Rotary injection molding

Rotary injection molding

What Is rotary molding?

Also known as Rotary table injection molding or vertical injection, rotary injection molding is not a distinct molding method per se, but rather a variation of a standard injection molding machine with a rotating platen or table. It is commonly used in two-shot (or multi-shot) injection molding or for simultaneous injection and demolding. 

In this injection process, the carousel moves in a regulated manner, enabling each mold to go through various stages such as plastic injection, accurate cooling, and the removal of finished parts.

1. Process

Plastic for the first layer of the part is injected into one half of the mold.

Once the first shot is complete, the rotary table or platen rotates (often 180 degrees, but multi-station rotary molds can have more positions). This brings the first shot under a second mold cavity while simultaneously positioning the next part to receive its first shot.

With the first shot now in a new position, a second material or color is injected, adhering to the initial shot. This second injection can be done using a different material or color, allowing for multi-material or multi-color parts.

After the second shot, the part can be ejected, and the process starts over. The rotation allows for simultaneous injection and cooling/demolding, increasing production efficiency.

2. Advantages

By using a rotary table, it’s possible to perform injection and cooling/demolding operations simultaneously, reducing cycle times.

The ability to use different materials or colors in a single cycle allows for complex, multi-material, or multi-colored parts without the need for manual assembly or post-molding processing.

Since the second shot is molded directly onto the still-hot first shot, there’s typically excellent bonding between the two materials.

The rotary mechanism ensures that the second shot is aligned precisely with the first, ensuring accurate multi-material parts.

3. Applications

Multi-material buttons or keypads, where you might have a soft-touch material combined with a harder plastic.

Seals, gaskets, or other parts where a rigid plastic may be combined with a softer rubber-like material.

Multi-material medical devices or components.

Multi-colored or multi-material toys produced in a single molding cycle.

4. Challenges

The machinery and mold design for rotary injection molding can be more complex and expensive than standard single-shot molds.

When producing multi-material parts, it’s essential to ensure that the materials are compatible and bond well together.


In conclusion, rotary injection molding offers a solution for producing complex parts that require multiple materials or colors in a single molding cycle. The simultaneous nature of the process enhances efficiency, making it an attractive option for certain high-volume or specialized applications.

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