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How to deal with the problem of cloaking in the process of injection molding
There are both mold and process reasons for the formation of drape. To check the cause of the process, first check whether the clamping force is sufficient. Only when the clamping force is guaranteed to be sufficient and the burr still occurs, then check the cause of the mold.
Ways to check whether the clamping force is sufficient:
1. Gradually increase the injection pressure. With the increase of the injection pressure, the puncture will increase accordingly, and the puncture is mainly produced on the parting surface of the mold, indicating that the clamping force is not enough.
2. Gradually increase the clamping force of the injection molding machine. When the clamping force reaches a certain value, the drape on the parting surface disappears, or when the injection pressure is increased, the drape on the parting surface will no longer increase. This clamping force value is considered to be sufficient.
According to the occurrence of several situations of cloaking, there may be the following reasons for cloaking:
The first situation: As mentioned above, under the condition of low temperature, low speed, and low pressure, when the product is not full of glue, the front has already been produced. The main possible reasons are: the precision of mold manufacturing is not enough, and the fit clearance is too large;
The second situation: when the product is just full of glue, there is local shrinkage, and no edging occurs; when the injection pressure is increased to improve the local shrinkage of the product, edging occurs. Possible reasons are:
1. The material temperature is too high. If the temperature of the material is too high, the viscosity of the melt is low, the fluidity is good, the stronger the ability of the melt to break into the gap of the mold, it will lead to the generation of the front.
2. The injection speed is too fast, and the injection pressure is too large (leading to filling oversaturation,. Too fast speed, excessive injection pressure, especially excessive injection pressure, will enhance the ability of the melt to break into the mold fit gap, resulting in drape front generated.
3. The fluidity of plastic is too high. The better the fluidity of the plastic, the lower the viscosity of the melt, and the stronger the ability of the melt to penetrate into the fit gap of the mold, and it is easy to produce a front. When the mold making has been completed, the depth of the vent groove of the mold, and the matching clearance of the mold have been finalized, another plastic with good fluidity is used for production, and the front will be produced.
4. The strength of the mold is insufficient. When the design strength of the mold is not enough, when the mold cavity bears the pressure of the plastic melt, it will deform and expand, and the colloid will break into the gap of the mold, resulting in edging.
5. The product design is unreasonable. The local glue position of the product is too thick, and the shrinkage is too much during injection molding, which will lead to local shrinkage. In order to adjust the problem of partial shrinkage of the product, it is often necessary to use higher injection pressure and longer injection time to fill and maintain the pressure. As a result, the mold is insufficiently strong and deformed, resulting in edging.
6. The mold temperature is too high. A high mold temperature can not only keep the plastic fluidity good, and the pressure loss is small, but also reduce the strength of the mold, which will also lead to the occurrence of edging.
The third situation is the most frequently encountered problem in injection molding production. Usually, all technological means cannot be used to solve it, and it is the most troublesome for injection molding technicians. For this kind of situation, the most important method is to solve it by repairing the model. The solutions are:
1. Partial glue reduction of the product. Reduce the shrinkage of the part of the product. After the glue is thinned, the shrinkage of the product can be improved, the injection pressure will be reduced, the deformation of the mold will be small, and the front can be suppressed. This is the most effective and most commonly used method.
2. Increase the glue inlet point. Increasing the pouring point can reduce the injection molding process, reduce the injection pressure, and the pressure on the mold cavity will be reduced, which can effectively solve the problem of burrs. Increasing the pouring point, especially at the position where the product shrinks, can have an immediate effect on reducing the injection pressure of the cavity. It is also one of the more commonly used methods.
3. Strengthen the part of the mold. Sometimes the deformation of the template can be strengthened by adding a brace between the movable template and the ejector plate.
At the same time, as the recent research of Vowin Rapid Prototyping shows, the benefits of improved productivity and firm performance can make implementing basic management practices worth it.
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