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Work-holding motor spindle ASD-Px

As it can be seen on the test results, our high-efficient thin-film liquid cooling technology gives a spindle soak time from cold and standstill to 10,000 rpm and warmed through of under 9 minutes. This allows a stationary operation after this time at the same speed and is industry leading.

The spindle design itself also compensates for thermal axial shaft growth with axial growth resulting from centrifugal load and gives a total axial shaft displacement from cold and standstill to 10.000 rpm and warmed through of under 0.7 micron. While the shaft expands and gets shorter due to centrifugal expansion, temperature increase due to the bearing and motor losses compensates greatly for this and gives a max. shaft growth under any condition of under 1 micron.

The user not only benefits from a very short soaking time, but also from a market leading low axial shaft growth. In most cases, no warm-up cycle is needed.

Tool motor spindle xASD-H25/A and xASD-H32/A

As it can be seen from the measurement below, the thin-film liquid cooling and the cartridge design of our tool spindles xASD-H25/A, xASD-H32/A and xASD-Cx result in a spindle soak time from cold and standstill to top speed and warmed through of less than 3 minutes. For the user this means that after 3 minutes the spindle doesn’t change its properties, doesn’t matter for how long you use it at top speed. Not only that this time is 5-20 times faster than with any other spindle solution on the market, the user also can use the spindle at 80,000 rpm for an unlimited period of time (unlimited S1-time).

The optimized design also compensates for axial growth. Where the centrifugal load on the shaft causes a reduction in length, the increase in temperature causes an increase. That’s why these spindle models have a total axial shaft growth of less than 3 micron from cold and standstill to 80,000 rpm and warmed through. With our ASD060H25 and ASD060Cx and 60.000 rpm even a value of under 2 micron can be specified.

High-speed tool motor spindle xASD-H20A

Even more exciting is the the thermal and dynamic behavior on axial shaft growth with our high-speed semicon spindle with HSK-20 tooling xASD-H20. Designed for dynamic and thermal stability we managed to minimize the spindle soak time with under 3 minutes as well as the thermal shaft growth with under 1 micron even further.

Our patented bearing technology allows bearing stiffnesses no other aerostatic technology can reach. The increase in stiffness with speed due to centrifugal load and temperature was a design and optimization goal of the rotor dynamics and guarantees a resonance-free operation of all of our spindle products from standstill to top speed. Here the analytically optimized shaft-bearing design makes sure that the spindle speed (= rotation frequency) always stays far below any shaft bending or rigid mode critical. If not, the operation of a spindle at a critical speed would result in tremendously high vibrations and run-out at the tool.
The measurement below was taken with a high-resolution capacitive probe measuring against the spinning tool. Due to its bandwifdth the probe not only picks up the tool run-out, but also its vibration. An FFT analysis can be done for any spindle speed resulting in a resonance spectrum with spindle speed and the residual shaft imbalance as exciting vibration. This spectrum now includes the exciting frequency (=spinning frequency) as well as any system natural frequency. Doing this at every spindle speed leads to a 3D waterfall-chart with the spindle speed as additional dimension. As the amplitude is of no interest at this point, it is easier to look top-down where the dark aereas now represent peaks (=natural frequency) and the light areas valleys.

As it can be seen on a measurement with our ASD060H25 with a max. speed of 60.000 rpm, the exciting frequency (= spinning frequency) never gets close to any natural frequency. For the user this means that, at what ever speed he uses our ASD060H25 or any other model spindle, the spindle spinning frequency (fundamental) never is close to any system natural frequency what is usually the case for any other spindle on the market. This makes sure that, at what ever speed it is used, vibrations and tool run-out is low.

The bearing-shaft design of our spindles are strictly optimized for best shaft dynamics. Means, design goal was a light and stiff shaft design combined with high bearing stiffness values for a resonance-free operation from standstill to top speed.

In combination with our highly specialized production technologies, spindle taper a run-out of less than 50 nm can be guaranteed.

As a result, the user not only gets a robust high-speed spindle with a load capacity better than with any other aerostatic high-speed spindle, he also gets a dynamically neutral spindle operation over the entire speed range with a dynamic tool run-out of better 0.8 micron.

Definition
“Error-Motion” (DIN ISO230-7) is defined by the deviation of the shaft’s rotation axis from its ideal, including all synchronous and asynchronous errors, minus the fundamental (run-out).

Problem
For a Spindle Error Analysis (SEA), sensors measure the change in distance to an artifact (master ball e.g.) that is attached to the shaft or against the shaft itself. As the artifact or the shaft always have shape errors and because these repeat, they are identified as synchronous errors. There are manual methods like the “Donaldson Reversal” to overcome this problem, but these are error-prone, time-consuming and inconsistent.

Levicron’s unique Solution

Using a multi-sensor system that uses more than 2 sensor for a radial measurement, Levicron has developed complex FFT methods to separate the artifact shape from the spindle synchronous errors and transferred it to a selling product – our ShakesBear Spindle Analyzers. Not only that there is a fully automatic and simultaneous error-separation, with sub-nanometer resolutions and a bandwidth of 100 kHz, even high-speed spindles can be analyzed without using any reversal method or changing the test set up.

With our highly specialized production, a spindle taper run-out of under 50 nm is guaranteed. With the same manufacturing technology our HSK tool holders UTS-x are machined for which we guarantee a tool run-out of less than 0.8 micron and a balancing quality of G0.3 mm/s at 60.000 rpm.

The upper picture shows a tool run-out measurement of our ASD-H25 at a customer site and at 185 mm in front of the spindle nose. A value of below 0.5 micron confirms the clamping accuracy and repeatability of our toolholders when used with our spindle solutions.

As a standard test, the tool change repeatability of every spindle is tested by our 4 x 90° reversal balancing test at top speed (lower picture). For this the residual imbalance of one of our UTS-x HSK tool holders is measured at 0°. Then the residual imbalance is measured after the holder was rotated by 90° against the shaft. This is done three times. The distance from the midpoint of the resulting square to one of its corner represents the tool clamp repeatability, where the imbalance is defined as an eccentricity of the tool holder mass. With this method we can guarantee a tool clamp repeatability of less than 0.2 micron.