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6 key Comparison between stretch forming VS roll bending

Stretch forming and roll-bending processing

Aluminum Profile Bending
Aluminum Profile Bending

Stretch forming and roll-bending processing are two commonly used stretch forming processes for aluminum profile bending manufacturers.

Stretch forming process

The stretch forming process requires higher precision, larger length and curvature radius requirements, and smaller transverse dimensions for bending parts. Stretch forming is performed on a dedicated stretch bending machine.

During stretching and bending, the entire thickness of the plate is subjected to tensile stress, so only elongation deformation occurs, and the deformation caused by spring-back after unloading is small, which is easy to ensure accuracy.

If you want to compare the process methods between stretch forming and roll bending, you need to compare the following aspects:

Suppress straight profile sinking

Using a universal sinking die to suppress sinking for straight profiles.

Make holes

There are a lot of pilot holes on the profile parts that need to be processed. The drilling method is relatively flexible and can be used for parts of different sizes and thicknesses. The quality of the holes obtained is higher, and it is currently the most widely used.

The punching method is more efficient than drilling, and it is worthy of promotion.

Make bevel

The oblique angle of the general straight profile can be stamped with an oblique die.

The bevel angle of the profile part with curvature is generally made simultaneously in the bending process.

Making gaps

The edge milling work of the long stringer and the beam edge is generally processed by vertical milling or arm milling according to the template (model).

The structure of the die for punching the small corners of the pillar and other end shapes is simple and simple.

Profile inspection

The inspection items of profiles are surface Quality, appearance, length, angle, sag, etc.

Surface Quality:

In addition to the surface of the profile, there should be no deep hammer marks and shrinkage machine tooth marks. The most important thing is that no cracks are allowed.

Profile shape:

The shape can be inspected according to the shape template, inspection template, or three-dimensional inspection mold.

The shape template is used for the inspection of general single-curvature profiles;

The inspection template is used for the inspection of mass production parts with large output and high-quality requirements;

Hyperbolic complex profiles generally require special inspection equipment. A combined template frame or a rubber-sand reverse mold tire can be used according to the different component coordination systems.

Poor profile outside description

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

The allowable deviation of profile shape is:

±0.2- 0.3mm related to the shape of the aircraft ±0.5mm not related to the shape of the aircraft

The unevenness of the profile web:

The gap between the flat or curved web of the straight profile and the inspection platform should not exceed 0.5mm when the profile length is less than 500mm, and should not exceed 1mm if the length is greater than 500mm.

The bevel angle of profile:

The angle (bevel) tolerance of contour parts is ±30′, and that of non-contour parts is ±10.

Profile length:

The deviation of the length of the profile relative to the sample plate or drawing is ±1?1.5mm.

Thickness and width of the profile:

When the relative bending radius is less than 5, the thinning of the edge strip is allowed up to 30%, and the width change is allowed up to 10%.

Sag depth and length:

The allowable deviation of the profile sink depth H: +0.3mm for depths below 1.5mm; +0.5mm for depths above 1.5mm;

The tolerance of the sag length l is +1~2mm.

Notch depth:

The allowable deviation of the profile edge milling notch depth is ±0.5mm.


The offset of the center of the assembly hole relative to the template is 0.3mm, and the offset of the pilot hole is 0.5mm.

Stretch Forming vs. Roll Bending

Stretch forming and roll bending are two distinct metal forming techniques used to create curved shapes in various materials, including sheet metal and profiles. Each method has its advantages and limitations, making them suitable for specific applications based on factors such as material type, geometry, tolerances, and production volume. In this comparative analysis, we’ll explore the differences between stretch forming and roll bending, examining their respective processes, capabilities, and typical use cases.

Stretch Forming

Stretch forming involves securing the material at its ends and then stretching it over a form die to achieve the desired curvature. The stretching force and controlled deformation ensure uniform shape and consistent material thickness along the curve.

  • Advantages:
    • Precise Curvature: Stretch forming allows for precise control over the curvature, making it suitable for applications that require tight radii and complex shapes.
    • Uniform Material Thickness: Stretch forming maintains a more consistent material thickness, which is beneficial for structural integrity and surface finish.
    • Ductile Materials: It is particularly effective with ductile materials like aluminum, allowing for precise forming without cracking or material failure.
  • Limitations:
    • Bend Radius: There are practical limits to how tight the bend radius can be achieved in stretch forming, depending on material thickness, ductility, and other factors.
    • Tooling Costs: Developing custom tooling for stretch forming can be expensive, making it more suitable for larger production runs.
  • Typical Use Cases:
    • Aerospace: Stretch forming is commonly used for aircraft components requiring precise curvature.
    • Architectural Panels: It’s suitable for creating smooth, curved surfaces in architectural applications.

Roll Bending

Roll bending, also known as roll forming, involves passing a material through a series of rollers, gradually bending it to the desired shape. The rollers can have different profiles to achieve various curvature radii.

  • Advantages:
    • High Production Rates: Roll bending is efficient for high-volume production, as the continuous process can rapidly form multiple parts.
    • Cost-Effective: Roll forming can be more cost-effective for long production runs, especially with standardized tooling.
  • Limitations:
    • Tight Curvature: Roll bending may have limitations in achieving very tight radii compared to stretch forming.
    • Material Thinning: The material may experience non-uniform thickness distribution, with thinner areas on the inside of the bend.
  • Typical Use Cases:
    • Structural Profiles: Roll bending is often used to create structural shapes, such as beams, channels, and tubes.
    • Mass Production: It’s suitable for industries requiring high-volume production of standardized components.


While both stretch forming and roll bending are valuable techniques in metal forming, they serve different purposes. Stretch forming excels in achieving precise curvature with uniform thickness, making it ideal for applications demanding complex shapes and ductile materials. Roll bending, on the other hand, offers high production rates and cost-effectiveness, making it suitable for standardized profiles and large-scale manufacturing. The choice between the two methods depends on the specific requirements of the project, including curvature, material, volume, and cost considerations.