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What about the size of injection molded products?

Injection molding, temperature, pressure and time and other technical parameters, must be strictly in accordance with the requirements of the process control, especially the molding cycle of each plastic parts must be consistent, not arbitrarily change.


If the injection pressure is too low, the pressure-holding time is too short, the mold temperature is too low or uneven, the barrel and nozzle temperature is too high, plastic parts cooling is insufficient, will lead to the shape of the body size instability.


Under normal circumstances, the use of higher injection pressure and injection speed, the appropriate extension of mold filling and holding time, improve the temperature of the mold warm material, to overcome the size of unstable failure.


If the shape of molded parts is larger than the required size, the injection pressure and melt temperature should be reduced, the mold temperature will be reduced, the filling time will be shortened, the Gate section area will be reduced, and the shrinkage of the plastic parts should be improved.


If the size of the molded parts is smaller than the required size, the forming conditions should be taken in the opposite direction.


It is noteworthy that the changes in the ambient temperature on the shape of molded parts of the fluctuations also have a certain impact, should be based on the changes in the external environment in a timely manner to adjust the equipment and mold process temperature.


Improper selection of molding materials The shrinkage of the molding material has a great influence on the dimension precision of the plastic parts. If the molding equipment and mold precision is very high, but the shrinkage of raw materials is very large, it is difficult to ensure the size of plastic parts precision. Under normal circumstances, the larger the shrinkage of the molding materials, the more difficult to ensure the size of plastic parts. Therefore, in the selection of molding resin, it is necessary to fully consider the raw material after the shrinkage of the plastic parts of the impact of dimensional accuracy.


For the selection of raw materials, the range of shrinkage can not be greater than the size of plastic parts requirements. Attention should be paid to the different resin shrinkage ratio, according to the degree of crystallization of the resin analysis. Usually, the shrinkage rate of crystalline and semi crystalline resin is larger than that of amorphous resin, and the range of shrinkage is larger, and the corresponding plastic parts after the formation of shrinkage fluctuations are also relatively large; for crystalline resin, high crystallinity, molecular volume reduction, plastic parts of the shrinkage, resin ball crystal size of the shrinkage also has an effect, the ball crystal small,


The gap between the molecules is small, the contraction of the plastic parts is smaller, and the impact strength of the plastic parts is high.


In addition, if the shape of the raw material of the particle size uneven, dry, renewable raw materials and new materials mixed uneven, the performance of each batch of raw materials are different, will also cause plastic parts of the size of the fluctuations.


Die Failure


Mold structure design and manufacturing accuracy directly affect the size of the plastic parts, in the molding process, if the rigidity of the mold or die cavity under the molding pressure is too high, so that the mold deformation, the liver caused by the formation of plastic parts of the dimensional instability.


If the matching clearance between the guide pillar and the guide suite due to poor manufacturing accuracy or too much wear and tear, will also make the plastic parts of the molding dimension accuracy.


If there is a rigid filler or glass fiber reinforced material inside the molding material which causes the mold cavity to wear seriously, or the use of one-mode multi-cavity molding, the various types of cavities between the error and gate, flow and other errors such as feed mouth imbalance and other causes of the failure of the mold is inconsistent, will cause dimensional fluctuations. Therefore, in the design of molds, should be designed enough strength and rigidity of the mold, strict control of the processing accuracy, mold cavity materials should use wear-resistant materials, the cavity surface is best for heat treatment and cold hardening treatment.


When the dimensional precision of the plastic parts is very high, it is best not to use a multimode structure, otherwise, in order to ensure the molding precision, the mold must be set up a series of supporting equipment to ensure the accuracy of the mold, resulting in high production costs. When the plastic parts appear bias thickness error, it is often caused by mold failure. If it is under the condition of one mode cavity, the thickness of the plastic parts is biased, which is usually due to the installation error and poor positioning of the mold, which leads to the relative position deviation between the mold cavity and the core.


At this time, for those who have a very precise thickness of the plastic parts, can not only rely on guide pillars and guide sleeve to locate, you must add other positioning devices. If the error is caused by the thickness of a multimode cavity, under normal circumstances, the formation of the beginning of the error is small, but the continuous operation of the error gradually become larger, this is mainly due to the mold cavity and the error between the core caused, especially the use of hot runner molding the most likely to produce this phenomenon. For this, the two cooling loops with very small temperature difference can be set in the mould.


If the formation of thin-walled round container, can be used floating core, but the core and mold cavity must be concentric. In addition, in the production of molds, in order to facilitate the mold, the general is always accustomed to the cavity is smaller than the required size, the core to do than the requirements of larger size, set aside a certain amount of repair mold allowance. When the plastic parts of the hole diameter is less than the outside diameter, the core pins should be done larger, this is because the molding hole in the plastic parts are always greater than other parts, and to the Concent direction of contraction. Conversely, the core pins can be smaller if the inner diameter of the molded hole is close to the outside diameter.


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