Any manufacturer of XXL machine tools can probably come up with gigantic data and fantastical characteristic values. But the real size of this kind of investment is often not seen until after years of operation, as a visit to satisfied Starrag customer NEUMAN & ESSER GmbH & Co. KG in Übach-Palenberg showed.
Sometimes all it takes to make you listen is a brief comment. “And there at the back is the Droop+Rein, one of our best workhorses in the stable,” says Alexander Peters, Managing Partner of NEUMAN & ESSER GmbH & Co. KG from Übach-Palenberg near Aachen (NEA GROUP), while on a tour of the company. “We are very satisfied with this machine tool, its performance and the service provided by the manufacturer.”
He is talking about a Starrag portal machining center with adjustable crossbeam and movable clamping table (Droop+Rein T 30 40 DT R50 C). Currently the largest machine tool investment in the history of the NEA GROUP has proven itself in the complete machining of components – and especially demanding machine components – since 2011. These are primarily components for piston compressors in compressor systems handling all technical process gases and for pendulum-mill housings in crushing technology.
“We have had the portal machining center in continuous operation since 2011,” says Simon Prell, Manager of Mechanical Production. “We mainly use it to machine crankcases and spacers as part of three-shift operation. It stops gas escaping from the cylinder into the crankcase and oil from moving into the cylinder from there.” The Rhineland-based company also uses the machine tool to produce cast components for pulverisers. This usually entails complete machining, which is performed with or without coolant depending on the workpiece. Minimal-volume lubrication, however, is not required owing to the high-strength materials, such as iron and steel alloys with a high nickel or chromium content.
The new arrival went down well in Übach-Palenberg even during the commissioning phase eight years ago. The company says it was one of the smoothest introductions they had ever experienced, despite involving switching to a completely new form of machining. At that time, crankcases were still machined on a horizontal drilling rig, one of the main problems with which were long periods of non-productive time due to time-consuming clamping processes. By contrast, a portal machining center machines the extremely heavy workpieces more elegantly and quickly in a single clamping process, thereby greatly reducing machining times. The crankcases can also be machined in their operating position. According to Prell, the portal machine is particularly distinguished by the fact that the different machining heads can be optimally positioned and aligned.
Right from the start, Production Manager Dipl.-Ing. Achim Hoch was aware of the portal machining center, which in his experience is “a workhorse that you can always rely on.” “When machining crankcases on a horizontal drilling rig, we always had to reclamp them several times and move against the angle,” recalls Hoch. “However, each additional reclamping process led to faults. And finally, after an informative visit to the Munich BMW tool shop which had several Droop+Rein portal machining centers, we decided to invest in this machine.”
Technician Jürgen Seek, who was working on a 45-tonnes crankcase made of ductile cast iron (GGG 40) during our visit, is also satisfied with this investment. “Thanks to the use of ceramic tools, we can largely manage without coolant,” Seek explains about the dry machining process. He is glad he no longer has to reclamp the workpiece multiple times. The gigantic component is machined in three steps: After milling the lower, lasered surface, Seek rotates the housing by 180° to allow the bottom of the housing to be machined. He then turns the GGG 40 component back to its initial position for complete machining.
Although it sounds hard to believe, this is a routine job for the machinist. “The machine can do much more,” he explains to us. “We’ve never been able to really wear it out – not even when even test-machining titanum.” But what has been his most difficult job so far? Seek thinks for a moment and then says: “Retrofitting a 27-tonnes crankcase was extremely complicated. The crankcase, which was not assembled, was very unstable and difficult to clamp. Yet despite these unfavorable conditions, we had to machine it exactly to hundredths of a millimeter.”
The NEA GROUP has not regretted their decision. The investment has paid off because, depending on the size, the machining time has fallen by an average of 30 to 40%, and accuracy has doubled even in critical areas. Tolerance in the bearing race is now only 20 µm instead of 40 µm.
Starrag checks the geometry completely every two years and realigns it if necessary. Prell: “So far the realignment has been to such a small degree that we could actually go without it. This unusually high permanent accuracy benefits us, for example, in retrofitting work with a high proportion of machining.” To ensure that even such demanding jobs are performed with precision, the NEA GROUP measures the components using complex 2D and 3D laser technology.
In eight years of continuous operation, there has not been a single failure, with Starrag only having to replace the ball spindles once. According to Prell, this replacement is not unusual with operations where “we often have to move the moving crosshead”. While he and his team have rarely seen Starrag service technicians, the department manager has always been satisfied with their very high-quality work. “We have a permanent contact who knows us well,” says Prell. “You can see that there is a good communicative relationship between our employees and the Starrag service.”
But can satisfaction with the Droop+Rein T series portal milling machine be substantiated and summarized? “As a typical single-part manufacturer of classic German mechanical engineering with small batch sizes, it’s difficult for us to name specific production improvements,” says Hoch, Production Manager. “Furthermore, how long the machining process takes is not the most important thing for us. We prioritise quality and the portal milling machine is excellent.” “The machine does exactly what we hoped it would,” adds Prell. “So far we haven’t exceeded the limits of its abilities.”