The overhead gantry milling machine (FOG) series of Starrag's Droop+Rein product range celebrates its quarter centenary this year. Reason enough for Ulrich Wiehagen, Head of Sales and Plant Manager at Starrag Technology GmbH in Bielefeld, to take an exciting look back at such highlights as the world's first high-gantry machine for simultaneous roughing and finishing.
Mr Wiehagen, you've been part of the scene since 1999 and have guided and supported a large part of the FOG success story. How did it all start, and what were the first highlights?
Ulrich Wiehagen: At the suggestion of notable customers in the field of toolmaking, the company Droop+Rein developed a highly dynamic milling centre in 1993 in which the tool performs all movements and therefore the workpiece is no longer moved. The beds are not installed at floor or corridor level as with more familiar gantry machines, but rather on columns. This eliminates the moving columns and means that the tilting movement typical of floor-guided gantries is no longer an issue. The new development thus meets all requirements for a highly dynamic, extremely precise HSC machine for the production of high-end surfaces in toolmaking. It is a concept that has now been copied by many competitors. There are even some that are bold enough to claim that they supplied the first machine with roughing and finishing capabilities for toolmaking — but we can prove that we did this as early as 1998. And since 2000, we have even offered a fork-type milling head in which both mechanical spindles and motor milling spindles can be used.
The FOG series isn't just used in toolmaking now though is it?
Ulrich Wiehagen: Soon afterwards we also began supplying to the aviation sector, where machines with 40 kW spindles for highly dynamic and high-precision milling of the outer cylinders of aircraft landing gears are tried and tested. Thanks to these machines we have now captured a global market share of over 80%.
But machining heavy workpieces quickly and precisely on a machine also requires a highly rigid base. Why do you rely on a U-shaped foundation?
Ulrich Wiehagen: It's something we introduced about 15 years ago as it offers a very high degree of rigidity and also lowers the necessary foundation depth by about a third, thus reducing the construction effort. In addition, the dynamic load capacity increases. Another important cost-saving effect is the way in which the geometry of the machine remains constant for a very long time, so the effort required for re-calibration during the life of the machine is much less. After all, the calibration of a large portal milling machine can take between five and ten days, during which it is not earning any money. The U-foundation is the most rigid—and therefore the best—variant for setting up a high-gantry machine.
What would you say is your unique selling point?
Ulrich Wiehagen: We are the only manufacturer to date to offer a standard machine with integrated tool for surface hammering or machine hammer peening (MHP). During machining, a pulsed impact ball hammers rapidly at a defined power and frequency. This process, known as peening, compresses the boundary surface layers to a depth of 10 µm. So in principle, the peening tool behaves like any normal tool that can be inserted into the machine and then controlled by the CNC. MHP technology has been so well received that a major German automobile manufacturer is already using it at three toolmaking locations. It is the only MHP application in industrial-series production anywhere in the world.
What sets the FOG series apart from competitor machines?
Ulrich Wiehagen: In toolmaking and mould making, this multifunctional machine guarantees the highest surface quality and exceptionally efficient production. There are benchmark tests in which 15-year-old FOGs perform better than the latest developments from competitors. The FOG produces high-precision surfaces of consistent quality and with a proven availability of 94% — and does so for years. A special version of the machine is also used in the high-precision production of aircraft construction in which, for example, complex drilling patterns on large workpieces must match to a few hundredths of a millimetre. We adhere to the strict regulations governing interchangeability of parts apply to ensure that the drilling patterns of workpieces machined independently of one another at different locations also fit together. This is one of many examples of how successfully the FOG series has already proven itself as a reliable means of production in a wide range of applications and in a variety of industrial sectors.
What happens at the end of a machine's life?
Ulrich Wiehagen: To date, not a single FOG has ended up on the scrapheap. If a Droop+Rein FOG is 15–20 years old, for example, it is worth modernising the control system and possibly some of its mechanical components. Thanks to this retrofit, which usually only costs a third of what it would to invest in a new machine, the customer receives a production tool in mint condition for the next 15–20 years. With a FOG, however, we can expect a service life of more than 30 years.
A regular customer inspired you to build the FOG: Has it happened again?
Ulrich Wiehagen: Indeed, and more than once. The latest innovation is the new Droop+Rein FOGS HD (heavy duty), which was inspired by CONCAD GmbH in Walldürn (in Germany's Neckar-Odenwald district). This particular company was looking for a machine for the high-precision complete machining of large, heavy tools, especially for outer skin parts in vehicle body construction and machine components in a single clamping operation. However, because there were no machine types that combined all of the ideal features, we crossed the two machine types FOGS and the portal machine Droop+Rein TF to form a new machine concept in which we placed the modules of the portal machine on top of the foundation: A high-gantry machine for heavy and precise machining with hydrostatic guides in all linear axes.
How was the new product received by customers?
Ulrich Wiehagen: It was met with an unusually positive response from many interested parties. Our FOGS NEO N40 is the first choice for tool and mould makers who need to produce first-class surfaces with high dynamics and high precision and who require the additional benefit of 40-kW roughing performance.
If customers primarily need milling power of between 50 and 100 kW for heavy-duty machining tasks and require dynamic finishing capability without compromising surface quality as an additional benefit, then our new FOGS HD is the first port of call. The HD is also ideal for use in mechanical engineering for workpieces that are difficult to machine and have high precision requirements. In general, we have noticed that more and more FOG machines are replacing table-top portal machines with fixed crossbeams. The high-gantry version requires approximately 40% less installation space for the same working area. The workpieces do not enter the dynamic mass, multiple clamping is possible during machining time, and the guideways are optimally protected above the clamping surface.
