Stretch Forming Basics of Aluminum Extrusion Profiles

Stretch Bending Precision: Radius error: up to 0.4mm, Flatness: 0.1mm-0.5mm, Perpendicularity: 0.5mm

Classification of Aluminum Extrusions

By Structure:
- General profiles
- Thermal break profiles (also known as insulated profiles)
By Surface Treatment:
- Anodized aluminum extrusions
- Coated aluminum extrusions
By Hardness State:
- Aging (high-temperature homogenization) and non-aging aluminum extrusions, assuming the same material (chemical composition)
By Use:
- Industrial use
- Construction use

For example: Based on the drawings and instructions, the selected profiles for this project are construction profiles. Anodized general aluminum extrusions are used for balconies, while thermal break coated aluminum extrusions are used for doors and windows. The material is 6063, and the hardness state is usually T5.

Stretch Forming Basics of Aluminum Extrusion Profiles: Characteristics and Requirements

Stretch forming involves applying a predetermined tensile force (within the yield limit) to the profile and using rotation and mold to alter the deformation interface (moving inward) of the profile cross-section to induce plastic deformation.

Preparation Length for Stretch Forming Aluminum Extrusions

Generally, the preparation length should be the effective arc length of the required bending material plus the process segment. The process segment is equal to 2.1 times the deformation width (t), where the deformation width (t) is equal to the outer radius (R_outer) minus the inner radius (R_inner).

The following provides you with the formula for the length of the preparation for aluminum extrusion bending:
Preparation length = effective arc length + 2.1 t
Of course, the specific preparation length can be considered according to the actual situation to save the process section.

Quantity of Material Preparation for Stretch Forming Aluminum Extrusions

Typically, 1-2 additional pieces are prepared based on different cross-sections, radii, and arc lengths beyond the actual need to be used for mold testing. This backup does not account for potential losses during transportation, processing, and installation after bending.

Requirements for Effective Arc Length of Each Bent Aluminum Extrusion

Usually, it should not exceed a 180-degree arc.

Requirements for the Hardness State of Aluminum Profiles

When the elongation rate meets the deformation requirements, the T5 state (e ≤ 10%) should be selected. The national standard for aluminum profiles in China is e ≥ 8%.

The following is the calculation formula for the elongation of aluminum profile bending:
e = t / R_inner × 100% = (R_out-R_inner) ÷ R_inner × 100%
Otherwise, the To~T4 state should be selected. Of course, profile manufacturers are generally unwilling to produce T1~T4 state profiles for customers.

Surface Treatment Requirements for Aluminum Profiles

Usually, anodizing or coating can be selected for post-bending processing (the elongation rate of the coating is much higher than that of the profile). Since there is no relative displacement between the aluminum profile and the mold during stretch bending, the aluminum profile will not be damaged. If the coating peels off during bending, it indicates insufficient adhesion, often due to inadequate pre-treatment or insufficient heating and heating time. Surface protection should be applied for ease of transportation and installation.

General Requirements for Elongation During Stretch Forming of Aluminum Profiles

Elongation Calculation Formula

Calculation formula for elongation:
t (deformation width) = R_out – R_inner
e (elongation) = t/ R_inner × 100%
China’s national production standard for aluminum profiles (6063, T5) e (elongation) ≥ 8%

General Requirements for Elongation Rate in Stretch Forming Aluminum Profiles

Aluminum Profile (6063, T5): When e (elongation rate) ≤ 10%, generally, the aluminum profile can be stretch bent.
Aluminum Profile (6063, T5): When e (elongation rate) ≥ 10%, if the profile wall is thick, the cavity is closed, the geometry is relatively simple, the force is symmetrical in the bending direction, and the width-to-height ratio is less than 1, the stretch bending elongation rate can generally be within the range of 10% to 16%.
If the above conditions are not met, other hardness states of the aluminum profile, such as T0 to T4, should be considered. Generally, the elongation rate of aluminum profiles (6063) in the T0 state can reach 20% to 28%.
In conclusion, the elongation requirements for stretch bending aluminum profiles should be determined based on specific design requirements and material selection (geometry, wall thickness, cavity closure, symmetry of force in the bending direction, tensile strength, etc.).

5 Key Points for Bending Aluminum Profiles for Doors and Windows

Image source: BIT Aluminum Bending Machine

Material: The aluminum profiles used for bending must be free of paint and untreated (not heat-treated). Soft, untreated aluminum is easier to bend due to its low hardness and good flexibility, making it ideal for achieving smooth curves.
Bending Process: There are two aluminum bending processs: stretch bending and roll bending. For irregular shapes, roll bending is more suitable as it allows for easier adjustment. This step is crucial, as success depends largely on the technique used.
Joining: If screws are used for assembly, gaps are likely to occur. Welding is generally preferred to ensure a seamless connection. After welding, grinding can be done to smooth out any deformations or scratches caused during bending.
Coating: After grinding, the profile is ready for coating. Post-processing and then spraying can solve many issues, such as hiding imperfections from the manufacturing process. However, this requires a specialized large-scale coating line, and the defect rate can be high. The advantage is that defects can be repaired and resprayed until the surface meets the same quality standards as regular aluminum profiles.
Assembly and Glass Installation: This step is relatively simple. The most challenging part is installing the glass bead, which requires a bit of skill.