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Fabrication method and mechanical properties of new porous metal with lattice patternWednesday (07.10.2020) 13:00 - 13:20
To reduce the weight of automobile body and improve the collision safety, porous metals with millimeter sized pores, such as foamed aluminum or metallic hollow sphere structure, have been developed. However, these porous metals have some problems on homogeneity, controllability of their performance and production cost. To solve these problems, we propose a new porous metal fabricated by plastic forming process of thin sheet metal.
The fabrication method has three working processes. First, many holes are regularly cut out by shearing process. The holes are arranged at an interval on each line and position of the holes are shifted alternatively on the neighboring lines. Next, ridges are formed sequentially at each line by sheet forming. Finally, the formed sheets are stacked to be a porous structure. Since the first and second processes can be realized only by progressive die forming with punches and dies, dimensions of the formed sheet are high accurate and the production cost is low. By changing size of die, punch, sheet thickness, the pore size and cell wall thickness can be easily controlled to become the designed apparent density of the structure. The stacked sheets are strongly joined by spot welding. The tensile strength is large in the in-plane direction of the formed sheet to be able to apply for the bending impact energy absorber.
In the present research, we attempted to fabricate the new porous metal and tested its compressive and bending properties. The used sheet was thin steel one for deep drawing and the thickness is 0.16 mm. The ridge shape is hemisphere of 5mm. Thus, the structure which has the prescribed relative density of 7.5 to 8 % could be fabricated. By the compression and three supporting points bending tests, the proposed structure has good performances.