A special solid carbide roughing cutter with fully integrated chip breakers developed by LMT Fette for the Airbus plant in Varel, not only enabled axial feed rates on a Dörries Scharmann five-axis machining centre to be increased by 50 per cent to 13.5 mm/rev when machining wrought aluminium alloy, it totally eliminated previous erratic tool performance.
In addition, the new tool reduced power draw on the spindle, even when removing material at 3,000 cm3/min, and provided an in-cut time of 300 minutes before the tool needed changing.
The LMT Fette cutter 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 1100 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 4000 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 wher 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 Dörries 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 25 mm 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 22 mm long and a cutting angle radius of 4 mm. In producing the Typhoon air inlet flange, the Dörries Scharmann ACM-H HPC machining centre initially performs solid groove cutting at a depth of cut of 25 mm followed by line machining at 17 mm/min using a coolant pressure of 25 – 50 bar.
Cutting speed is maintained at 1,492 m/min using a spindle speed of 19,000 revs/min and a feed rate of 9 m/min. The axial edge of cut is 13.5 mm and pitch is set at 0.16 mm. 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 2 mm. 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.
