Tube specialist Schoeller Werk and laser manufacturer ROFIN are connected by a 25-year partnership.
The 19 manufacturing halls stretch over several kilometers along the small river Olef through the municipality of Hellenthal. Here, at the edge of the Eifel National Park not far from the Belgian border, more than 1000 people work in the numerous production sites of the Schoeller plants, one of the leading international manufacturers of longitudinally-welded stainless steel tubes. Since the installation of the first laser welding systems 25 years ago, there has been a close partnership between Schoeller Werk and the Hamburg laser specialists from ROFIN.
Schoeller Werk: A company with a long tradition and stability
Schoeller Werk can look back at almost 200 years of history in which the company has continuously been in family hands and remained true to the Hellenthal location. After starting as an ironworks, the first TIG tube welding line was put into operation in 1959 for manufacturing longitudinally-welded stainless steel tubes. Schoeller Werk quickly became established and sold its tubes to the chemical industry as well as apparatus and plant engineering, among others. By commencing serial production of tubes made of ferritic and austenitic steels for car exhaust tubes in 1975, the Eifel Company soon got its foot into the important automotive industry market, which presently accounts for around 50% of sales. Today, 57 years after starting up the first system, 109 welding stations now produce more than 90 million meters of tubes per year and generate sales of around EUR 220 million in 2015.
As cars subsequently continued to develop in the 1980s, the demands placed on the installed tubes increased as well, which had to adapt to the more compact bodies through bending. Since TIG welded tubes are not suitable, or are only conditionally suitable for bending, a new joining technology was needed: the laser. Laser welding has many advantages. The welding process has low heat impact, which can be seen in the narrow heat impact zone, low evaporation during melting as well as minimum separation of alloy elements, among other things. The fine-grained structure of the narrow laser weld seam allows a high degree of deformation, often without the heat treatments required in TIG welding, and is also up to three-times faster than conventional methods.
Hubert Reder, longstanding employee and currently manager of maintenance at Schoeller Werk, completed his engineering studies during that time. He certainly caught the attention of his company management with his thesis on the topic of laser welding of tubes. “My experience from my studies and the thesis came just at the right time,” says Hubert Reder looking back. The Eifel resident covered many kilometers every day on the company’s bicycle between the manufacturing halls in which he also supervised the laser tube manufacturing.
“At that time, we checked out all laser manufacturers and their welding stations in a feasibility study. And it seems odd, but we chose ROFIN because their cross-flow laser had the worst beam quality,” says Reder grinning. “And that was very beneficial to us, because our strip edge preparation at that time was simply inadequate for better beam qualities.” An RS 850I, a 5 kW DC-stimulated, cross-flow CO2 laser with a beam guidance system for tube welding, was delivered initially. This predecessor of today’s ROFIN Profile Welding System had been a proven tube welding system for about 10 years at that time with patented mechanical seam tracking. The concept was developed together with Stefan Ziesemer, the Hamburg project manager from ROFIN. “Actually, one could say that we learned from each other at the beginning,” says Ziesemer as he describes the situation 25 years ago. Only the year before did he start supporting the first tube welding projects. “Just like with Mr Reder, tube welding with a laser was quite a new field for me as well at that time. But, together we tackled the task and the questions that emerged.” Obviously it was successful, because the working relationship between Hubert Reder and Stefan Ziesemer has lasted to this day and has resulted in a total of 14 welding stations at Schoeller Werk equipped by ROFIN. Although there are still considerably fewer of them than the 90 TIG stations, the results of the 18 laser systems in total are convincing, and they produce the same tonnage of tubes per year as the conventional systems.
So, as the strip edge preparation at Schoeller Werk and hence the gap accuracy improved considerably, ROFIN developed, among other things, the CO2 Slab laser of the DC Series that was patented at that time. Since then, these lasers with the so-called no-flow principle have been a very efficient laser solution not only at Schoeller Werk, and, equipped with outstanding beam quality, they are an alternative to the flow CO2 lasers known at that time. “Naturally, we also test other technologies on our lab system such as fiber lasers. So far, however, we achieve better results for us and our requirements with CO2 lasers,” says Huber Reder as he explains why only CO2 lasers have been used to date.
The system that was just installed replaces the currently oldest laser, an almost 17 year old RS 880HF, with a new 6 kW DC 060 laser and the latest Profile Welding System (PWS). The motorized axes will be used on the PWS for the first time. With this, Schoeller Werk is pursuing the goal of storing all process parameters in a database to improve the reproducibility of the processes and simplify operation of the systems. In addition, seam inspection will be used downstream from the welding process, which will be analyzed directly at the welding station with all process parameters. People in the Eifel seem to be very satisfied with the new configuration of the welding station: “The simple, easy to operate design of the weld sensor, and the known evaluation of the weld seam by the Falldorf seam inspector, pave the way for a quick start into production,” says Hubert Reder.
Reliable partnership for more than a quarter of a century
“To us, the employees of ROFIN Service and our project manager Stefan Ziesemer have been very good partners for the past 25 years, who have developed solutions together with us and adapted the systems to our requirements,” says Reder. The Eifel Company also makes use of the offer of the ROFIN Training Center to train employees in Hamburg to make them able to carry out individual maintenance and repairs on their own. “A clear time and cost benefit,” adds Reder and then looks at his watch; the next appointment awaits.