Climate change is pushing the auto industry to transition to thinner, stronger, and more environmentally friendly steel and inventor Paul Ericson thinks arrays of very shallow overlapping bistable domes, or OBDs, might help.
Ericson was granted two patents for using rows of flex actuated OBDs to create contact shape digitizing sensors and pumps that pump when bent. He explains and illustrates the concept at Bistabledome.com.
In a video, Ericson demonstrates how rows and closely packed arrays of OBDs turn tough flat .006” and .03” 302 stainless steel into stiffer adjustable structures that are only a few times thicker in profile than the original sheet material.
He suggests they might help address the springback problems common in forming strong thin metals, as well as reduce tooling and prototyping costs.
The inventor also demonstrates that a row of OBDs formed in .03” thick steel is significantly more resistant to deformation and collapse than the original flat material the same size while being only twice as thick in profile.
Ericson stamps OBDs from both sides to give them two stable states. He explains that OBDs can be equally bistable or have a bias for one side. The inventor demonstrates in the video how biased OBDs can give metal a predisposition for particular curvatures.
Ericson explains OBD arrays can be stamped with low pressure if they are formed incrementally starting at an edge. “For the sensor and the pump the rows of OBDs were stamped in bands of metal about as wide as the dome diameter. The edge would buckle slightly near the overlap, functionally shortening the edge relative to the metal through the middle of the dome row, which wants to occupy a larger radius,” says Ericson. He explains that with arrays of closely packed OBDs the material deformation is incorporated in neighboring OBDs, which can also switch sides to compensate.
According to the inventor, adjacent equally bistable overlapping domes alternate orientation when flattened, one side or the other. When bent they are forced to the outside of the curvature in numbers proportional to curvature, stabilizing the new shape. “The same generic OBD array structure can stabilize in multiple curvatures of different radii along different axes,” says Ericson.
“Managing OBD characteristics such as bistability bias, dome shape and diameter relative to material thickness, degree of overlap, etc., can be used to create desired curvature in flat material. If all OBDs have a strong bias for one side they want to curl into a tube but more complex curvature is possible. Bistability can allow the part to be formed and stored flat until needed.”
The inventor suggests a single machine that can form OBDs with different characteristics, like an impact printer for domes instead of letters, could ‘print’ a wide range of shape. “That might help reduce prototyping and tooling costs,” says Ericson. “And because of the low pressure required, printing tools for forming thin metal OBDs could be made with common 3D printing materials. Same with rollers that might be used for large scale production.”
“OBD structures may be combined with other metal forming technologies,” says Ericson. “They may be ideal for the large radius curvature common in auto, boat, train, and aerospace related engineering. They may also be useful for storage and containment structures.”
Ericson believes two or more OBD array layers welded or laminated together could reduce the need for framing and bracing. “OBD arrays of different shape, size, and bistability could be overlapped in layers to produce more complicated curvature,” says Ericson. He suggests flexibility and deformation resistance of OBD structures could be controlled with coatings or glues that manage the ability of domes to switch sides.
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