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Injection Molding Product Flash, Overflow And Other Solutions

Flash Overflow In Injection Molding

Flash Definition

Flash, also known as overflow, etc, mostly occurs at the opening and closing positions of the mold, such as: the parting surface of the mold, the sliding fitting part of the slider, the gap of the insert, the pore of the ejector rod, etc.

If the flash is not resolved in time, it will further expand, causing local collapse of the imprinting mold and causing permanent damage. The gap between the insert and the hole in the ejector will also cause the product to get stuck on the mold, affecting demoulding.

The tip is essentially the excess left on the product after the plastic material enters the gap between the mold mating parts and is cooled. It is very simple to solve the problem of cape, that is, to control not to let the melt enter the mold fitting gap.

Two situations

There are generally two situations when plastic melt enters the mold fitting gap.

In one case, the mold fitting gap is originally large, and the colloid can easily enter it; in the other case, the mold fitting gap is originally small, but the molten colloid is forced in due to pressure.

On the surface, it seems that Pi Feng can completely solve the problem simply by strengthening the manufacturing accuracy and strength of the mold. It is absolutely necessary to improve the manufacturing accuracy of the mold, reduce the matching gap of the mold, and prevent molten colloid from entering. However, in many cases, the strength of the mold cannot be infinitely strengthened until the colloid cannot break into it under any pressure.

The emergence of Pi Feng has both mold and process reasons. To check for process-related reasons, first check whether the clamping force is sufficient. Only when the clamping force is sufficient and cracks still occur, can the mold-related reasons be checked.

How to check whether the clamping force is sufficient

  • Gradually increase the injection pressure. As the injection pressure increases, the cape also increases accordingly, and the cape is mainly produced on the parting surface of the mold, indicating that the clamping force is insufficient.
  • Gradually increase the clamping force of the injection molding machine. When the clamping force reaches a certain value, the caps on the parting surface disappear, or when the injection pressure is increased, the caps on the parting surface no longer increase. It is considered that this clamping force value is sufficient.

How to check whether the mold manufacturing accuracy is causing the flaw

Use a lower material temperature, a lower filling speed, and a lower injection pressure to fully fill the product (the product will shrink slightly). At this time, it can be considered that the ability of the melt to penetrate into the mold fitting gap is very weak.

If a sharp edge occurs at this time, it can be judged that there is a problem with the mold manufacturing accuracy, and the mold needs to be repaired to solve it. You can consider giving up using craft methods to solve the problem of capes.

It should be noted that the above “three low” conditions are indispensable. High material temperature, fast filling speed, and high injection pressure will cause the local pressure in the mold cavity to increase and enhance the risk of melt intruding into the mold fitting gap.

Ability to expand the mold to produce a sharp edge, although the product is not fully glued at this time.

The analysis of the cause of the cloak 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 cloak. The following analysis is based on the condition that the clamping force is sufficient. Please pay attention to this.

Depending on the several situations in which the cloak appears, the possibility of the cloak occurring

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 glitch has already occurred. The possible main reasons are: insufficient mold manufacturing accuracy and excessive fitting clearance

Second situation

When the product is just full of glue, there will be local shrinkage and no burrs will occur; when the injection pressure is increased to improve the local shrinkage of the product, burrs will occur.

Possible reasons are
  • The material temperature is too high. If the material temperature is too high, the viscosity of the melt is low, the fluidity is good, and the melt has a stronger ability to penetrate into the mold fitting gap, which will lead to the occurrence of sharp edges.
  • The injection speed is too fast and the injection pressure is too high (leading to oversaturated filling). Excessive speed, excessive injection pressure, especially excessive injection pressure, will enhance the ability of the melt to penetrate into the mold fitting gap, resulting in the formation of edges.
  • 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 mold fitting gap, making it easier to produce edges. When the mold production has been completed, the depth of the exhaust groove of the mold, and the matching gap of the mold have been finalized, if another plastic with good fluidity is used for production, a cape will occur.
  • 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, causing a chip.
  • The product design is unreasonable. If the local glue level of the product is too thick and shrinks too much during injection molding, it will cause local shrinkage. In order to adjust the problem of local shrinkage of the product, higher injection pressure and longer injection time are often used for filling and pressure holding. As a result, the mold is insufficiently strong and deformed, resulting in chipping.
  • The mold temperature is too high. High mold temperature not only allows the plastic to maintain good fluidity and small pressure loss, but also reduces the strength of the mold, which can also lead to the occurrence of burrs.

The third situation

It is the most common problem encountered in injection molding production. It usually cannot be solved by all technological means, and it troubles injection molding technicians the most. For this situation, the most important method is to solve it through mold modification.

The solution is
  • The product has partially reduced glue. Reduce the glue in the shrinkage part of the product. After the glue level is thinned, the product shrinkage problem can be improved, the injection pressure will be reduced, the mold deformation will be small, and the distortion can be suppressed. This is the most effective and commonly used method.
  • Increase the glue entry point. Increasing the pouring point can reduce the injection molding process and injection pressure, and the pressure on the mold cavity will be reduced, which can effectively solve the problem of glitches. Increasing the pouring point, especially increasing the pouring point at the shrinkage 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.
  • Reinforce parts of the mold. Sometimes the deformation of the template can be strengthened by adding a support head between the movable template and the ejector plate.

Contact Person: Alex Chu
WhatsApp/ WeChat: 0086 18968677763
Email: sc10@solidcomould.com
Website: www.solidcomould.com

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