EspañolThis article mainly discusses some of the molding defects that can occur in a part during the process of double injection molding, and ways to fix and avoid them.
Flash
- Description –2nd material penetrating between 1st material and its’ It observed frequently where 1st material shrinkage is big and cooling time for 1material is too long. It is mainly due to too fast shrinking of 1stmaterial.
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- Optimizing holding pressure & Cooling time to get min shrinking of 1stmaterial till before 2nd shot
- Select less shrinkage ratematerial for 1st
- Changing design as preventive
Rainbow
- Description – Because of too high melt temperature or shear, 1st molded material remelt and flow with 2nd
§ Solution
- Lower 2nd material melt temperature or minimize
- Use low melt resin or low viscosity material as 2nd
- Changing the sequence of material.( Clear – 1st shot, Opaque- 2nd shot)
Washout
- Description – Because of too high melt temperature or shear, 1st molded material remelt and flow with 2nd
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§ Solution
- Lower 2nd material melt temperature or minimize
- Use low melt resin or low viscosity material as 2nd
- Changing the sequence of material.( Clear – 1st shot, Opaque- 2nd shot)
Wash-out @ Gate
- Description – 2nd material flow digs the 1st material due to high temperature and high It looks like sink mark from view of 1stmaterial.
§ Solution
- Lower 2nd material melt temperature or minimize
- Use low melt resin or low viscosity material as 2nd
- Enlarge 2nd shotgate
- Increase 2nd gate area
Most of the two shot injection molding defects mentioned above can be prevented in either design or molding process. Making double injection molds is both an art and a science as the manufacturing process requires high levels of technical expertise and attention to detail for the prevention of small mistake that may cost big money.