Challenging established grinding techniques

Citation

(2002), "Challenging established grinding techniques", Aircraft Engineering and Aerospace Technology, Vol. 74 No. 2. https://doi.org/10.1108/aeat.2002.12774bab.002

Challenging established grinding techniques

Keywords: Aerospace industry, Technology, Grinding

Bridgeport Machines, a Goldman Industrial Group companyhas introduced the Bridgeport 1000 Flexible Grinding Centre, which the company believes is set to make a big impact in the field of production grinding. Moreover, the company asserts that in spite of it being a totally new concept, such is the pace of its development that the FGC 1000 already can be offered as proven technology (Plate 1).

Plate 1 The Bridgeport FGC 1000 flexible grinding centre

VIPER, a Rolls-Royce acronym for Very Impressive Performance Effective Removal, is a five axes machining centre fitted with a special coolant delivery system for the creep feed machining process. As such it reportedly represents a radical move away from conventional methods previously used for the production of components such as small gas turbine blades, for which work, astounding savings – in the ratio of 4 to 1- readily can be achieved.

Designed to take full advantage of an earlier partnership with Rolls-Royce, Mantech Division, and a core of other specialist companies, the VIPER process claims to bring a new meaning to the philosophy encapsulated in the term "lean manufacturing". The process is said to achieve all this by:

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  All but eliminating the component traffic flow inherent in extensive work in progress trials;

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  Huge savings on both capital investment and manufacturing time by reducing the number of machines and machine set-ups needed, with consequent increased accuracy and consistency;

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  A concomitant – and substantial – reduction in manpower costs;

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  Lower consumable costs.

Bridgeport asserts that despite the technique being so radically different from that of the older, heavyweight and inflexible machine tool systems previously used, the time taken to establish the practicality of the FGC 1000 has been remarkably short and free from set backs. The fact that it uses such a well- developed and universally-accepted machine tool, namely the Bridgeport 1000 VMC, as its basis, is said to be an important part of the story, added to which is the tremendous zeal and enthusiasm shown by all of the engineers concerned. This applies equally with all development partners concerned and lead customers and is the reason that it is now possible to offer a machine process for general use with such a high level of confidence.

The company points out that it is the following novel collection of features embodied in the Bridgeport reconfigurable machining centre that makes so many advantages possible. These include high rigidity, rapid rates, fast processing times and high feed rates, the FGC 1000 has the ability to make tool changes in cycle. Adaptive fixturing methods allow more faces to be ground in a single setting, thereby reducing operations and increasing accuracy.

Another key to the effectiveness of the process is stated to be the grinding wheel technology that utilises, instead of the more familiar large and costly aluminium oxide wheels or CBN wheels, much smaller, low- cost aluminium oxide wheels, having a maximum diameter of only 220 mm. Yet another beneficial aspect claimed is the high pressure (up to 70 bar) coolant system that keeps the wheel clean and the component cool and for which an optional chiller unit can be supplied. Bridgeport uses a novel thermal compensation system on the machining centre, as standard, with an optional cooled- head to further reduce thermal distortion of the spindle head.

The whole process is made easier for use on the shop floor with special customised grinding cycles incorporated into the control system. The special cycles can include linear and radial grinding in X and Y axis, wheel dressing cycles and updating of wheel radius. In keeping with the Bridgeport Policy of offering customers the widest possible choice, controls can be specified from any of three world leaders in the CNC field: GE Fanuc, Heidenhain, or Siemens.

For the VIPER process, the innovative toolchanger, which has a capacity of 30 standard tools with diameters up to 75 mm, can accept 10 grinding wheels of up to 220 mm diameter. The machine specification includes the 4th and 5th rotary axis necessary for the manufacture of complex turbine blade components and there is an option for larger capacity devices if needed. Another valuable option is a probing capability that provides facilities for fixture identification, up-dating for tool wear, and in-process gauging.

According to Bridgeport, the FGC 1000 marks a great step forward in the production of components such as: turbine blades, compressor blades, stator blades, smaller nozzle guide vanes, honeycomb heat shields and some casing components. Materials involved are normally nickel alloys and some stainless steels. Other components for which the system is well-suited include small parts in difficult-to-machine materials that have tight geometric tolerances.

Details available from: Bridgeport Machines Ltd. Tel: +44 (0) 116 2531122; Fax: +44 (0) 116 2539960; Website: http://www.bridgeport.co.uk