CAM developer Delcam and tooling supplier Technicut have partnered to produce a novel method for blisk machining that delivers remarkable savings in both time and cost. The new method covers the machining of the blisk from start to finish and combines new tooling concepts from Technicut with advanced machining strategies in Delcam’s PowerMILL software for the rough, semi-finish and finish machining of integrally bladed rotors.
A video of the new process can be seen on the Delcam AMS channel on YouTube at www.youtube.com/watch?v=W1nqbQHV1Ew In this example, the cycle time was reduced to 35 hours, less than half the time that would have been needed using conventional methods, while the costs for milling were reduced by 45%. The initial billet was 804 mm diameter Ti6-4 titanium, while the completed blisk had 31 blades, each 84mm in length with a root radius of 4mm and scallop height of 10µm.
Blisks are used increasingly in place of a series of individual blades fixed into a central hub. They offer advantages in weight, efficiency and through-life servicing but are challenging to manufacture because of their highly complex shapes and the hardness of the materials used, usually titanium or nickel alloys.
As with most machining projects, the new blisk machining method comprises roughing, semi-finishing and finishing operations. The initial rough machining operation cuts between the blades with a series of slotting cuts using Technicut’s new Titan X-Treme Ripper endmill. As well as removing the bulk of the material between the blades, this operation relieves any stresses in the billet introduced during the forging process.
Both the semi-finishing and finishing operations on the individual blades are then undertaken in a series of vertical sections, working from the tip downwards. The lower sections are left in the rough state to maintain the stiffness of the blade in the area being machined and so to minimise push-off of the blade tip by the cutter.
In addition to the specific toolpaths for blisk machining in PowerMILL, the key to the new method is the use of barrel cutters from Technicut for both semi-finishing and finishing. The tooling designs incorporate a much larger radius on the cutting surface that the ball-nose cutters that would normally be used and so can achieve the same cusp height with a stepdown up to three or four times as large. This larger stepdown means fewer cutting passes are needed to achieve the target smoothness in the surface, meaning that machining times can be reduced significantly.
