Vertical Efficiency for LSR Processes: How ENGEL insert halves cycle times and maximizes quality

Hydrogen mobility is considered a key technology for a climate-neutral future. Fuel cells, in particular, are a central element and place the highest demands on manufacturing technology. A critical process is the precise and reliable application of liquid silicone rubber (LSR) seals to sensitive gas diffusion layers (GDL). At K 2025 ENGEL demonstrated a solution that combines maximum precision with high cost-effectiveness and high output.

The fuel cell is a complex system in which every component must function flawlessly and precisely. Gas diffusion layers (GDL membranes) play a central role: They ensure the even distribution of hydrogen and oxygen across the catalyst layer, conduct electrons, and specifically remove the reaction water. To reliably fulfill these tasks, the GDL membranes must be processed with absolute leak-tightness—without damaging their fine, porous structure. Overmolding these sensitive components with a thin liquid silicone gasket places the highest demands on manufacturing and requires precisely coordinated interaction among the injection molding machine, the mold, and automation.

GDL membranes are extremely sensitive and must be handled with the utmost care. Götz Scheibe, Sales Manager at ACH Solution — a specialist in silicone injection molds and dosing technology — describes the requirements: “The challenge begins with the individual removal of the membrane films, which are delivered in stacks. Exactly one piece must be removed without damaging adjacent membranes.” After removal, precise positioning in the mold is required, which is typically achieved via a pre-centering station with a tolerance of ±0.1 mm.

In the mold, the sealing surface must be designed so that silicone does not get under the GDL diaphragm and the GDL diaphragm is not damaged by clamping pressure. The highest precision requirement, however, concerns the wall thickness of the gasket: “We’re talking here about a consistent wall thickness of ±0.01 mm for a component length of 550 mm,” explains Scheibe. This accuracy is crucial because up to 300 of these sealing elements are stacked on top of one another in a fuel cell. “Even the slightest tolerance deviations would add up—with the risk of mechanical stress or functional malfunctions in the fuel cell stack.”

To transfer this precision-critical process to series production while ensuring cost-effectiveness, ENGEL has developed a highly automated production solution based on a vertical injection molding machine from the insert machine range. The central element of the solution presented at K 2025 is an ENGEL insert 150 rotary US, with a clamping force of 1,500 kN and an integrated rotary table. The concept enables parallel processes: While the gasket is being molded in one mold station, the finished part is removed and the next GDL diaphragm is inserted in the second station simultaneously. With a cycle time of just 50 seconds, this allows part output to be nearly double.

Like all ENGEL tie-bar-less injection molding machines, the vertical insert machine range is characterized not only by excellent mold accessibility but also by a very uniform distribution of clamping force across the entire clamping surface. Franz Pressl, Head of Product Management for Tie-Bar-Less and Vertical Machines, explains: “At ENGEL’s vertical insert injection molding machines, platen parallelism is ensured by the proven FlexLink technology, which automatically compensates for frame expansion. Additionally, the robust mold mounting platen contributes to very uniform compression of the mold. This ensures extremely consistent wall thickness for parts that are both large and thin.”

The vertical design offers further decisive advantages for this application. Götz Scheibe explains: “The vertical design makes optimal use of gravity. This prevents lateral torques, and the mold closes exclusively in the direction of gravity. This protects the guides and contributes to long-term dimensional accuracy and process stability—a clear advantage over horizontal machines.” In addition, the machine concept of the ENGEL insert machine range is particularly compact: The control cabinet is vertically integrated into the machine, significantly reducing the footprint of the production cell—an important consideration when designing for limited production areas. The machine employed here is equipped with a hydraulic injection unit driven by the energy-saving ENGEL ecodrive drive system. At ENGEL, even the hydraulic injection units offer the high level of accuracy required for these applications as standard.

The insert machine range offers injection molding companies maximum flexibility: With a wide range of possible combinations of electric and hydraulic drives, each machine can be configured individually and tailored to the specific application.

Regarding the rotary table concept, Scheibe explains: “In principle, this application could also be implemented without a rotary table. However, given the required production volumes, we cannot afford any mold downtime. The combination of a vertical injection molding machine and a rotary table allows the injection time to be used in parallel for part handling — this nearly doubles productivity.”

An innovative two-cavity mold from ACH Solution ensures the precise shaping of the intricate seal geometry. Equipped with the ACH SERVOSHOT 2G, the servomotor-driven needle-valve nozzles enable highly precise, individually controllable filling of the cavities. “We achieve an adjustment accuracy of two thousandths of a millimeter,” emphasizes Götz Scheibe. This high degree of precision is crucial for preventing underfilling of the cavities and flash formation. The entire system is fully integrated into the CC300 control system of the ENGEL machine. Scheibe sees this as a clear advantage: “The integration into the ENGEL control system is particularly convenient. Adjustments can be made either during the running process or externally, without interrupting production.”

The integration also offers a graphical visualization that immediately shows how the individual nozzles are fine-tuned. Another key module for process stability is the cold runner, which is precisely balanced both thermally and rheologically. This makes it easier for the application technology engineer to quickly return to the process after extended downtime. Scheibe explains: “Our SERVOSHOT system enables precise optimization of the weld lines. This ensures that material convergence always occurs exactly at the intended location—a fundamental prerequisite for stable and repeatable processes.”

An ACH MAXIMIX 3G Pro system ensures the precise processing of the low-viscosity LSR material—in this case, ELASTOSIL® LR 3003/30 from WACKER. It is specifically designed for small shot weights, such as the 20.3 grams used here, and guarantees a precise mixing ratio as well as high process stability. This system is also fully integrated into ENGEL’s CC300 control system.

An ENGEL easix articulated robot, which is fully integrated into the control system, handles all operations involving the delicate GDL membranes and finished components. In the first step, it retrieves the membrane sheets from a feeding system and positions them precisely in the front mold station of the rotary table. After the turntable rotates 180 degrees, the injection molding process takes place in the rear station. At the same time, the robot removes the finished components from the front and inserts new membrane sheets. The tight synchronization between the injection molding process and the robot’s movements via the central CC300 control system ensures a stable and precisely coordinated sequence.

Removing the overmolded diaphragms from the hot mold presents a particular challenge. “As is well known, silicon adheres strongly, and tear resistance is critical at elevated temperatures,” explains Götz Scheibe. “A thin silicone skin can be very easily damaged when hot. This requires individually tailored demolding strategies.” Targeted demolding aids in the mold ensure that the delicate gasket reliably detaches from the cavity wall. After removal, the sprue bridges are removed in a separate work step.

To ensure consistently high component quality, ENGEL’s iQ weight control digital assistance system is used. It analyzes the injection pressure curve in real time and compensates for fluctuations in material viscosity within the same cycle. “The iQ weight control system detects viscosity differences in real time and automatically compensates for them,” says Götz Scheibe. “This significantly increases process stability, even though none of the holding pressure phases are required to counteract part shrinkage with LSR. This makes it even more important that the injection volume remains constant at all times.” The result of the constant injection volume is consistent part weight. Scheibe emphasizes: “The primary goal is shot weight consistency. It is a crucial quality standard, because the part weight reveals a great deal about the quality of the product.”

The system really comes into its own during color changes, which with silicone, are often associated with significant changes in viscosity. Scheibe explains: “Color changes are particularly critical with silicone, as different pigments can sometimes have a major impact on viscosity behavior. The iQ weight control assistance system compensates for these fluctuations, thereby ensuring consistent part quality.”

After removal, each component undergoes an integrated camera inspection. This checks the LSR gasket and ensures that the cavity has been completely filled and that the gasket has no defects or flash. “The flash is simultaneously trimmed off during this process,” adds Scheibe. “The combination of precise mold technology, intelligent process control, and integrated 100% inspection results in extremely stable and reliable production.

The choice of liquid silicone as a sealing material is no coincidence. The material really comes into its own, particularly in the field of future mobility. “Especially in electric vehicles with fast-charging capabilities, increasingly higher temperatures are being reached. Silicone is indispensable here due to its high temperature resistance,” summarizes Götz Scheibe. Silicone materials are also increasingly being used in cooling systems and batteries due to their heat-dissipating properties. These characteristics make LSR the ideal material for demanding sealing applications in electric mobility and fuel cell technology.

The production cell developed by ENGEL and its partners is desinged for near-series production and impressively demonstrates how maximum precision can be combined with short cycle times. The system is designed for high throughput—each fuel cell stack requires 50 to 300 cells, for which two GDL layers must be produced per cell. The entire concept is aimed at maximum production efficiency and the lowest possible energy consumption. Thanks to its compact design and the complete integration of all components—from the machine to automation and mold control to dosing technology—the cell can be easily integrated into existing production lines. ENGEL and ACH deliver a perfectly coordinated system solution, thereby underscoring their expertise in demanding multi-component processes.

The automated production of LSR seals on GDL diaphragms provides an example of how the challenges of hydrogen mobility can be adressed with modern injection molding technology. The combination of a high-precision vertical machine, innovative mold and cold runner technology, and seamlessly integrated automation enables a stable, economical, and high-quality series production process. The presented solution for overmolding thin membrane films with a precisely positioned LSR gasket in a confined work area is particularly efficient and can be easily integrated into existing production lines. Such solutions are key to helping fuel cell technology achieve a breakthrough and make the mobility of the future more sustainable.