Making injection molding is both an art and a science. High levels of technical expertise and attention to detail are required to prevent small mistakes from costing companies big money when it comes to the mass-production of novel parts.
As a manufacturer of injection molding products, some knowledge of common molding defects and how to avoid them can help you cut costs related to product returns.
Some molding defects may be difficult or costly to address. Others can be prevented by adjusting the molding process, without the need to redesign the mold tooling or replace other production equipment. You can typically avoid these defects relatively easily simply by adjusting the flow rate, temperature, or pressure of your mold.
Let’s look at the most common quality defects related to injection molding, what causes them and what you can do to prevent them. Hope they can help you.
1. Flash
Description:
Flashing issues are one of the most common defects you'll run into with injection molding. It is caused when molten plastic escapes out of the mold cavity.
Cause:
켥 A poorly designed or worn and degraded mold켥 Excessively high mold temperature
켥 High injection pressure
켥 Material flow performance is too nice
Remedies
켥 Retool or redesign the mold or adjust the mold켥 Increase plate clamping force to confine material flow to the channel
켥 Increase the clamp pressure to ensure that the mold parts remain shut during shotS
켥 Adopt optimal molding conditions like injection speed, injection pressure, mold temperature, and proper gas venting
켥 Change other lower flow performance raw material
2. Sink mark(shrinkage)
Description:
Sink marks are small craters or depressions that develop in thicker areas of the injection molded prototype when shrinkage occurs in the inner portions of the finished product. The effect is somewhat similar to sinkholes in topography, but caused by shrinkage rather than erosion
Cause:
켥 Mold temperature too high켥 Parts wall thickness too thick
켥 Cooling time is too insufficient
켥 Injection pressure insufficient
Remedies:
켥 Increase holding pressure and time켥 Reduce mold temperature(add mold water load)
켥 Increase cooling time
켥 Redesign the parts with thinner wall thickness if available
3. Jetting
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Description:
Jetting often appears as a squiggly line in the surface of the finished component, typically leading from the initial gate of injection.Being fluid, the molten plastic solidifies in a state that shows the wavy folds of the jet stream on the surface of the injection molded part.
Cause:
켥 Melt temperature is too low켥 The viscosity of the molten plastic becomes too high
켥 Injection pressure too high
켥 Injection molding gate location fault
Remedies:
켥 Reduce injection pressure켥 Increasing material and mold temperature
켥 Increasing gate size
켥 Redesign the injection gate located such that the material is directed across the mold, rather than lengthwise(this point looks very important,see right image,like 1 2 3 4 any location make a gate is right,fit 5 is wrong)
4. Flow lines
Description:
Flow lines are going to typically show as off-color, wavy patterns on the narrow sections of molded parts, or as the ring-shaped near the entry point of the mold.
Cause:
켥 Low injection pressure/speed켥 Low mold/material temperature
켥 Injection gate or channel too small
켥 Injection gate location fault
Remedies:
켥 Increasing injection speed, pressure, or material temperature 켥 Round the corners of the mold where wall thickness increases to help keep flow rate consistent
켥 Redesign injection gates
켥 Increasing injection gate or channel
5. Weld lines
Description:
Weld line is the line where two flow fronts meet when there is the inability of two or more flow fronts to “knit” together, or “weld,” during the molding process. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part.”
Cause:
켥 Mold/material temperature too low켥 Injection molding pressure/speed tool low
켥 Mold injection gate too small
켥 Material flow performance too low
Remedies:
켥 Increasing injection speed/pressure켥 Increasing mold or material temperature
켥 Increasing injection gate
Conclusion
Injection molding typically requires significant upfront investment in tooling. That’s why it’s especially important to design your mold right the first time, rather than having to start again after finding serious defects. Defects related to the molding process or material tend to be easier and less costly to solve. But no matter the cause, defects in molded products can hurt your bottom line tremendously.
If you're still not sure what's going on, contact us now. Our Engineering is highly experienced in complex injection molding projects, they are here to ensure you understand what it takes to manufacture the part you want.
