High-speed spindle (liquid-cooled motor spindle for machining centres and grinding machines, with automatic tool interface and vibration checks)

01

Fix the tool interface, cooling, coolant feed and drive

GMN lists three tool interfaces for automatic tool change: hollow taper shank with flat contact face (HSK) to DIN 69893, steep taper with flat contact face (SK) to DIN 69871, and polygonal hollow taper with flat contact face (PSC) to ISO 26623-1; HSK-C is the form developed for manual tool change. [1] FISCHER lists milling motor spindles with diameters of 35-360 mm, speeds of up to 90,000 rpm, outputs of up to 200 kW and torque of up to 1,000 Nm, and says its CSC shaft cooling "minimizes the heating and expansion of the spindle shaft". [5]

GMN equips its high-speed spindles with a liquid cooling sleeve at the bearings and at the motor, and states that maximum performance is reached at a coolant temperature of 20 °C to 25 °C and that small coolant temperature differences reduce axial shaft displacement. For coolant through the shaft it offers low-pressure seals (sealing gas or air lock, up to 120,000 rpm, maximum 4 bar, filter fineness below 0.1 mm) and a high-pressure seal (touching sealing discs, up to 75,000 rpm, up to 50 bar depending on the spindle, minimum 3 bar, filter fineness below 0.01 mm, pressure surges must be avoided). [2]

GMN runs its motor spindles from inverters: without speed control by U/f characteristic up to 3,000 Hz output frequency with acceleration times in the range of 10 seconds, or with field-oriented control up to 1,400 Hz, speed constancy "approx. 0.5%" and acceleration in the range of 1 second, with a rotary encoder for C-axis positioning; it notes that maximum output frequency depends on the inverter maker. [3]

Editorial calculation: speed in min⁻¹ equals 60 × frequency ÷ pole pairs, so a motor with one pole pair at 1,400 Hz turns at 60 × 1,400 = 84,000 min⁻¹ and with two pole pairs at 42,000 min⁻¹ (synchronous speed; an induction motor runs slightly below it). The pole count is an assumed example; ask the spindle maker for the motor's pole number and frequency at maximum speed.

Give the spindle maker the machine (machining centre, milling head, grinder), mounting diameter, tool interface and size, maximum speed, power and torque curve, coolant through the shaft and pressure, cooling water temperature and flow available, drive (inverter type, encoder, C-axis), sensors required (temperature, vibration, clamp status), tool masses and lengths, and quantity.

02

Check imbalance, critical speed and vibration with your tools

GMN explains that unbalanced rotating parts (spindle shaft and tool) create imbalance vibrations that increase with speed, and that speed-intensive processes need an imbalance test and, if necessary, balancing of the tools; its residual imbalance guidance is "valid for short tools", and long cantilevered tools may need better balancing. [4]

GMN also notes that the natural frequencies of the rotating system cause critical speeds, and that tools can lower the critical speed range of the spindle-tool system and so the usable speed; it offers a calculation of static and dynamic behaviour for tools of exceptional size or weight. Vibration monitoring devices capture spindle movement, switch off at critical values and can show wear-related vibration in the bearings. [4]

FISCHER cites short start-up times and reliable tool changes for its motor spindles. [5] Ask for the run-in and acceptance data of the spindle you buy: speed steps, temperature rise, vibration and runout at the nose.

03

Rotor shaft, cooling sleeve, tool clamp, coolant seal and sensors

In a motor spindle the rotor sits on the shaft, so the cooling sleeve has to take heat from both the motor and the bearings.

04

Speed, power, inverter frequency and coolant data for a motor spindle

The range figures come from one maker's milling line (up to 90,000 rpm, 200 kW, 1,000 Nm); the frequency row ties that speed to the inverter.

05

Send machine, tool and drive data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Machine: [type; mounting diameter]
Tool interface: [HSK/SK/PSC; size]
Speed and power: [max speed; power; torque curve]
Cooling: [water temperature; flow]
Coolant through shaft: [pressure; filtration]
Drive: [inverter; encoder; C-axis]
Tools: [mass; length; balancing]
Tests: [run-in; vibration; runout]
Quantity: [units]

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