Analyzing the cause of the drape is based on the premise that the clamping force is sufficient. When the clamping force is insufficient, it is difficult to analyze the cause of the drape. The following analysis is based on sufficient clamping force. According to several situations of Pifeng, Pifeng may have the following reasons:
The first situation: As mentioned above, under the conditions of low temperature, low speed, and low pressure, when the product is not full of glue, the front has been produced. The possible main reasons are: insufficient mold manufacturing precision and excessive fit clearance;
The second situation: when the product is just full of glue, there will be partial shrinkage, and no flare occurs; when the injection pressure is increased to improve the partial shrinkage of the product, flare occurs. The possible reasons are:
1) The material temperature is too high. If the material temperature is too high, the viscosity of the melt is low, and the fluidity is good. The stronger the melt's ability to penetrate into the mold fit gap, it will lead to the occurrence of drape.
2) The injection speed is too fast and the injection pressure is too high (resulting in oversaturation of the filling). Too fast speed, excessive injection pressure, especially excessive injection pressure, will enhance the ability of the melt to penetrate into the matching gap of the mold, leading to the occurrence of flare.
3) The fluidity of the 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 mold fit gap, and it is easy to produce flare. When the mold production has been completed, the depth of the mold's exhaust groove, and the mold's matching gap have been finalized, another kind of plastic with good fluidity will be 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 insufficient, when the mold cavity bears the pressure of the plastic melt, it will deform and expand, and the colloid will protrude into the gap of the mold to produce a flare.
5) The product design is unreasonable. Part of the product is too thick, and too much shrinkage during injection molding will cause local shrinkage. In order to adjust the partial shrinkage of the product, it is often necessary to fill and hold the pressure with a higher injection pressure and a longer injection time. As a result, the mold strength is insufficient and deformed, resulting in a flare.
6) The mold temperature is too high. The high mold temperature can not only keep the plastics good fluidity and low pressure loss, but also reduce the strength of the mold, which will also lead to the production of flare.
The second situation is the most frequently encountered problem in injection molding production, which usually cannot be solved by all the technological means, and it is the most troublesome for injection molding technicians. In this case, the most important method is to solve the problem through mold modification. The solutions are:
1) Partial reduction of product glue. The shrinkage of the product is reduced. After the glue position is thinned, the shrinkage problem 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 commonly used method.
2) Increase the glue point. Increasing the pouring point can reduce the injection process and reduce the injection pressure, and the pressure on the mold cavity will be reduced, which can effectively solve the occurrence of the front. Increasing the pouring point, especially in the shrinking position of the product, can have an immediate effect on reducing the injection pressure of the mold cavity. It is also one of the more commonly used methods.
3) Reinforce the mold part. Sometimes the deformation of the template can be strengthened by adding a support between the movable template and the thimble plate.