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Section Distortion Control of Angle Aluminum Profile Stretch Forming

Aluminum alloy profile has many advantages such as being lightweight, high strength, good formability, corrosion resistance, and recyclability, and it is more and more widely used in rail transit. Rail vehicle body components have large geometric dimensions and high precision requirements. In order to obtain high-quality rail vehicle body components, the stretch forming process is commonly used to form aluminum alloy profile bending parts.

The stretch forming process can apply tangential tension to the profile while the profile bending improves the stress state of the section, thereby reducing spring-back and improving the contour accuracy of the formed part. However, the cross-section of rail vehicle body components is complex, and various cross-sectional distortion defects are prone to occur during the stretch forming process.

Aluminum angle profile

Section Distortion Control of Angle Aluminum Profile Stretch Forming
Figure 1: Common section distortion defects of angle aluminum part

Common angle cross-section aluminum profile members for rail vehicles, the common cross-sectional distortion defects of this type of members are the collapse of the horizontal side and the inclination of the vertical side. The angle cross-section aluminum profile member is shown in Figure 1, and its cross-section includes two parts: the vertical side and the horizontal side. The member is formed by drawing and bending 6005A-T4 aluminum alloy profiles. In order to meet the assembly and use requirements, the cross-sectional shape accuracy of the profile is high, and the flatness of the horizontal and vertical sides is less than 1 mm.

Computer simulation results

The equivalent plastic strain simulation results of the initial model are shown in Fig. 2. It can be seen that the deformation of the bending part is the most serious at the R1232. The section is clearly distorted.

Section Distortion Control of Angle Aluminum Profile Stretch Forming
Figure 2

Lateral flow displacement

Section Distortion Control of Angle Aluminum Profile Stretch Forming
Figure 3

Figure 3 shows the lateral flow displacement of the section material at the R1232. 4 mm arc position. It can be seen that the excessive baffle gap in the stretch bending process leads to insufficient restriction of the vertical edge, and the lateral flow space of the cross-sectional material is large, while the lateral flow degree of the upper and lower parts of the vertical edge is inconsistent, which eventually causes the vertical edge to tilt. Therefore, the vertical edge is inclined The defect is mainly caused by the unreasonable setting of the baffle gap.

Longitudinal flow displacement

Section Distortion Control of Angle Aluminum Profile Stretch Forming
Figure 4

Figure 4 shows the longitudinal flow displacement of the section material at the R1232. 4 mm arc position. It can be seen that during the bending process, the material flows vertically downward, and the rounded corners of the horizontal edges cannot be effectively supported, resulting in collapse. The collapse of the transverse edge is mainly caused by the reduction of the section stiffness due to the contraction of the standing edge. The tangential elongation of the profile during stretch bending, according to the volume constant rule, the section shrinks, and the shrinkage of the vertical edge leads to insufficient contact between the bottom of the vertical edge of the profile and the support surface of the stretch bending mold, the profile cannot be effectively supported, and the stiffness is low.

Stretch Forming Process of Aluminum Alloy Automobile Roof Rack【Stretch Forming Machine】

Section Distortion Defect Control

Vertical wall obliquing defect control

Section Distortion Control of Angle Aluminum Profile Stretch Forming
Figure 5

The vertical edge inclination defect is mainly caused by the insufficient restriction of the vertical edge of the profile by the baffle plate. Therefore, the vertical edge inclination defect is controlled by optimizing the gap of the baffle plate. The variation trend of the vertical edge inclination with the baffle gap is shown in Figure 5, where the vertical edge inclination is measured by the lateral distance ΔC from the bottom of the vertical edge to the top of the vertical edge. Within a certain range, as the baffle gap δ decreases, the inclination of the standing edge decreases gradually. When the baffle gap δ is reduced to less than 10.5 mm, the inclination degree of the standing edge does not change much, and they are all small. In addition, too small a baffle gap will make it difficult to clamp the profile. Therefore, the baffle gap δ is selected as the best value of 10.5mm.

Horizontal wall obliquing defect control

Section Distortion Control of Angle Aluminum Profile Stretch Forming
Figure 6

The collapse defect of the transverse side is mainly caused by the shrinkage of the vertical side, which leads to the fact that the profile cannot be effectively supported by the stretch bending dies, so it is controlled by correcting the depth of the support surface of the stretch bending dies. When the elongation of the aluminum alloy profile is 10% of the profile length, based on the shrinkage of the vertical edge at the corresponding position, the depth of the support surface of the stretch bending die is reduced, so that the vertical edge of the profile can be effectively supported during the stretch bending process, thereby controlling the lateral Edge collapse defect. The degree of collapse of the transverse edge at different corrections is shown in Figure 6. It can be seen that the collapse of the transverse edge decreases significantly as the depth of the support surface decreases; when the correction is 1.2 times the shrinkage of the vertical edge, the transverse degree of edge collapse is the smallest; when the correction amount is too large, new horizontal edge lift defects will be generated (Figure 7). Therefore, the reasonable depth correction of the support surface of the mold surface is 1.2 times the shrinkage of the standing edge.

Section Distortion Control of Angle Aluminum Profile Stretch Forming
Figure 7

Stretch bending test

Section Distortion Control of Angle Aluminum Profile Stretch Forming
Figure 8

According to the simulation analysis, it can be seen that the optimal baffle gap during the bending process of the L-section profile is 10.5 mm; when the elongation of the aluminum alloy profile is 10% of the profile length, the optimal depth of the support surface The correction amount is 1.2 times the standing edge shrinkage. Based on the simulation results, the stretch bending forming die is designed, as shown in Fig. 8, and the stretch forming test is carried out. The cross-section accuracy of the test piece is good, as shown in Figure 9, which overcomes the original cross-section distortion defect of the profile, and effectively controls the vertical edge tilt and transverse edge collapse defects, which verifies the effectiveness of the defect control measures in this paper.

Section Distortion Control of Angle Aluminum Profile Stretch Forming
Figure 9
Section Distortion Control of Angle Aluminum Profile Stretch Forming
Figure 10

In conclusion

The main section distortion defects of angle aluminum cross-section aluminum profile stretch-bending are vertical edge inclination and transverse edge collapse. The inclination of the vertical edge is mainly caused by the excessive clearance of the baffle plate and insufficient restriction of the vertical edge. The collapse of the transverse edge is mainly caused by the shrinkage of the vertical edge of the profile, which leads to the inability of the profile to be effectively supported by the stretch bending die.
Optimizing the baffle gap can effectively control the vertical edge inclination defects. Within a certain range, the inclination degree of the vertical edge of the angle aluminum section profile member decreases with the decrease of the baffle gap. For this part, the optimal baffle clearance is 10.5 mm.
Based on the shrinkage of the vertical edge, reducing the depth of the support surface of the stretch bending die can effectively control the collapse defect of the transverse edge. In addition, excessive depth correction of the support surface of the mold will easily lead to the defect of lateral edge warping. When the stretching amount of the aluminum alloy profile is 10% of the profile length, the reasonable support surface depth correction amount is 1.2 times the standing edge shrinkage.