When bending U-shaped aluminum square tubes, surface wrinkles and cracks mainly arise from insufficient material plasticity, excessively small bending radius, surface defects, mismatched process parameters, and mold design flaws. To effectively prevent these problems, a comprehensive approach is needed, encompassing material pretreatment, process optimization, mold improvement, and post-processing, to ensure uniform material deformation and reduce stress concentration during bending.
Material pretreatment is fundamental to preventing wrinkles and cracks. Before bending, aluminum square tubes require thorough softening treatment, using annealing to reduce material hardness and improve plasticity. Annealing temperature and time must be appropriately set according to the aluminum grade (e.g., A3003, A1100, etc.) to avoid excessively high temperatures leading to grain coarsening or insufficient softening due to low temperatures. Simultaneously, the surface of the aluminum square tube must be cleaned to remove oxide scale, oil stains, scratches, and other defects to prevent stress concentration at defective areas during bending, which can trigger cracks. For products with high surface quality requirements, sandblasting or polishing can be used to further improve the surface condition.
The appropriate selection of the bending radius is crucial for preventing wrinkles and cracks. A bending radius that is too small will cause excessive stretching on the outside and excessive compression on the inside of the material, resulting in cracks or wrinkles. Therefore, the minimum bending radius must be determined based on the wall thickness, material, and bending angle of the aluminum square tube. It is generally recommended that the bending radius be no less than 1.5 times the tube diameter. For complex bending parts, a step-by-step bending or multiple bending process can be used to gradually release stress and avoid excessive deformation in a single bending. Furthermore, the bending direction must be consistent with the rolling direction of the aluminum square tube to reduce the impact of anisotropy on bending quality.
Precise control of process parameters is crucial to preventing wrinkles and cracks. Excessive bending speed will lead to uneven material deformation and localized stress concentration; excessive bending force may cause material fracture. Therefore, the bending speed and force must be set reasonably according to the material and dimensions of the aluminum square tube. For hydraulic bending machines, the cylinder pressure and holding time can be adjusted to ensure uniform material deformation during bending. Simultaneously, the bending temperature must be controlled to avoid increased material brittleness due to bending at low temperatures. For bending parts requiring high precision, a heated bending process can also be used to reduce the material's yield strength and bending resistance through localized heating.
Die design and improvement directly impact the prevention of wrinkling and cracking. The die working zone must be kept smooth to avoid excessive surface roughness that could scratch the material. For U-shaped aluminum square tubes, the die cavity must perfectly fit the tube cross-section to prevent excessive gaps between the tube and the die during bending, which could cause wrinkles. Furthermore, the die should have appropriate drainage channels and vents to ensure smooth metal flow during bending and prevent surface defects caused by air stagnation. For complex bending parts, multi-station dies can be used, allowing for gradual forming in multiple passes to reduce deformation per pass.
Lubrication is an important auxiliary means of preventing wrinkling and cracking. During bending, friction between the die and the material can cause localized temperature increases, increasing the risk of material breakage. Therefore, a lubricant, such as graphite emulsion or specialized bending oil, should be applied to the die working zone or the material surface to reduce the coefficient of friction and minimize heat generation. The lubricant should be applied evenly, avoiding localized accumulation or gaps, to ensure continuous and stable lubrication during bending.
Post-processing plays a crucial role in eliminating bending stress and improving surface quality. After bending, the aluminum square tube needs to undergo stress-relief annealing. Low-temperature heating eliminates residual stress generated during bending, preventing deformation or cracking due to stress release during subsequent use. For products with high surface finish requirements, sandblasting or wire drawing processes can be used to further improve surface roughness and conceal minor wrinkles or cracks.
Quality control and inspection are the final guarantee against wrinkles and cracks. After bending, the aluminum square tube must undergo comprehensive inspection, including visual inspection, dimensional measurement, and performance testing. Visual inspection mainly checks for cracks, wrinkles, or scratches on the surface; dimensional measurement uses calipers, dial indicators, and other tools to verify that the bending angle and radius meet design requirements; performance testing simulates actual working conditions, subjecting the bent part to load-bearing or vibration tests to observe for cracking or deformation. For unqualified products, the causes must be analyzed promptly, and process parameters adjusted to ensure stable quality in subsequent production.
