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There has been a distinct shift towards highly specialised cylindrical grinding applications in the UK requiring bespoke solutions for large, high value, and increasingly complex components in difficult and unusual materials. Solutions reports.
Users, due to the high risk often associated with the type of component, are also demanding ever higher orders of production consistency over size, geometry and surface finish with an increasing requirement for machine and process reliability over extended periods of production life.
Dick Aldrich, sales director of RK International, based in Erith, has been involved for some 12 years in meeting this progressive change in the demands of the industry through RK’s relationship with Robbi, the Italian specialist in cylindrical and internal grinding. “To be successful in providing a viable grinding solution you have to be able to respond with ever higher application specific solutions particularly for aerospace and defence,” he explains.
Robbi, based in Veronella, Italy, was originally founded in 1936 as a specialist reconditioning company for crankshaft grinding machines. Now in the third generation of private family ownership it specialises in application engineering using its range of Omicron modular-based cylindrical and sliding gap machines having a swing over table up to 995mm and up to 6,000mm between centres. Its internal IGR-250 grinding machine can be programmed to produce up to eight diameters in the same part up to a maximum diameter of 355mm. Robbi also produces a range of complementary bore finishing vertical and horizontal honing machines with a capacity up to 460mm diameter by 2,500mm hole depth.
“Due to the level of application expertise and problem solving capability available through Robbi, we have opened doors to successful installations as diverse as wind turbines, rollers for the food industry and machine tool bearings,” adds Mr Aldrich.
Projects such as these also demand greater emphasis on the effective operational life expectancy and reliability of machines as users do not want to be faced with the high costs of replacement or upgrading during the lifespan of components being produced. Indeed, they often require the added flexibility of being able to change over to different components as new developments come into production.
Mr Aldrich recounts recent projects that are pushing the boundaries of grinding technology and where application expertise has been paramount in the process being accepted as viable. “The problem with grinding is that the process involves a whole host of variables including the material being ground. It has to account for varying stock levels, the intricacies of wheel development and progressive in-cycle influence of wheel wear, the setting of feed variation points and dwell times, providing different dressing frequencies, the influence of coolant, filtration and thermal effects – all points that make experience and knowledge very high on the agenda in any application involving high technology machines.”
Here, Robbi’s expertise generated from worldwide applications means full advantage can be taken to create higher productivity solutions. Evermore on the agenda is the application of electronic support to the process with the likes of in-process gauging, automatic wheel balancing and programmable dressing – all vital ingredients to ensure customer requirements can be met.
There are, for example, aerospace applications in the UK where RK and Robbi have engineered solutions such as the grinding of stellite bearings, ceramic materials and demanding gearbox motor shafts destined for helicopters and meeting the increasing requirement for the grinding of carbide wear parts. At one customer, RK has recently installed a Robbi internal grinder for producing highly specialised aerospace bearings up to 300mm diameter by 30mm deep that had to be concentric within 0.0003mm TIR.
As Mr Aldrich confirms, to achieve this level of component geometry requires a matched set of quality of mechanical build with an ability for higher than normal production application technology expertise.
But it is not only aerospace applications in the UK that are setting the challenge to RK and Robbi engineers. Other project areas are becoming equally demanding, especially in the food related sector where a recent project involved a Robbi machine grinding 400mm diameter cast iron rolls.
The machine, installed in a purpose designed temperature controlled environment had to maintain 0.0002mm on size over a 3,000mm part length aided by specialised closed loop measurement and process control. Machines for producing multi-diameter pump shafts for both the water and the nuclear industries between 300mm and 400mm diameter by up to 2,000mm long have also been recently installed as well as a gas project requiring a special cylindrical Robbi grinder to produce 1,200mm diameter components that were 5,000mm long.
All bases covered
The Omicron cylindrical range covers conventional machines designated R and E with up to 2,030mm between centres, 455mm swing over table and able to support up to 300kg between centres. The semi-automatic Omicron T5 is available in four basic capacities for smaller batch production, it has automatic dressing compensation and up to 995mm swing over table with 6,000mm between centres.
Meanwhile, for medium to high volume production using Siemens 840 Di controls, the Omicron Teach-in and full CNC versions have similar capacities to the T5 with the ability to optimise in-process grinding with automatic measuring devices. With CNC, an additional axis can be added that allows the interpolation of a profile on the grinding wheel to enable high precision crowning to be produced on a component.
Breaking new ground is the Omicron T5 universal sliding gap machine with a capacity of up to 1,000mm diameter by 2,030mm between centres. It has two wheelheads each having hydrodynamic spindles which are carried on independent carriages on its cast iron bed. It incorporates a split table that also enables long tapers to be ground. As both wheelheads are totally independent, they can be applied to separately grind both a face and OD with the advantage of applying different wheels and grinding data.
Controlled by Siemens 810D, the wheelhead can be rotated 180° with an index swivel of 2.5° using either manual or auto-positioning. Using the PLC-based control, up to eight different diameters can be programmed on the same part, each having total independence for setting factors such as speeds, feeds and spark out routines. Marposs Micromar E9 can also be incorporated for precise closed loop control of the process. The machine also has the option to carry an internal spindle for integrated external, face and internal processing.