Various problems can arise during the stretch forming process of industrial aluminum profiles, significantly affecting product qualification rate, production efficiency, and costs. In response to this demand, this article analyzes common problems in the stretch forming of industrial aluminum profiles and proposes relevant improvement measures as effective references.
6 Existing Problems
- Deviation in contour profile: Contour profile refers to the degree of conformity between the post-bending profile of the profile and the contour template or inspection mold. The main factors causing deviation in contour profile include the curvature rebound variation of the stretch forming mold, unstable material properties of different batches of metallurgical extruded profiles resulting in uneven hardness in local areas, excessive variation in stretch forming curvature radius, and uneven cross-sectional area of the profile blank.
- Surface defects: Surface defects such as cracks, shrinkage wrinkling, and concave surfaces may occur after stretch forming.
- Twisting after stretch forming: Asymmetric profile cross-sectional area and unbalanced stresses on the inside and outside edges may cause twisting problems.
- Poor perpendicularity: Asymmetric profile cross-sectional area and unbalanced stresses on the inside and outside edges may result in poor perpendicularity.
- Process length of profiles: The process length of stretch forming refers to the length of material required for the stretch forming process, which exceeds the actual length of the part, bending molds, fixtures, and equipment.
- Safety in production: Safety is the most important concern in the industrial production process. During profile stretch forming, unexpected fractures may occur, causing equipment damage and personnel injuries, which can have a severe impact on the company’s development.
Adjustment of mold contour curvature
- The curvature of the mold can be adjusted based on theoretical analysis to calculate the springback amount. Through tensile tests and approximation corrections, the mold can be modified to achieve better conformity between the post-stretching profile and the contour template or inspection mold. Considering the instability factors of the profile, it can be over-bent as per the requirements of later correction. To solve the issue of curvature center asymmetry in stretch forming, an additional cylinder can be added vertically to the front end of the mold to ensure proper alignment between the bent aluminum profile and the mold, without any gap between the stretch forming mold and the profile being bent. This method can address the stretch forming asymmetry caused by the opposite curvature center.
- During the design process, the form of the profile cross-sectional area and the thickness of each part should be considered. To address the asymmetry of the profile cross-sectional area and the deviation caused by unbalanced stresses on the inside and outside edges, the stretching force can be appropriately increased during pre-stretching.
Handling surface defects
- Cracks occur in profiles due to excessive tensile forces when the edge stress is insufficient. Insufficient edge placement can cause shrinkage wrinkling, also known as “wood ear” edges. This can be resolved by improving the profile cross-sectional area or adjusting the tension.
- Concave surfaces mainly occur in hollow profiles. These profiles need to be filled with fillers in the bent portion. Open hollow sections can be filled with stacked spring steel plates or polytetrafluoroethylene (PTFE) fillers, while closed hollow sections typically use sand filling methods.
- By properly adjusting the mold clearance based on the location of side indentation, the occurrence of side marks can be reduced. Improving the mold material can effectively avoid scratching the profile.
Dealing with twisting after stretch forming
Twisting after stretch forming mainly results from asymmetric cross-sectional area and unbalanced stresses on the inside and outside edges. To improve this problem, increasing the profile bending force of the profile can be an effective measure. This can be achieved by adding a vertically acting top cylinder to the front of the bending mold. Additionally, applying pressure for a certain period after stretch forming will yield better results. Moreover, post-correction is required to address the minimal deformation caused by the instability of extruded profiles.
Addressing poor perpendicularity
Poor perpendicularity after stretch forming is caused by asymmetric cross-sectional area and unbalanced stresses on the inside and outside edges. To address this issue, the mold contour curvature variation can be adjusted. If necessary, over-bending can be applied, and post-correction is needed to address the minimal deformation caused by the instability of extruded profiles.
Determining the process length of profiles
The raw material length for stretch forming profiles consists of the part length, the extension portion of the mold curvature (part length, extension portion, and the mold end corner collectively called the effective mold length), the clamping portion of the equipment chuck, and the gap between the chuck and the mold during rotation. Apart from the part length, this is collectively known as the process length. For mass production, the process length directly determines the cost of the parts. Therefore, it is recommended to minimize the effective length of the mold while meeting the bending part forming requirements. If necessary, notches can be created at the rear ends of the mold to allow the machine chuck to enter freely, thereby reducing the excess material on both ends.
Strengthening safety in production
Safety is the primary concern in the industrial production process. Therefore, it is necessary to install protective devices in front of the profile operating table, establish corresponding rules and regulations, and provide comprehensive training to technical operators. Additionally, personnel should be strictly prohibited from standing at the front end of the equipment during the profile stretching process.
By designing appropriate profile cross-sectional areas and molds, as well as implementing corresponding improvement measures, the quality of products can be improved, production costs can be reduced, and safety in production can be ensured. Post-correction is an effective remedial method for addressing instability in extruded profiles.