Grain Direction In Sheet Metal Bending

Working with grain direction.

Grain direction in sheet metal bending.

In the example above perhaps were using a certain type of steel and specific bend radius whereby we need to be careful to ensure the sheet metal does not crack due to bending. In addition the grain direction needs to be considered when the bend radius is less than twice the thickness depending on the material and its hardness. The grain direction is in the rolling direction of the sheet as it was being manufactured. That has negligible impact on part strength.

This can drastically limit the length of parts being formed as most materials grain runs in the long direction but as stated previously reducing the material s grain size may be a solution to this. When the sheet is made its particles become elongated in the direction of rolling. Bending with the grain gives a different result than bending against it. Bends that run perpendicular to the material s natural grain require slightly more pressure than those running parallel to the grain.

The grain direction is established during the metal rolling process. Applying this to metal bending be it plate bending press braking or any other type of metal forming consideration must be given to the grain direction before any process is carried out. The grain direction created in the direction the sheet is rolled at the mill runs the length of the full sheet. This is because sharper or tighter bends can be made across the grain without cracking.

During sheet metal processing rolling operation material grains are arranged in the direction of rolling. This occurs because bending along the grain allows for separation of the grain boundaries. Two rollers compressing the hot metal cause the polycrystalline material to elongate in the direction of rolling. Whereas bending parallel to rolling direction can lead to cracks because of destruction in grain structure.

As a general rule the grain line must run perpendicular to the bend to avoid the potential for cracking or fracture. We can manually control the grain direction of the metal in the flat pattern and subsequently how the bounding box is oriented to address these concerns. You can see it on a new piece of sheet metal by noticing the direction of visible lines running through it. Bending with the grain or parallel to the grain direction can be a contributor to material failure as bending along the grain allows for separation of the grain boundaries.

A metal s grain direction is usually only a factor when bending however. Once the crystallites are elongated they appear as the grain that we see in cold rolled steel. The grain direction of the metal also contributes to the amount of springback that occurs in a bending operation. Bending metal against the grain or perpendicular to the grain is a common way to prevent material failure or cracking.

This micrograin impacts the design in terms of strength and appearance.