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Fig. 1: More than 1000 people work in 19 manufacturing halls at the Schoeller plant in Hellenthal.

Fig. 2: Laser welding is up to three-times faster than conventional methods.

Fig. 3: Hubert Reder (left, Schoeller Werk) and Stefan Ziesemer (right, ROFIN) have worked together for 25 years on solutions and concepts for tube welding at Schoeller Werk.

Fig. 4: The latest PWS system with a Falldorf seam inspector

Fig. 5: ROFIN Profile Welding System PWS with double monitor for monitoring the optionally integrated seam inspector

15.04.2016
25 Years – a strong connection between tube specialist and laser manufacturer

Hamburg/Hellenthal, Germany, April 2016: 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.  

 

Prelude: Laser welding

 

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. 

 

About Schoeller Werk GmbH & Co. KG

Schoeller Werk is one of the leading international manufacturers of longitudinally welded stainless steel tubes. The company was founded in 1827 and has its headquarters in Hellenthal in the Eifel where it has a workforce of more than 1000 employees. The product range comprises TIG and laser welded stainless steel tubes, drawn precision tubes in straight manufactured lengths and fixed lengths, as well as ring tubes. The innovation-driven company continues to further develop its system technology and production range in accordance with customer and market requirements. The foundation for the high-quality manufacturing of the products is the modern machinery. Around 90 million meters of stainless steel tubes are manufactured here yearly, which are used in a great variety of applications in the automotive, industrial and energy sectors. Customers receive everything from a single source from Schoeller Werk, starting with the technical consulting, application-specific product development and tube manufacturing, continuing with quality inspections that meet requirements up to individual logistics services.

 

About the ROFIN Profile Welding System PWS

The PWS is a complete laser welding system for tubes and profiles with integrated process sensors for gap recognition and seam tracking.

The “Weld Sensor”, which works in real time, makes it possible for the user to observe the welding process and use the integrated control system to make automatic corrections to the welding position at speeds of up to 60 m/min with positional accuracy of just a few µm.

The control panel makes easy and clear operation of all system functions possible. The optionally available seam inspector can also be controlled and monitored via the panel.The modular design of the PWS and standardized interfaces facilitate easy integration – even in existing systems. The proven beam control system allows for safe operation under industrial conditions. The PWS works with almost zero maintenance and is not sensitive to oil, dirt, dust, moisture or electrical disturbance variables, which are the best conditions for use even in rugged industrial environments.

Adaptations to customer-specific requirements and local conditions are easily accomplished thanks to the modular design of the system. The PWS can be combined with different ROFIN beam sources, for example fiber lasers of the FL Series or CO2 Slab lasers of the DC Series, making it optimally adaptable to the requirements of the customer.

 

Author:

Dipl. Wirtschtaftsing (FH) Sonja Oelmeyer, PR & Marketing, s.oelmeyer@rofin.de

 

Contact:

ROFIN-SINAR Laser GmbH
Corinna Brettschneider
Tel.: 040-73363-4380
Fax: 040-73363-4138
C.Brettschneider(at)rofin.de