Application of laser scanning vibrometer in drilling (2)

For plane vibration measurement, a scanning vibrometer can be used. With this scanning method, scanning is performed on many measuring points on the surface of the object in a fast order (Fig. 1). By scanning the laser beam on the surface of the object and high spatial resolution, a series of single points can be generated. Measurement results. From these vibration data, the form of the vibration of the work is measured and visualized either for the synchronous motion process in the time range or within the frequency range of the frequency band. Continuous measurement can be integrated under conditions where the vibration process can be accurately repeated. This can be achieved by a trigger signal generated on the oscillator in a specific frequency band range.

Figure 1 Scanning point distribution for bending and torsional vibration measurements

For the vibration measurement performed on the IWF, Polytec's laser scanning vibrometer can be used to measure the modal parameters such as the self-frequency ωo and the yield N(ω) of the single-edged drill . As the measurement object for the experimental analysis, a single-edge drill having a full hard metal head (circular C shape) having a diameter of 11.76 mm and φ7.22 mm was used. The drill pipe and tensioning sleeve (error: φ20 g6) are made of tempered steel, and the single-edged drill has a total length of 335 mm. In order to be able to measure bending and torsional vibrations in an experimental analysis, it is first required to define the corresponding grid lines required to determine the measurement points. In this regard, the selection of the measurement points is carried out in a shape of a shape, and the laser beam sequentially scans them. In the absence of propulsion, the measurement points that are directly distributed in a vertical array are on one plane; when the single-edged drill is vibrated, the drill is deflected. In the case of torsional vibration, the drill bit is twisted, and the results of the stroke changes at the overlapping points detected by the laser beam are different. In the evaluation, this phenomenon is represented by the color change of each overlapping measurement point (Fig. 1).

Specific measurement situation

In order to avoid external vibrations in the experimental analysis, a large-quality steel measuring platform was used. First, the spindle and center of gravity of the single-edged drill must be calculated so that the longitudinal vibration direction of the drill can be directly aligned with the center of gravity of the drill and the lateral direction of the spindles on both sides. For vibration in the longitudinal direction of the drill bit, the vibrator and the single-edged drill bit are tensioned against each other on a tiger table or a jig with a liner and a clamp . The free end of the drill has a hardened vibrating apex with a Piezo load cell and an aluminum adapter. These devices can be connected to the vibrator under the action of tension. The controller transmits an sinusoidal signal and a specific frequency band through an amplifier to a vibrator that vibrates at the other end to the single-edged drill bit. The load cell feeds the force signal back to the controller through a load-carrying amplifier, and the controller calculates the modal parameters through the frequency-dependent stroke change signal transmitted by the laser scanning vibrometer.

Figure 2 Frequency of flexibility in the first main axis direction (34)

Fig. 2 shows the flexibility frequency range of the φ11.76mm single-edged deep-hole drill bit in the first main shaft direction (34), and the curve conforms to the characteristics of the conventional three-position vibrator. This experimental approach is appropriate because the three-position distribution involves drill bits, drill rods and tensioning sleeves for single-edged drills. The 880Hz self-owned mode is easy to recognize, which is a bending vibration; and the other own mode is 2000Hz torsional vibration. The third typical self mode is still bending vibration with a frequency of 3300 Hz. For ease of comparison, the flexural frequency range of the single-edged drill bit when the drill shown in Figure 3 is subjected to vibration in the feed direction. The first measured mode is 580 Hz and the second own mode is 850 Hz. These are all bending vibrations. An atypical vibration amplitude observed in the direction of the first major axis is the first torsional vibration of 2000 Hz. Typical examples are the 2600Hz, 3300Hz, and 3860Hz modes, which are bent from vibration.

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