The Influence of Materials on Sheet Metal Processing

Influence of Material on Bending Process

For sheet metal requiring bending and forming, sufficient plasticity and a relatively low yield strength are essential. Sheets with high plasticity are less prone to cracking during bending, while materials with lower yield strength and lower elastic modulus exhibit less springback after bending, making it easier to achieve accurate bent dimensions. Materials with good plasticity, such as low-carbon steel (carbon content <0.2%), brass, and aluminum, are easy to bend and form. For more brittle materials, such as phosphor bronze (QSn6.5–2.5), spring steel (65Mn), hard aluminum, and super-hard aluminum, a larger relative bending radius (r/t) must be maintained during bending; otherwise, cracking is likely to occur. Special attention should be paid to the selection of material temper conditions, as this significantly affects bendability. For many brittle materials, bending may lead to cracking at the outer radius or even fracture during the process. Similarly, for high-carbon steel sheets, if a hard temper condition is selected, bending can also cause outer radius cracking or fracture. These issues should be minimized as much as possible.

Influence of Material on Drawing Process

Sheet metal drawing, especially deep drawing, is one of the more challenging processes in sheet metal fabrication. It requires not only minimizing drawing depth, simplifying part geometry, and ensuring smooth transitions, but also demands good material plasticity. Otherwise, issues such as overall part warping, local wrinkling, or even cracking at drawn sections can easily occur.

Materials with low yield strength and a high normal anisotropy coefficient (r-value) generally exhibit better drawability. A lower yield ratio (σs/σb) indicates better stamping performance and allows for greater deformation in a single operation. When the r-value is greater than 1, deformation in the width direction occurs more easily than in the thickness direction. A larger drawing radius (R) reduces the risk of thinning and cracking during the drawing process, thereby improving drawability.

Common materials with good drawing performance include: pure aluminum sheet, 08Al, ST16, and SPCD.

Influence of Material on Hardness

In sheet metal structure design, it is often encountered that the stiffness of sheet metal structural components does not meet requirements. Structural designers may resort to using high-carbon steel or stainless steel to replace low-carbon steel, or opt for harder, higher-strength aluminum alloys in place of ordinary aluminum alloys, hoping to improve part stiffness. In reality, this yields no significant effect.

For materials of the same base type, strength and hardness can be substantially increased through heat treatment or alloying, but stiffness changes very little. To enhance the stiffness of a part, it is necessary to either change the material type or alter the shape of the part to achieve a noticeable effect. The elastic modulus and shear modulus of different materials can be found in Table 1-2.