Double Sheet Detection during Hot Shaping of Steel Sheets

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The trend towards automotive lightweight construction continuous and even accelerates. One reason is the increasing use of high-performance steels for the production of car body components with hot shaping. But the weight reduction is not the only driving force, safety, stiffness and protection can be greatly increased with hot formed components. However, the high temperatures of steel sheets of around 1000 Celsius require adaptations in the production process.

Whenever blanks are automatically processed it is necessary to ensure that no double sheet ends up in the stamping dies resulting in damages to tools and machinery and, of course, downtime. In the regular stamping operations issues of double blank detection are meanwhile reliably solved with either single head or noncontact dual head double sheet detection systems. However, in hot shaping even reliably detected single sheets during the initial destacking operation can result in double blanks during transportation through the oven. These double blanks must be detected reliably before entering the discharge roller belt.

The use of normal double sheet detectors with typical temperature limitations of up to 80°C is not possible under the circumstances. For that reason special cooled sensor brackets made of ceramics had to be developed and installed at the discharge point of the oven (arrows in the picture). After passing the double sheet sensors detected double blanks are manually removed whereas single sheets are centered and placed into the stamping dies with robot grippers.

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