The basic principle of aluminum profile stretch bending forming is that the stretch bending mold is fixed to the table, and the support arm stretches the profile to rotate around the stretch bending mold, causing plastic deformation of the profile material under the action of tension and bending moment, gradually fitting with the mold, and obtaining the required shape of the parts.

The characteristics of tension bending parts are large curvature radius, large rebound, and axial variation of curvature. Aluminum profile manufacturers are widely used in the aviation, aerospace, automotive, construction, and high-speed train industries for forming bending parts, such as fuselage, wing stiffeners and frames, curved house frames, curved door frames, window frames, train front and roof contour supports, window frames, and curved door frame frames.

Considering the need for the industrialization of aluminum profile stretch bending forming and the current situation of aluminum profile stretch bending forming, we analyzed the common problems in aluminum profile stretch bending forming and proposed several relevant improvement measures, hoping to provide effective reference for everyone.

1、 Common Problems in Aluminum Profile Bending Forming

(1) Profile deviation

Profile refers to the degree to which the profile of a profile, after being bent and stretched, matches the contour of the profile template or inspection mold. The main factors that cause deviation in the contour of aluminum profiles are: ① the curvature rebound change of the tension bending mold; ② The material of each batch of metallurgical extruded profiles is unstable, and the hardness of local areas of each material is uneven; ③ Excessive variation in bending curvature radius; ④ The cross-sectional area of the profile blank is uneven.

(2) Surface defects

Surface defects include cracks, shrinkage wrinkles, curved surface depressions, and side sags after bending the profile.

(3) Twist after bending

The reason for the occurrence of twisting and twisting after tensile bending is due to the asymmetry of the cross-sectional area of the profile, and the imbalance of stress between the edge closing and edge placing of the profile.

(4) Perpendicularity out of tolerance

Perpendicularity refers to the angular deviation between the vertical reference of the cross-sectional area of the bent profile (perpendicular to the curvature radii of the mold) and the inspection platform.

(5) Aluminum profile process length

The length of the stretch bending process for profiles refers to the length of process materials required for stretch bending molds, fixtures, and equipment that exceeds the actual length of the part.

(6) Safety production of aluminum profiles

Safety issues are the most important issues of concern in industrial production processes. When the profile is bent, it may suddenly break due to accidental factors, bounce outward, cause equipment damage and casualties, and thus have a serious impact on the development of the enterprise.

2、 Solution measures

(1) Adjusting the curvature of the mold contour

Calculate the rebound amount based on theoretical analysis, and use tensile tests to obtain a corrected approximate value to correct the mold. Try to make the profile profile of the stretched part match the profile template or inspection mold tire as much as possible. Considering the instability of the profile, it can be stretched a bit according to the needs of later correction.

Due to excessive changes in the curvature radius of the bending, certain deviations can be caused. Therefore, additional cylinders can be added at the front end of the mold and perpendicular to the mold direction to ensure that the bent profile matches the mold, while there should be no gap between the tension bending mold and the bent profile. This method can solve tension bending on the opposite side of the curvature center (with a larger curvature radius).

In the design process, it is necessary to consider the form of the cross-sectional area of the profile and the thickness of each part. In response to the asymmetry of the cross-sectional area of the profile, the deviation caused by the imbalance of stress between the edge closing and edge placing of the profile can be appropriately increased during pre stretching.

(2) Surface defect treatment

The cracking of the profile after bending is caused by high tensile force and insufficient stress on the edge. Improper edging of profiles can cause shrinkage and wrinkling, commonly known as wooden ear edges. This can be solved by improving the cross-sectional area of the profile or adjusting the tension.

Curved surface depressions mainly occur on hollow profiles. Before bending this type of material, it is necessary to fill the curved part of the cavity with filling material. The open cavity can be stacked with spring steel plates or filled with polytetrafluoroethylene, while the closed cavity is usually filled with sand or other methods.

Adjusting the mold gap appropriately based on the location of side sags and improving the mold material can effectively prevent scratches on the profile.

(3) Twisting treatment after stretching and bending

After bending, the main reason for twisting is the asymmetry of cross-sectional area and the imbalance of stress between the edge closing and edge placing of the profile. In view of this, increasing the tensile force of the profile can be adopted to improve this problem, that is, adding a vertical pushing cylinder before the bending mold, and at the same time, holding the pressure for a period of time after the bending will be better. In addition, the slight deformation caused by the instability of extruded profiles needs to be corrected in the later stage.