98 Aprile 2014 www.techmec.it

DEVELOPING A TAILOR-MADE PIECE OF EQUIPMENT BACKED UP BY THE RELIABILITY OF A MACHINE ALREADY AVAILABLE IN THE CATALOGUE: GIORIA SUCCEEDED IN MATCHING THESE FACTORS TO PROVIDE A PRESTIGIOUS US ENDUSER WITH A SOLUTION FOR ALL REQUIREMENTS.

The R/152 5000x1000 CNC is a heavy duty cylindrical grinding ma-chine for the machining of outside

diameters and faces; it is a machine de-rived from a catalogue model although it stands out for remarkable innovations. The machine is composed by two beds, the wheel bed and the workpiece bed. The first mirrors already existing machine models, even if the structure was enlarged to account for the diameters to grind which range 100 to 2000 mm. For this purpose the spacing between the wheel carriage guideways has been increased to grant the support of the wheel slide over the entire cross travel. Besides, in this application, a rotary B Axis of the wheelhead was specified, with a consequent increase of the weight of the whole carriage.

FOR THE LARGEST PLANT IN THE WORLD FOR GAS TURBINES MANUFACTURING The grinding machine is aimed at grinding tur-bine shafts and is used at the world largest manufacturing site for the production of gas tur-bines in South Carolina, USA. Many other GIORIA grinding machines belonging to the same fam-ily are used in several other sectors, such as the grinding of rolling mill rolls. In those cases com-ponents are as heavy as gas turbine shafts but they are as a rule ground on steadies and cen-tres are only needed to prevent axial sliding. In the specific case of the R/152 5000x1000 CNC, steady rests cannot be used due to the shaft ge-ometry and the type of machining therefore the weight rests only on the centres.

[ MOVING-WHEEL CYLINDRICAL GRINDING MACHINE ]by Andrea Pagani

R/152 5000x1000 CNC

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This grinding machine can grind parts with maximum length of 5 metres (200”) and di-ameters up to 2 metres (80”). A such size of parts weighing up to 30 tons (66000 lbs) supported only between centres, rose doubts about the use of mechanical bear-ings for the work spindle and the tailstock quill in live execution. For this reason, GIO-RIA designers opted for a hydrostatic so-lution to avoid an excessive sizing of the rotating spindles in workpiece bed directly responsible for the achievement of machin-ing accuracy.This is not a new concept at GIORIA: the company has been using hydrostatic bear-ings for the wheelhead spindle for quite a long time and this technology has been simply transferred to other rotary axes.

MAKING GREAT STRIDES The shaft is the fulcrum of any gas turbine and its accurate grinding is crucial to grant the efficiency, the operating runout and the turbine lifetime. The grinding of the hydro-static bearings of the turbine shaft and the seats where the blade crowns are mounted must happen within an overall runout tol-erance of 0,003 mm. This has justified the use of the hydrostatic solution. Large me-chanical bearings capable of granting simi-lar tolerances are difficult to mount and not easily available. Moreover, keeping the precision for the whole service life of the machine posed a further deterrent for me-chanical bearings.Other grinders installed at the customer’s site several years ago could barely provide the required accuracy only thanks to op-erators skills and “virtuosity”. Those table-moving machines, where linear and rotary movements sum up on the workpiece line, proved totally unable to grind shafts ex-ceeding a certain weight within the pre-scribed tolerances. Hiring subcontractors was the only possibility, however since the shaft is key for the proper operation of the turbine, it was decided to rise up to 30 tons the weight of parts ground in-house by in-vesting in the new grinding machine.The grinding machine is completely made of

cast iron: the castings of the wheel bed and the workpiece bed are positioned side by side and are spaced basing on the diameter range to grind. In this respect, the machine is very much versatile for it can grind ODs from 100 to 2000 mm, thanks to a wheel-head cross slide travel of almost one meter.The use of cast iron for the structures is fundamental for vibration damping. This is an irremissible factor at GIORIA, which can rely on its own foundry. This has allowed

The machine is intended for the machining of gas turbine shafts

HYDROSTATIC SOLUTION THE R/152 5000X1000 CNC MUST GRIND SHAFTS FIVE-METERS LONG WITH A DIAMETER OF UP TO TWO METERS WEIGHING UP TO 30 TONS ONLY SUPPORTED ON LIVE CENTRES. FOR A SUCH DEMANDING TASK THE USE OF MECHANICAL BEARINGS IN THE WORK SPINDLE AND TAILSTOCK QUILL WAS DISCARDED. IN ITS PLACE, THE HYDROSTATIC BEARING OF THESE ROTATING ELEMENTS ON THE WORKPIECE BED DIRECTLY ENTRUSTED WITH THE ATTAINMENT OF MACHINING PRECISIONS WAS SELECTED.

MACHINE OF THE MONTH

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MACHINE OF THE MONTH

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Gioria - R/152 5000x1000 CNCBy Domenico Mulinello and Giovanni Mapelli

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Gioria - R/152 5000x1000 CNCIDENTITYCARD:

developing a really tailor-made machine, selecting the best solution for the custom-er’s requirement with no compromise.Moreover, in pursue of an ongoing techno-logical growth, GIORIA will exhibit at EMO

NAME R/152 5000x1000 CNC FANUC 31i - B MODEL Moving wheel cylindrical grinding machine MANUFACTURER GIORIA S.p.a. Via Moncucco, 55 - 21015 Lonate Pozzolo (VA) - Italy Phone: +39 0331 301540 - Fax +39 0331 301662 E-mail: info@gioria.com - www.gioria.com

TECHNICAL SPECIFICATIONSDistance between centres 5000 mmHeight of centres 1000 mmMinimum grinding diameter 100 mmMaximum grinding diameter 2000 mmRadial/axial bearing of work spindle and tailstock quill Hydrostatic Maximum weight admitted between centres 30 tonsGrinding wheel motor power 60 kWGrinding wheel diameter 1270 mmCNC Fanuc 31i – BControlled axes Z axis: wheel carriage longitudinal movement X axis: wheelhead slide cross infeed B axis: wheelhead swivelling A axis: tailstock positioning on workpiece S1 axis: work spindle speed of rotation S2 axis: wheelhead spindle speed of rotation

OTHER CHARACTERISTICS Machine equipped with acoustic sensors for gap control Dynamic and automatic wheel balancerTouch probe for the detection of part axial position Adjustable V-supports for part pre-positioning on the machinePart centering devices

Up: wheel bed provided with a rotary B-axis for wheelhead swivellingDown: Hydrostatic bearings of work spindle and tailstock quill allow supporting shafts weighing up to 30 tons

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MACHINE OF THE MONTH

2015 in Milan a grinding machine featuring similar characteristics, but with a centre dis-tance of 7000 mm. It will likely be the largest cylindrical grinding machine ever exhibited at an international machine tool show.

FROM ONE WEEK TO ONE DAY The R/152 5000x1000 CNC is equipped with a sophisticated roll centering device consist-ing of flanges mounted on work spindle and tailstock quill to offset the alignment of the centres according to the runout reading on the turbine shaft clamped between the cen-tres before being ground. When the shaft is clamped, the centering devices equipped with high-torque double-thread screws al-low the operator to displace the centreline axis, thus improving the runout of the part before grinding. These set-ups on 30-ton components are not simple. In the past the customer used some levers to force the po-sitioning, making the equipment unusable after each tooling. The solution conceived by GIORIA engineers was so convincing to the customer that it was adopted also on other grinders installed in their workshop: this and other purposely developed solutions al-lowed improving precision and profitability in the use of the machine as well as enhanc-ing its repeatability.Still about size, it is not easy to move and load a five-meter long shaft with a diam-eter of two meters, therefore GIORIA has foreseen a set of acoustic sensors to po-sition the grinding wheel on the part or

the diamond automatically to provide op-erators the safety and user-friendliness in handling the machine even with reduced visibility because of part size.Furthermore, as previously noted, the use of steady rests is not possible due to the peculiar geometry of these shafts, however the machine was equipped with pre-posi-tioning supports to make loading and un-loading easier. In this way the shaft is laid on the supports slightly below the centre-line close to the work spindle so that when the tailstock is operated by an additional CNC-controlled axis the clamping between centres happens automatically at the pro-grammed clamping force, once the part is lifted from the supports it will turn freely.Each centering device can be tooled with centres of different length to match differ-ent types of centre-holes recessed inside the

largest diameter of the turbine shaft. At any rate, the tip of the centres have a diameter fit for clamping the centre-holes of any cus-tomer’s shaft.In addition to OD grinding, this GIORIA grind-ing machine can grind also faces. Tolerances in the rotation of blade crowns, which on these turbines can be up to 16, are very tight. Each crown must rotate within a combined axial and radial runout strictly defined.Machine runoffs confirmed the accuracy of face grinding with the attainment of the cross hatch pattern. This particular texturing is produced on the face of the part only when the wheel face exactly matches the part face thanks to a thorough geometrical set estab-lished during machine manufacturing.Any machine feature has been designed to improve precision and reduce cycle time. A meaningful value is the time required to

IT ALL STARTS FROM THE TURBINE SHAFT THE GRINDING OF THE SHAFT IS KEY FOR THE PRECISION AND THE OPERATING RUNOUT OF TURBINE BLADES DEPEND ON IT. THE SHAFT IS THE FULCRUM OF A GAS TURBINE, THE GRINDING OF THE HYDROSTATIC BEARINGS OF THE TURBINE SHAFT AND THE SEATS WHERE THE BLADE CROWNS ARE MOUNTED MUST GUARANTEE A COMBINED RADIAL/AXIAL RUNOUT WITHIN 3 MICRONS.

Left: view of the CNC panel. A supplementary panel is provided on top of the wheel carriage to facilitate set-ups Right: the tip of the live centres has a diameter suitable to match to the centre holes of any customer’s turbine shafts

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MACHINE OF THE MONTH

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R/152 5000x1000 CNC

complete the grinding of a turbine shaft; thanks to the solutions integrated in the new GIORIA grinder, customer can now complete the full machining from not less than one week as it used to be in the past to just one day.

A VALUE THAT GOES BEYOND THE WORKSHOPAt the end of the day, what benefits does this utmost precision bring to the manufac-turing of a turbine? The accuracy in the radial/axial rotation of the turbine blades coupled to the proprietary de-sign of the gas injectors and to other manufac-turing elements, allow these turbines to run on unrefined natural gas directly from the field. The advantages in terms of cost savings for the electrical companies using them to gener-ate power are glaring.

This has a positive repercussion on the service life of the turbines too, in fact besides manu-facturing brand new turbines, the mainte-nance of those already on the field is required.One of the most common reasons for a pre-mature failure of these complex units is the detachment of one or more blades frequently caused by vibrations deriving from an excessive runout sometimes in conjunction with the pres-ence of foreign bodies either in the compression chambers (upstream) or the combustion cham-bers (downstream). Reducing runout within strict limits thanks to the available workshop machinery already at the designing stage rep-resents a strategic factor to reduce breakdowns and to extend the life of each turbine.

CUSTOMIZED HARDWARE AND SOFTWAREThe grinding machine is equipped with a CNC Fanuc 31i - B. Although the initial proposal was for another control, in the customer’s workshop were mainly installed Fanuc CNC so customer’s request for a Fanuc was accomo-dated for reasons of commonality. However the programming HMI interface developed by GIORIA was so convincing for the customer that they solicited the modification of the standard Fanuc interface to operate with the same programming architecture.The graphical interface relies on video pages where the operator can execute any prelimi-nary machining operations such as defining wheel types and shapes in the memory of the CNC, executing part zeroes and diamond

zeroes with the use of acoustic sensors, pro-gramming dressing or profiling cycles accord-ing to the grinding operations to perform. When compiling a part program, the maxi-mum flexibility is given to the operator, who can execute the program to grind the entire turbine, including ODs and faces or select just single features to grind. Moreover, it is pos-sible to set the parameters of the grinding process, splitting the stock removal between rough, semi-fine and fine grind with pro-grammable spark-out cycles and intermedi-ate automatic or manually recalled diamond dressing. Specific graphics and descriptions are also provided to guide the operator step by step until all operations are safely pro-grammed. Still in the software, since face grinding is as important as OD grinding, three differ-ent grinding processes are available: in the first one defined “to size”, the operator sets a value that the control executes. With face grinding “by handwheel” the grinding wheel positions at a given distance from the face and afterwards the electronic handwheel is ebabled so that the operator can infeed the grinding wheel in the face and grind as long as he requires. Finally, the “gap control” mode foresees the use of the acoustic sen-sor: the grinding wheel positions at short distance from the face to be ground and infeeds automatically while the sensor is set to detect the wheel/part contact: after the touch, the grinding of the programmed stock removal is started. ■

Left: the work rests in the forefront can be adjusted for safely loading the shafts on the machine Right: machine running test at GIORIADown: the grinding diameter ranges from 100 to 2000 mm

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