Manufacturing Technologies

2K and 3K injection molding, also know as multi-component injection molding, involves combining two or three different plastics into a single component in a single injection molding cycle. This process enables product designs that would be difficult to achieve otherwise and reduces the need for additional assembly steps, resulting in unique, low cost assemblies. 2K injection molding is often used to combine rigid and flexible plastics into a single part. The rigid part is molded first, followed by the injection of a flexible material, often a seal, directly onto or around the rigid component in the same process. This results in a complete, two-material component from the mold. The 2K process can provide a mechanical and hermetic seal between the two components without requiring additional assembly steps. Similarly, 3K processes can accommodate and mold three different materials in a single injection molding cycle.

Multi-component injection molding offers many advantages, but it also presents numerous challenges. RKT’s extensive experience provides the technical expertise to recognize and effectively address those challenges head-on. For instance, in a 2K tool, managing multiple hot runners and different material temperatures within the same mold is crucial. Temperature differences can be significant. Rigid plastics require mold temperatures of at least 100° Celsius, while soft plastics such as TPE/TPU are processed at a temperatures of 20° to 60° C.

Ensuring a reliable seal between the first and subsequent materials is essential to prevent unwanted flashing during the injection cycle. Additionally, designing 2K or 3K products often involves incorporating holes that must be meticulously specified to avoid flash and visual inconsistencies. Different shrinkage rates of the materials must also be taken into consideration in the product design and mold process. Planning for the shrinkage of the initial material after the first injection step and its alignment with subsequent materials requires careful consideration and expertise to ensure proper adhesion, sealing, and overall molding quality.

Cavities in a mold form the injection-molded part. A tool can contain one or more cavities, allowing multiple parts to be produced in each injection cycle. Generally, more cavities in a tool enhances efficiency and cost-effectiveness. Cavities are often in exponent multiples of 2 (e.g., 2, 4, 8, 16, 32, 64) to ensure a balanced flow of plastic Molds with over eight cavities are considered high-cavity molds, suitable for smaller, less complex components. RKT excels in developing both low and high-cavity tools effectively. Single cavity tools are typically used for prototypes or low-volume needs, while 8, 32, and 64 cavity tools are used for higher-volume production. RKT currently employs 128 cavity molds for a very high-volume project. Proper product design, meticulous tool fabrication, and proper molding processes are crucial to providing uniformity in part dimensions and surface finish across all cavities.