Gentle grip

"We recommend the special STGG grippers for this, as they can handle the sensitive films with high dynamics," explains Dr. Maik Fiedler, Head of the Vacuum Automation and Vacuum Handling business units at Schmalz. The STGG alternately grips the anode, separator, cathode and separator again in order to place them on top of each other. Speed is just as important here as precise positioning. The gripper must not leave any marks or contaminate the sensitive coating. "Our solution is PEEK," says Fiedler.

Schmalz uses the highly chemically resistant polyetheretherketone to produce a suction plate with many small holes that grips the entire surface. The flat surface minimizes surface pressure. The active blow-off function of the STGG accelerates the pick & place process, while the high volume flow prevents particle residues on the electrodes. Pneumatic vacuum generation without moving parts makes the special gripper suitable for clean and dry rooms.

The STGG special gripper is also suitable for separating and depositing thin separator films. Separators usually consist of very fine-pored flexible plastic or nonwovens. They spatially separate the anode and cathode from each other and prevent a short circuit. At the same time, they are permeable to the positive lithium ions that flow from the anode to the cathode during discharging and return when charging. "The STGG works with a high volume flow and therefore also grips porous materials securely," explains Dr. Fiedler. The ESD-compliant surface also reliably dissipates electrostatic charge and thus protects against unwanted adhesion.

Cell by cell

Once the cell stack is ready, the protruding conductor flags are shortened and the stack is packed in a pouch foil. Sealed all around, the pouch cell is ready for the electrolyte injection. "The pouch cells are sensitive and must not be deformed by the gripper under any circumstances. They can also vary in shape depending on the application," explains Fiedler. The SLG lightweight gripper is suitable for any geometry. Schmalz manufactures it additively after the customer has configured it online.

Structured suction cups from the SFF or SFB1 series are used to prevent the aluminum composite film of the pouch cell from being drawn in during gripping. Both variants combine support surfaces in the form of honeycombs on the suction surface with a soft and particularly flat sealing lip. This allows them to grip gently yet with a high suction force without deforming the surface of the pouch cell.

Working with vacuum

Vacuum is just as important. How and where it is generated is the key to highly dynamic and absolutely safe handling. "Our decentralized vacuum generators from the SCPM series meet all of these requirements. They are compact and powerful at the same time," says Fiedler. They are so small that they can be mounted close to the suction pad and thus minimize power losses. The valve of the compact ejector closes when no current is applied. This allows the gripper to hold the battery cell securely, even if the power fails. "Another advantage is that users can integrate special functions into the system, such as redundant vacuum generation or workpiece detection," adds Dr. Fiedler.

The appropriate handling system places the individual cells in a module, where they are connected in series or parallel. Several modules result in a battery pack that combines fewer or more pouch cells, depending on the manufacturer and vehicle category.

Round instead of flat

The advantage of pouch cells is that they are flat and can therefore dissipate heat well. They are versatile and make optimum use of the available volume in a battery module. Their disadvantage is that the casing is sensitive and does not protect the anodes, cathodes and separators from mechanical influences. There is also a risk that they will swell due to ageing processes, for example. Cylindrical hard-case cells are therefore used in some electric cars. "For the handling of round cells in module assembly, we have to offer users grippers that they can freely configure. Depending on how large the individual cells are in diameter, in which arrangement and how many are to be gripped," explains Fiedler.

"Thanks to 3D printing, this is easily possible from a batch size of one." If the user chooses suction cups made from the low-impression special material HT1, they can grip the cells directly at the pole - the material also acts as an insulator. This means that even charged cells can be positioned safely. A high volume flow is also important here for the fast and clean pick & place process.

"This is where integrated vacuum generators come into their own. The ejectors have a safety valve that maintains the vacuum even without power, thus ensuring safe handling," adds Fiedler. If the round cells need to be gripped lengthwise, Schmalz recommends the SGM magnetic gripper in the high-performance version. Here, a permanent magnet secures the handling. "They are compact, lightweight and still develop high holding forces," says Fiedler, listing the advantages. These are effective as long as the battery casing is ferromagnetic.

Finale - fully automatic or manual

Now it's almost done: foils have become cells. The cells are combined into modules, which are now connected in battery packs and completed with cooling plates, cabling and electronics. "Flexibility is extremely important here. The storage geometries can differ, as can the surface structures," explains Fiedler. Even if the modules are heavy, they must not be damaged by the gripper - vacuum manages this. The FQE area gripper is modular and ideal for fully automated pick & place applications. The FMP area gripper is just as universal. Its sealing foam also adapts to structured surfaces. With their energy-efficient, integrated vacuum generation, both ensure low operating costs.

Manual lifting aids such as the JumboFlex vacuum lifter take the strain off the fitters during the work steps that are not automated. This could be the cooling modules or the cover plates, which have to be placed on the battery housings manually at the end. The Safety+ operating unit offers extra safety: the two-handed concept for detaching protects particularly sensitive workpieces when placing them down. The lowering speed can also be reduced.

The battery pack is now ready for the leak test - the housing and cooling system must not have any leaks. The battery management system receives the latest software, suitable for the type of car, and the first charging/discharging process in the pack takes place under strict supervision. If the cabling and electronics are in order and the battery management system and all subcomponents are working properly, the job is done. After labeling with warnings and ID tags, the batteries are ready for transport. "It's a long and laborious process from powder to finished energy storage system. We know how to handle each individual process step safely and develop tailor-made solutions for our customers," says Dr. Maik Fiedler.