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“The highest degree of accuracy is required when machining high precision blades for turbines”, explains Marc Weiß, Senior Manager Flexible Production Systems at MTU Aero Engines in Munich. The company is among the leading group of manufacturers of civil and military aerospace propulsion systems of all performance classes as well as stationary industrial gas turbines. Turbine blades are cast parts, usually made of nickel-based alloys that are difficult to cut. Highly complex geometries need to be machined with extremely high precision. During operation, the blades have to endure the most extreme conditions – tremendous centrifugal forces, temperatures close to melting point and heavy vibrations. A break could lead to destruction of the power plant. For this reason, extremely strict quality requirements apply for all steps of the manufacturing process. For the development of a new, highly automated production system, therefore, only partners that were able to guarantee the highest level of quality and reliability were considered.
A quantum leap in automation
“The requirements of MTU were vast and necessitated more than a ten-fold increase in staff productivity”, remembers Michael Appel, Regional Sales Manager for Automation Systems at Liebherr-Verzahntechnik GmbH in Kempten. Productivity had to be massively increased in order to meet the enormous increases in demand. In the past, one employee was needed to manually operate one to two machines in a production chain of individual stations. In contrast, the new solution relies on just one employee to achieve a very high processing depth at four parallel-operating, fully-automatic grinding machining cells. Each cell consists of a PROKOS XT 6-axis grinding machining centre from BLOHM, which is supplied by a robot from AMT. The robot receives workpieces, clamping fixture, dressing tools and gripper tongs from a fully-automatic Liebherr pallet handling system (PHS). Thanks to its 250 pallet slots, it is able to supply the machining centres for at least 66 hours unmanned to allow the systems to work through a complete weekend also with flexitime operation. A loading portal (LP) - also from Liebherr - runs on the other side of the manufacturing cells via which the machines can be supplied with tools and grinding discs. The “brains” of the outfit is a control system from SOFLEX, which networks all of the plant units together and enables self-organised production to the furthest degree. This new flexible production system (FFS) can machine a mixture of about 15 different component types in any number required. Moreover, the workplace for the machine operators has also been laid out in a disabled-friendly manner.
Liebherr is one of the world’s leading specialists in automation solutions. The Liebherr Automation Systems product division is part of Liebherr-Verzahntechnik GmbH in Kempten and has decades of experience. Projects can be implemented in all areas of manufacturing and installation with a wide range of products such as linear gantries, pallet handling systems and conveyor systems. In cooperation with renowned machine manufacturers, the Automation Systems division implements line linking, the automation of machining centers and the system integration of machine tools.
Grinding machining centers
Gear grinding machines from Blohm Jung GmbH are regarded as the benchmark for productivity, performance and precision worldwide. Customized production systems are also manufactured in addition to standard machines for surface and profile grinding in single pieces and small series. A modular system enables solutions for almost any workpiece size. Blohm Jung GmbH is part of the UNITED GRINDING Group, which is represented internationally by its own subsidiaries in India, China, Russia and the USA. It is a technology leader in the aircraft turbine industry. The systems used at MTU have six axes and a rotary swivel table with a zero-point clamping system, a profiling station with diamond-tipped dressing rolls for the grinding bodies and a tool changer for grinding wheels, drills, hobbing cutters and measuring probes. The machining software used was specially developed by MTU.
The AMT installation robots used in the individual cells perform a very difficult task. AMT is an installation and fittings specialist with extensive experience, including in the automotive industry. The robots must remove the individual blades from frames, place them in a special clamping fixture with extreme precision and then clamp them together with a fitting. The clamping fixture, including the clamped part, is then transferred to the grinding machining center where it is fixed using a zero-point clamping system. This operation is extremely difficult and requires a great deal of expertise with regard to both the transfer and the sensitivity of the fitting operations. The turbine parts must be treated like raw eggs here, because even the smallest damage or scratches on the surface would be unacceptable.
The system that we have created together is very complicated and way more advanced than the technology employed to date
A control system from SOFLEX is used for the manufacturing control. This digitalizes, networks and organizes people, machines, systems, logistics and products directly with each other and optimizes the entire value chain up to the fully automated provision of workpieces and operating equipment. The software plans and organizes order processing, controls workpiece throughput and the provision of tools, NC data, clamping fixtures, etc. and transmits the required manufacturing information to the processing machines or the manual workplace. At the same time, the system acts as a link between manufacturing and the higher management levels by automatically exchanging information with the other IT structures in corporate planning (ERP, CAD/CAM and PDM systems).
Close partnership with engineering
“The actual challenge for Liebherr was to select our modular automation components in such a way and to link them with the other systems that a smooth interaction was facilitated”, adds Michael Appel. Liebherr also took on the responsibility for CE certification of the entire system. Cooperation in the very small, but very efficient engineering team was coordinated by MTU. The partner organisations, in each case are among the top providers in their markets, worked on equal footing as a team. They exchanged ideas and developed the decisive characteristics of the system in dialogue. This also included details like an auxiliary function for the operator where a laser pointer indicates the position to which the next part to be sorted belongs.
Criteria for partner selection
“The system that we have created together is very complicated and way more advanced than the technology employed to date”, says Marc Weiß enthusiastically. Reportedly, Liebherr impressed not just by having suitable products in the area of automation: The fact that the technology used is very well established and has proven itself very well in practice among many users was also important. A particular highlight was said to be the competence of the sales department. Technically, Mr Appel proved to be an extremely capable partner who became heavily involved and was able to provide many good ideas. The ramp-up of the overall system went successfully and the results so far have met the planning specifications. With the new system, MTU considers itself to be well equipped for the requirements of the future and the expected shortage of skilled workers.