Process expertise in turbine manufacturing

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aerospace

Process expertise in turbine manufacturing

At the Aerospace & Turbine Competence Center (ATCC) in Rorschacherberg, Starrag develops, tests, and optimizes complex machining processes. Recently, the facility has begun manufacturing casings for mobile gas turbines – a contract from Siemens Energy Indianapolis, USA. For Starrag, this is essentially an R&D project.

For many decades, Starrag has been accumulating process expertise in turbine manufacturing at its headquarters in Rorschacherberg. Knowledge that the aviation and energy industries around the world are putting to good use. After all, Swiss mechanical engineers are primarily suppliers of manufacturing solutions. Klaus Struebel, Starrag’s Sales Director for Asia Pacific and a turbine expert, explains: “Most customers don’t just want our premium machines. They purchase them as part of functional, efficient processes – often integrated into complete manufacturing systems. This requires up-to-date process expertise at all times.”

Starrag secures this business through contracts for testing and small-batch production, among other things, which customers use, for example, to manage production peaks. A current order being manufactured at the ATCC is from Siemens Energy Indianapolis. Starrag is responsible for the complete machining of housings for the SGTA05 and KB7X gas turbines, which are produced in only small quantities, for the American company.

Learning by doing

According to Dr. Markus Ess, Director of Technology of the Starrag Business Unit HPS, this order has a special background: “We’re not actually a parts supplier, even though we already have experience in casing manufacturing. However, since the scope of the Siemens contract covers the entire process chain – from unmachined parts to housing components ready for assembly – we saw this as an opportunity to expand and improve our process expertise. After all, our customers are increasingly seeking this extensive expertise.”

Siemens Energy also recognizes that Starrag is not a traditional supplier. The request was made out of necessity. This is because small-batch production was no longer economically viable for the previous supplier, and no other service provider with the necessary expertise and machinery could be found. Starrag, on the other hand, can use its ATCC facility in Rorschacherberg for the majority of the work, as it offers the ideal conditions for machining housings. Spanning approximately 2,000 m2, it is equipped with the latest four- and five-axis Starrag machining centers. In addition, experienced application specialists and developers are on site. “From an economic perspective, it’s an advantage that we don’t have to invest in new machines for the Siemens contract,” says Markus Ess. “For the Siemens casings, we use the STC 1250MT and STC 800MT machines available at the ATCC, which are suitable for cutting and turning, depending on the casing size and requirements.”

Casing manufacturing for Siemens – what needs to be done?

Gas turbines typically consist of several stages: the air inlet (with a booster, if necessary), the compressor (usually a multi-stage unit), the combustion chamber, the turbine itself – which converts the thermal energy of the hot gases into mechanical or electrical energy – and the exhaust. This is also the case with the Siemens SGT-A05, which requires six different casing components for its housing. The newer KB7X generation includes an additional casing.

Each of the rotationally symmetric casings must meet different requirements and varies in size and geometry. The materials also vary depending on the prevailing temperatures. Titanium is used in the cold section, while Inconel is used in the hot section (up to 2,000° C).

Under the contract, Starrag will manufacture the housing components for gas turbines and ship them to the United States as shipsets. A “shipset” refers to a complete set of casings for a turbine.

A mix of very small quantities and great diversity

Ten shipsets are to be delivered in 2025. “We have agreed with Siemens on two deliveries, each consisting of five shipsets,” reports Klaus Struebel. “For us, this means that we manufacture each of the seven different casings in batch size 5, thereby keeping setup and heat treatment costs to a minimum.” Nevertheless, sophisticated production planning is required that takes into account not only machine utilization but also the supporting processes. “In this case, we are not only responsible for turning, cutting, and drilling operations, but also for additional EDM and welding work, heat treatments, and measurement and testing processes,” explains Markus Ess, Head of Technology. “It is precisely this knowledge of process chains that we generate here that is so valuable to us.”

Short preparation time

Only six months were available for technology development. Not exactly abundant, given the wide variety of casings, each with very different requirements. This starts with materials that are difficult to machine and extends to limited access to certain features, such as holes. In order to position attachments such as blades with precision, tight tolerances must be observed. In addition, there are surfaces that require a high degree of surface finish. In addition to the machining processes performed on the Starrag machines, supplementary work must be carried out. Pressure tests are therefore required for deep-hole drilling. Welding and EDM tasks, heat treatment and hardening processes, as well as Cerakote coating, are outsourced to certified external partners. The same applies to the required Fluorescent Penetrant Inspection (FPI) process.

Markus Ess points out that “many of these operations are intermediate processes that take place outside our direct control and interrupt the in-house process. However, our experienced staff succeeded in implementing a well-functioning process chain and completing the order to our client’s satisfaction.” Klaus Struebel adds: “Since our client is based in the United States, we developed a comprehensive project management system that includes weekly online meetings to discuss and monitor progress. Because Siemens wanted to know exactly how the work was progressing and whether we were on schedule.”

Carbide milling cutters developed and ground in-house contribute to optimized machining performance.

Critical one-time costs

Technological development was also subject to economic constraints. After all, Starrag didn't just want to gain expertise. Thus, one-time costs were a major factor, and the clamping device was one of them. Stanislav Stankevich, Senior Application Engineer, explains: “We had originally planned to use four different devices, but that would have made the project uneconomical. That’s why we came up with an innovative, modular clamping concept – a combination fixture that allows us to clamp all seven housing types using a single device.” For this purpose, a matrix is marked on the pallet that specifies the clamping positions for each casing. In this process, the same grooves are always used, but different standard vertical clamping elements are employed. This allows an experienced operator to reconfigure the device relatively quickly.

Further in-house developments were necessary to ensure an efficient machining process. Stanislav Stankevich, who has extensive expertise in the field of casings, was responsible for running in the process and the tools, as well as optimizing the equipment. He explains: “To enable drilling and cutting even in hard-toreach areas, our experts developed extraslim angle heads that feature a special interface providing exceptional rigidity and are capable of handling heavy-duty cutting.” Carbide milling cutters developed and ground in-house contribute to optimized machining performance, and other tools such as deep-hole drills and reverse countersinks also originate from Starrag’s own R&D department.

At the end of the manufacturing process, each part is marked with a serial number in accordance with regulations. Bolts, pins, T-nuts, and supplied components are installed. The shipset is then placed in the reusable packaging in which the blanks were originally delivered. The casing set is then shipped to Siemens in the United States, where the turbine is fully assembled and tested.