double injection graphic.

Double injection molding, also called 2K molding, two shot molding

Due to the appearance, decoration or the function requirements, such as “partial ABS area electroplating”, some product should be designed using two or three different colors or materials to do injection molding, mostly is two. One very common example in our daily life is the toothbrush. It is designed to be soft combined with hard plastic. The purpose on the one hand is to make it strong enough, on the other hand is to make the user feel comfortable.

Two shot mold consists of two same cores (A1, A2) and two different cavities (B1, B2). A1 is completely same as A2 (A1=A2), thus with a strict accuracy requirements.

The runner system of the two molds is different and they work at the same time. Every cycle has two times injections.

After the first shot, gate will be ejected automatically and core A1 rotates to the position of core A2 by 180°to start the second injection.

toothbrush double injection

Toothbrush double injection example in our daily life

Advantage of double injection mold

  • High production efficiency
  • Lower cost compared with overmolding and assembly parts
  • Good looks and feelings
  • High precision and stable part quality

Double injection molding notice:

  1. Temperature difference;The melt point of the two injection material must have at least 30~60° difference. see the table as follows:
  2. Enough contact area and apply a rough texture to the first shot part so they can be bonded strongly. Engineers can also design the dome versus recess to keep them together structurally.
  3. Transparent lens double injection with opaque part; First shot of PC with a higher melt temperature brand; Second shot of PMMA or PC with a relatively low melt temperature
  4. Choose compatible bonding materials, see the table as follows:

mold melt temperature table

Material combination table

Anyway, double injection is a good option for your high-end product both for the part quality and unit price, as well as aesthetic requirements. BDM Ltd. provides you the professional solutions.

For any double injection molding requirements, feel free to contact with us to get a quote.

For any two shot molding questions, don’t hesitate to contact with us:

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