June 30, 2014
A niche tube producer that formerly used GTAW exclusively, Esta Rohr began changing over to laser welding in 2005. The change is now complete, with substantial changes. The company has reduced its number tube production lines from five to three, but its output has increased tremendously. Meanwhile, laser welding has allowed it to cut some costs, helping its products compete against others.
Esta Rohr GmbH, a small, family-owned tube producer, shuns mainstream markets and focuses on specialty applications. It employs about 100 employees at two sites in Germany: Siegen and Erndtebrück. As a niche player, the company specializes in tubing products that have higher-than-average requirements regarding dimensional tolerances, heat treatment, forming characteristics, and weld seam properties.
The Erndtebrück facility manufactures large steel tubes from 15.75 in. to 14.75 ft. dia. Its Siegen location manufactures stainless steel tubing, mainly for domestic drinking water installations, the automotive industry, equipment engineering, and applications that require bending. The bulk of the Siegen product is between ½ in. and 23⁄8 in. dia. in material thicknesses from 0.020 to 0.080 in. The company has created a successful niche in the drinking water market, manufacturing a line of stainless steel tubes and press fittings under its own brand name, SIMPLESTA®.
Until 2005 the company used conventional production processes: gas tungsten arc welding (GTAW, commonly known as tungsten inert gas [TIG]), followed by heat treating to anneal the weld seam. Since that time it has converted to laser welding.
The introduction of laser technology at Esta Rohr was intended to improve production efficiency and allow the company to grow by opening the doors to new markets, and both have happened. The company also has found that laser welding cut costs in a handful of ways.
For example, the company manufactures about 3.3 million ft. of tubes per year for automotive fuel delivery components. The specific steel alloy used for this application, combined with the laser welding process, means that these tubes can be formed easily without a postweld anneal. This also has allowed the company to reduce the number of annealing lines.
Another example is in the manufacture of drinking water system components, which is the bulk of the facility’s output. The combination of the laser welding process and the alloy, mainly ferritic stainless steel alloy AISI 444 (EN 1.4521), provides specific corrosion-resistant properties. Certified by the German Technical and Scientific Association for Gas and Water (DVGW) for use as drinking water lines, these ferritic steels are less expensive than austenitic (CrNi) steels, and therefore have a larger market share.
The company’s SIMPLESTA tubes are laser-welded products made from AISI 439 (EN 1.4520). Intended for closed water circuits, these components are used to make heating and refrigerant circuits. Since the company introduced these tubes to the market in 2013, it has sold more than 200 tons of them. Similarly, it produces tubes with polished inner seams, which are well-suited to producing the press fittings that belong to the SIMPLESTA system. This allows homebuilders to use stainless steel for all pipes in their construction, which brings significant savings compared with the traditional material, copper.
The key to the laser’s usefulness in these applications is the laser beam’s energy density. A laser’s heat is focused in an extremely small area, so it makes a suitable weld by putting less heat into the material than conventional welding processes, minimizing the heat-affected zone (HAZ). Less heat means the weld puddle experiences less combustion activity, which results in less separation of the alloying elements, so the weld seam characteristics are more similar to those of the parent material. The fine-grained structure of the welding seam allows for high degrees of shaping without the heat treatment.
The company uses three Rofin DC series CO2 lasers with outputs from 4.5 to 6 kW. The beam quality, K=0.95 (M2≤1.05) optimizes seam welding on medium to thick workpieces. According to Rofin, the resonator’s use of diffusion cooling rather than gas circulation and the machine’s use of just a few long-service-life components result in an uncomplicated unit that reduces the need for service calls.
Esta Rohr also uses Rofin’s profile welding system (PWS), a package of integrated process sensors for gap recognition, seam tracking, and beam guidance. It operates almost maintenance-free and is resistant to oil, dirt, dust, moisture, and electrical interference—essential prerequisites in harsh industrial environments.
One of the PWS components, the weld sensor, tracks the actual welding position in relation to the joint gap. It also offers the operator a view of the process that enables him to adjust the linear offset of the joined edges or the roller pressure.
“In the case of critical automotive tubes, we can weld more safely than before,” said Frank Lohmann, production operation manager.
Automatic correction of the welding position takes place over the integrated regulation circuit. Linear drives allow fast laser positioning accuracy within a few microns at welding speeds of up to 200 FPM.
The PWS’s modular design and standardized interfaces ease integration into new and existing systems.
In 2006 Esta Rohr processed 3,000 tons of steel with one laser and four TIG lines; these days it does all of its day-to-day production on three laser lines. That said, it hasn’t abandoned TIG welding.
“Today TIG-welded tubes are actually produced only in exceptional cases, for example, when specified in construction plans or for complex inspection requirements for power plants,” said Technical Director Sven Pitzer. When necessary, it converts a line back to TIG.
Despite reducing the number of tube production lines from five to three, the company has increased its annual production by 50 percent, to 4,500 tons of stainless steel.
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