With the rapid development of the new energy vehicle industry, battery module end plates, as the core structural components of power battery packs, have extremely high requirements for structural strength and temperature resistance. The material selection of corresponding injection molds directly determines the service life, forming accuracy and long-term production stability of the molds. This article systematically determines material standards for mold bases, cavities and cores, inserts, vulnerable parts, and heat treatment processes.
1. Mold Base Material Selection RequirementsThe mold base bears the full force of repeated mold opening and closing, injection pressure, and clamping force, requiring excellent rigidity and fatigue resistance. Standard 45# refined steel plates are preferred for conventional mass production molds, with surface quenching treatment to improve surface hardness and wear resistance. For large molds with high clamping force, P20 steel mold bases can be selected to enhance overall structural stability and reduce the risk of deformation under long-term high pressure. All mold bases must undergo stress relief treatment after processing to eliminate internal stress and prevent dimensional deviation during later use.
2. Cavity and Core Material Selection StandardsBattery module end plates are mostly made of high-temperature resistant, flame-retardant modified engineering plastics, often containing glass fiber fillers, which impose high requirements on mold surface hardness and wear resistance. For conventional PP/ABS-based modified materials, 718H pre-hardened steel is used for cavities and cores, with hardness controlled at 28–32 HRC to balance processing performance and wear resistance. For glass fiber reinforced and high-temperature resistant materials, NAK80 or S136 high-hardness mirror steel is recommended, which has excellent corrosion resistance and wear resistance, effectively avoiding surface scratches and material buildup in long-term production. The mold surface must be polished to a high standard to ensure the smoothness and flatness of the end plate surface, meeting the assembly and safety requirements of battery modules.
3. Insert and Sliding Block Material Selection
The end plate structure often includes special-shaped holes, mounting bosses, and undercut positions, requiring a large number of inserts and sliding blocks. These components are in direct contact with high-flow and high-temperature plastic melts, so they must have high hardness, wear resistance, and impact toughness. SKD61 hot work die steel is the preferred material for inserts and sliding blocks, with surface nitriding treatment to improve surface hardness and wear resistance, effectively extending service life. For parts prone to wear, such as side core-pulling sliding blocks, DC53 cold work die steel is recommended to enhance anti-cracking performance and reduce the risk of fracture under repeated impact loads.
4. Vulnerable Parts and Fastener Material SelectionEjector pins, return pins, guide pins, guide sleeves, and other vulnerable parts are key components affecting mold stability. Ejector pins and return pins should use SKD61 steel with nitriding treatment to improve surface hardness and wear resistance, preventing bending and breaking under long-term ejection loads. Guide pins and guide sleeves adopt SUJ2 bearing steel with high hardness and wear resistance, ensuring accurate mold opening and closing alignment. Fasteners such as screws and bolts use high-strength 12.9-grade alloy steel to avoid loosening and failure under high vibration and high temperature conditions.
5. Heat Treatment Process RequirementsDifferent mold materials require targeted heat treatment processes to give full play to their performance advantages. Pre-hardened steels such as 718H and P20 do not require secondary quenching, but stress relief annealing must be performed after rough processing to eliminate processing stress. High-hardness steels such as S136 and NAK80 need vacuum quenching and tempering treatment to ensure uniform hardness, good dimensional stability, and no deformation. All nitriding-treated parts need to control the nitriding layer thickness at 0.1–0.3mm to improve surface hardness without affecting the internal toughness of the material.
6. Anti-Corrosion and Surface Treatment Standards
New energy vehicle battery parts often use halogen-free flame-retardant modified plastics, which may produce corrosive gases during injection molding. Therefore, mold cavities and cores should be passivated or plated with hard chromium to improve corrosion resistance and avoid surface pitting and corrosion. For parts that are difficult to polish, such as deep holes and narrow grooves, electroless nickel plating treatment is recommended to ensure uniform surface coverage and enhance anti-corrosion performance.
7. Mold Material Matching and Cost ControlDifferent functional parts of the mold can adopt graded material selection to balance performance and cost. The main mold base can use standard 45# steel, while the core forming parts use high-grade steel to ensure key forming accuracy. For molds with small production batches, 718H pre-hardened steel can be used to reduce heat treatment costs and shorten the production cycle. For mass production molds, high-hardness wear-resistant steel should be selected to extend service life and reduce long-term maintenance costs.
