How to solve the problem of sharp edges in injection molded products?

Phi front, also known as flying edge, overflow edge, overflow material, etc., mostly occurs in the mold's parting position, such as the mold parting surface, the sliding part of the slider, the gap of the insert, the hole of the top bar, etc. The overflow material will be further expanded if not solved in time, thus forming local collapse of the embossing mold and causing permanent damage. The phi-front of the gap of the insert and the hole of the top bar will also make the products stuck on the mold, affecting the release. 

Phi front is essentially plastic material into the mold fit parts of the gap after cooling excess left on the product. To solve the problem of phi front is very simple, that is to control not to let them melt into the mold fit-gap to go. Plastic melt into the mold with the gap to go, there are generally two cases: one case is the mold with the gap is originally large, the gel is easy to enter it; another case is the mold with the gap was not large, but because of the molten gel under pressure to force into the.

On the surface, it seems that the phi front can be completely solved by strengthening the manufacturing precision and strength of the mold. Improve the manufacturing accuracy of the mold, reduce the mating gap of the mold, to prevent the molten gel from, completely necessary. However, the strength of the mold, in many cases, can not be strengthened indefinitely, strengthened to any pressure, the gel can not burst into it. 

The production of phi-front has both mold-related reasons and process-related reasons. Check the process side of the cause, the first check whether the clamping force is sufficient, only to ensure that the clamping force is sufficient, the phi front is still generated, then check the mold side of the cause.  



The method to check whether the clamping force is sufficient. 

(1) gradually increase the injection pressure, with the increase of injection pressure, the phi front also increases accordingly, and the phi front is mainly generated 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 phi on the parting surface disappears, or when the injection pressure is increased again, the phi on the parting surface no longer increases. Then the clamping force is considered sufficient.

To check whether the phi is caused by the mold manufacturing accuracy, the following methods are used. 

With lower material temperature, lower filling speed, and lower injection pressure, the product is just filled (the product has slight shrinkage). At this time, it can be considered that the ability of the melt to burst into the mold gap is very weak, at this time, if the phi front is generated, it can be judged that the mold manufacturing precision problems, need to repair the mold to solve. Consider giving up the process to solve the production of phi. It should be noted that the above "three low" conditions are indispensable, high material temperature, faster glue filling speed, higher injection pressure, will lead to increased local pressure in the mold cavity, enhance the ability of the melt to burst into the mold with the gap, expand the mold and produce phi, although the product is not full of glue.    

Analysis of the causes of the phi is based on the premise that the clamping force is sufficient, when the clamping force is insufficient, it is difficult to analyze the causes of the phi. The following analysis is based on the condition that the clamping force is sufficient. According to the several cases of phi-fronts, the possible causes of phi-fronts are as follows. 

The first situation: as mentioned above, in the case of low temperature, low speed, low pressure, when the product is not full of glue, the phi has been generated. The main reasons that may arise are insufficient precision in the manufacture of the mold, with too large a gap. 

The second situation: when the product is just full of glue, there is a local shrinkage phenomenon, no phi front generated; when the injection pressure is increased to improve the local shrinkage of the product, the phi front is generated. Possible causes are. 

(1) the material temperature is too high. Material temperature is too high, the viscosity of the melt is low, good fluidity, the stronger the ability of the melt to burst into the mold with the gap, it will lead to the production of phi.

(2) injection speed is too fast, the injection pressure is too large (resulting in filling oversaturation). Too fast speed, too much injection pressure, especially too much injection pressure, will enhance the ability of the melt to burst into the mold with the gap, resulting in the phi front. 

3) The fluidity of the plastic is too high. The better the fluidity of the plastic, the lower the viscosity of the melt, the stronger the ability of the melt to burrow into the mold fit the gap, it is easy to produce phi. When the mold production has been completed, the depth of the exhaust slot of the mold, the mold with the gap has been set, change another liquidity of good plastic to produce, will produce phi. 

4) The strength of the mold is not enough. When the design strength of the mold is not enough, when the mold cavity withstands the pressure of the plastic melt, it will deform and expand, and the gel will burst into the gap of the mold, resulting in phi. 

5) The product design is unreasonable. The product local glue bit is too thick, too much shrinkage during injection, which will lead to local shrinkage. In order to regulate the problem of local shrinkage of the product, often need to use a higher injection pressure, longer injection time to fill, and pressure retention, resulting in insufficient mold strength deformation, resulting in phi. 

6) The mold temperature is too high. High mold temperature, not only can make the plastic maintain good fluidity, pressure loss is small, but also reduces the strength of the mold, the same will lead to the production of phi front. 

The second situation, the most commonly encountered problem in injection molding production, usually using all the process means can not be solved, the biggest trouble for injection molding technicians. For this situation, the main means is to solve it by repairing the mold. The solution methods are. 

1) Product localized glue reduction. The product shrinkage of the local reduction of glue, glue position thinning, product shrinkage can be improved, injection pressure will be reduced, mold deformation will be small, phi can be suppressed. This is the most effective and most commonly used method. 

2）Increase the feeding point. An increase into the pouring point, can reduce the injection process, reduce the injection pressure, the mold cavity will be reduced by the pressure, can effectively solve the phi front generation. An increase in the pouring point, especially in the product shrinkage position to increase into the pouring point, to reduce the mold cavity injection pressure can play an immediate effect. It is also one of the more commonly used means. 

3) Strengthen the mold locally. Sometimes the deformation of the template can be strengthened by increasing the support between the moving template and the ejector plate.