The introduction of machining STRATEGIST CAM software, developed and supplied by NC Graphics, has transformed machining efficiency at the Aircraft Research Association in Bedford. Being used to program the complex toolpaths required for roughing of 1/30th scale models of various aircraft for wind tunnel testing, this advanced CAM system has produced major benefits in terms of reduced programming time, higher metal removal, shorter lead times and extended tool life.
Typically, model aircraft wings and fuselages are machined from solid steel billets on multi-axis CNC bed mills and the roughing sequence involves the removal of some 70% of the raw material. Basic surface data is taken from CAD files (usually IGES) supplied by the customer and this information is imported into machining STRATEGIST to generate the part program instructions required. The complex nature of these forms and the multi-plane curved surfaces that have to be generated and blended, place heavy demands on conventional programming systems.
machining STRATEGIST has been developed specifically to simplify such intricate 3D work and to optimise metal cutting routines by way of unique machining strategies developed for high speed machining and the use of modern carbide insert cutters and solid carbide tools. This includes the use of helical-style tool paths (instead of ones with sharp corners), to provide a smoother and overall faster cutter path so that the tool is never overloaded or forced to dwell. The helix is automatically calculated to clear the material from the middle of the cutter, reducing load and wear on the tool and the machine itself. Roughing toolpaths also have radii added, giving the cutter is in continuous linear movement. Combined with ease of use and other advanced operating features (like boundary machining and automatic slope detection), the system can boost machining speed and efficiency.
Richard Sale, ARA’s Projects Manager - Design and Manufacture, outlined the difference that machining STRATEGIST made to production operations.
"Brought in to compliment our existing CAM software, the system has had a big impact on the way we do things here now, releasing us from the ties of programming and machining routines, which were historically built-up over the years. For we now have a new and more flexible way of programming such work and this has enabled us to improve the efficiency with which we can rough out the complex 3D model forms required. Short learning curves have also proved to be a feature of the system, too."
Quantifying the advantages of the new CAM system is not that straightforward, as each aircraft model is a one off, presenting its own particular problems. However, Mr Sale summed up the benefits of the software in general terms.
"On average, we have cut the time it takes to generate toolpaths by a factor of three. Machining cycles are now around 20% faster, tool life has been significantly extended and there is far less wear and tear on our CNC machines."
Combined with other set-up and workholding improvements, the introduction of machining STRATEGIST will eventually help reduce typical lead times from 21 to some 14 weeks -- at present, the company is about half way toward meeting this target.
Looking at specific components, the new system has already enabled ARA to reduce the time it takes to produce a pair of aircraft wings, (carved out of solid 1m by 400mm by 100mm thick steel billets), from 14 to just 8 weeks. Metal removal rates have been more than doubled, as machining is now carried out with 35mm diameter Depo-style tooling at a depth of cut of 2mm, (formerly 1mm) and a feed rate of 1m/min, (formerly 750mm/min). These forms are roughed out to within 1.2mm of the final profile, compared with the previous allowance of 3mm plus, reducing the amount of finishing work required.
ARA is an independent non-profit-making research and development organisation, originally set-up in 1952 as a wind tunnel test centre for the UK aircraft industry. Today, it provides confidential services in aerodynamic related technologies for UK aircraft and aero engine industries, MoD and major aerospace firms from mainland Europe, America and further afield. The 150-strong company’s main strength lies in its ability to offer a range of aerodynamic services including computational fluid dynamics to develop aerodynamic lines, the design and manufacture of scale aircraft models for wind tunnel testing and in-depth analysis of how these models actually perform. Models can be tested in their transonic wind tunnel at speeds from Mach 0.2 to 1.4.
ARA’s manufacturing operations are centred firmly around three large bed-type CNC mills (including one twin-spindle model), which produce these complex 3D model forms from solid. All these machines have recently been upgraded in terms of controls and drives and have had high speed heads fitted to optimise their performance.
The introduction of machining STRATEGIST is the latest stage in this overall modernisation programme. The company has two of these CAM systems, one in the design office and the other on the shop floor itself. While most of the programs are created off-line and downloaded to the appropriate machine via DNC, the shop floor system provides added programming flexibility. Firstly, it capitalises on the company’s highly skilled workforce and this is used to good effect when modifications, changes or new work comes in. Shop floor programming also helps to keep the work flowing smoothly as any specific machining problems can be tackled quickly and effectively at source.
The impact that machining STRATEGIST was to bring to the company’s machining operations was obvious, from the initial demonstration presented by NC Graphics. However, ARA was also looking at a number of other CAM systems and had actually tried and tested several. So the next step in the justification programme, was to give NC Graphics a real job to program and machine � a 300mm� section of a wing root that involved complex 3D forms and blended curved surfaces. This was completed at NC Graphics’ Cambridge headquarters on their own Bridgeport VMC 1000, which has a 15,000rev/min spindle and Heidenhain TNC 426 high-speed controller.
Working from an imported IGES file, the wing root form was programmed in less than 15 minutes and roughed out in just 3.5 hours. ARA watched the work in progress and was impressed, as it would have taken almost two days to program and rough out this component. During a further trial on-site at ARA, second-stage programming and machining of a special cryogenic model (which had previously been partially machined by ARA itself), convinced Mr Sale and his engineering team that machining STRATEGIST was the ideal CAM system to streamline manufacturing routines.
Although machining STRATEGIST has only been in action at ARA for a short while, it has already improved their capability, speed and efficiency on a wide range of different components. Such has been the software’s all-round performance that the first two systems installed have already paid for themselves!
NC Graphics (Cambridge) Ltd, Silverwood Lodge, Ely Road,
Waterbeach, Cambridge, CB5 9NN, England, United Kingdom
Tel: +44 (0) 1223 861539
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