Process optimization through low-stress and flat sheets

Cutting, punching, folding, bending, milling, turning, welding, assembly: In all areas of sheet metal processing, stresses in the sheet metal sometimes have a considerable impact on a smooth production process. Together with the flatness of blanks, they have a significant influence on productivity and quality in the production of folded and bent parts and in the manufacture of welded assemblies. Straightened sheets, on the other hand, are low-stress, have the required flatness and therefore enable optimum further processing.

Eko Međimurje GmbH, based in Croatia, which primarily manufactures complex sheet metal constructions, also appreciates these advantages. Whether driver’s cabs or tanks for mining machines of well-known brands such as Liebherr, Komatsu and Caterpillar or baking ovens for the food industry – time-consuming reworking, distortion during welding and inconsistent results are a thing of the past since the use of a Kohler part leveling machine. Eko Međimurje GmbH employs around 400 people and processes around 500 tons of steel per month. Eko’s 20,000 m² production facility boasts state-of-the-art machinery: laser machines, various plasma cutting systems and press brakes as well as 110 welding machines, two robot welding stations, cobot welding robots, numerous machining centers and a modern paint shop form the backbone of production. To increase quality and reliably reduce throughput times, production was recently expanded to include a Peak Performer 85P.2000 part leveler from Kohler Maschinenbau GmbH.

Straightening: Precision right from the start

The straightening of sheet metal using a roll straightening machine is nothing more than a bending process that is applied several times. In this straightening process, the material is subjected to increasingly smaller alternating bends, which are created by offset straightening rollers. The bending process can be visualized as a decaying sine curve. During the first straightening rollers, the material is subjected to strong alternating bends, which become smaller and smaller as the straightening process progresses. In the end, the curvatures and deflections are reduced to such an extent that the sheet metal is transferred to the flat state without further springback. Due to the alternating bends and continuous reduction in forming, the material is virtually stress-free after the straightening process. Areas in the straightened material that were previously under tension are stretched and compressed beyond the yield point around the so-called neutral fiber, resulting in the desired reduction in tension.

Relaxed straightening for high-precision welded constructions

“We supply customers who are primarily based in Europe. The products supplied must meet the highest quality standards. At the same time, the quality of the purchased sheet metal is not sufficient for the production process in terms of flatness and tension,” explains Zoran Zdolec, Manager of Electrical Facilities at Eko Međimurje GmbH. “When manufacturing our steel structures, be it cabins, tanks or various machine parts, the highest precision must be guaranteed. The largest product we manufactured had a total weight of no less than 74 tons.” “In the past, however, we were only able to achieve the desired flatness during welding with a great deal of effort. Extensive work during production and a lot of manual reworking were necessary. In many cases, we used specialists who laboriously straightened the parts with a flame so that they could then be welded with the desired precision to form assemblies that sometimes weighed several tons. The results were often satisfactory, but not always of a consistent standard and, above all, not productive enough,” recalls Zoran Zdolec. “We finally came across Kohler through Karmet Bulgaria Ltd. Karmet, as a close sales partner of Kohler, was able to present a machine that exactly matched our requirements. Extensive straightening tests were then carried out with some of our key parts in Kohler’s well-equipped straightening center. We then incorporated these parts into our production process and were immediately able to see the enormous improvements that could be achieved with the straightened parts in terms of quality and productivity during subsequent bending or welding. We have already seen from this that this investment will play a central role in the further development of our company. After placing the order, we were able to successfully commission the Peak Performer 85P.2000 part leveling machine at the end of 2023 after a smooth process. By using the Kohler part leveling machine, we were able to minimize the need to adjust the sheets before welding or distortion during the welding process,” continues Zdolec.

Maximum efficiency thanks to innovative features & functions

Regular cleaning of the straightening rollers and support rollers to remove dirt particles is essential, especially as up to 90 percent black steel is processed. Eko was particularly impressed by the user-friendliness of the ACS extended cleaning system, which is exclusively available from Kohler in this performance class. Weekly cleaning is almost child’s play with the extended cleaning system. Cleaning prevents the build-up and accumulation of abrasion on straightening rollers and support rollers as well as on the straightening material. “Thanks to the fully extendable straightening cassette, the rollers and rollers can be cleaned quickly and easily. This additional feature not only improves our straightening results by preventing contamination, but also significantly extends the service life of the rollers,” emphasizes Zoran Zdolec.

Simple operating concept & high energy efficiency

Kohler was also able to impress the Croatian sheet metal specialist with the operation of the Peak Performer 85P.2000 part leveling machine. The human-machine interface and the “Expert Calculation System” tool installed as standard are designed to be so simple and intuitive that operators can quickly find the right material-dependent setting. Already saved settings for known parts can also be accessed quickly, which makes work much easier. Last but not least, Kohler was able to score points with the environmental plus at Eko. The Peak Performer 85P.2000 is not only powerful, but also energy-efficient and therefore environmentally friendly. All Kohler part levelers work without hydraulics and are therefore noticeably superior to conventional levelers. The result: consistently excellent straightening results across the entire material spectrum with low maintenance, no leakage, insensitivity to the high temperatures in Croatia, higher energy efficiency and thus improved environmental compatibility. “The low power consumption is extremely pleasing. In stand-by mode, the Kohler part leveler consumes less than 2 KW and just 2.5 KW in idle mode. This is due to the electromechanical leveling gap control and the direct drive of the individual leveling rollers. The leveling gap control, a patented feature from Kohler, guarantees outstanding leveling results even with complex geometries. The direct drive provides a separate drive for each straightening roller. The consequence of this is that a large transfer gearbox with an oversized central drive gives way to individual drives equipped with planetary gears. All in all, we are highly satisfied. And so the investment decision can be described as a success! The part leveler will have paid for itself in a very reasonable time,” concludes Zoran Zdolec. Web: www.kohler-germany.com