New energy extruded profiles (battery pack casings, water-cooled plates, motor casings, energy storage frames, etc.) have extremely high requirements for wall thickness uniformity, flatness, dimensional accuracy, surface quality, and molding stability. The following types of problems frequently occur in molds during the mold trial and mass production stages:
1. Profile surface defects
1. Surface pitting, pitting, and raised particles
1. Reasons: The working belt of the mold is not polished enough and aluminum sticks to the working belt; there are many impurities in the aluminum liquid; the hardness of the mold is insufficient and surface wear produces aluminum tumors; the extrusion temperature is too high and the aluminum sticks to the mold.
2. Impact: Many new energy profiles require subsequent welding/spraying, and pitting will cause poor spraying and weld defects.
2. Scratches, drawings, and strains
1. Reasons: The working belt has local edges and burrs; the hardness of the working belt is not enough, and the metal flow is scratched; the roughness of the mold cavity is poor; the diversion angle is unreasonable, and the friction of the aluminum material in the mold is large.
3. Bubbles, peeling, and delamination
1. Reasons: There is air in the mold diversion cavity; oil stains and oxide scale are brought into the surface of the blank; the metal flow rate in the mold cavity is uneven, and the surface layer is separated from the matrix; the design of the mold welding chamber is unreasonable and the welding pressure is insufficient.
Battery pack profiles are very sensitive to delamination and peeling, which will directly reduce the overall strength.
2. Dimensional and geometric tolerance issues (the most important issue for new energy sources)
1. Uneven wall thickness
1. Reasons: Unbalanced flow distribution of each split hole; unreasonable working belt length ratio; elastic deformation of the mold (the mold deflects due to extrusion force); mold core deviation.
2. Performance: The wall thickness of the profile is thicker on one side and thinner on the other side, and the battery pack shell is prone to unqualified assembly gaps.
2. Flatness is out of tolerance, warping, and wavy bending
1. Reasons: The metal flow rate is inconsistent in various parts of the section; the elastic deformation of the mold is inconsistent; the cooling is uneven; the traction and straightening parameters do not match.
2. Typical: The battery pack is a large plate with an arch in the middle or wavy edges, making it impossible to assemble.
3. twist (twist)
1. Reasons: The shunt hole is asymmetrical, the flow velocity difference between the left and right sides of the metal flow is large, and the length of the working belt is asymmetrical.
4. The opening size is unstable and the mouth is expanded/closed. For hollow cavity type materials (water-cooling cavity, battery frame), the mold core undergoes elastic displacement under pressure, resulting in fluctuations in the size of the inner cavity.