Do you know two shot plastic injection molding and how dose it work?
- Issue Time
What is it?
Producing two color or two component injected molded parts from two different thermoplastic materials in one process, quickly and efficiently:
- Two-shot plastic injection molding, co-injection, two-color and multi-component molding are all variations of an advanced molding technology
- Combining hard plastics with soft materials
- Two step process performed during a single press machine cycle
- Consolidates two or more components thus eliminating additional assembly costs
The technology of injection molding continues to become increasingly sophisticated. Up-to-date fabrication technology allows processors to produce injection molded parts from two different thermoplastic materials. By combining these different materials with the ever-improving molding technology, complex functional parts can now be produced economically and efficiently in massive quantities.
The materials may differ in polymer type and/or hardness, and can be fabricated from molding techniques such as dual injection molding, two-shot molding, two color molding, two component molding and/or multi-shot molding. Whatever its designation, a sandwich configuration has been made in which two or more polymers are laminated to take advantage of the properties each contributes to the structure. The thermoplastic parts from these moldings offer excellent performance characteristics and reduced cost.
How Does it Work?
- Two shot machine with two independent injection units
- Molding one part using two different materials or colors
- Two cavity mold (one + one)
- First material injected into first cavity, mold opens and rotates to second cavity position, mold closes and second material is injected. After sufficient part cooling, the mold is opened and the part is ejected.
- Critical factors:
- material(s) melt temperature
- mold wall temperature
- injection speed
- delay time between injections
- component part temperature
The two-shot plastic injection molding process requires a machine with two independent injection units, each of which shoots different material. The first material is injected through a primary runner system, as in a normal injection molding cycle. During the injection, the mold volume to be occupied by the second material is shut off from the primary runner system. The mold is then opened and the core plate rotated 180 degrees. The mold is again closed and the secondary runner system is connected to the volume to be filled. After sufficient part cooling, the mold is opened and the part is ejected.
The two-shot process can also be accomplished with an indexing system (a round table rotating around a horizontal axis) with a primary and secondary station. While the first injection is accomplished at station #1, the second injection is accomplished at station #2. Each injection station is run by an independent injection unit. This allows injection speeds and pressures to be controlled for each material being utilized.
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