Most sophisticated VIPER grinding cell yet from Hardinge

VIPER grinding (very impressive performance extreme removal) is a grinding process first introduced within Rolls-Royce in 1998/9, in collaboration with Tyrolit (01788 823738). The process employs small diameter vitrified wheels, dressed by diamond rolls to support creep-feed grinding undertaken on machining centres, supported by programmable coolant nozzles and high pressure coolant delivery. The original process was upgraded a few years later, to VIPER 2, which saw an additional coolant nozzle added. It is used on nickel alloy parts - typically engine hot end components. (Raysun [01788 541777] originated another process for cold end titanium parts, specifically root features – see http://bit.ly/fSsv48). Hardinge (0116 286 9900) has been involved in supplying VIPER grinding technology since 2000, first using a standard machining centre frame, but now, since MACH 2004, on dedicated travelling column machines, in the form of its FGC2 machine (flexible grinding centre). The company has, up to now, delivered almost 84 machines over 10 years. However, its most recent FCG2 order, from India's Hindustan Aeronautics, is, according to project manager Mukund Patel, the company's most sophisticated iteration so far. The £1.9 million cell, won against international competition, is for the production of a number of low and high pressure jet engine nozzle guide vanes (NGVs). It is Hindustan Aeronautics' first FCG2 installation, but already there are further machines in the offing, following successful pre-acceptance of this first one. Information released regarding part and process detail are restricted, but the cell comprises an FCG2, a Hexagon DEA CMM, a part load/unload station, with a Kuka robot (0121 585 0800) suspended from a Güdel overhead frame (024 7669 5444) servicing all of these elements. The cell will be housed in a temperature-controlled environment, once installed. Image: Parts produced on the VIPER?cell. Top left, low pressure parts are machined, then welded (top right) prior to finish machining. The cast triple high pressure unit can be seen bottom left and the welded triple high pressure unit is to its right Six different components are processed through a total of 32 operations to make six part variants (three welded low pressure double, requiring two LP NGV components; a welded high pressure triple, requiring three HP NGV parts; and a single piece cast high pressure triple HP NGV). There are 12 low pressure finished components per engine set and 19 high pressure parts per engine set. FCG2 operations can include grinding, milling, drilling and boring (reaming could not be performed, as the coolant, suitable for grinding, is not suitable for reaming – Master Chemical C270 (01449 726800). The cell undertakes one drilling operation on the LP components. Image: A view across the front of the cell, towards the CMM at the far left of the set-up There are a number of process route possibilities. For individual parts with a lot of material on, the process is: measure, align, rough grind; unload and transport to CMM for measurement to accommodate material movement; then finish ground and measured for a final time. For parts that have less material on, only a finishing cycle is required. All welded assemblies are ground after joining, however. Part cycle times vary from 20 to 10 mins. The sophistication in the cell comes with the communication between four separate controllers – cell load station, CMM, robot and machine – and in the way data is stored and applied to maintain a controlled process. Unmachined parts are first loaded to a fixture, each of which has a Balluf data chip (0161 282 4700) embedded within it. The chip is non-volatile, since the cell must deal with power outages. The chip initially holds data pertaining to the fixture's location surfaces' offsets, the component serial number and the operation number. The fixture and part are then moved by robot to the CMM to establish datum (achieved by probing the curved vane trailing edge surface to find the high point). This operation generates data for offsets required in the FCG2's various axes of X, Y, Z, A and B. This operation will also check whether the part/operation combination loaded to the chip by the operator is correct, since the CMM will 'see' a discrepancy between what it expects and what it has, should the two be in conflict, as the chip-held part serial number and operation number are what the CMM uses to select the appropriate CMM program. The part is then loaded to the machine by the robot, with the non-volatile chip being read on the way by approaching an external-to-the-machine reader. Following reading, the machine's datum table is updated from the chip. The machine also uses information stored on the chip – part status (rough machined, new part, welded assembly etc), process number, fixture number – to select the correct machining program. Image: The Kuka robot loads parts to the VIPER machine BACK AND FORTH Once the machining cycle has concluded, parts are then removed by the robot and taken back to the CMM. If the part has been rough machined (all low pressure and single high pressure NGVs), then the component is re-probed and new offsets generated – these being different to the first, since the part has likely moved, due to the release of internal stress. If the part has been finish machined (either as an individual prior to welding or as a machined welded assembly), it is measured and then taken to the unload station for removal by the operator – its position on the unload station indicates whether it is a pass or fail. Image: View from a distance, but the guarding sheilds the detail In the case of rough machined parts, the CMM measuring process also records data about the machined surfaces, whether they are material off or material on. According to a set of rules, this information informs the follow-on process. For all parts, there is a full data trail related to every part, including time and date stamps relating to all the various stages, which helps in the analysis of any problems. Image: A view towards the front of the cell; the load/unload station, with the robt transporting a part towards the CMM for initial measurement All the grinding cycles held within the Heidenhain CNC have been created by Hardinge and this, says David Martin, manager, new machining processes, allows the company to generate any new ones at short notice. Indeed, he instances a need to generate a new cycle that grinds through a specified path, effectively a sixth axis, to create a surface – a requirement for which arose on a Friday afternoon and which was satisfied on the following Monday. The cell has been work-in-progress for some six months now, but will be shipped in April and commissioned in July. Box item Machine details in brief The FCG2 has axis travels of 800, 600 and 510 mm in X, Y and Z, respectively, plus A and B, 360° and ±110°. Working table is 1,400 by 650 mm and load is 25 kg. It can take 16 by 220 mm diameter wheels or 12 by 250 diameter wheels, and the toolchanger can accommodate a combination of 10 wheels and five end mills, for example. Coolant is temperature controlled, filtered to 0.005 mm, with grinding coolant supplied at 40 bar and wheel scrubbing coolant at 70 bar. First published in Machinery, March 2011