Success Story

Unmachined parts go in, finished parts come out

Starrag FMS enables fully automated turbine blade production

The latest flexible manufacturing system (FMS) designed and created by Starrag is heading to China. A company active in the Chinese aviation industry annually machines 35,000 Inconel or titanium-forged turbine blades right through to completion via a fully automated process. The operator simply inserts the unmachined parts into the magazine and then removes the ready-to-install blades at the other end. 

Flexible manufacturing systems are becoming a global trend. The aviation and energy industries in particular capitalize on the qualitative and economic benefits offered by automated series production. Starrag is a premium supplier for these highly demanding systems and has been designing and supplying FMSs for manufacturing turbine parts and structural components for aircraft for over twenty years. Around 60 automated multi-machine systems have been created during this time, allowing the company to accumulate a wealth of technological experience. 

Dr Markus Ess, Head of Development at the Starrag site in Rorschacherberg explains: "In addition to our core competences in the fields of machine tools, tools, fixtures and the CAM system, we have an extensive amount of expertise in turn-key projects. In the FMS, we are supplementing our machining technology with automation components and all other necessary components so that we can provide the customer with a complete, reliable production system."

The benchmarks set by the latest plant are higher than ever before. The FMS ordered by this Chinese aviation company must be able to process 35,000 turbine blades via automated processes each year. This total volume comprises four different blade types in sizes ranging from 80 mm to 200 mm. These blades are known as "variable guide vanes" and they are positioned in the vertical part of the turbine so that they can be adjusted to allow the flow or thrust to be modified as needed. As the actual batch sizes for the four types equal around 200 parts, the FMS must ensure a high level of precision and the corresponding throughput while also exhibiting a high degree of flexibility. 

A demanding production process

Blade production was previously carried out without major automation across various individual machines and turbine blades were still polished by hand as a final stage. This is why the customer had a clear idea of what they wanted from the new Starrag FMS and of the added advantages they wanted to benefit from: The process had to be streamlined through modern production technology, with maximum process reliability and a higher level of quality in the final product. Particular emphasis was placed on automating the system to prevent any errors arising from manual operation.

"To some extent, the FMS should be a black box system in which the operator only loads a magazine with unmachined parts at the start of the process and then removes the ready-to-install turbine blades at the end", explains Markus Ess. "Designing the overall process was a major challenge. Which sequence of operations is useful? How should handling be performed?"

For example, to prevent the operating company from having to shut down the entire plant when carrying out maintenance work, the development team led by Markus Ess arranged the system into two almost identical, redundant sections. Each section contains a setup area, a handling robot mounted on a 20-meter-long gantry, a washing system, a polishing robot, a coordinate measuring device and a labelling system. The main task of machining the product is completed by a total of seven Starrag LX 021 machining centres, four of which are assigned to one side while the other three are assigned to the other side.

markus ess

A robot is responsible for the entire handling process

A material repository that the plant operator loads with unmachined parts serves as the interface for the automated cell to a certain extent. It is from this repository that the gantry robot picks up a forging blank, clamps it in the first fixture and transports it to the machining centre. The first stage in the machining centre is a measurement process, during which the intended geometry of the finished part is measured against the blade blank. This process takes place in the machining centre itself. This first operation also includes milling the clamping point for the second setup. The robot then clamps the component in another fixture that transports it back to the machine. In doing so, the component is loaded into a pallet system that also acts as a compact means of intermediate storage, thus decoupling the transport mechanism from the machining process.

Starrag FMS

Starrag centres take over complete hybrid machining

The next step is the machining of blanks forged from Inconel or titanium. In addition to the turbine blades undergoing a five-axis milling process, two shaft attachments must be rotated to allow the blade to be adjusted during subsequent use. "Our LX 021, a machining centre designed to work on small components—primarily for aircraft engine blades—is well-suited to this complete hybrid machining process", says Markus Ess.

Starrag developed the LX series specifically with the highly precise, efficient, simultaneous five-axis machining of turbine blades in mind. The smallest version is the LX 021 — "As the first blade machine, the rotation speed of this system is really something", emphasises the Head of Development. "To make this happen, the LX 021 is equipped with a rapidly rotating circular axis, which reaches speeds of up to 4,000 rpm. This is essential for the complete machining of small blades with shaft attachments of approximately 10 mm." As far as the milling process is concerned, the LX 021 provides the high level of precision required on the free-formed turbine blade, thanks not only to the high-quality machines, but also the skill of the machining process: The RCS CAM software developed by Starrag is used to generate the milling programs, while the company's solid carbide milling tools ensure optimum cutting performance.

Based on the annual quantity of parts to be produced, the Starrag developers calculated that seven of the LX 021 machining centres would need to be integrated into the FMS. All seven of the machining centres have the same features and can perform the same tasks. 

High-quality components complement
the automated production cell

After machining, the gantry robot transports the components to the washing station. Once all coolant residue has been removed from the components, they undergo a polishing process. A robot programmed especially for this task ensures that the stringent surface requirements are met. The final check is then carried out in a 3D coordinate measuring cell, where all features specified by the customer are checked. Next, the turbine blade is labelled with a unique identification number so that each production step can be traced at a later stage. Finally, the gantry robot takes the completely manufactured component from the final fixture and places it back in the material repository, where the operator can then remove the finished part.

The entire plant is controlled by a cell controller with a PPC system. All of the system's necessary functions and strategies were defined by the development team led by Markus Ess. The Head of Development points out that it is not just the cell that is included in the order — Starrag is also responsible for coupled auxiliary processes, such as setting up the tools. "We supply suitable equipment for shrinking and measuring and ensure that data is transferred reliably to the FMS, thus ensuring that the machining centre controls are always provided with the correct tool geometries."

As Starrag usually acts as a general contractor in the deployment of such manufacturing systems and assumes complete responsibility for the process—from the design of the plant to the delivery of the turn-key system—the company closely monitors the associated partners and suppliers involved with any additional components. From the customer's perspective, Markus Ess believes that the following is a "must": "We work exclusively with leading companies that are able to match our high level of performance and availability."

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