filling, high internal stress, surface flow lines, etc. The main reason is that there is a problem with the exhaust of the mold.
When the mold is injection-molded, the various gases generated in the mold mainly have the following sources and sources: there is air present in the cavity and the pouring system, and the moisture contained in the plastic raw material is evaporated at the injection temperature. Water vapor, a gas produced by the decomposition of plastic at high temperatures. At the same time, in order to ensure the complete demoulding during the forming process, and to reduce the molding defects of the product, it is also necessary to pay attention to the design of the system in which the mold discharges excess gas.
In the process of plastic filling of the injection molding machine, in order to maintain the fluidity of the molten plastic in an optimal state, it is necessary to increase the temperature and the injection pressure of the molten plastic, but also because the residual stress of the product is accompanied by the pressure. Increasing, the possibility of warpage around the product and the cracking of the plastic increases. For example, when the exhaust of the mold is normal, the injection speed can be increased, and the filling and holding pressure can be easily achieved in an optimal state without additionally increasing the temperature of the barrel and the nozzle. Such a product has a small residual stress and a small warpage deformation.
In the process of injection molding, if the mold is poorly ventilated, the gas in the cavity will be compressed and will generate a large back pressure, which will greatly hinder the normal and rapid filling of the plastic melt, making injection molding difficult; The pressure is constantly increased during the injection, the holding time is increased, the molding cycle is prolonged, and the efficiency of the injection molded parts is continuously reduced. Sometimes corrosive gases form scale on the surface of the cavity, reducing the life of the mold under normal use.
We also need to consider how to vent when injection molding, a good exhaust system will improve the quality of plastic parts.
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