Investigation on Cold Drawing Process of Unequal-Wall-Thickness Battery Shell Based on 3003 Aluminum Alloy Extruded Blanks

The aluminum alloy shell fabricated by ‘bending + high-frequency welding’ is the core component of the Chinese new energy vehicle battery pack. Still, this process cannot produce the next generation of shell products with unequal wall-thickness. In this study, we take the unequal-wall-thickness square 3003 aluminum alloy battery shell with a wall thickness of less than 0.5 mm and a tolerance range of ±30 µm as the research object. According to the cold work, hardening characteristics of 3xxx series aluminum alloys, hot extruded hollow blanks were prepared, and a new cold drawing process was attempted to be developed on this basis. Based on the analysis of the stress-strain field during cold drawing of defective workpieces, the size of the die inlet’s R angle and the blank’s size were optimized to solve the problems of local fracture and tearing of the blank. The results show that the maximum stress during cold drawing occurs at the fillet where the sizing zone intersects with the wall-thinning zone. This location is subjected to tensile stress, normal pressure from the inner and outer dies, and tangential friction force, causing a material accumulation phenomenon; the material flow velocity along the cold drawing direction is inconsistent, which will cause U-shaped patterns on the surface of finished products; the strain value along the cold drawing direction first increases and then decreases with the rise of R angle, reaching the maximum when the R angle size is 1.5 mm. After optimization, the maximum equivalent stress decreased from 205 MPa to 190 MPa, and the average strain along the cold drawing direction increased from 0.15–0.22 to over 0.3. This study successfully prepared precisely ultra-thin lithium iron phosphate battery shells by optimizing cold drawing process parameters and die structure.