40 Focus | Additive manufacturing space. Compared to conventional metal 3D printing using lasers, the equipment construction cost is low, and AM can be performed quickly using commercially available welding materials, making it more economical. Metal AMusing welding techniques has limitations in realising complex structures, because it is a limited process of building one layer at a time. That in turn is because subsequent layers are laminated after complete solidification, preventing the moltenmetal fromflowing down. This slows down the process, as a cooling time is required and the conditions that can be laminated are limited to specific examples. To solve this problem, computer analysis precisely controls the surface tension of the molten metal and the solidified volume according to convection/conduction. This can be used in all conditions, including horizontal, vertical, inclined and overhead positions. By continuously laminating the metal in the liquid phase before it fully solidifies, the manufacturing time is shortened. There are no boundaries between layers, and it forms a dense microstructure with excellent mechanical properties. In the case of ductility, the technology gives a 24.5% improvement compared to the existing Wire Arc AM process, based on Inconel 625. Plastic-metal interfaces Linking plastic andmetal components is also a challenge. However, a newmultimaterial digital light processing 3D printing (MM-DLP3DP) process can fabricate metal-plastic composite structures with arbitrarily complex shapes. This MM-DLP3D process starts with the preparation of the active precursor chemicals that are converted into the desired chemical after 3D printing. Palladium ions are added to light-cured resins to prepare the active precursors to enable electroless plating (ELP), a process where the catalytic reduction of metal ions in an aqueous solution forms a metal coating. Next, theMM-DL3DP system is used to fabricatemicrostructures containing nested regions of the resin or the active precursor. Thesematerials are then directly plated, and 3Dmetal patterns are added to themusing ELP. Various parts with complex topologies have been built to demonstrate the manufacturing capabilities of the technique. They had complex structures withmulti-material nesting layers, June/July 2023 | Uncrewed Systems Technology Solid-state batteries lend themselves to AM processes to form custom shapes. The technology is being used with lithiummetal cathodes and 3D-printing solid electrolytes for batteries with high energy density. The technology is now coming to market, allowing batteries to be printed close to where vehicles and systems are assembled rather than requiring gigafactories. AM is also being used for sodium batteries, building on the experience of using it on lithium-ion batteries. While they are lower in energy density than lithium-ion cells, sodium is more readily available and has fewer safety issues than lithiummetal batteries. These are set to be demonstrated by 2025 at a pilot plant in Germany. Constructing a sodium solid-state battery cell using AM increases its energy density and improves many of its safety aspects. The prototype method of producing sodium batteries is designed in such a way that a variety of active materials can be used, and changes for different products can be made quickly. The printing process is a key factor, and allows volumetric optimisation in addition to geometric adaptation. 3D printing also simplifies production. The process can print entire battery cells, from anode through electrolyte to cathode, including the casing. It is also flexible enough to print the materials for a typical lithium-ion battery cell chemistry, as well as future battery technologies, with capabilities to print a range of cathode and anode materials as well as solid-state electrolytes. This replaces the four-step wet process of coating, drying, calendaring and notching with a simple deposition and cure process in 3D printing. It can reduce the production cost for a 24 kWh automotive battery by more than £480/€550, remove environmentally damaging N-methyl pyrrolidone solvents from the cell production process, and generate up to 85% less waste. One fully industrialised process for printing batteries uses a proprietary multi-material, multi-layer approach in a parallel, dry process, instead of slow layer-on-layer wet printing or screen printing. These wet processes require a lot of energy to remove unwanted solvents, and are susceptible to poor printing quality and unreliable production. The first printed batteries have demonstrated successful cycling performance at C/5 and 1C current rates, and they are expected to achieve densities of 800- 1000 Wh/litres using a lithiummetal battery chemistry. Using patterned battery printing enables a more effective use of battery cell volume with new pathways for thermal regulation. It also allows fixtures and sensors to be added to the cells during assembly, as well as new patterned designs, especially when thin sub-cell battery structures are stacked with identical patterned openings for improved thermal management. 3D-printing batteries 3D-printing a lithium-ion battery allows for more complex shapes (Courtesy of Sakuu)
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