29 April 2014

Well-rounded - laser welding of quality tubes

Welded stainless steel tubes are the foundation of medium-sized company Esta Rohr GmbH, located in Siegen-Kaan-Marienborn, Germany. With advancements in welding technology from TIG to laser, new production and market opportunities appeared.

Laser welding – less equipment, more output, higher quality
There is something different now at tube manufacturer Esta Rohr compared to our visit there eight years ago. The place is still filled with noise from the machines and from finished tubes falling into the collection containers. But the heat from the annealing lines, which was noticeable eight years ago, is distinctly lower now. “Yes, that’s true”, Sven Pitzer confirms, Technical Director of Esta Rohr. “This is due to the fact that we have rebuilt our production and now only run three instead of five tube production lines but with constant growth.” In 2006 alone, Esta Rohr processed 3,000 tons steel with one laser and four TIG lines. Since then, they replaced many of the TIG systems and are completely committed to laser welding. Last year, they laser welded tubes from 4,500 tons of stainless steel. “Today, TIG welded tubes are actually only produced in exceptional cases, for example, when specified in construction plans or complex inspection requirements for power plants”, Pitzer explains. In these special cases, Esta Rohr is flexible and can still reconvert one of the lines to TIG. Pitzer adds: “However, the advantages of laser welded tubes are so numerous that we completely switched to laser in the meantime.”

On the right track

After commissioning the first laser system in 2005, expectations for the new technology were high. Production was supposed to become more cost-efficient and new markets were to be conquered. Esta Rohr rose to the challenge: for example, today, the company manufactures about one million meters of tubes per year for automotive fuel delivery components using three new CO2 Slab lasers from ROFIN, with output powers of 4.5 to 6 kW, combined with the Profile Welding System (PWS). The demands for this special pipework can only be met by laser welded tubes – other technologies like the traditional TIG welding are not authorized by customers. These tubes are extremely special because they are made from a specific steel alloy and are easily shapeable without annealing – another reason why it is no longer as hot in the hall. Years ago, all five TIG systems still had annealing lines; today, however, only two laser systems are still equipped with it.

With one million meters of tubes per year for the automotive sector alone, a reputable list of customers, and many automobile classes that are exclusively supplied – and yet, Esta Rohr still sees itself as a niche manufacturer in the automotive market. "There are huge amounts of stainless pipes that are fabricated for exhaust systems for automobile manufacturing. However, for this, HF-welded tubes with sufficient quality for this application are used." Therefore, the main part of production concerns drinking water lines. Here, mainly ferritic steel – material number 1.4521 / AISI 444 – is processed. As a laser welded tube, it is certified by the German Technical and Scientific Association for Gas and Water (DVGW) as a drinking water line due to its corrosion resistance properties – contrary to other welding techniques. Furthermore, ferritic steels are – especially due to high nickel prices – less expensive than austenitic (CrNi) steels and therefore have a larger market share.

But even beyond the automotive industry, Esta Rohr has another promising market in focus: under the brand name SIMPLESTA®, the company has developed laser welded stainless steel tubes from material 1.4520 / AISI 439 for closed water circuits, used for example, in heating systems or refrigerant circuits. Since their introduction to the market in 2013, more than 200 tons of these tubes have already been sold. Similarly, tubes with polished inner seams have also been produced, which among others are very suitable for the production of the press-fittings that belong to the SIMPLESTA® system. This allows house builders to use stainless steel for all pipes in their construction realizing significant savings. Because of the increased raw material prices for copper, the new stainless steel tube system made from material 1.4520 / AISI 439 is a more cost-effective alternative.

One decade of proven partnership

After the very successful integration of the first laser system with the laser specialist ROFIN from Hamburg, Sven Pitzer also entrusted Stefan Ziesemer from ROFIN with two other new laser systems. “We are acting on a par with ROFIN and really have a good business relationship. Even after almost 10 years of cooperation, we can say that ROFIN is the right partner for tube welding for us," says Pitzer. The 44-year-old has now been working for the company for 25 years and has played a decisive role in all decisions regarding the shift from TIG to laser welding, right from the start. As to the partnership with ROFIN, he is thrilled by the opportunity to test innovations and to feel that his feedback is finding open ears. Stefan Ziesemer confirms that. He is the Product Manager & Project Engineer, and often the first point of contact for customers at ROFIN for all matters relating to tube welding: "We need partners too, who accompany us on our way, who tell us their honest opinion and who give us constructive feedback for our ongoing development. This is the only way to further develop ourselves and particularly our products in the interest of our customers."

And so, Esta Rohr has recently put ROFIN's new Weld Sensor to the test. The new Weld Sensor has advantages in being able to track the actual welding position in relation to the joint gap. Furthermore, it offers the operator a very reliable view at the process that enables him or her to adjust the linear offset of the joined edges or the roller pressure. "Specifically, in the case of critical/sensitive automotive tubes, we can weld more safely than before", Production Operation Manager Frank Lohmann shouts out over the noise of the machines and points to the PWS control panel that is mounted onto a supporting arm. Here, he and his colleagues can closely monitor the welding process. Furthermore, an automatic correction of the welding position takes place over the integrated regulation circuit. Fast and precise linear drives which allow positioning accuracies of the laser beam within a few µm at welding speeds of up to 60 m/min, further ensure the highest degree of production reliability. The narrow laser weld seams have lower heat influences, which result in a minimal heat-affected zone, a low combustion behavior, respectively a minimum demixing of the alloying elements. The fine-grained structure of the welding seam allows for high degrees of shaping without the heat treatment processes that are often necessary for TIG welding.

Future focus
Esta Rohr is a satisfied customer because their expectations have been met and because they have backed the right horse despite the high investment costs. There are still fresh ideas for the future but one thing is certain: "We will definitely buy another laser welding system this year. And we also definitely know from whom."


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