Fundamentals of Multi-position Progressive Die Design
The fundamentals of multi-station progressive die design encompass the fundamental theories, core principles, and key technologies of die design, and are essential for ensuring die performance. As complex stamping equipment integrating multiple processes, its design requires comprehensive consideration of part manufacturability, die structural rationality, manufacturing feasibility, and production economics. This is built on a solid theoretical foundation and extensive practical experience. Mastering the fundamentals of multi-station progressive die design provides guidance for subsequent detailed design and optimization, avoiding directional errors.
A part’s processability analysis is the starting point for multi-station progressive die design, primarily assessing the part’s stamping feasibility and economic viability. The part’s material properties (such as strength, plasticity, and thickness), structural shape (including complex forming, small holes, and sharp corners), dimensional accuracy (such as tolerance grade and form and position tolerances), and surface quality requirements must be analyzed to determine its suitability for production using a multi-station progressive die. For example, parts thicker than 6mm are not suitable for continuous stamping using a progressive die due to their high resistance to deformation. Parts with deep holes (depth > 5 times the diameter) require an assessment of punching feasibility, and if necessary, a step-by-step punching process should be employed. The processability analysis also includes recommendations for improving the part’s structure, such as increasing excessively small corner radius (R<0.5t) to R≥t and replacing sharp corners with rounded corners to reduce die edge wear and improve stamping stability.
The overall mold structure is the core of multi-station progressive die design. The mold type, number of stations, guiding method, and feeding method must be determined. The mold type is determined by the nature of the process, such as a punching progressive die, a forming progressive die, or a compound progressive die. The number of stations is determined by the number and complexity of the processes, generally ranging from 5 to 20, with each station completing one or two steps. Guides are guided by rolling pins and bushings to ensure high-precision guidance (fit clearance ≤ 0.01mm). The feeding method is selected based on production efficiency requirements, with mechanical feeding used for low-speed production and servo feeding used for high-speed production (>300 strokes/min). The overall structural design must ensure mold rigidity and strength. The upper and lower die bases are constructed of HT300 cast iron or ZG310-570 cast steel. The thickness is determined by the mold size, generally ranging from 100 to 300mm. Large molds require reinforcing ribs.
The design of the working parts is crucial for multi-position progressive die design, encompassing the structure and dimensions of cutting edge components such as the punch, die, and die-die. The punch’s structure is determined by the process type. Punches for blanking are either stepped or straight, while forming punches conform to the part’s shape. Dies can be either monolithic or pieced, with complex shapes utilizing pieced dies to reduce processing complexity. The material selection for the working parts must meet both wear resistance and strength requirements. Punching parts are made of Cr12MoV or high-speed steel W6Mo5Cr4V2, achieving a hardness of HRC 58-62 after quenching. Forming parts can be made of 45 steel, case-hardened (HRC 40-45), ensuring both wear resistance and toughness. The dimensional accuracy of the working parts must be two to three grades higher than that of the part itself. For example, if the part tolerance is ±0.05mm, the mold tolerance should be within ±0.01-±0.02mm.
The design of the positioning and feeding system is the basis for ensuring the accuracy of multi-station progressive dies. The positioning system includes side blades, guide pins, and stop pins, while the feeding system includes feed rollers, clamps, and servo motors. The side blades are used for rough positioning. Their length is equal to the feed step, and their width is determined by the material thickness (1.5-2 times the material thickness). The guide pins are used for fine positioning and cooperate with the pre-punched holes. The gap is 0.01-0.03mm, and the number of guide pins increases with the number of stations to ensure positioning accuracy. The accuracy of the feeding system must match the positioning system. The step accuracy of servo feeding can reach ±0.01mm, meeting the requirements of precision stamping. The coordination of feeding and positioning must be achieved through an electrical control system to ensure that stamping can be carried out after feeding is completed to avoid interference. For thin or easily deformed materials, auxiliary positioning devices (such as pressure plates and side pressure plates) are required to prevent the strip from shifting during feeding.
The design of a mold’s auxiliary systems, including discharge devices, ejectors, waste handling devices, and safety devices, is essential for proper mold operation. The discharge device utilizes a spring-loaded discharge plate with a discharge force of 10%-20% of the blanking force. The springs or rubber components must be evenly arranged to ensure smooth discharge. The ejector is used to eject the formed part from the die. The ejection force must be determined based on part size to ensure reliable ejection. The waste handling system includes a waste cutter, a material discharge hole, and a chute to ensure that waste is promptly discharged from the mold to prevent accumulation. Safety devices include safety interlocks and overload protection to prevent mold overload damage and personal injury. The design of the auxiliary systems must be coordinated with the main system. For example, the discharge plate’s stroke must match the punch’s stroke, and the ejector’s operation must be synchronized with the stamping cycle. By systematically designing auxiliary devices, mold reliability and safety can be improved, extending its service life.
The design fundamentals of multi-station progressive dies also include manufacturability and cost control. The mold structure must be easy to process, assemble, and maintain. For example, standardized parts (such as guide pins, guide bushings, and screws) should be used to reduce custom processing; consumable parts (such as punches and dies) should be removable for easy replacement. Cost control should be considered from the design stage. Optimizing the structure can reduce the use of expensive materials. For example, large dies can be constructed with modular components instead of monolithic ones, saving on Cr12MoV. Furthermore, a balance must be struck between mold manufacturing cost and mold life. High-precision molds, while costly, have a long lifespan and are suitable for large-scale production. Low-precision molds, on the other hand, have low manufacturing costs and are suitable for small-batch production. By comprehensively considering manufacturability and cost factors, an economical and practical multi-station progressive die can be designed.
