A Profimat MC 607 five-axis CNC grinding machine manufactured by Blohm Jung in Germany has been supplied to the University of Sheffield AMRC with Boeing after a rigorous tender process that involved evaluating hundreds of parameters and included grinding trials at the machine builder’s factory in Hamburg.

The moving-column grinding machine is located within the Design, Prototyping and Testing Centre — a major expansion of the original AMRC building on the Advanced Manufacturing Park, which is supported by the High Value Manufacturing Catapult and the European Regional Development Fund.

The centre concentrates on the development of high-value manufacturing technologies, mainly for the aerospace, Formula One and high-end automotive sectors.

Medical applications will also be developed, as earlier this year a new facility called Medical AMRC was set up within the centre to concentrate specifically on this industry.

One application will be to investigate the finish-grinding of prosthetics that have been ‘3-D printed’ layer by layer from a cobalt-chrome powder. Knee joints will be a particular target due to their multiple profiled planes.

Capable of producing highly complex components, the Blohm Profimat MC will support the centre’s aim of looking at how the design process can reduce manufacturing costs in the long term, particularly by combining different technologies. The Profimat has many features that will assist in R&D programmes, as well as evaluating wheel consumption against metal removal for achieving different levels of accuracy and surface finish.

Simultaneous interpolation

The latest Siemens Solutionline 840D control, which includes a Blohm user interface, allows the machine’s five CNC axes to interpolate simultaneously, enabling complicated surfaces to be generated without using profiled wheels.

Alternatively, one or both of the rotary axes on the table can be clamped while the others move simultaneously — a strategy that allows the number of separate machining operations for producing a component to be reduced, often to one. The result is a reduction in manufacturing cost and an increase in accuracy (through less tolerance build-up).

All wheel-dressing options are available on the machine, including continuous, pulse and table dressing, as well as contour generation of grinding-wheel profiles. If one of the in-process methods is chosen, either of two diamond dressing rolls can be selected under program control from an overhead swivelling unit.

The machine’s flexibility of use is further extended by its ability to deploy mills, drills and other cutters in addition to grinding wheels; all tools are housed in a 24-position tool magazine to the left of the machine, ready for automatic change into and out of the spindle.

Grinding wheels up to 400mm in diameter x 100mm wide can be used.

The machine will accommodate all types of wheel, including aluminium oxide, CBN, vitrified CBN and diamond electro-plated steel.

Design upgrades

The AMRC’s machine — supplied through Hinckley-based JRA Bennett Ltd (www.jrabennett.co.uk) — weighs some 8.5 tonnes and is the latest Profimat MC version.

It offers a 30m/min feed rate for the X axis and 12m/min for the Y and Z axes. Direct drives and larger ball-screws than on previous models allow this rapid positioning, which is significantly higher than previously — especially in the Y and Z axes, which have also benefitted from larger linear roller guideways.

The latest design upgrade has also resulted in the acceleration in all axes being increased to 2m/sec2 — double the previous figure. Linear scales are also fitted.

A 52kW motor, HSK-A 80 grinding spindle and reinforced wheelhead, coupled with increased machine rigidity, support high levels of productivity and component accuracy, as required for the type of advanced research being carried out at the AMRC.

A more accessible swivelling control panel that is adjustable for height, stainless steel guarding and an automatic door as standard are extra new features, as is ‘double wiring’ to provide redundancy for critical operating functions.

The machine also has a RazorTec wheel-cleaning system, which projects filtered coolant at the wheel at a pressure of 30-40 bar in order to force metallic debris out of the porous structure of the wheel.

This has the effect of keeping it sharp and maintaining its profile while allowing the use of increased in-feed rates for maximised stock removal; it also lowers the risk of burning the workpiece.

Moreover, the flow rate and pressure of the coolant are programmed for each application to give the best results. Consistency of grinding is ensured by automatically maintaining the same angle between the nozzle and wheel as the latter wears; this is achieved by mounting the nozzle on a positioning unit that is programmable in X and Y so that its distance from the wheel and its orientation remain the same.

The cleaning jets are mounted just above the coolant nozzle, which is angled directly at the point of grinding. The carriage carrying both sets of nozzles is also adjustable automatically or manually in the Z axis.

Grinding trials have already been carried out on Inconel and aerospace-grade steels, with more exotic materials destined for evaluation shortly — along with the cobalt-chrome alloy for medical applications.