Mold processing process
The mold manufacturing process refers to the series of steps from mold design to finished mold delivery, encompassing rough machining, semi-finishing, finishing, heat treatment, assembly, and mold trialing. Each step is subject to strict technical requirements and quality control standards. A well-defined process ensures the machining accuracy, surface quality, and service life of mold components, while also improving production efficiency and reducing manufacturing costs. The mold manufacturing process must be tailored to the mold type (e.g., stamping, plastic, or die-casting), material properties, and precision requirements, ensuring high specificity and flexibility.
The preliminary preparation phase of mold processing marks the starting point of the entire process, primarily encompassing mold design, process plan development, and material procurement. Mold design is based on product drawings, using CAD software to create 2D and 3D models. The mold structure, component dimensions, and precision requirements are determined, while strength verification and lifespan estimation are also performed. The process plan development requires selecting appropriate processing methods and equipment, determining the processing route and process parameters for each component. For example, for a Cr12MoV steel die, the typical process route is: forging → annealing → rough machining → quenching and tempering → semi-finishing → quenching → finishing → assembly. Material procurement requires selecting mold steel based on design requirements (e.g., Cr12 is commonly used for stamping dies, and P20 is commonly used for plastic molds). Raw materials are then inspected (chemical composition analysis and mechanical property testing) to ensure that the material quality meets requirements.
Blank preparation and pretreatment are fundamental to ensuring the quality of mold parts. These primarily include forging, annealing, and aging. Forging improves the material’s internal structure, eliminates casting defects, and enhances its mechanical properties. For example, Cr12 steel requires repeated forging to refine its grain size and improve its toughness. Annealing reduces material hardness and improves cutting performance. For high-carbon steel and alloy tool steel, spheroidizing annealing (heating to 750-800°C, holding for 3-4 hours, and slow cooling) is typically used to reduce the hardness to 200-250 HB, facilitating subsequent cutting. Large mold parts also require aging to eliminate internal stresses generated by forging and rough machining, preventing deformation during processing and use. Aging treatment is performed at a temperature of 150-200°C for 4-6 hours.
The primary tasks of the roughing and semi-finishing stages are to remove the majority of the stock, initially establishing the part’s shape and dimensions, and laying the foundation for finishing. Roughing utilizes efficient machining methods such as milling, turning, and grinding to remove 70%-80% of the stock, leaving a 2-5mm stock allowance after machining. For example, rough machining of mold cavities utilizes CNC milling with high-speed steel or carbide tools at a cutting speed of 50-100 m/min and a feed rate of 0.2-0.5 mm/r to ensure efficient machining. Semi-finishing aims to improve the part’s form and dimensional accuracy, utilizing CNC milling and grinding . A finishing allowance of 0.1-0.5mm is left after machining, with dimensional tolerances controlled within ±0.05-±0.1mm and a surface roughness Ra of 3.2-6.3μm. For parts with complex shapes, scribing and inspection are performed during the semi-finishing stage to ensure accurate benchmarks for subsequent machining.
Heat treatment and finishing are critical steps in ensuring the ultimate performance and precision of mold components. Heat treatment processes are selected based on the material and component requirements. For example, the punch and die of a stamping die require quenching and tempering (Cr12 steel heated to 950-1000°C, oil quenched, and tempered twice at 200-250°C to achieve a hardness of 58-62 HRC) to improve wear resistance and service life. The mold cavity of a plastic mold requires nitriding (500-550°C, hold for 3-5 hours) to form a 0.1-0.3mm hardened layer with a hardness of HV800-1000, enhancing surface wear resistance. Finishing utilizes high-precision machining methods such as EDM, grinding, and honing to ensure that component dimensional accuracy (±0.001-±0.01mm), geometric accuracy (flatness ≤0.005mm/100mm), and surface roughness (Ra0.1-0.8μm) meet requirements. For example, the finishing of the die cutting edge adopts coordinate grinding, with an accuracy of ±0.002mm and a surface roughness of Ra0.4μm.
Mold assembly, trial runs, and commissioning are the final stages of the production process and directly impact the mold’s performance. Assembly must be performed according to the assembly drawings, utilizing either group assembly or fitting methods to ensure the relative positioning accuracy of each component (e.g., uniformity of the punch and die gap ≤ 0.01mm) and its movement flexibility. Trials are conducted on dedicated equipment, simulating actual production conditions to verify the mold’s forming quality, dimensional accuracy, and production efficiency. For example, during trial runs of stamping dies, parts must be inspected for burrs, deformation, and dimensional deviation. During trial runs of plastic molds, the surface quality, dimensional accuracy, and demolding performance of the plastic parts must be checked. Based on the trial results, commissioning is performed, such as adjusting the punch and die gap, modifying the cavity dimensions, or replacing consumable parts, until the mold meets production requirements. After commissioning, the mold undergoes surface treatment (e.g., painting and rustproofing), and an instruction manual is prepared before delivery to the user.
