Typical structure of bending die
The typical structure of a bending die is designed based on the part’s shape, precision requirements, and production batch size. Different bending die structures exhibit significant differences in forming efficiency, precision control, and ease of operation. Common bending die structures include single-step bending dies, compound bending dies, progressive bending dies, and universal bending dies. Each structure has its own application scenarios, and choosing the right structure can effectively improve production efficiency and product quality.
A single-step bending die is the most basic bending die structure, completing one bending step in a single stroke. It is suitable for simple bending parts (such as V-, U-, and L-shaped parts) and small- to medium-volume production. A V-shaped bending die consists of a punch, a die, a positioning plate, and a lower die base. The die is open, facilitating easy access to the workpiece, while the positioning plate ensures accurate placement of the blank. For example, an L-shaped bracket bending die has a 90° punch angle and a die opening width of 10t (where t is the material thickness). Positioning pins control the blank’s position, allowing a 90° bend to be completed in a single stroke. Single-step bending dies offer a simple structure, short manufacturing cycles, and low costs. However, complex parts require multiple die sets for step-by-step forming, resulting in low production efficiency.
U-shaped bending dies are used to form U-shaped or groove-shaped parts. Their structure consists of a punch, a die, a pressure plate, and a push-up device. The side walls of the die must be designed with a certain slope (0.5°-2°) to reduce springback. A push-up device (spring or rubber) can be installed at the bottom to support the workpiece during the bending process and prevent the bottom from sinking. For example, a U-shaped groove bending die has a 1° slope on the side walls of the die and a spring push-up device at the bottom. The push-up force is 10% of the bending force, ensuring a flat bottom after bending and a vertical error of ≤0.1mm/100mm on both sides. U-shaped bending dies require strict control of the gap between the punch and the die, typically 1-1.1 times the material thickness. The uniformity of this gap directly affects the accuracy of the workpiece.
Compound bending dies can complete multiple bending steps in a single stroke, even punching and bending simultaneously. They are suitable for medium-complexity bent parts and large-scale production. Their structural characteristics include an inverted design, with the punch at the bottom and the die at the top, and a punching mechanism that ejects the workpiece. For example, a compound die for U-shaped parts with holes can simultaneously punch and bend. Workpiece positioning is achieved using locating pins and a retaining plate, while the pressure plate also serves as the punching die. Finished products can be obtained in a single stroke, increasing production efficiency by 3-5 times compared to single-step dies. Compound bending dies can reduce workpiece positioning errors and improve dimensional accuracy, but their complex structure, manufacturing difficulty, and high cost make them suitable for large-volume, high-precision parts.
Progressive bending dies integrate multiple bending processes into a single die, completing the bending process step by step through continuous feeding. They are suitable for the large-scale production of small, complex bent parts (such as electronic connectors and small brackets). Progressive dies typically include feeding, positioning, bending, and cutting stations, each coordinated to achieve automated production. For example, a progressive bending die for Z-shaped parts uses a 45° pre-bend in the first station, a 90° bend in the second, correction and shaping in the third station, and cutting in the fourth station. Production rates can reach 300 pieces per minute. Progressive bending dies require high-precision guides (such as ball guides and bushings) and automatic feeding mechanisms to ensure positional accuracy (≤±0.01mm) at each station. While initial investment is high, long-term production efficiency is excellent.
Universal bending dies are suitable for high-variety, low-volume production. By replacing the punch, die, and positioning elements, they can form bent parts of varying shapes and sizes, reducing mold costs. The die itself features a modular design with adjustable width and angle. The punch is designed according to a standard series and can be quickly replaced with bolts. For example, a universal V-shaped bending die features a shim-adjustable die opening width (ranging from 20-100mm). The punch angles are available in various configurations, including 90°, 60°, and 120°. The positioning plate can be adjusted with a sliding mechanism to accommodate various V-shaped bending requirements. Universal bending dies offer high flexibility, but their forming accuracy is lower than that of specialized dies. They are therefore suitable for applications with rapid product updates.
The structural design of bending dies also needs to consider the demolding method for the workpiece. For parts with springback, a push-out device or unloading device is required to ensure smooth demolding. For asymmetrical bent parts, an anti-roll mechanism (such as a balance block) is required to prevent the workpiece from shifting during bending. With the development of automation technology, bending dies are gradually being integrated with robots, conveyor belts, and other devices to achieve fully automated loading and unloading, further improving production efficiency and safety.
