What Is The Difference Between Extrusion And Cold Bending in Aluminum Processing?

1, Process principle: The essential difference between plastic flow and elastic deformation
The essence of extrusion molding is the plastic flow of metal under triaxial compressive stress state. Taking 6061-T6 aluminum alloy as an example, its processing requires placing a cylindrical billet heated to 450-500 ℃ in an extrusion cylinder, and applying 3000-5000 tons of pressure through a hydraulic press to force the metal to flow directionally through a specific mold hole. During this process, the metal undergoes severe plastic deformation, and the grains are elongated along the extrusion direction, forming a typical fibrous structure. This process can achieve the manufacturing of profiles with highly complex cross-sections, such as the aluminum alloy space truss structure used in a certain airport terminal. The node components are formed by extrusion once, and the cross-section contains 12 irregular cavities. Traditional processing requires 17 steps to complete.
Cold bending molding achieves the elastic plastic transformation of metal through multiple progressive deformations. Taking 3mm thick 6063 aluminum alloy plate as an example, the cold bending equipment applies progressive pressure to the plate through a continuous arrangement of roller sets, with each deformation controlled at 5% -8%. In the processing of the curtain wall keel of a high-rise building, the cold bending process gradually bends the flat plate into L-shaped and C-shaped sections, and the final bending radius of the product can reach twice the thickness of the plate, while maintaining a surface smoothness of Ra0.8 μ m. Unlike extrusion molding, the metal flow during cold bending only occurs within the surface 1-2mm range, and the core maintains its original grain structure. This layered deformation characteristic makes it more suitable for manufacturing thin-walled profiles.
2, Equipment structure: Comparison between 10000 ton press and precision roller set
The extrusion equipment exhibits obvious characteristics of heavy weight. Taking the 2500 ton forward extruder as an example, its core components include:
Pre stressed frame tension column: capable of withstanding an instantaneous stress of 350MPa
Squeezing cylinder: inner diameter 250mm, working temperature 480 ± 5 ℃
Mold system: including complex structures such as splitter molds and tongue molds, with a mold life of up to 5000 extrusions
Hydraulic system: master cylinder pressure 315MPa, flow rate 2000L/min
This equipment configuration enables it to process oversized billets with a diameter of 250mm and a length of 800mm, and can produce 12 meter long special-shaped pipes in a single extrusion.
Cold bending equipment emphasizes precision control and continuous production. Typical configurations include:
Uncoiler: capable of carrying 10 tons of steel coils, with tension control accuracy of ± 0.5%
Straightening system: using a combination of 9 rollers for straightening, with a straightness error of ≤ 0.5mm/m
Roller set: usually includes 15-20 passes, with a gap adjustment accuracy of 0.01mm per pass
Cutting device: flying shear cutting, speed up to 60m/min
The continuous cold bending production line adopted by a certain automobile manufacturing enterprise can achieve online forming of 0.8-3.0mm thick aluminum alloy plates, with a production speed of 40m/min and a product section complexity coefficient (section circumference ²/area) of up to 80, far exceeding the traditional stamping process's upper limit of 30.
3, Material properties: the game between fiber reinforcement and isotropy
Extrusion molding achieves directional strengthening of material properties through severe plastic deformation. Taking 6082-T6 aluminum alloy as an example, the longitudinal tensile strength of the extruded product can reach 345MPa, which is 22% higher than the original billet, but the transverse strength only increases by 8%. This anisotropic characteristic has been cleverly applied in a certain bridge project: the designer takes the longitudinal direction of the extruded profile as the main force direction, and increases the overall stiffness of the structure by 30% through reasonable arrangement of nodes. At the same time, the transverse low modulus characteristic is used to achieve energy dissipation under earthquake action.
Cold bending molding maintains the isotropic characteristics of the material. Experimental data shows that after cold bending, the yield strength of 6063 aluminum alloy only increases by 5% -8%, but the elongation remains in the range of 18% -22%. This performance stability makes it the preferred process in the field of architectural decoration. The cold-formed aluminum plate used in the curtain wall system of Shanghai center Building has an in-plane deformation capacity of L/180 (L is the length of the plate) within the temperature variation range of -20 ℃ to+60 ℃, far exceeding the L/360 limit of extruded profiles, which effectively solves the problem of wind vibration response of super high-rise buildings.
4, Application scenario: Division of labor between structural load-bearing and surface decoration
In the field of building steel structures, extrusion molding dominates the manufacturing of core load-bearing components:
Space structure: The "Ice Ribbon" of the National Speed Skating Oval uses 22 aluminum alloy extruded tubes with a diameter of 1.2 meters, and achieves a span of 198 meters through a truss structure
Bridge engineering: The aluminum alloy crash barrier used for the Hong Kong Zhuhai Macao Bridge consists of three closed chambers with a torsional stiffness of 1.2 × 10 ⁴ kN · m ²
Modular architecture: A data center in Singapore adopts extruded aluminum alloy frames, achieving a 98% prefabrication rate of components and reducing on-site assembly time by 70%
Cold bending molding focuses on surface decoration and lightweight requirements:
Curtain Wall System: The cold-formed aluminum panels used in the Burj Khalifa in Dubai are seamlessly joined through a 0.5mm radius rounded transition, with a surface anodized film thickness of up to 25 μ m
Automobile manufacturing: The Tesla Model Y body cover adopts 6016 aluminum alloy cold bending process, reducing weight by 15% while maintaining A-level surface accuracy
Photovoltaic bracket: The cold-formed aluminum profile of the Talatan Photovoltaic Power Station in Qinghai maintains a straightness of 0.2mm/m at -40 ℃ to ensure the optimal inclination angle of the photovoltaic modules
5, Technological Development Trends: Collaborative Innovation and Boundary Breakthrough
Currently, two processes are showing a trend of integrated development:
Squeezing Cold Bending Composite Process: A certain aviation component manufacturer has developed a "Squeezing Pre Forming+Cold Bending Finishing" route, which corrects 6061 aluminum alloy extruded pipes through cold bending, reducing straightness error from 3mm/m to 0.2mm/m and reducing machining allowance by 30%.
Intelligent control technology: The digital twin system developed by Siemens can simulate the metal flow during the extrusion process in real time, reducing the occurrence rate of "shrinkage" defects from 8% to 0.5%; The introduction of AI visual inspection in the cold bending production line has increased the product qualification rate to 99.97%.
New material adaptation: A low-temperature extrusion process (350 ℃ extrusion+180 ℃ aging) has been developed for 7075 high-strength aluminum alloy, which increases the mold life from 200 times to 1000 times while maintaining the T6 strength; In the field of cold bending, 5052-H32 aluminum alloy special lubricant has been developed, reducing the minimum bending radius from 3t (where t is the plate thickness) to 1.5t.