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Emerald Group Publishing Limited
Copyright © 2008, Emerald Group Publishing Limited
Tool development solves swarf bird nesting on Airbus aluminium machining
Article Type: Aerospace technology From: Aircraft Engineering and Aerospace Technology: An International Journal, Volume 80, Issue 3.
A special solid carbide roughing cutter with fully integrated chip breakers developed by LMT Fette for the Airbus plant in Varel, is reported to have not only enabled axial feed rates on a Domes Scharmann five-axis machining centre to be increased by 50 per cent to 13.5mm/rev when machining wrought aluminium alloy, but it also totally eliminated previous erratic tool performance. In addition, the new tool reduced power draw on the spindle, even when removing material at 3,000cm3/min, and provided an in- cut time of 300min before the tool needed changing.
The LMT Fette cutter is said to have totally solved the problem of swarf “birds nesting” around the spindle and cutting tool, the original reason LMT's specialist was called in by Volker Dittmar, Airbus' Manager of Pre- production, to try to provide a solution during the machining of air inlet flanges for the Typhoon aircraft.
The Varel site in Germany produces complex structural components and tooling, for all seven Airbus sites in Germany. It employs 1,100 people and produces more than 2.5 million single components a year. Of this number, there are 19,000 different components that require milling at the site and more than 4,000 parts are destined for the A380 Airbus.
LMT's development engineer Matthias Maack recounts how the previous tooling, based on solid shank endmills, could not reduce the bird nesting problem that caused problems with quality of the workpiece and the cutters continuously drew excessive power from the machine. He said: “It was clear that we had to develop with Airbus' engineers a solid carbide tool where a fluid transition from the radius to the milling teeth could be used to form an effective chip breaker.”
While simulations were performed on LMT Fette's CAD system to try and optimise cutter geometry, cutter length, number of teeth and the geometry of the chip breaker, it was regular trials on the Domes Scharmann machine at Airbus that provided the chance to optimise the cutters with the material and the machine under production conditions. Adds Mr Maack: “It's a bit like F1, despite all the work behind the scenes, the driver makes a crucial contribution to the team's success.”
The final 25mm diameter tool from LMT's Airline Series, specially developed for aluminium processing, incorporates the special chip breaker and has helical internal coolant passages. While the geometry of the chip breaker actively breaks up the swarf, the emulsion coolant fed direct to the cutting zone also helps to prevent built-up edge on the tool. The tool also has three helical cutting edges 22mm long and a cutting angle radius of 4mm.
In producing the Typhoon air inlet flange, the Domes Scharmann ACM-H HPC machining centre initially performs solid groove cutting at a depth of cut of 25mm followed by line machining at 17mm/min using a coolant pressure of 25-50 bar. Cutting speed is maintained at 1,492m/min using a spindle speed of 19,000revs/min and a feed rate of 9m/ min. The axial edge of cut is 13.5mm and pitch is set at 0.16mm.
Although successful, Airbus and LMT engineers are now attempting to further improve milling performance. Currently, they are experimenting to see the effects of a reduction in the radius of the cutting angles to 2mm. If that can be achieved, it would enable the radial depth of cut to be increased further and by introducing LMT Fette's micro cutting edge geometry, even higher performance should be achievable.
For further information, please contact: LMT (UK) Limited, Tel.: +44 (0) 2476 369770, Fax: +44 (0) 2476 369771, web site: www.LMT-tools.com