energy

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Berthiez RVU vertical grinding machine in General Electric’s gas turbine production

At General Electric Energy Products France, the end to the previous demanding machining of gas turbine components across multiple work steps was marked with a simple “C’est fini”. With that, the Group is now shifting the high-precision complete machining of drive elements over to Berthiez RVU 2800/250 grinding machines.

The energy revolution stands and falls with new, efficient gas turbines, which are used in the new clean and efficient gas and steam power plants, for example. There are particularly high requirements on plants for maximum-precision, low-vibration and at the same time highly productive machining of the drive elements. The Berthiez product range of Starrag SAS from Saint Etienne has made a very good name for itself in this aspect of the energy sector, with its large vertical lathes and grinding machines. The factory of GE Energy Products Europe in Bourogne, France, manufacturers gas turbine discs made of steel and Inconel using four Berthiez machine tools whose high-precision machining (concentricity and axial run-out less than 2.0 µm) is not the only are where they are setting standards. A fifth machine will be delivered in 2019.

30% productivity gains

Focus on XXL: Hydrostatics allow very large components weighing up to 20 t to be positioned within 5 μm on the rotary table of the Berthiez RVU 2800/250 vertical grinding machine. 

Post-processing is a thing of the past

“The key objective in purchasing this machine is to bolster our production capabilities,” explains Patrick Kaufmann, Project Manager at GE Energy Products. “This is achieved in part by reducing machine cycles and post-processing steps, which means that our quality criteria can be met faster.” 

The new formula for success is all about complete high-precision processing, and GE's aspirations in this regard are highly specific: “Due to the specific requirements of our products, we're not really in a position to be repeatedly post-processing workpieces across several work steps. We have therefore chosen to shift production to a multifunctional machine. The new machine fulfils all of our processing requirements. The workpiece only needs to be clamped once. Moreover, stringent requirements around precise dimensions are adhered to.”

The pieces of equipment in question are the new Berthiez RVU 2800/250 machining centers, which are suitable for grinding, turning, drilling, cutting and performing inline measurements on large components (diameter: max. 98.4 inches; height: up to 59.1 inches) weighing up to 20 t in a single clamping operation. The investment was necessary given the huge changes to production conditions seen since purchasing the first two Berthiez RVM vertical grinding machines in 2002. The size of components is continuously increasing, while tolerances are becoming ever more constricted. “We thus had to find a machine manufacturer who was able to combine durability, processing stability and accuracy,” stresses Mr Kaufman. “The situation is further complicated by a specific, changing environment. We therefore need machines that allow us to further refine our products with as little investment expenditure as possible.”

To 5 µm exactly: positioning workpieces weighing several tones

The large facing head has an important role to play in high-precision machining, for example. Rotating at up to 200 rpm with a 68 hp drive, hydraulic collet chuck and hydrostatic positioning unit, it helps position even particularly heavy workpieces with a deviation of 5 µm. The various tools bring into position a multifunctional tool head that can swivel through ± 90° and travel along the linear X and Z axes. A 60 hp milling spindle (max. speed of 6,000 rpm) drives the grinding discs and the drilling and milling tools. Lathe tools and probes are attached separately.

One of the main advantages of the multifunction head is the integration of two complementary and independent retainers, each of which has a diamond dressing roll and a nozzle that are tailored to the shape of the grinding disc. These two attachments are arranged on two controlled linear axes that follow the wear of the grinding disc and ensure continuous dressing and efficient lubrication (40 bar, 18,307 in3/min) of each grinding disc. This makes dressing on a distant dressing station completely unnecessary. Simplified working processes also boosts productivity considerably.

Further boosts to productivity: Unmanned shifts with a robot

To further bolster productivity, the long-standing Starrag customer from the energy sector ordered three further Berthiez RVU 2800/250 machines with new robot tool change systems in 2015. These machines now enable unmanned shifts. Automation has had a positive impact on production: Integrating a robot into the tool loader enables all tools to be housed together in a single storage facility. “The greatest benefit we have seen in all of this is the elimination of components used in our previous lathes, including those with a measuring rod and slide bar,” reports Mr Kaufman. “The machine is also able to process larger elements.” By using a robot instead of a pallet changer, the company requires fewer tools in storage, given that a single tool can now be used for various applications. “This has enabled us to considerably reduce our costs. We believe we can still make further headway with this.” All things considered, experts predict productivity gains of around 30 %.

The robot has direct access to seven pallets, as well as 78 lathe tools, drilling tools and milling tools. Each pallet consists of the grinding disc, its dressing roller and its nozzle, both tailored to the shape of the grinding disc. The robot selects the required tool or grinding system and attaches it directly to the tool head. Operation and programming are facilitated by a digital control system (Siemens Sinumerik 840 D sl) with the Berthigrind user interface from Starrag, which also factors in the special features of the new robot change system. It is the digital icing on the cake for a successful model expanded for the purposes of “Industry 4.0”. It ties into the strategy of the major energy group rather well, which as Mr Kaufman puts it, “continually seeks out new, powerful technologies with the capacity to adapt to various processes, thereby ensuring continuous improvements to the quality of our products.” 

Berthiez RVU 2800 grinding machines

Sabine Kerstan
Sabine Kerstan
Starrag Content Manager

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