EuroWire September 2017

Technical article

New stretch-bend-levelling line for very thin copper strips is energy efficient and operates with minimal tolerances By Volker Lüdecke, Burghardt + Schmidt GmbH, Remchingen, Germany

Flatness requirements for metal strips have increased steadily in recent years. At the same time there is a trend – particularly in the electronics industry – towards increasingly thinner materials. Here, quality improvements through stretch-bend-levelling facilitate further processing considerably. As a result, for example, dimensional accuracy is increased in the stamping process and thinner surface coatings can be achieved. Hence, the cutting and levelling machine specialist Burghardt + Schmidt GmbH (B+S) developed an innovative solution for the levelling of extremely thin copper strips for a Chinese manufacturer. The line is suited for all alloys of the material as well as for phosphor bronze, and allows strips just 30µm thick to be processed with minimal tolerances. Depending on the starting material, flatnesses down to one I-unit can be achieved. The client in China manufactures parts for the electronics industry that need to satisfy exacting requirements with regard to surface quality as well as flatness or dimensional accuracy. In this case, extremely thin metal strips are used. At a plant to be redesigned, these are to be prepared for further processing. The aim of the new purchase was to keep the shape tolerance within tight limits during the stamping process. This is vitally important in regard to the automated assembly of electronic components. Besides flatness, the client also defined exclusion criteria relating to the surface quality. This means that the optical density of the end product should not be changed through the processing.

All photographs courtesy of Burghardt + Schmidt GmbH

▲ ▲ Since the old lines noticeably reached their control limits when it comes to the processing of very thin materials, Burghardt + Schmidt has developed a new stretch-bend-levelling line. This allows the levelling of copper strips with thicknesses of as little as 20µm and the achievement of evennesses down to one I-unit, depending on the starting flatness

levelling were ultimately the decisive factors in winning the contract from China.

“Given the clearly recognisable trend for ever thinner strips, the B+S lines constantly reach their control limits. Due to customer requirements as well as the results of corresponding market analyses, we have therefore pressed ahead with basic developments for some time. These generally allow the levelling of metal strips that are just 20µm thick,” said Volker Lüdecke, technical manager at B+S. The concept presented and the company’s extensive experience in stretch-bend-

Cassette with 8mm levelling rollers

For the build-up of tension, the line has four rollers on the braking side, ie, in front of the levelling machine. Around these rollers runs the metal strip. Together with the decoiler, they generate the back

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September 2017