The bending process of aluminum grilles is a core factor determining their surface quality. Different process paths have significantly different impacts on material properties, forming accuracy, and appearance. From cold bending to hot bending, and then to roll bending and stretch bending, each technique requires balancing material properties and process parameters to avoid surface defects.
Cold bending uses mechanical pressure to deform the profile at room temperature. Its advantages are simplicity and low cost, but it is prone to surface scratches and stress concentration. Because aluminum has low plasticity in a cold state, friction between the profile and the die during bending can cause micro-scratches on the local surface, especially when the bending radius is small, as the pressure from the die edges exacerbates surface damage. Furthermore, residual elastic stress inside the profile after cold bending can cause springback, leading to deviations in the bending angle and affecting the overall assembly accuracy and surface flatness of the aluminum grille.
Hot bending reduces the yield strength of aluminum by heating, significantly increasing material plasticity, thereby reducing springback and the risk of surface damage. However, temperature control is a key challenge in this process: insufficient heating leads to insufficient material plasticity, potentially causing cracks during bending; while excessive temperature can trigger oxidation and discoloration, even damaging the surface treatment layer, resulting in coating peeling or uneven color. Furthermore, uneven heating during hot bending can easily cause localized deformation, forming wavy bends or twists, further affecting surface smoothness.
Roll bending utilizes multiple sets of rollers to continuously roll and bend the profile, suitable for forming long, narrow aluminum grilles with large radii of curvature. This process reduces stress concentration during a single bending process through progressive deformation, thereby reducing the risk of surface damage. However, roll bending requires high straightness of the profile; if the raw material is bent or twisted, uneven stress during roll bending can easily lead to an uneven surface. In addition, friction between the rollers and the profile can cause localized heating; if not cooled promptly, this can create a heat-affected zone, leading to changes in material hardness or surface oxidation. The stretch bending process applies tangential tension during bending, altering the stress distribution within the profile cross-section to achieve greater uniformity, thus significantly reducing springback and improving forming accuracy. This process is particularly suitable for processing aluminum grilles with complex curved surfaces or small-radius bends, ensuring consistent curvature across each profile and maintaining overall shape harmony. However, the stretch bending process demands extremely high equipment precision and process parameter control: insufficient tension may lead to excessive springback, while excessive tension may cause excessive thinning of the outer wall or even breakage; simultaneously, asymmetrical profile cross-sectional areas or unbalanced stress between the tapered and unbent edges can easily lead to twisting deformation, affecting surface flatness.
The generation of surface defects is also closely related to the profile cross-sectional design. Hollow-section aluminum grilles, lacking supporting material within the cross-section, have lower bending stiffness on the upper side during stretch bending, making them prone to cross-sectional indentation under the combined action of tensile force and bending moment. In addition, open-cavity profiles need to be filled with spring steel plates or PTFE fillers, while closed cavities require sand filling to support the internal structure. Otherwise, bending can easily lead to deformation instability due to internal voids, resulting in surface depressions or wavy bends.
Mold design is another key factor affecting surface quality. Changes in mold curvature springback need to be precisely compensated using CAD/CAM technology to ensure a reasonable difference between the mold shape and the final product shape to offset the springback effect. Simultaneously, mold clearance, surface finish, and material hardness must strictly match the profile characteristics: excessive clearance can easily cause profile slippage and offset, forming side marks; a rough surface may scratch the profile; and insufficient mold hardness may cause dimensional deviations due to wear, further affecting surface quality.
Post-processing is equally important for improving surface quality. Stress relief treatment after bending, such as natural aging or artificial aging, can reduce internal stress, stabilize the shape, and prevent surface deformation due to stress relaxation. For existing surface scratches, oxidation, or dents, repair methods such as grinding, polishing, sandblasting, or recoating can be used to restore surface smoothness and color uniformity. Furthermore, regular maintenance and standardized construction are crucial for ensuring surface quality. By inspecting the installation condition, the degree of surface oxidation, and the quality of materials, timely repair or replacement of problematic aluminum grilles can effectively extend their service life and maintain their aesthetic appeal.
