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What Are the Reasons and Solutions for the Difficult Demolding of Injection Molds?

What Are the Reasons and Solutions for the Difficult Demolding of Injection Molds?

Ⅰ. Reasons for the difficulty of demolding in plastic injection mold processing


1. Waterway design;


2. There are grooves inside the mold;


3. The demolding situation of the front and rear molds;


4. The mold finish is not high;


5. Insufficient draft angle;


6. Whether the setting of the inclined top and the thimble are consistent.


Insufficient draft angle is one of the important reasons for the difficulty of drafting. Therefore, during injection mold design and products processing, the slope should be marked on the drawing, usually between 1-2 degrees, and it is allowed to be more than 0.5 in special occasions. During operation, in order to smoothly release the plastic product from the mold, a release agent containing silicone oil is used, but only a little bit can be used. If the spray is too thick, it is very difficult to wipe off. At the same time, it will also cause the second processing of the printed mark to become poor. Once the release agent is applied to the mold, it will be attached to the plastic product and it is very difficult to wipe it off. It should be noted that the injection pressure should not be too high. If the plastic product is too tightly attached to the injection mold, demolding will become very difficult.


Difficulties in demolding plastic injection molded parts are often encountered in our injection molding production process. Poor demolding has a great impact on the quality of injection molded products. Mild poor demolding may cause scratches or patterns on the surface of the product; serious poor demolding will lead to warping, deformation, or even cracking and damage of the product. Therefore, solving the problem of poor release of the injection molding process of the injection mold affects the quality of the final injection product.


After the plastic part is injection molded, the plastic part is ejected from the mold cavity. Whether it is a single or multi-element ejection mechanism, the demolding work is generally completed at one time. But sometimes due to the special shape of the plastic parts or the needs of production automation, after a demolding work is completed, the plastic injection molded parts are still difficult to take out from the cavity or cannot fall off automatically. At this time, another demolding action must be added to make the plastic pieces fall off. Difficulty in demolding is mainly because the gate or plastic parts are tightly packed in the mold.


Ⅱ. The solution to the plastic injection mold problem

1. In terms of equipment: insufficient ejection force and insufficient ejection stroke.


The ejection force is the force control used by the injection molding equipment for demolding. For injection molding machines of different important levels, the maximum ejection force is different. The preset ejection force of the ideal injection molding process machine is basically sufficient, but it is not ruled out that the injection molded part is larger than the maximum injection range or the structure of the injection molded part is too complicated, and the grip force in the mold is too large. Comprehensive consideration of these issues is helpful to analyze the suitability of the ejection force. 


2. Injection molds, injection molding processing molds


(1) Unreasonable demoulding structure or improper position;


(2) The draft angle is not enough;


(3) Mold temperature is too high or poor ventilation;


(4) The sprue wall or cavity surface is rough;


(5) The nozzle does not conform to the mold feed port or the nozzle diameter is larger than the feed port diameter.


3. Injection mold processing technology


(1) The barrel temperature is too high or the injection volume is too much. When the mold temperature is too high, the molten material in the cavity is not cooled in place, and the volume does not return to the preset size, which causes the situation that the mold cannot be removed;


(2) The injection pressure is too high or the holding and cooling time is too long. The injection temperature includes barrel temperature, nozzle temperature, etc. If the temperature is too high, the melt enters the cavity and cannot be cooled for a predetermined time, which also affects the demolding effect;


(3) Excessive injection volume. The injection volume exceeds the cavity capacity, which is what we often say is the expansion of the mold. When the pressure is released, the injection of too much melt will expand, so that the expansion cannot be removed from the mold. Adjust the injection volume to solve it;


(5) Improper injection cycle. If the injection pressure is too high, the holding time or the cooling time is too long during injection molding, it will also cause the hidden danger of difficult demolding. The completely cooled product is also not conducive to demolding. The injection cycle must be appropriate.

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