Square tubes (SHS steel) are structural tubing with a square cross-section. They are typically produced by bending steel strips or plates into shape and then welding the seam. Seamless square tubes are also available, manufactured through cold-drawing or hot-rolling processes for higher strength and uniformity. Thanks to their symmetrical geometry and excellent load-bearing capability, square tubes are widely used in applications that require strong support or frame structures.
Why Square Tube Bending Is Technically Challenging
Bending square tubes is a common but highly demanding process in structural fabrication. Because square tubes have a closed cross-section and flat sidewalls, issues such as wrinkling, twisting, wall thinning, and cross-sectional deformation can occur easily during bending. Mastering the correct bending method, equipment, and parameters is essential for achieving high-quality results.
Basic Principles of Square Tube Bending
Square tube bending is the process of applying external force to plastically deform the tube, changing its axial shape.
During bending:
The outer wall of the tube is subjected to tensile stress
The inner wall experiences compressive stress
The neutral layer (center) is the zone with minimal change
Compared to round tubes (CHS), square tubes have less inherent rigidity against deformation due to their flat sides. This makes them more prone to:
Concave/convex distortion
Wrinkling on the inner radius
Flattening of the outer radius
Therefore, bending methods must be selected based on factors such as wall thickness, material strength, bending radius, and angle.
Common Methods for Bending Square Tubes
1. Cold Bending
Cold bending is performed at room temperature without heating.
Suitable for:
Thin-wall square tubes
Low-to-medium strength materials
Typical equipment:
Manual tube benders
Hydraulic bending machines
Characteristics:
Simple, cost-effective
Limited bending radius—too small a radius may cause distortion or cracking
2. Hot Bending
Hot bending involves heating the tube to increase ductility and reduce the risk of cracking.
Suitable for:
Thick-wall or high-strength square tubes
Heating methods:
Local flame heating
Induction heating
Furnace heating
Bending characteristics:
Reduces internal stress
Allows tighter bending radii
Requires tight temperature control to avoid altering the metallurgical structure
Typical temperature reference for carbon-steel square tubes:
300°C – 650°C: Suitable for plastic deformation
>700°C: May affect grain structure and should be avoided
Uniform heating is essential. Post-bending straightening or weld-repair may be required.
3. Die Bending (Forming with Molds)
Die bending uses dedicated molds to ensure precision and consistency.
Best for:
High-volume production
Applications requiring strict dimensional accuracy
Equipment:
CNC bending machines
Specialized die-forming machines
Characteristics:
Highest bending accuracy
Excellent repeatability
Higher tooling cost, ideal for mass-production environments
Conclusion
Although bending square tubes may appear simple, it is a process with high technical requirements. Whether used in construction, mechanical structures, or architectural design, selecting the right bending method, proper bending radius, and reliable equipment is key to preventing deformation and ensuring both structural integrity and visual quality.
