Blanking die positioning device
The blanking die positioning device is a key component to ensure the dimensional accuracy and shape consistency of the blanked parts. Its function is to accurately position the sheet material or process parts at a specific position of the die before each punching, ensuring that the punch and die can be blanked in the correct position. The accuracy of the positioning device directly affects the dimensional deviation and form and position tolerance of the blanked parts. During design, it is necessary to select the appropriate positioning method and structural form based on the shape, size, thickness of the sheet material and the characteristics of the blanking process. Common positioning devices include stop pins, guide plates, positioning plates, side blades, guide pins, etc. Different positioning devices are suitable for different production scenarios and usually need to be used in combination to improve positioning accuracy.
The simplest positioning device, a stop pin is primarily used to control the sheet metal feed distance (stepover) and ensure accurate positioning during each punching operation. Stop pins can be categorized by structure as fixed, movable, and starting stop pins. Fixed stop pins are mounted directly on the die or stripper plate and are suitable for applications with smaller stepover distances and lower precision requirements. Movable stop pins extend and retract using a spring or lever mechanism, retracting as the sheet metal is fed and then ejecting once in position, making them suitable for automatic feeding dies. Starting stop pins are used for initial positioning of the sheet metal, ensuring accurate feeding of the first sheet. The working diameter of a stop pin is typically 3-10 mm, and its height should be slightly greater than the sheet metal thickness (generally 1.2-1.5 times the thickness) to ensure reliable stoppage. In practice, stop pins are often used in conjunction with guide plates, with the stop pin controlling longitudinal positioning and the guide plate controlling lateral positioning, forming a complete positioning system.
Guide plates are used to guide the sheet metal in the correct direction during feeding, preventing it from drifting during feeding. They primarily control the lateral position of the sheet metal. Guide plates are available in fixed or movable versions. Fixed guide plates are directly attached to the die or lower die base and are suitable for general applications. Movable guide plates can be adjusted to adjust their spacing, making them suitable for positioning sheet metal of various widths. The spacing between the guide plates should be 0.1-0.3mm larger than the sheet metal width to ensure smooth feeding and effectively limit lateral deviation. The length of the guide plates is generally 2-3 times the feed distance to ensure consistent guidance of the sheet metal during feeding. For thin sheets (less than 0.5mm), the gap between the guide plate and the sheet metal should be appropriately reduced to prevent wrinkling. For thicker sheets, the gap can be increased to reduce feeding resistance. The working surface of the guide plate should be ground to a surface roughness of Ra 1.6μm or less to minimize friction with the sheet metal.
Locating plates and locating pins are used for precise positioning of process parts and are commonly used in progressive or compound dies for secondary positioning of previously processed workpieces. Locating plates achieve positioning by conforming to the contours of the process part, offering high precision and suitable for complex-shaped parts. Locating pins achieve positioning by inserting into locating holes in the part, making them suitable for parts with prefabricated holes. The locating surface of the locating plate should conform to the contours of the part, with a clearance of 0.02-0.05mm typically ensuring accurate positioning. The diameter of the locating pin should be 0.01-0.03mm smaller than the locating hole , and the pin head should be conical or spherical to facilitate insertion of the part. When designing the locating plate and locating pin, consideration should be given to ease of loading and unloading the part. The edges of the locating plate should be sloped or rounded, and the locating pin height should be moderate to ensure reliable positioning while not interfering with the placement and removal of the part.
Side blades and guide pins are commonly used high-precision positioning devices in progressive dies. Their combined use enables precise control of the step distance. A side blade is a special punch, rectangular or stepped in shape, that creates a notch of a specified width on the edge of the sheet metal. The notch interacts with a stop block to control the feed distance. The side blade’s length is equal to the feed distance, while its width is determined by the sheet metal thickness, typically 1.5-2 times the thickness. Guide pins are mounted on the punch mounting plate and, during the blanking process, are inserted into the notch created by the side blade or into the locating holes punched in the previous step. This allows for precise positioning of the sheet metal and compensates for feed errors. The diameter of the guide pin should be 0.01-0.02mm smaller than the locating hole. The head is conical, typically with a 60° angle, to facilitate smooth insertion into the locating hole. The side blade and guide pin achieve a positioning accuracy of ±0.01mm, making them suitable for the continuous production of precision blanked parts such as electronic connectors and watch parts.
The design of the positioning device needs to comprehensively consider factors such as production batch, punching part accuracy, feeding method, etc. For large-scale production automatic lines, automatic positioning devices such as pneumatic positioning and photoelectric positioning should be used to realize the automation of the positioning process; for small-scale production, manual positioning devices such as positioning blocks and manual stoppers can be used to reduce mold costs. The layout of the positioning device should ensure that the positioning datum is consistent with the design datum to avoid positioning errors. At the same time, it should be easy to operate and maintain to ensure reliable positioning. By rationally designing the positioning device, the dimensional accuracy and consistency of the blanked parts can be significantly improved, the scrap rate can be reduced, and production efficiency can be improved.
