TRANSVERSE LONGITUDINAL BEND – What types of bend is needed for materials during the forming process?

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When developing bends on metal parts through a process of forming or running a strip of material through the progressive dies, the questions you might want to ask yourself are: what are transverse and longitudinal bending and what are the best materials that give excellent formability?

Transverse bends, otherwise known as poor way, is where the bend goes along the grain of the materials whereas the longitudinal bend, or good way, goes against the grain in a perpendicular matter. Below are a couple of images of a transverse bend and longitudinal bend.

Figure 1: Text example of two types of bends. Source: DeGarmo’s Materials and Processes in Manufacturing

Figure 2: Bend orientation on BeCu strip. Source: Materion: Tech Briefs, Formability of Materion Brush Performance

To know if the material has the right formability, the material’s formability is expressed in a ratio, R/t, where the R is the bend radius and the t is the strip thickness, which helps better understand what material is best used for formability. A material with an R/t value of 0 can develop sharp corners with no failures (cracking). [3] If a material has a large R/t ratio, the material would have less formability and require a bend radius greater than the material thickness.

For example: if the R/t ratio was 3, it would require a bend radius 3 times the material thickness. It is important to note that if a material is cold rolled or mill hardened, the strength increases, formability decreases, increasing the R/t ratio, and formability becomes directional. [2] Adding tolerances along with setting a minimum bend radius on stronger materials is needed when the formed part is present.

The table below (Figure 3) shows the R/t ratio for different alloys with Heat-Treated Tempers. If you compare the 25 1/4H and the 25 1/2 H, you can see that the 1/2H requires a greater R/t due to it having a greater temper than the 1/4H resulting in lower formability.

Figure 3. : Table of Alloy with R/t Ratio Source: Materion: Formability of Materion Brush performance.

So when an engineer or a designer develops a part or product, they must consider the bend radius of the part or product in development, the thickness of the material, find the material formability, and decide which material would be best suited for their part or product that meets the material’s formability and its minimum bend radius, smallest bend radius where no metal cracks are found during the forming process. [1]

At Leader Tech, we use a Beryllium Copper, BeCu C17200 25 Alloy, with ¼H strips to form our fingerstock gaskets to achieve bend radius in either transverse or longitudinal bends. Our BeCu can have a thickness ranging from 0.002” to 0.007”, depending on which application is needed for our fingerstock gaskets.

When you choose our fingerstock gaskets, be sure to decide which plating is needed for our fingerstock gaskets. Check our post on Plating Selection for Beryllium Copper Fingerstock Gaskets.
If you have any questions or are interested in our BeCu Fingerstock Gaskets, contact us at Leader Tech and our engineering team will assist you.

References
1. Black, J.T. and Kosher, R.A., “Design for Bending” in “Sheet-Forming Process,” Chapter 19, DeGarmo’s Materials & Processes in Manufacturing 12th Ed., Wiley, New Jersey, pp. 394-396 (2017)
2. “Forming of Strip” in Processing and Fabrication Guide”, Materion: Guide to High Performance Alloys, pp. 47 (2015)
3. “Formability of Materion Brush Performance Alloys Strip Products”, Materion: Tech Briefs, https://materion.com/-/media/ files/alloy/tech-briefs/at0008-0311—tech-briefs—formability-of-brush-performance-alloys-strip-materials.pdf