At the Aerospace & Turbine Competence Centre (ATCC) in Rorschacherberg, Switzerland, Starrag develops, tests, and optimises complex machining processes. Recently, the facility has begun manufacturing casings for mobile gas turbines under a contract with an American customer. For Starrag, this is essentially an R&D project.
For many decades, Starrag has built process expertise in turbine manufacturing at its headquarters in Rorschacherberg, knowledge that the aviation and energy industries worldwide 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, which customers use to manage production peaks. A current order is being manufactured at the ATCC. Starrag is responsible for the complete machining of a small quantity of housings for various gas turbines for the American customer.
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 part supplier, even though we already have experience in casing manufacturing. However, since the scope of the 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.”
The customer also recognises that Starrag is not a traditional supplier. The request was made out of necessity 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 most of the work, as it offers ideal conditions for machining casings. Covering approximately 2,000m2, the facility is equipped with the latest 4 and 5-axis Starrag machining centres. In addition, experienced application specialists and developers are on-site. “From an economic perspective, it’s an advantage, as we don’t have to invest in new machines for this contract,” says Markus Ess. “For the 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 – what needs to be done?
Gas turbines typically consist of several stages. This includes the air inlet, the compressor (usually a multi-stage unit), the combustion chamber, the turbine, which converts the thermal energy of the hot gases into mechanical or electrical energy, and the exhaust. This is also the case with the smaller casings, which require six different casing components for their housing. The newer generation includes an additional casing.
Each of the rotationally symmetric casings must meet different requirements and vary 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 at up to 2,000 degrees Celsius.
Under the contract, Starrag will manufacture the gas turbine housing components 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 were delivered in 2025. “We agreed 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 batches of five, thereby keeping setup and heat treatment costs to a minimum.”
Nevertheless, sophisticated production planning is required to consider machine utilisation and the supporting processes. “In this case, we are responsible not only 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. These range from materials that are difficult to machine to limited access to certain features, such as holes. To position attachments such as blades with precision, tight tolerances must be maintained and a high degree of surface finish achieved.
In addition to machining on Starrag machines, supplementary work is needed. Pressure tests are required for deep-hole drilling. Welding, EDM, heat treatment, hardening, and Cerakote coating are outsourced to certified partners, as is the Fluorescent Penetrant Inspection (FPI).
Markus Ess points out: “Many of these operations are intermediate processes that occur outside our direct control and interrupt the in-house process. However, our experienced staff implemented a well-functioning process chain and completed 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. This kept the customer informed on how the work was progressing and whether we were on schedule.”
Critical one-time costs
Technological development was also constrained by economics. After all, Starrag didn’t just want to gain expertise. One-off costs were a major factor, and the clamping device was among 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 to specify 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 quickly.
Further in-house developments were necessary to ensure efficient machining. Stanislav Stankevich, who has extensive expertise in the field of casings, was responsible for overseeing the process and the tools, as well as optimising the equipment. He explains: “To enable drilling and machining hard-to-reach areas, our experts developed extra-slim angle heads that feature a special interface providing exceptional rigidity for heavy-duty cutting.” Carbide milling cutters developed and ground in-house contribute to optimised 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 the United States, where the turbine is fully assembled and tested.
