Measures to reduce springback of bent parts
Springback in bent parts can lead to reduced dimensional accuracy, increased assembly difficulty, and even product rejection. Therefore, targeted measures are needed to minimize springback. These measures should be integrated throughout the bending process design, mold construction, material handling, and production process. By optimizing process parameters, improving mold structure, and adjusting material properties, the elastic recovery ratio can be reduced and the dimensional stability of the bent part improved. Different springback reduction measures are required for different bent parts (e.g., simple V-shaped parts, complex U-shaped parts, and high-strength steel parts) to ensure effectiveness and cost-effectiveness.
Optimizing bending process parameters is a fundamental measure for reducing springback. This primarily involves selecting the relative bend radius, bending angle, and bending speed. The smaller the relative bend radius (r/t), the higher the proportion of plastic deformation and the lower the springback. During design, r/t should be minimized while avoiding cracking. For example, controlling r/t for mild steel within the range of 1-5 reduces springback by over 60% compared to an r/t of 10. The larger the bend angle, the greater the cumulative springback. For polygonal parts, step-by-step bending, with each step yielding a smaller angle (e.g., 30°-60°), can reduce springback by 40% compared to a single bend with a larger angle (e.g., 120°-180°). Bending speed also affects springback. Slow bending speeds (10-30 mm/s) are more conducive to full plastic deformation than high bending speeds (50-100 mm/s), reducing springback by 10%-20%. This is particularly effective for highly viscous aluminum alloys. For example, the original springback of a brass U-shaped part (r/t=8) is 4°. After reducing r/t to 4, the springback is reduced to 1.5°. At the same time, when the bending speed is reduced from 60mm/s to 20mm/s, the springback is further reduced to 1.2°.
Improving the die structure is a key measure to reduce springback. In addition to the commonly used angle compensation and correction structures, the following special structures can also be used: First, the elastic die, which is supported by a spring or rubber. When bending, the die produces a certain elastic deformation, exerting continuous pressure on the workpiece to reduce unloading springback. It is suitable for bending thin materials (t<1mm), and the springback can be reduced by 30%-50%; second, the stepped punch, which is designed to be stepped. When bending, it first contacts a part of the workpiece and gradually completes the bending, making the deformation more uniform. It is suitable for U-shaped parts and can control the springback difference of the two side walls within 0.5°; third, the controllable gap die, which reduces the springback by 20% compared with the fixed gap die by adjusting the gap between the punch and the die (usually 0.9t-1.0t). The smaller the gap, the better the correction effect, but it is necessary to avoid scratching the workpiece surface. For example, after a stainless steel (304) V-shaped part used an elastic die (spring stiffness 50N/mm), the springback was reduced from 5° to 2.5°, with significant results.
Auxiliary processes can effectively reduce springback. Stretch bending and warm bending are the most commonly used auxiliary processes. Stretch bending applies axial tension (typically 20%-40% of the material’s yield strength) to the workpiece during the bending process, placing the material in a tensile stress state. This reduces elastic recovery after bending and is suitable for slender bent parts (such as door and window profiles and automobile bumpers), keeping springback to less than 1°. Warm bending involves heating the material to a specific temperature (150-300°C for aluminum alloys and 500-800°C for high-strength steel) before bending. This reduces the material’s yield strength, increases its plasticity, and significantly reduces springback. For example, a 6061 aluminum alloy part exhibited 8° of springback when bent at room temperature, but only 2° after heating to 250°C. Furthermore, low-temperature tempering (120-200°C for 1-2 hours) after bending can eliminate some internal stresses and reduce springback, particularly for high-strength steel. Tempering can further reduce springback by 10%-15%.
Adjusting material properties is a fundamental measure to reduce springback. This is primarily achieved through heat treatment, which reduces the yield strength or improves plasticity. For high-strength steel (such as HSLA steel), annealing (heating to 600-700°C and slow cooling) before bending can reduce yield strength by 20%-30%, correspondingly reducing springback. For cold-rolled steel plate, reducing rolling precision can preserve a certain plasticity reserve, reducing springback by over 25% compared to fully hardened plate. For example, a certain cold-rolled plate (DC04) exhibits a 4° springback when bent in the fully hardened state. After annealing (650°C for 1 hour), the yield strength drops from 300 MPa to 220 MPa, reducing springback to 2.5°. However, adjusting material properties requires balancing springback with component strength. For load-bearing components, the strength of the treated material must meet service requirements to avoid excessive softening that could affect product performance.
Automated control and online compensation technologies are advanced measures for reducing springback in modern production. Through real-time monitoring and adjustment, springback can be dynamically compensated. On automated bending production lines, laser goniometers or coordinate measuring machines are installed to measure the angle of the bent part in real time. This data is fed back to the PLC control system, which automatically adjusts the punch stroke, pressing force, or die compensation to achieve closed-loop control. For example, an automotive parts production line uses online compensation technology. When a bent part angle is detected to be 0.5° out of tolerance, the system automatically increases the punch stroke by 0.2mm, restoring the angle of subsequent parts to normal, reducing the scrap rate from 3% to 0.5%. Furthermore, adaptive mold technology, which installs piezoelectric ceramics or servo motors within the mold to adjust the mold shape based on real-time springback data, can compensate for springback of 0.5°-2°. This technology is suitable for high-variety, small-batch production and significantly improves flexible manufacturing capabilities.
Reducing springback in bent parts requires appropriate measures tailored to the part’s characteristics and production conditions. For simple parts, process parameter optimization and die structure improvements are prioritized. Complex or high-strength parts require a combination of auxiliary processes and material handling. Automated control technology should be employed for mass production. In practice, a combination of measures is often necessary. For example, a high-strength steel U-shaped part achieved a springback reduction from 7° to 1° by employing a combination of “r/t optimization (from 6 to 3) + a stretch-bending process (with a tensile force of 200kN) + an elastic die.” With technological advancements, springback reduction measures are becoming more precise and intelligent. By simulating the entire bending process through digital twin technology, springback can be predicted and optimized in advance, further improving the dimensional accuracy and production efficiency of bent parts.
