Eliminating 'springback' to help make cars more environmentally friendly

A team of researchers, led by Dr Komgrit Lawanwong, at Hiroshima University has engineered some subtle refinements to metal forming techniques that have allowed them to prevent a problem called ‘springback’, which plagues the process of bending high-strength steel (HSS).

HSS is widely used in automotive structural components to help them withstand impacts without increasing their body weight. This has potential environmental benefits, as lightweight cars burn less fuel, and therefore have lower emissions.

The most serious problem in the press-forming of these steel sheets is their large 'springback': the tendency of a metal to return to its original shape after compression or stretching. A simple example of springback is the small gap that will remain if you fold a metal sheet in half with your fingers and then release it. On an industrial scale, springback causes defects when metals are press formed.

"The problems become particularly acute when high-strength materials are used," Dr Lawanwong said. "So a new technique to eliminate springback is urgently needed in the stamping industry."

To avoid these problems, the Hiroshima group proposed a four-step process: clamping of a sheet between a punch and a counter punch; U-bending while maintaining constant clamping force; pushing up of the bottom section of the U-bend with a counter punch; and removing the sheet from the die. The new component of this process is the counterpunching.

To make a U-shaped channel with no springback, three geometrical qualities are important: a precise bending angle with no springback, a sharp corner bend, and a flat bottom.

To study the effectiveness of this technique the researchers compared it with the existing approach on 980Y steel. With the existing method, a large degree of springback was seen, and the bottom part of the U-bend remained curved.

According to the researchers, the flat bottom method delivered a springback angle of almost zero.

Dr Lawanwong concluded: "This method is a useful way to eliminate the springback of high-strength steel in press forming."

Tom Austin-Morgan

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