Air turbine spindles can be toolchanged
1 min read
BIG Daishowa has introduced two new air turbine spindles, the RBX5 version, operating at between 30,000 and 50,000 rpm, and the RBX7, which runs at 60,000 up to 80,000 rpm.
Available in the UK through NCMT, the air-driven tools come with a variety of BIG-PLUS face-and-taper-contact back ends to fit any BT 30/40/50 or HSK-A63/A100 machining centre spindle. These are held stationary while compressed air is delivered through a stop block installed on the spindle face to power the turbine.
The air spindle can be exchanged automatically to and from the tool magazine like other toolholders, allowing micro-machining to be mixed with other metalcutting operations in one uninterrupted cycle. This is in contrast to electrically powered turbine spindles, which require a power supply lead to be connected manually, preventing automatic tool change.
The air supply of the RBX is turned on and off by M-code, the air pressure determining spindle speed.
Shank diameters up to 4 mm can be held in the air spindle. Cutting tools down to 1 mm in diameter are clamped in a microcollet using a notch-free nut, tightened using a special wrench, to eliminate unbalance at high speeds. Maximum static TIR (total indicated runout) is 1 micron at the collet nose, while dynamic run-out is 4 microns at 80,000 rpm, a combination of precision and speed that is impossible using gear- or belt-driven spindle speeders due to the vibration and heat that they generate.
Dramatic improvements in productivity and tool life are possible. For example, the RBX spindle can be used to cut 63 micron walls in aluminium and drill the material without a centre drill. Even after drilling 3,500 holes in a test cycle, the cutting tool edge showed no wear.
A 0.50 mm carbide drill in the air turbine has been shown to produce 1,200 holes at 50,000 rpm, whereas a drill on a machining centre at 12,000 rpm produced only 500 holes.
In another comparative machining example, a 0.10 mm ball nose end mill in an air turbine cut a complex, 2D shape in HRC40 tool steel at 80,000 rpm in 120 minutes. With the tool in the spindle of a 20,000 rpm machining centre, the same job took nearly four times longer (450 minutes).
