aerospace

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State-of-the-art manufacturing solutions for turbine housings – including machines, tools and processes

In turbine construction for the aviation and energy sectors, manufacturing companies rely on Starrag machines – because they are among the most powerful and precise solutions the market has to offer. This applies not only to the manufacture of engine blades and blisks, but also to turbine housings. Decades of experience have gone into the wide range of Starrag machine tools for turning, milling, drilling and grinding. And that’s not all: Starrag offers solutions for the entire manufacturing process. In-house, individually developed devices, special tools, angle heads and spindles through to fully automated production systems ensure maximum productivity.

“Within the Starrag Group, we have extensive technical expertise in the machining of aero-engine, gas and steam turbine housings, which we turn into advanced, turnkey solutions.”

Klaus Struebel, Segment Sales Manager Aerospace & Turbines

T he housings for aircraft engines, steam, and gas turbines – also known as casings – are available in small and large sizes. They are becoming ever more complex and are increasingly made from materials that are difficult to machine. This usually requires several processing technologies, ideally combined in one machine or in flexible manufacturing systems. Thanks to its wide range of machines, Starrag can meet all requirements.

The Starrag STC series covers a large area of turbine casing machining, with its various sizes and designs capable of handling casing diameters up to 130 in. (3,300 mm). The machines are destined for economical 5-axis heavy-duty machining of sophisticated casings made of titanium and Inconel. For machining smaller casings, Starrag can offer the Heckert X series in MT design. They allow high-precision turning and milling on one machine.

The 5-axis X variants of this compact series add another option: The positioning axis in the rotary swiveling table is ideal for angled holes, which are often required in casings. If the huge steam and gas turbine housings with diameters of up to 472 inch (12 meters) need to be machined, Starrag can rely on correspondingly large Droop+Rein portal machining centers, which are built at Starrag Technology GmbH in Bielefeld.

The large vertical Dörries lathes, which are also used for steam and gas turbine housings, are also produced there. Vertical turning and grinding is also the specialty of the Berthiez machines from the Starrag plant in St. Etienne, France, which are mainly used in aircraft construction.

For ultra-precision machining on casings, for fine boring and milling as well as precision grinding, Starrag has the SIP jig boring machines – horizontal or vertical – in its range, which are produced in Vuadens in Switzerland. The Bumotec CNC turning/milling centers, which produce small, high-precision, and complex parts in five axes and with accuracies of just a few micrometers, also come from this plant. In the production process of casings, they are used for components to be mounted, such as injection nozzles.

The UK subsidiary TTL, which performs MRO (maintenance, repair, and overhaul) tasks, fulfils an important role in the turbine housing sector. Specializing in Siemens NX CAM, which is commonly used in the turbine environment, and as a process developer for adaptive milling, TTL is the ideal partner to take on maintenance and repair tasks on casings. After build-up welding and subsequent high-precision milling, the expensive housings are almost as good as new.

Klaus Struebel, Segment Sales Manager Aerospace & Turbines

“ Standardized interfaces and pallets allow us to speed up the process and increase accuracy.”

Alexander Fitz, Sales Director for Aerospace & Turbine at Starrag AG, explains: “Machine tools are one of our core competences, which no other company in the world can offer in terms of their technological breadth and varying sizes. We also have an in-depth technical understanding of the entire process chain required to manufacture ready-to-install turbine housings.”

This expertise enables Starrag to combine various machining operations in one machine. Klaus Struebel is Segment Sales Manager Aerospace & Turbines at Starrag with decades of expertise in the field of turbines. He points out that the integration of milling, turning, and grinding with self-developed angle and other machining heads can reduce clamping positions and increase productivity. “If one machine is not sufficient for machining, we can combine our different product ranges in flexible manufacturing systems, for example a Starrag STC with a Berthiez vertical turning-grinding center,” says Struebel. “Standardized interfaces and pallets allow us to speed up the process and increase accuracy. If required, we integrate additional washing, drying, and measuring processes.”

It is not only in such automation solutions that the process expertise gained over many years is reflected in numerous projects. “We have been involved in aero-engine casings since the 1980s and, in addition to processes, we also develop numerous components, from carbide tools, tool heads and spindles, through to devices,” mentions Klaus Struebel.

Gaining a market advantage from tools adapted to the process

Starrag in Rorschacherberg has been developing and grinding carbide milling cutters for aircraft and turbine components made of difficult-to-cut materials such as titanium, Inconel, or high-alloy steels for many years. In most cases, these are customized products that are adapted to the respective machining process, to the component, the machine, the material and other concomitant circumstances. They ensure faster machining and have a longer service life than standard tools – an important contribution to a stable, repeatable process.

Machining expert Struebel cites the required bores, “especially the internal ones, as a major challenge in housing machining. We develop special interchangeable angle heads for this purpose, and these also have to be able to cope with the limited space available.” This requires a great deal of experience – as does deep-hole drilling with very small diameters in titanium or Inconel. Tight tolerances must be maintained for the drill holes so that add-on parts – such as blades – can be fitted precisely.

Klaus Struebel, Segment Sales Manager Aerospace & Turbines

“We provide our customers with higher productivity by looking at the entire process.”

Another of Starrag’s strengths is the gear spindle manufactured in Rorschacherberg, which remains thermally and mechanically stable and is extremely durable even when processes are running for 80 hours. It is used on STC machining centers and Droop+Rein gantry machines. For the latter, different special heads are available, including angle heads in various lengths, with different torques and speeds. Another advantage mentioned by Klaus Struebel is “that we can balance on almost all machines. Because the roundness of the casings is extremely important.” Once the fixture and workpiece are mounted on the pallet, an optimization process takes place in which the imbalance is determined and corrected. Klaus Struebel summarizes: “We provide our customers with higher productivity by looking at the entire process. We don’t just sell a product, we make sure that the machine fits the machining application in terms of size, technology, axis configuration and kinematics, and then optimize the process with the appropriate peripherals.” This usually takes place at the ATCC (Aerospace Turbine Competence Center) in Rorschacherberg, which offers the best conditions for this. Covering an area of around 21,528 sq ft (2,000 m2), it is equipped with the latest 4- and 5-axis Starrag machining centers. Developers and application specialists are also on call. The ATCC is also able to produce test and small series for customers.

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