Single-shot molding delivers two-color part in a single tool

The two-color injection molding process has been simplified through a development at Trelleborg Sealing Solutions (Stuttgart, Germany) that employs a single shot and a single tool to manufacture partially colored liquid silicone rubber (LSR) components. Utilizing an innovative and proprietary tool construction, the process has the capability to add color pigment to part of the transparent silicone material stream just prior to its injection into the tool cavity.

Ursula Nollenberger, Product Line Director for LSR Components at Trelleborg Sealing Solutions, says: "Our first application of this revolutionary technology is for a leading automotive tier-one supplier. The company was looking for a solution to visually differentiate geometrically identical parts that Trelleborg produces off a single tool for various vehicle platforms, without impacting the overall aesthetics of the finished product. This new process offered an ideal solution that was both practical and cost-effective."

"This novel technology can be applied to any size and number of cavities per tool. Depending on part geometry and size as well as production capacity needed, we construct tools anywhere between 1 and 128 cavities with possibilities even beyond," adds Nollenberger.

Jarno Burkhardt, General Manager of the Trelleborg Sealing Solutions European center of excellence for LSR component solutions in Stein am Rhein, Switzerland, comments: "The advantage of the two-colored LSR components to our customer, as well as to the OEM they supply, is that it gives, without adding significant extra cost, product traceability. The beauty of the novel tool design is that it will allow an unlimited number of color combinations from a single machine, in a single tool and in one single shot."

The process involves the two components of LSR raw material being mixed in a ratio of 1:1. On the way into the injection tool, this homogenous mass is then divided. Color is added via an additional mixing unit to one part of the volume stream and injected into the tool cavity via a proprietary valve design.  Simultaneously, the colorless material is being injected via a second stream.

"Expertise in tool design is fundamental to our core competences within Trelleborg Sealing Solutions," emphasizes Jarno. "Developing the two-color process required additional considerations during the design and construction of the tool to make sure the flow of the clear and the colored material portions must be kept strictly separated.